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FS: Collins 32V-3 HF Transmitter NICE!!!
FS: Collins 32V-3 HF Transmitter NICE!!!
This has plate modulation so when you key 120 watts on AM you get about 450 Watts or so out. If you're looking for a clean 32V-3 this is it. Non smoker and it works 100 Percent!! I hardly use it. Looking for someone to pick it up locally here in Essex County NJ or you pay shipping UPS. Price: 1000.00 To read up on it, Go to: www.collinsradio.org/html/32v-3.html Reply To: |
Collins 32V-3 HF Transmitter NICE!!!
120 watts on AM you get about 450 Watts or so out.
No seriously, what the F*** are you talking about??? wrote in message ... FS: Collins 32V-3 HF Transmitter NICE!!! This has plate modulation so when you key 120 watts on AM you get about 450 Watts or so out. If you're looking for a clean 32V-3 this is it. Non smoker and it works 100 Percent!! I hardly use it. Looking for someone to pick it up locally here in Essex County NJ or you pay shipping UPS. Price: 1000.00 To read up on it, Go to: www.collinsradio.org/html/32v-3.html Reply To: |
Collins 32V-3 HF Transmitter NICE!!!
"YT" wrote in message t... 120 watts on AM you get about 450 Watts or so out. No seriously, what the F*** are you talking about??? A 120 watt fully-modulated carrier has a PEP of about 480 watts. It really doesn't mean much... Pete |
Collins 32V-3 HF Transmitter NICE!!!
On Mon, 23 Jan 2006, Uncle Peter wrote: "YT" wrote in message t... 120 watts on AM you get about 450 Watts or so out. No seriously, what the F*** are you talking about??? A 120 watt fully-modulated carrier has a PEP of about 480 watts. It really doesn't mean much... Pete My understanding of AM transmitter technology would estimate that a 32v3, with ~120 DC input (two 6146s, or were they still using one 4D32?) would have at most (class C, plate modulated) 70% X 120 = 80 watts of CW carrier output. 60 watts of audio on that final tube (as a non-linear high level mixer) will at best, double the _instantaneous_ (peak) input voltage, therefore power to 240 watts (plate current will _not_ double even if the plate voltage doubles on peak audio cycle [look at your tube curves again of iP vs vP at constant biases]) which you could only attempt to measure with an oscilloscope. Peak output? Could it be more than 240 x 0.7 = 168 watts? I doubt it (unless he's got something like "super-modulation" in the rig). |
Collins 32V-3 HF Transmitter NICE!!!
"Straydog" wrote in message My understanding of AM transmitter technology would estimate that a 32v3, with ~120 DC input (two 6146s, or were they still using one 4D32?) would have at most (class C, plate modulated) 70% X 120 = 80 watts of CW carrier output. 60 watts of audio on that final tube (as a non-linear high level mixer) will at best, double the _instantaneous_ (peak) input voltage, therefore power to 240 watts (plate current will _not_ double even if the plate voltage doubles on peak audio cycle [look at your tube curves again of iP vs vP at constant biases]) which you could only attempt to measure with an oscilloscope. Peak output? Could it be more than 240 x 0.7 = 168 watts? I doubt it (unless he's got something like "super-modulation" in the rig). Without delving into the limitations of the 32V3, according to the info from an ARRL publication: "..since the amplitude at the peak of the upswing is twice the unmodulated amplitude, the power at this instant is four times the unmodulated, or 400 watts." Average power, on the other hand, will be 1.5 times carrier. A Class C amplifier with high level modulation should produce an instaneous PEP of 4x carrier power. Pete |
Collins 32V-3 HF Transmitter NICE!!!
You guys are right both in facts and spirit.
" Uncle Peter" wrote in message news:6xwBf.11951$bF.2404@dukeread07... "Straydog" wrote in message My understanding of AM transmitter technology would estimate that a 32v3, with ~120 DC input (two 6146s, or were they still using one 4D32?) would have at most (class C, plate modulated) 70% X 120 = 80 watts of CW carrier output. 60 watts of audio on that final tube (as a non-linear high level mixer) will at best, double the _instantaneous_ (peak) input voltage, therefore power to 240 watts (plate current will _not_ double even if the plate voltage doubles on peak audio cycle [look at your tube curves again of iP vs vP at constant biases]) which you could only attempt to measure with an oscilloscope. Peak output? Could it be more than 240 x 0.7 = 168 watts? I doubt it (unless he's got something like "super-modulation" in the rig). Without delving into the limitations of the 32V3, according to the info from an ARRL publication: "..since the amplitude at the peak of the upswing is twice the unmodulated amplitude, the power at this instant is four times the unmodulated, or 400 watts." Average power, on the other hand, will be 1.5 times carrier. A Class C amplifier with high level modulation should produce an instaneous PEP of 4x carrier power. Pete |
Collins 32V-3 HF Transmitter NICE!!!
On 1/24/06 12:57 PM, in article 6xwBf.11951$bF.2404@dukeread07, "Uncle
Peter" wrote: "Straydog" wrote in message My understanding of AM transmitter technology would estimate that a 32v3, with ~120 DC input (two 6146s, or were they still using one 4D32?) would have at most (class C, plate modulated) 70% X 120 = 80 watts of CW carrier output. 60 watts of audio on that final tube (as a non-linear high level mixer) will at best, double the _instantaneous_ (peak) input voltage, therefore power to 240 watts (plate current will _not_ double even if the plate voltage doubles on peak audio cycle [look at your tube curves again of iP vs vP at constant biases]) which you could only attempt to measure with an oscilloscope. Peak output? Could it be more than 240 x 0.7 = 168 watts? I doubt it (unless he's got something like "super-modulation" in the rig). Without delving into the limitations of the 32V3, according to the info from an ARRL publication: "..since the amplitude at the peak of the upswing is twice the unmodulated amplitude, the power at this instant is four times the unmodulated, or 400 watts." Average power, on the other hand, will be 1.5 times carrier. A Class C amplifier with high level modulation should produce an instaneous PEP of 4x carrier power. Pete Getting back to basics: A 120W (input) power, class C stage, will require 60W of audio (using a high-level, e.g. plate, modulator) for 100% modulation. If we assume 85% efficiency, then the output will consist of a Carrier of 102W and two sidebands of 25.5W each. In my opinion, any other explanation is useless. Do remember that the carrier amplitude does NOT vary with modulation. Don |
Collins 32V-3 HF Transmitter NICE!!!
On Tue, 24 Jan 2006 13:40:54 -0800, Don Bowey
wrote: On 1/24/06 12:57 PM, in article 6xwBf.11951$bF.2404@dukeread07, "Uncle Peter" wrote: "Straydog" wrote in message My understanding of AM transmitter technology would estimate that a 32v3, with ~120 DC input (two 6146s, or were they still using one 4D32?) would have at most (class C, plate modulated) 70% X 120 = 80 watts of CW carrier output. 60 watts of audio on that final tube (as a non-linear high level mixer) will at best, double the _instantaneous_ (peak) input voltage, therefore power to 240 watts (plate current will _not_ double even if the plate voltage doubles on peak audio cycle [look at your tube curves again of iP vs vP at constant biases]) which you could only attempt to measure with an oscilloscope. Peak output? Could it be more than 240 x 0.7 = 168 watts? I doubt it (unless he's got something like "super-modulation" in the rig). Without delving into the limitations of the 32V3, according to the info from an ARRL publication: "..since the amplitude at the peak of the upswing is twice the unmodulated amplitude, the power at this instant is four times the unmodulated, or 400 watts." Average power, on the other hand, will be 1.5 times carrier. A Class C amplifier with high level modulation should produce an instaneous PEP of 4x carrier power. Pete Getting back to basics: A 120W (input) power, class C stage, will require 60W of audio (using a high-level, e.g. plate, modulator) for 100% modulation. If we assume 85% efficiency, then the output will consist of a Carrier of 102W and two sidebands of 25.5W each. In my opinion, any other explanation is useless. Do remember that the carrier amplitude does NOT vary with modulation. Don I don't remember the 32v3 specs but a pair of 6146B's is rated for 120 watts carrier output on AM. 6146A's are rated for 100 watts output on AM. Assuming the 120 watts carrier output, when modulated 100% the voltage doubles and the current also doubles on modulation peaks. Doubling the voltage and doubling the current works out to 4 times the power. This is of course Peak Envelope Power of the signal which would be 480 watts. You can not just add the audio power to the carrier power to find PEP. You must first add the voltages together. Peak envelope power is what the FCC is concerned with for maximum allowable power of 1500 watts. Although when advertising an AM transmitter it is common to state the carrier power and not try to confuse people by stating the PEP power and not stating that is what is being speced. 73 Gary K4FMX |
Collins 32V-3 HF Transmitter NICE!!!
"Gary Schafer" wrote in message ... Although when advertising an AM transmitter it is common to state the carrier power and not try to confuse people by stating the PEP power and not stating that is what is being speced. 73 Gary K4FMX Agreed.. I was just giving an explanation of the seller's somewhat cryptic sales pitch. Pete |
Collins 32V-3 HF Transmitter NICE!!!
Uncle Peter wrote:
"Gary Schafer" wrote in message ... Although when advertising an AM transmitter it is common to state the carrier power and not try to confuse people by stating the PEP power and not stating that is what is being speced. 73 Gary K4FMX Agreed.. I was just giving an explanation of the seller's somewhat cryptic sales pitch. Pete How much would it be in P.M.P.O. watts? Coupla hundred kilowatts? :) -Bill |
Collins 32V-3 HF Transmitter NICE!!!
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Collins 32V-3 HF Transmitter NICE!!!
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Collins 32V-3 HF Transmitter NICE!!!
I think Gary Schafer's analysis (below) is basically correct but I have minor comments to add (in addition to my earlier post, also quoted below, claiming the 400+ peak output just could not be possible, but I think I was wrong about that). See below. On Tue, 24 Jan 2006, Gary Schafer wrote: On Tue, 24 Jan 2006 16:07:30 -0800, Don Bowey wrote: On 1/24/06 2:31 PM, in article , "Gary Schafer" wrote: On Tue, 24 Jan 2006 13:40:54 -0800, Don Bowey wrote: On 1/24/06 12:57 PM, in article 6xwBf.11951$bF.2404@dukeread07, "Uncle Peter" wrote: "Straydog" wrote in message My understanding of AM transmitter technology would estimate that a 32v3, with ~120 DC input (two 6146s, or were they still using one 4D32?) would have at most (class C, plate modulated) 70% X 120 = 80 watts of CW carrier output. 60 watts of audio on that final tube (as a non-linear high level mixer) will at best, double the _instantaneous_ (peak) input voltage, therefore power to 240 watts (plate current will _not_ double even if the plate voltage doubles on peak audio cycle [look at your tube curves again of iP vs vP at constant biases]) which you could only attempt to measure with an oscilloscope. Peak output? Could it be more than 240 x 0.7 = 168 watts? I doubt it (unless he's got something like "super-modulation" in the rig). Without delving into the limitations of the 32V3, according to the info from an ARRL publication: "..since the amplitude at the peak of the upswing is twice the unmodulated amplitude, the power at this instant is four times the unmodulated, or 400 watts." Average power, on the other hand, will be 1.5 times carrier. A Class C amplifier with high level modulation should produce an instaneous PEP of 4x carrier power. Pete Getting back to basics: A 120W (input) power, class C stage, will require 60W of audio (using a high-level, e.g. plate, modulator) for 100% modulation. If we assume 85% efficiency, then the output will consist of a Carrier of 102W and two sidebands of 25.5W each. In my opinion, any other explanation is useless. Do remember that the carrier amplitude does NOT vary with modulation. Don I don't remember the 32v3 specs but a pair of 6146B's is rated for 120 watts carrier output on AM. 6146A's are rated for 100 watts output on AM. My Viking had a 4D32 final and it would load to well over 100W. Assuming the 120 watts carrier output, when modulated 100% the voltage doubles and the current also doubles on modulation peaks. Doubling the voltage and doubling the current works out to 4 times the power. This is of course Peak Envelope Power of the signal which would be 480 watts. Where does the double voltage come from at 100% modulation? I can only account for a 50% rise in voltage. You can not just add the audio power to the carrier power to find PEP. You must first add the voltages together. Good idea, if one knows the voltages...... Peak envelope power is what the FCC is concerned with for maximum allowable power of 1500 watts. Although when advertising an AM transmitter it is common to state the carrier power and not try to confuse people by stating the PEP power and not stating that is what is being speced. 73 Gary K4FMX My point is that listing the PEP capability of an AM transmitter isn't as useful as stating it can output about 100 watts. Don I agree stating PEP output of an AM transmitter does little. I also think it doesn't mean much even for an SSB signal (which is difficult to compare with AM coming from the same station) because the S-meter damping makes it difficult to measure signal strength. Also, for the power in two sidebands (only one of which is needed) and the waste in the carrier, the usual efficiency of a linear amp is about half of that for a (non-linear) AM final amp. But a properly operating transmitter should be able to give pep at 4 times the carrier power. I think this contradicts something you said below, and contradicts what I said in my post, above. See more below. Some transmitters do not have that capability because of a poor modulator or too small finals, or power supply etc. I, like Peter, was trying to dispel the somewhat misleading add of the original poster. As far as the voltage doubling with modulation, you only need to look at the output on an oscilloscope at the composite signal and you will easily see that it does. Set the scope to show the carrier level at say 2 divisions on the screen. With modulation you will see the positive peaks reach 4 divisions on the scope. The negative peaks will reach zero on the scope. Yes, and I have done this, myself and seen a carrier "band" on my scope, and when speaking into the microphone (on a Johnson Ranger), seen the high peaks go up to about double the height of the carrier and the valleys go down to about zero (below zero would take the carrier away thus leading to splatter). Another way to look at this is when modulating the final the peak audio voltage must equal the plate voltage for 100% modulation. In order for the modulation to go to negative 100% the audio voltage must cause the plate voltage to swing down to zero. By the same note in order to reach 100% positive modulation the audio voltage must cause the plate voltage to go to twice the dc voltage. Yes, but none of this explains where the "4X pep" statement comes from. In fact, even at the instantaneous double the plate voltage, there is no plate current increase. The (non-linear) tube is not a (linear) resistor where you double the voltage accross the resistor and cause the current to double, thus a quadrupling of power. Look at the curves in your tube manuals for any given control (triodes if no other grids are present) or screen grid (tetrodes or pentodes) bias. Above some threshold plate voltage the plate current is independent of plate voltage. Plate current is only affected by grid voltages. It may seem confusing because if you add the average output power up a 100 watt transmitter is only 150 watts. 100 watts carrier and 25 watts in each side band. I think this is right. However if you add the voltage of the carrier plus the voltage of each audio side band and then calculate the power you will see that it is 4 times the carrier power. I don't think this is quite right and, after thinking about all of this, part of the reason I already gave above is also not quite right. Here is another way I think we can look at this question (see below): 100 watts into 50 ohms = 70.7 volts 25 watts into 50 ohms = 35.35 volts 25 watts into 50 ohms = 35.35 volts Total voltage = 141.4 volts (which is 2 x carrier voltage) I think this is a bit of a mistake and it would be better to calculate peak power in the following manner: First, there is no peak output power from the carrier, the carrier is always there and at the same strength no matter if there is modulation or not. So, power contribution FROM THE CARRIER (whether modulated or not) is still only your 100 watts, period. The carrier contributes NO extra power to the peak power we're all interested in. Now, lets look at the power in the sidebands. I'll accept that 25 watts as converting to 35 volts, but that 35 volts is not added to carrier power because it is in the 2-3 kc spectrum above or below the carrier. So, use your formula below and get (35 X 35)/50 = 1225/50 = 24 watts. And, for the second (other) sideband, there will be another 24 watts. Total: 48 watts of audio translated to RF in addition to the 100 watt (constant) carrier. Thus peak power is 148 watts. Where is the conflict between my analysis and yours? Its in the way we think about modulator power output (usually stated as audio power must be about half of final DC input, thus a 120 w DC input class-C final needs about 60 watts of audio). So, when you look up, for example the specs on a pair of 6146s in modulator service (go look in the back of your ARRL handbooks, any of them) and see them talk about 110-130 watts for the pair in either AB1 or AB2! They don't tell you that is _peak_ audio power! For the same tube in class C, they are showing 50-70 watts (continuous RF) out for one tube. Not much difference in power specs per tube, but you won't get anywhere near those 110-130 watts of audio in continuous (i.e. average) power because the heat dissipation will melt the plates since class AB is much less efficient than class C. So, your example of 25 watts per sideband is more like an _average_ power specification and what we should be looking at is what is the peak audio power (or voltage) coming out of the modulator. That peak audio voltage out of the modulator has to be equal to the plate voltage and in the same direction to double the final amp plate voltage, and valley bottom audio equal to the final amp plate voltage but in the opposite direction to reduce plate voltage to zero or near zero. Final B+ voltage plus the audio peak thus shows up on the scope, transiently, as RF output voltage at double the height of carrier alone, and final B+ minus the negative audio peak, at the negative peak, causes the height of the scope trace to go, transiently, to zero. So, when THEY talk about 60 watts of audio power to modulate a 120 w DC input final amplifier, they are talking about more like 60 watts average power which really means something like 120 watts of peak power (and is in all of the tube manuals where specs for all of the amplifier classes are shown next to each other! [this is not the case for receiving tube manuals which talk about average signal output for tubes like 6L6s in classes A and maybe AB]). This gets us into the audiophiles' endless arguing about what audio power means and under what conditions and specifications (eg. the distortions) need to be made for considering peak audio power, especially in music audio (with eg. drum beat transients) rather than voice audio (more or less steady). My general feeling is that in the AM transmitter situation (and the SSB situation, too) that talking about peak power has only theoretical value and almost no practical value and is confusing. You can only measure it on a scope and S-meter readings will be subject to the damping factor in the mechanical needle, electronic fudging by so-called "peak reading" meters including the bar graph things, and any asymmetry in the voice waveform, and distortions and non-linear characteristics in the rest of the electronics. I have heard guys on the air using the same amplifier in a linear class mode who switch from AM mode to SSB mode and my S meters (on lots of receivers) show the same peak value on SSB as the steady value on AM, plus or minus maybe one or two db, at most. Guys would be best off talking about final amp measured DC input watts (continous) and/or final amp measured carrier (continuous) RF output watts and not say too much about their modulator power unless they have a scope on the instantaneous modulator output voltage and current and can actually make a real, valid, representative measurement of both peak and average power and be able to say "Oh, my actual, real, measured-on-a-scope instantaneous peak whatever is X plus or minus Z accuracy." Now, how about peak power input to your 100 watt incandescent light bulb at home? Remember your house AC line voltage (117 VAC) is measured and speced as RMS (root mean square), so peak voltage is 1.41 X 117, peak current is 1.41 x 1 amp, and peak power is thus 1.41 X 1.41 X 100 watts? About 200 watts? Is that meaningful? No, because it isn't. Think DC and why RMS specs are always used for AC circuits and VOM voltmeter scales. Thanks for your attention, sorry to be long-winded. Art, W4PON P= E squared / R 141.4 x 141.4 = 19994 19994 / 40 = 400 watts 73 Gary K4FMX |
Collins 32V-3 HF Transmitter NICE!!!
Let's review some definitions to start: AVERAGE POWER Average power is found by squaring RMS voltage and dividing by resistance. Or RMS voltage times RMS current. PEP It helps to fully understand exactly what PEP is in an SSB transmitter. Then it is easier to see in an AM transmitter. Peak envelope power is important because that is how the FCC defines how much power we can run. Let's look at the FCC definition of Peak Envelope Power: "Peak envelope power output of a transmitter is the AVERAGE power at the crest of the modulation envelope over at least one rf cycle." NOT TO BE CONFUSED WITH AVERAGE POWER READ ON A METER as it swings around! If you think about what that is saying it will make sense. If you transmit just a carrier with an SSB transmitter of say 100 watts. That is 100 watts average power output. It is also 100 watts PEP output. (in this case the envelope is infinitly long) If you were to key it on and off in the CW mode the power relationship would be the same. 100 watts PEP on each CW dash or dot sent. If you now switch to the SSB mode and modulate the transmitter so that the peaks on the scope looking at that signal reach the same height, the transmitter will be putting out 100 watts PEP. If you were to modulate that same SSB transmitter with 2 equal amplitude tones you would get a scope pattern that looks similar to an AM signal modulated with a single tone. The crest (or peak) of the waveform represents 100 watts PEP same as with voice but with the tones it is easier to see as the waveform will be stable. If you were to increase the speed of the time base on the scope and spread the waveform out you would see that each crest of the audio wave form has within it many cycles of the RF frequency. These many cycles of RF are the AVERAGE power contained in the signal. You will note that the maximum AVERAGE power is only reached for several RF cycles at the crest of each audio cycle. This is what is known as PEAK ENVELOPE POWER. (see definition above again) PEP WATTMETERS A true PEP reading watt meter will show the peak envelope power of the above signals as described. There are a lot of so called PEP watt meters on the market. Not all are able to properly read. Even the Bird meters have problems with some types of wave forms. S METER READINGS S meter readings will vary according the particular receiver being used but most all S meters are peak responding circuits. Most will read pretty close to the peak values, depending on the decay time of the circuit some may not hang up there like others do. If you think about it if you have ever been plagued with pulse noise like ignition noise it only takes a very narrow pulse occurring at a rather slow rate to hold the S meter up high. Increasing the rate will not increase the meter reading. Likewise with an SSB signal, once the station is transmitting his peak power on a regular basis, increasing mike gain or increasing compression will not raise the S meter reading maximum. The AVC circuit in the receiver must respond to the peaks or the receiver would overload the detector if the gain was not cut back when a peak was received. The S meter reads AVC voltage. AM TRANSMITTER It is best to try and understand the output signal of the AM transmitter before trying to coralate it with what goes on at the input side. Swapping back and forth can be confusing. Take our 100 watt carrier output transmitter again. Measuring the output voltage of the RF we find that it is 70.7 volts RMS across our 50 ohm load. P = I squared / R so 70.7 x 70.7 = 5000. 5000/50 = 100 watts. Let's modulate 100% with a single audio tone. We get out of it a 100 watt carrier and two 25 watt side bands. 3 distinct signals. As you stated before the carrier always remains constant. If we look at the output signal on our scope we will see that it looks similar to the SSB signal that was modulated with 2 tones. We see the modulation envelope. We can again expand the scope's time base and look at the RF cycles within each modulation peak. Same as with the SSB signal, at the crest of the modulation envelope is the peak envelope power of the composite signal. Now let's get back to measuring that PEP. We know that the carrier alone had a power of 100 watts which produced 70.7 volts across a 50 ohm load. If we look at the scope with and without modulation we see that the voltage output doubles with modulation so it will be 141.4 volts RMS at the crest of the modulation wave form. Again P = E squared /R. 141.4 x 141.4 = 20000. 20000 / 50 = 400 watts PEP. If we were to measure this with a good PEP wattmeter we would see the meter also indicate 400 watts PEP. Again some so called PEP meters do not do well on this type of wave form. The carrier tends to confuse the meter as it causes an offset in the voltage being read by the meter and the meter tries to average it so the net result is some gets subtracted from the reading. It is due to the way in which the particular meter circuit operates. CONVERTING RMS TO PEAK It would seem at first glance that you could find the peak power of the 25 watt side bands and add things together but that doesn't work. You can not convert power. THERE IS NO RMS IN POWER! There is a wide misconception that there is something called RMS power. There is no such thing! There is only AVERAGE power and PEAK power. (note the FCC definition of PEP) You find average power by using RMS voltage. But once you multiply or divide, RMS term, the RMS goes away. So once you have power you can not multiply it by 1.414 to find peak power. To find peak power you must first add the voltages together or find the peak voltage of an rms voltage by multiplying by 1.414 then finding power. AM LINEAR Operating an SSB transmitter and amplifier in the AM mode, if properly set up, will produce exactly the same looking output signal as a plate modulated AM transmitter. If we have an SSB amplifier that will put out 1000 watts PEP on SSB it will also put out 1000 watts PEP on AM. But in order to do so the carrier output must be limited to 250 watts output. It must be tuned up in the CW mode for 1000 watts output. Then when switching to AM the carrier is reduced to 250 watts output without touching any tuning controls. The amplifier must still be tuned to be able to produce the 1000 watt peak envelope output. When we modulate the 250 watt carrier with AM the peak envelope power at 100% modulation will reach 1000 watts pep (or 4 times the carrier) just as it did with the plate modulated AM transmitter. Looking at the output with a scope we will see the voltage double with modulation verses just the carrier. POWER IN SIDE BANDS As a note is seems that having 2 side bands with the same information in an AM signal is useless but it is not. In the detector of the receiver the energy in both side bands combine and add together. So rather than using only 1 side band of 25 watts you are really using 50 watts of side band energy. So a 3 db addition. There is also another 3 db gained in the detector because of the voltage doubling with the side bands being coherent in the detector. So the carrier is really the only thing wasted. PLATE CURRENT AND VOLTAGE DOUBLING It is easiest to see with a triode tube that is plate modulated. Doubling the plate voltage will cause the plate current to also double. That is if the tube is capable of providing enough emission. This must be a linear function in order to avoid distortion when modulating. Tubes that are weak may not be able to provide this. That is one reason that PEP may not fully reach 4 times the carrier power with 100% modulation. Screen grid tubes are not linear in this respect. Plate current is somewhat independent of plate voltage. That is why you must also partly modulate the screen along with the plate when using a screen grid tube in the final. You want to have a linear plate voltage to plate current relationship. This is also why a lot of broadcast transmitters use triodes in the final. Easier to maintain linear modulation. HANDBOOK All this can be found in the AM section in some of the older handbooks. The newer ones do not cover AM very well. 73 Gary K4FMX |
man one grand for a 32v collins
remember when they sold for $100 to 200 all Collins 32V series transmitters used a 4D32 in the pa, nice tube mac w8znx |
Collins 32V-3 HF Transmitter NICE!!!
Gary (and anyone else who cares), since my last post, which responded to several other posts on the topic of PEP in an AM transmitter, I looked up some things and cleared up a major misunderstanding in my own mind. I will add that as comments to the part of your post, below, which is relevant to the issue. As far as all of your definitions below, PEP wattmeters, S-metes, SSB signals are concerned, I think you made a lot more mistakes than you realize. However, I'm going to delete all these irrelevant parts (most of what you said) and concentrate on the source of the confusion. I may make comments in a separate post on the parts I deleted fro this one. On Wed, 25 Jan 2006, Gary Schafer wrote: Let's review some definitions to start: AVERAGE POWER Average power is found by squaring RMS voltage and dividing by resistance. Or RMS voltage times RMS current. PEP deleted PEP WATTMETERS deleted S METER READINGS deleted AM TRANSMITTER deleted CONVERTING RMS TO PEAK deleted AM LINEAR deleted POWER IN SIDE BANDS deleted PLATE CURRENT AND VOLTAGE DOUBLING Here is the crux of the problem. Earlier today I looked in my old RCA receiving tube manual and transmitting tube manuals at the transfer characteristics of many dozens of tubes and I looked at them with this question of PEP for an AM signal. I will incorporate some of what I learned as comments on your comments. The basic fact that I was not aware of is that there is an apparent conflict between the relationship between plate current and plate voltage if you look at the curves that show plate current as independent of plate voltage and then ask how do you get, on modulation, a peak input power four times the unmodulated input power so you can get a peak, on modulation, output power that is four times the unmodulated output power. It is easiest to see with a triode tube that is plate modulated. Nah, "easiest" has nothing to do with it. Triode has nothing to do with it. The issue is that all of the triode transfer characteristics curves I saw showed plate current to be _proportional_ to plate current (but with offsets and some non-linearities, which are mostly unimportant). When I looked at all the tetrodes and pentode curves, then, yes, they all showed plate current independent of plate voltage. However, at any given plate voltage, plate current was also _proportional_ to screen voltage (also with and offset and some non-linearities). Now, it makes sense that if screen voltage is made proportional -- in some fashion (usually a screen voltage dropping resistor connected to the modulated plate supply)-- to plate voltage, then plate current will increase, or decrease, in parallel with plate voltage as modulator voltage adds, and subtracts, from the B+ plate voltage (all as the modulator output signal varies with audio input waveform) Doubling the plate voltage will cause the plate current to also double. From the curves, the relationship between plate current and plate current might not always be exactly a 1:1 relationship, but to an approximation this doubling is an acceptable understanding. And, that is how, on peak input from modulation one gets four times unmodulated input, and output will be proportional to input which can be looked at as average or peak, but the peak output on modulation will also be four times unmodulated output. That is if the tube is capable of providing enough emission. That is a separate issue and anyone designing a circuit and sellecting a tube for use needs to understand the specifications in the manuals. This must be a linear function in order to avoid distortion when modulating. Almost nothing is perfectly linear. All audio circuits will have measureable distortion (IM, harmonic, and others). The only criterion is whether the distortion is acceptable. Tubes that are weak may not be able to provide this. That is one reason that PEP may not fully reach 4 times the carrier power with 100% modulation. I think for this issue one needs at least an oscilloscope to even start measuring and investigating what is going on (and they need to be wideband or sampling scopes, too). "Meters" are just indicators. Screen grid tubes are not linear in this respect. Plate current is somewhat independent of plate voltage. That is why you must also partly modulate the screen along with the plate when using a screen grid tube in the final. There is an equally important reason why you must, and preferably, fully modulate the screen voltage as well as the plate voltage (and this is almost never discussed). If you ever have screen voltage above plate voltage, then screen current will go up dramatically and so will screen heat dissipation. You could melt the screen grid with just one word into the microphone. You can blow the screen grid almost instantly just by accidentally having screen voltage present without plate voltage. You want to have a linear plate voltage to plate current relationship. This is also why a lot of broadcast transmitters use triodes in the final. Easier to maintain linear modulation. I think, if you looked at as many transfer characteristics, as I did earlier today, for transmitting tubes, you might appreciate that there is more heterogeneity between triodes than tetrodes or pentodes in terms of plate I/V relationships. Broadcast AM transmitters never gave us any kind of high fidelity so linearity was never that much of an issue. In broadcasst FM transmitters, power and voltage linearity anywhere in the RF chain was irrelevant. HANDBOOK All this can be found in the AM section in some of the older handbooks. I was never very satisfied with much in the handbooks, whether early or late. The newer ones do not cover AM very well. They are covering tubes and analog subjects less well, too. Everything is going digital, solid stae, chips, and software. Art, W4PON 73 Gary K4FMX |
Collins 32V-3 HF Transmitter NICE!!!
On Wed, 25 Jan 2006 20:05:30 -0500, Straydog wrote:
Everything that I commented on was to try and help you understand the things that YOU brought up on the subject and apperently did not have a full understanding of. Gary (and anyone else who cares), since my last post, which responded to several other posts on the topic of PEP in an AM transmitter, I looked up some things and cleared up a major misunderstanding in my own mind. I will add that as comments to the part of your post, below, which is relevant to the issue. As far as all of your definitions below, PEP wattmeters, S-metes, SSB signals are concerned, I think you made a lot more mistakes than you realize. However, I'm going to delete all these irrelevant parts (most of what you said) and concentrate on the source of the confusion. I may make comments in a separate post on the parts I deleted fro this one. Yes I would be interested in where I "made mistakes". On Wed, 25 Jan 2006, Gary Schafer wrote: Let's review some definitions to start: AVERAGE POWER Average power is found by squaring RMS voltage and dividing by resistance. Or RMS voltage times RMS current. PEP deleted PEP WATTMETERS deleted S METER READINGS deleted AM TRANSMITTER deleted CONVERTING RMS TO PEAK deleted AM LINEAR deleted POWER IN SIDE BANDS deleted PLATE CURRENT AND VOLTAGE DOUBLING Here is the crux of the problem. Earlier today I looked in my old RCA receiving tube manual and transmitting tube manuals at the transfer characteristics of many dozens of tubes and I looked at them with this question of PEP for an AM signal. I will incorporate some of what I learned as comments on your comments. The basic fact that I was not aware of is that there is an apparent conflict between the relationship between plate current and plate voltage if you look at the curves that show plate current as independent of plate voltage and then ask how do you get, on modulation, a peak input power four times the unmodulated input power so you can get a peak, on modulation, output power that is four times the unmodulated output power. As I first explained, there is a direct relationship in a triode between plate voltage and plate current. That is why I said "it is easiest to see when looking at a triode". A tetrode does not have that same direct relationship so it gets a little more complicated to modulate a tetrode. It is easiest to see with a triode tube that is plate modulated. Nah, "easiest" has nothing to do with it. Triode has nothing to do with it. The issue is that all of the triode transfer characteristics curves I saw showed plate current to be _proportional_ to plate current (but with offsets and some non-linearities, which are mostly unimportant). When I looked at all the tetrodes and pentode curves, then, yes, they all showed plate current independent of plate voltage. However, at any given plate voltage, plate current was also _proportional_ to screen voltage (also with and offset and some non-linearities). Now, it makes sense that if screen voltage is made proportional -- in some fashion (usually a screen voltage dropping resistor connected to the modulated plate supply)-- to plate voltage, then plate current will increase, or decrease, in parallel with plate voltage as modulator voltage adds, and subtracts, from the B+ plate voltage (all as the modulator output signal varies with audio input waveform) Operating almost as a triode as far as modulation goes. Glad you understand. I assume that when you say "plate current and plate current" that you mean to say plate voltage and plate current. Doubling the plate voltage will cause the plate current to also double. From the curves, the relationship between plate current and plate current might not always be exactly a 1:1 relationship, but to an approximation this doubling is an acceptable understanding. And, that is how, on peak input from modulation one gets four times unmodulated input, and output will be proportional to input which can be looked at as average or peak, but the peak output on modulation will also be four times unmodulated output. The PEAK ENVELOPE POWER output will be 4 times the unmodulated output. Re-read the deffinition of PEP which you deleted. One tries to operate the tubes in the most linear portion of the curve. The non 1:1 relationship is called distortion. That is if the tube is capable of providing enough emission. That is a separate issue and anyone designing a circuit and sellecting a tube for use needs to understand the specifications in the manuals. It is not a seperate issue. It is an all important issue whether operating or designing. The cause of not enough emission can be from several causes. Too low fillimant voltage, improper screen voltage, final loaded too heavy, not enough grid drive, weak tube, etc. Any of these can be the cause for low PEP compared to carrier power. This must be a linear function in order to avoid distortion when modulating. Almost nothing is perfectly linear. All audio circuits will have measureable distortion (IM, harmonic, and others). The only criterion is whether the distortion is acceptable. "Must be a linear function" denotes as near linear as practicable. Of course nothing is perfectly linear. Tubes that are weak may not be able to provide this. That is one reason that PEP may not fully reach 4 times the carrier power with 100% modulation. I think for this issue one needs at least an oscilloscope to even start measuring and investigating what is going on (and they need to be wideband or sampling scopes, too). "Meters" are just indicators. Yes indeed a scope is a must to properly set up an AM transmitter. It also helps to understand what is happening. The reason I suggested "looking at the wave form on a scope". You do not need a wide band scope. Only one that will cover the RF frequency that you are operating on. Screen grid tubes are not linear in this respect. Plate current is somewhat independent of plate voltage. That is why you must also partly modulate the screen along with the plate when using a screen grid tube in the final. There is an equally important reason why you must, and preferably, fully modulate the screen voltage as well as the plate voltage (and this is almost never discussed). If you ever have screen voltage above plate voltage, then screen current will go up dramatically and so will screen heat dissipation. You could melt the screen grid with just one word into the microphone. You can blow the screen grid almost instantly just by accidentally having screen voltage present without plate voltage. It is not that great a problem. Audio has a very low dity cycle. If the screen is fed with a resistor the screen current will be somewhat self limiting. There are many transmitters that get abused in this manor. However it is best to control it properly. You want to have a linear plate voltage to plate current relationship. This is also why a lot of broadcast transmitters use triodes in the final. Easier to maintain linear modulation. I think, if you looked at as many transfer characteristics, as I did earlier today, for transmitting tubes, you might appreciate that there is more heterogeneity between triodes than tetrodes or pentodes in terms of plate I/V relationships. Broadcast AM transmitters never gave us any kind of high fidelity so linearity was never that much of an issue. As you learn more about AM transmitters you may change your mind on this point. Modulating the screen is not as linear as simply modulating the plate of a triode. Simply modulating the screen along with the plate works well for some type screen grid tubes but not others. Sometimes the amount of modulation to the screen must be limited. You can overmodulate the screen and have it cut off well before the plate voltage swings to the cutoff point. It will have the same splatter effect as overmodulating the plate. Other tubes need more audio applied to the screen to modulate properly. Distortion is usually highr when modulating a screen grid tube than when modulating a triode. In broadcasst FM transmitters, power and voltage linearity anywhere in the RF chain was irrelevant. I won't comment on FM transmitters for fear of being accused of introducing extranious information to the thread. :) HANDBOOK All this can be found in the AM section in some of the older handbooks. I was never very satisfied with much in the handbooks, whether early or late. There is some good stuff in the older handbooks regarding AM. 73 Gary K4FMX The newer ones do not cover AM very well. They are covering tubes and analog subjects less well, too. Everything is going digital, solid stae, chips, and software. Art, W4PON 73 Gary K4FMX |
Collins 32V-3 HF Transmitter NICE!!!
Good explanantion!
"Gary Schafer" wrote in message ... Let's review some definitions to start: AVERAGE POWER Average power is found by squaring RMS voltage and dividing by resistance. Or RMS voltage times RMS current. PEP It helps to fully understand exactly what PEP is in an SSB transmitter. Then it is easier to see in an AM transmitter. Peak envelope power is important because that is how the FCC defines how much power we can run. Let's look at the FCC definition of Peak Envelope Power: "Peak envelope power output of a transmitter is the AVERAGE power at the crest of the modulation envelope over at least one rf cycle." NOT TO BE CONFUSED WITH AVERAGE POWER READ ON A METER as it swings around! If you think about what that is saying it will make sense. If you transmit just a carrier with an SSB transmitter of say 100 watts. That is 100 watts average power output. It is also 100 watts PEP output. (in this case the envelope is infinitly long) If you were to key it on and off in the CW mode the power relationship would be the same. 100 watts PEP on each CW dash or dot sent. If you now switch to the SSB mode and modulate the transmitter so that the peaks on the scope looking at that signal reach the same height, the transmitter will be putting out 100 watts PEP. If you were to modulate that same SSB transmitter with 2 equal amplitude tones you would get a scope pattern that looks similar to an AM signal modulated with a single tone. The crest (or peak) of the waveform represents 100 watts PEP same as with voice but with the tones it is easier to see as the waveform will be stable. If you were to increase the speed of the time base on the scope and spread the waveform out you would see that each crest of the audio wave form has within it many cycles of the RF frequency. These many cycles of RF are the AVERAGE power contained in the signal. You will note that the maximum AVERAGE power is only reached for several RF cycles at the crest of each audio cycle. This is what is known as PEAK ENVELOPE POWER. (see definition above again) PEP WATTMETERS A true PEP reading watt meter will show the peak envelope power of the above signals as described. There are a lot of so called PEP watt meters on the market. Not all are able to properly read. Even the Bird meters have problems with some types of wave forms. S METER READINGS S meter readings will vary according the particular receiver being used but most all S meters are peak responding circuits. Most will read pretty close to the peak values, depending on the decay time of the circuit some may not hang up there like others do. If you think about it if you have ever been plagued with pulse noise like ignition noise it only takes a very narrow pulse occurring at a rather slow rate to hold the S meter up high. Increasing the rate will not increase the meter reading. Likewise with an SSB signal, once the station is transmitting his peak power on a regular basis, increasing mike gain or increasing compression will not raise the S meter reading maximum. The AVC circuit in the receiver must respond to the peaks or the receiver would overload the detector if the gain was not cut back when a peak was received. The S meter reads AVC voltage. AM TRANSMITTER It is best to try and understand the output signal of the AM transmitter before trying to coralate it with what goes on at the input side. Swapping back and forth can be confusing. Take our 100 watt carrier output transmitter again. Measuring the output voltage of the RF we find that it is 70.7 volts RMS across our 50 ohm load. P = I squared / R so 70.7 x 70.7 = 5000. 5000/50 = 100 watts. Let's modulate 100% with a single audio tone. We get out of it a 100 watt carrier and two 25 watt side bands. 3 distinct signals. As you stated before the carrier always remains constant. If we look at the output signal on our scope we will see that it looks similar to the SSB signal that was modulated with 2 tones. We see the modulation envelope. We can again expand the scope's time base and look at the RF cycles within each modulation peak. Same as with the SSB signal, at the crest of the modulation envelope is the peak envelope power of the composite signal. Now let's get back to measuring that PEP. We know that the carrier alone had a power of 100 watts which produced 70.7 volts across a 50 ohm load. If we look at the scope with and without modulation we see that the voltage output doubles with modulation so it will be 141.4 volts RMS at the crest of the modulation wave form. Again P = E squared /R. 141.4 x 141.4 = 20000. 20000 / 50 = 400 watts PEP. If we were to measure this with a good PEP wattmeter we would see the meter also indicate 400 watts PEP. Again some so called PEP meters do not do well on this type of wave form. The carrier tends to confuse the meter as it causes an offset in the voltage being read by the meter and the meter tries to average it so the net result is some gets subtracted from the reading. It is due to the way in which the particular meter circuit operates. CONVERTING RMS TO PEAK It would seem at first glance that you could find the peak power of the 25 watt side bands and add things together but that doesn't work. You can not convert power. THERE IS NO RMS IN POWER! There is a wide misconception that there is something called RMS power. There is no such thing! There is only AVERAGE power and PEAK power. (note the FCC definition of PEP) You find average power by using RMS voltage. But once you multiply or divide, RMS term, the RMS goes away. So once you have power you can not multiply it by 1.414 to find peak power. To find peak power you must first add the voltages together or find the peak voltage of an rms voltage by multiplying by 1.414 then finding power. AM LINEAR Operating an SSB transmitter and amplifier in the AM mode, if properly set up, will produce exactly the same looking output signal as a plate modulated AM transmitter. If we have an SSB amplifier that will put out 1000 watts PEP on SSB it will also put out 1000 watts PEP on AM. But in order to do so the carrier output must be limited to 250 watts output. It must be tuned up in the CW mode for 1000 watts output. Then when switching to AM the carrier is reduced to 250 watts output without touching any tuning controls. The amplifier must still be tuned to be able to produce the 1000 watt peak envelope output. When we modulate the 250 watt carrier with AM the peak envelope power at 100% modulation will reach 1000 watts pep (or 4 times the carrier) just as it did with the plate modulated AM transmitter. Looking at the output with a scope we will see the voltage double with modulation verses just the carrier. POWER IN SIDE BANDS As a note is seems that having 2 side bands with the same information in an AM signal is useless but it is not. In the detector of the receiver the energy in both side bands combine and add together. So rather than using only 1 side band of 25 watts you are really using 50 watts of side band energy. So a 3 db addition. There is also another 3 db gained in the detector because of the voltage doubling with the side bands being coherent in the detector. So the carrier is really the only thing wasted. PLATE CURRENT AND VOLTAGE DOUBLING It is easiest to see with a triode tube that is plate modulated. Doubling the plate voltage will cause the plate current to also double. That is if the tube is capable of providing enough emission. This must be a linear function in order to avoid distortion when modulating. Tubes that are weak may not be able to provide this. That is one reason that PEP may not fully reach 4 times the carrier power with 100% modulation. Screen grid tubes are not linear in this respect. Plate current is somewhat independent of plate voltage. That is why you must also partly modulate the screen along with the plate when using a screen grid tube in the final. You want to have a linear plate voltage to plate current relationship. This is also why a lot of broadcast transmitters use triodes in the final. Easier to maintain linear modulation. HANDBOOK All this can be found in the AM section in some of the older handbooks. The newer ones do not cover AM very well. 73 Gary K4FMX |
Collins 32V-3 HF Transmitter NICE!!!
On Wed, 25 Jan 2006, Gary Schafer wrote: On Wed, 25 Jan 2006 20:05:30 -0500, Straydog wrote: Everything that I commented on was to try and help you understand the things that YOU brought up on the subject and apperently did not have a full understanding of. Yes, and all of the threads, including my own reflection and further study, helped me develope a better understanding of an issue that never had been presented to me by others in a complete manner. This includes the apparent conflict between Ip/Vp curves which in all tetrodes and pentodes or nearly all that I've seen that show Ip independent of Vp over a range that would normally be used under real conditions in AM. I have more comments, below. Gary (and anyone else who cares), since my last post, which responded to several other posts on the topic of PEP in an AM transmitter, I looked up some things and cleared up a major misunderstanding in my own mind. I will add that as comments to the part of your post, below, which is relevant to the issue. As far as all of your definitions below, PEP wattmeters, S-metes, SSB signals are concerned, I think you made a lot more mistakes than you realize. However, I'm going to delete all these irrelevant parts (most of what you said) and concentrate on the source of the confusion. I may make comments in a separate post on the parts I deleted fro this one. Yes I would be interested in where I "made mistakes". On Wed, 25 Jan 2006, Gary Schafer wrote: Let's review some definitions to start: AVERAGE POWER Average power is found by squaring RMS voltage and dividing by resistance. Or RMS voltage times RMS current. PEP deleted PEP WATTMETERS deleted S METER READINGS deleted AM TRANSMITTER deleted CONVERTING RMS TO PEAK deleted AM LINEAR deleted POWER IN SIDE BANDS deleted PLATE CURRENT AND VOLTAGE DOUBLING Here is the crux of the problem. Earlier today I looked in my old RCA receiving tube manual and transmitting tube manuals at the transfer characteristics of many dozens of tubes and I looked at them with this question of PEP for an AM signal. I will incorporate some of what I learned as comments on your comments. The basic fact that I was not aware of is that there is an apparent conflict between the relationship between plate current and plate voltage if you look at the curves that show plate current as independent of plate voltage and then ask how do you get, on modulation, a peak input power four times the unmodulated input power so you can get a peak, on modulation, output power that is four times the unmodulated output power. As I first explained, there is a direct relationship in a triode between plate voltage and plate current. You (and others) talked about a doubling of plate current with a doubling of plate voltage and gave no basis for this statement. That is why I said "it is easiest to see when looking at a triode". And, I stand by my comment below. A tetrode does not have that same direct relationship so it gets a little more complicated to modulate a tetrode. And, you can use the same phrase -- "direct relationship"-- for triodes vs tetrodes and above. It is just that the "direct relationship" will be different and anyone who compares the characteristics of two or more tubes will see that. It is easiest to see with a triode tube that is plate modulated. Nah, "easiest" has nothing to do with it. Triode has nothing to do with it. The issue is that all of the triode transfer characteristics curves I saw showed plate current to be _proportional_ to plate current (but with offsets and some non-linearities, which are mostly unimportant). When I looked at all the tetrodes and pentode curves, then, yes, they all showed plate current independent of plate voltage. However, at any given plate voltage, plate current was also _proportional_ to screen voltage (also with and offset and some non-linearities). Now, it makes sense that if screen voltage is made proportional -- in some fashion (usually a screen voltage dropping resistor connected to the modulated plate supply)-- to plate voltage, then plate current will increase, or decrease, in parallel with plate voltage as modulator voltage adds, and subtracts, from the B+ plate voltage (all as the modulator output signal varies with audio input waveform) Operating almost as a triode as far as modulation goes. "almost" is another one of your mistakes because, "as far as modulation is goes," you will definitely need to modulate the screen grid which is in tetrodes and above but is irrelevant for a triode which has no screen grid. Glad you understand. I assume that when you say "plate current and plate current" that you mean to say plate voltage and plate current. Yeah, I make mistakes, too. Not my first, not my last. Doubling the plate voltage will cause the plate current to also double. From the curves, the relationship between plate current and plate current might not always be exactly a 1:1 relationship, but to an approximation this doubling is an acceptable understanding. And, that is how, on peak input from modulation one gets four times unmodulated input, and output will be proportional to input which can be looked at as average or peak, but the peak output on modulation will also be four times unmodulated output. The PEAK ENVELOPE POWER output will be 4 times the unmodulated output. Re-read the deffinition of PEP which you deleted. Yeah, I read it. Some of us have heard the rumor that the FCC has lawyers write its material, not engineers. I wasn't too impressed with that definition, by the way. One tries to operate the tubes in the most linear portion of the curve. The non 1:1 relationship is called distortion. I would make a distinction between non-linearity and distortion. I can think of situations where non-linearity is part of a characteristic of a device or circuit but distortion (a word which is a specification on an output signal which is less than perfect) is irrelevant. That is if the tube is capable of providing enough emission. That is a separate issue and anyone designing a circuit and sellecting a tube for use needs to understand the specifications in the manuals. It is not a seperate issue. It is an all important issue whether operating or designing. The cause of not enough emission can be from several causes. Too low fillimant voltage, It should be possible to assume that the tube has the correct fil voltage on it. improper screen voltage, Why would anyone build a circuit and not understand the need for the proper screen voltage? final loaded too heavy, Any time one sees output power go down with more loading, they should know better. not enough grid drive, In a class-C amplifier with self-generated control grid drive, the plate current has always gone up in my tubes (sometimes this is mentioned in the manuals and handbooks). Or, the clamp tube limits the plate current (eg. Johnson Rangers) or fixed bias from a separate control grid bias supply limits plate current (I've had this, too, in my homebrew creations) or a cathode resistor (and I've done this, too, in one of my homebrew rigs). weak tube, etc. Any of these can be the cause for low PEP compared to carrier power. All of the above are _abnormal_ situations or conditions. They are otherwise irrelevant to the fundamental question of the relationship between Ip and Vp and determining peak input power. This must be a linear function in order to avoid distortion when modulating. Almost nothing is perfectly linear. All audio circuits will have measureable distortion (IM, harmonic, and others). The only criterion is whether the distortion is acceptable. "Must be a linear function" denotes as near linear as practicable. Of course nothing is perfectly linear. And, acceptable can range from specifications of 5-10% audio harmonic distortion given in equipment reviews for some older rigs compared to some of the most recent rigs which are much much lower (mostly for purists, not me) Tubes that are weak may not be able to provide this. That is one reason that PEP may not fully reach 4 times the carrier power with 100% modulation. I think for this issue one needs at least an oscilloscope to even start measuring and investigating what is going on (and they need to be wideband or sampling scopes, too). "Meters" are just indicators. Yes indeed a scope is a must to properly set up an AM transmitter. It also helps to understand what is happening. The reason I suggested "looking at the wave form on a scope". I agree. You do not need a wide band scope. Only one that will cover the RF frequency that you are operating on. I have actually used both "narrow band" (DC to 500 kc) and "wide band" (DC to 20 mHz) scopes to do this and the narrow band scopes can have such a rapid decrease in sensitivity at the lowest ham bands that the only way to get vertical deflection is to raise the RF voltage up to hundreds of volts and you can't get that from a 50 watt rig without a RF transformer between the rig and the scope to raise the input voltage and then you may overheat the (usual) 1 megohm input swamping resistor in most scopes that is across the input terminals. This is another thing people need to think about before they just use "any old scope." The other option is to use a diode and capacitor (with an appropriate RC time constant) to measure the _envelope_ of the RF coming out of the transmitter, but I consider this kludge as a kludge to be avoided. Screen grid tubes are not linear in this respect. Plate current is somewhat independent of plate voltage. That is why you must also partly modulate the screen along with the plate when using a screen grid tube in the final. There is an equally important reason why you must, and preferably, fully modulate the screen voltage as well as the plate voltage (and this is almost never discussed). If you ever have screen voltage above plate voltage, then screen current will go up dramatically and so will screen heat dissipation. You could melt the screen grid with just one word into the microphone. You can blow the screen grid almost instantly just by accidentally having screen voltage present without plate voltage. It is not that great a problem. You can't say this without saying under what conditions it is not a great problem. The small external anode tubes (eg. 4X150, and on up) all have, in their spec sheets, a strict warning about losing plate voltage with screen voltage present. All of those physically small tubes have much lower max grid dissipations than the old big internal anode tubes. Audio has a very low dity cycle. If the screen is fed with a resistor the screen current will be somewhat self limiting. There are many transmitters that get abused in this manor. However it is best to control it properly. I think it unwise to present to people that this problem "is not that great" and you can't say things like "low duty cycle" when you also don't distinguish between voice typical duty cycle and a sine wave audio from a signal generator that could maybe triple the screen dissipation or more. Self limiting the screen current (with a screen bypass) may not be enough and even then an increased screen current for a continuous current (vs. a varying current with lower average value) could also damage the screen resistor. I would not treat this issue as lightly as you do. You want to have a linear plate voltage to plate current relationship. This is also why a lot of broadcast transmitters use triodes in the final. Easier to maintain linear modulation. I think, if you looked at as many transfer characteristics, as I did earlier today, for transmitting tubes, you might appreciate that there is more heterogeneity between triodes than tetrodes or pentodes in terms of plate I/V relationships. Broadcast AM transmitters never gave us any kind of high fidelity so linearity was never that much of an issue. As you learn more about AM transmitters you may change your mind on this point. I am thankful that an issue that has bothered me for decades has been considerably cleared up in the last two days. However, although people here talked about Ip doubling with Vp, no one here explained the descrepancy between this claim and all of the tube curves that show Ip (in tetrodes) as independent of Vp! I had to put that one together by myself. Modulating the screen is not as linear as simply modulating the plate of a triode. From all the curves I saw of both triodes and all screen grid tubes I can only say that you can't say one is "not as linear" as the other without specifying the tubes to be considered AND going into technical details that are far beyond the scope of our discussion. Simply modulating the screen along with the plate works well for some type screen grid tubes but not others. Sometimes the amount of modulation to the screen must be limited. You can overmodulate the screen and have it cut off well before the plate voltage swings to the cutoff point. It will have the same splatter effect as overmodulating the plate. Other tubes need more audio applied to the screen to modulate properly. Distortion is usually highr when modulating a screen grid tube than when modulating a triode. I would agree these are some of the details. I can think of more. In broadcasst FM transmitters, power and voltage linearity anywhere in the RF chain was irrelevant. I won't comment on FM transmitters for fear of being accused of introducing extranious information to the thread. :) Fine, I just wanted to give an example where linearity of any kind in the RF chain is irrelevant. HANDBOOK All this can be found in the AM section in some of the older handbooks. I was never very satisfied with much in the handbooks, whether early or late. There is some good stuff in the older handbooks regarding AM. Its a mixed bag for me. And, I'm an old timer that appreciated simpler circuitry and the situation that because of that it is easier to understand what one is doing. All contemporary rigs are so complicated that a high understanding of what is going on requires much more study, repairs often require sending the rig off for long periods, and if the rig is even not that old but specific chips are no longer available then sometimes it is easier and simpler to repair and maintain the even older tube rigs for which discrete devices are still available and there is enough extra space inside for kludge fixes if restoration fixes are imp.ossible. My two cents irrelevant to the original subject). Art, W4PON 73 Gary K4FMX Art, W4PON 73 Gary K4FMX |
Collins 32V-3 HF Transmitter NICE!!!
On Thu, 26 Jan 2006 19:26:21 -0500, Straydog wrote:
The PEAK ENVELOPE POWER output will be 4 times the unmodulated output. Re-read the deffinition of PEP which you deleted. Yeah, I read it. Some of us have heard the rumor that the FCC has lawyers write its material, not engineers. I wasn't too impressed with that definition, by the way. Well then if you don't believe anyone you should go and look it up for yourself. You will find that same deffinition in the ARRL handbook. Oh I forgot you don't believe what is in there either. Then try some of the Collins Radio SSB handbooks. Maybe Art Collins didn't know what he was talking about either? How about in the IEEE handbook. Keep in mind when trying to understand PEP that there is no peak power involved. It is all average power. Also when calculating side band power and carrier power that is all average power too. Forget about peak power. Once you understand how this works then you can work from there to figure out the rest. I have eliminated all the other stuff as you seem to be going round and round only for the sake of arguing and not for understanding. I would encourage you to go to your local library and look at some of Terman's books or get his radio handbook from ebay etc. Also the radiotron designer's handbook is excellent. 73 Gary K4FMX |
Collins 32V-3 HF Transmitter NICE!!!
On Thu, 26 Jan 2006, Gary Schafer wrote: On Thu, 26 Jan 2006 19:26:21 -0500, Straydog wrote: The PEAK ENVELOPE POWER output will be 4 times the unmodulated output. Re-read the deffinition of PEP which you deleted. Yeah, I read it. Some of us have heard the rumor that the FCC has lawyers write its material, not engineers. I wasn't too impressed with that definition, by the way. Well then if you don't believe anyone you should go and look it up for yourself. You will find that same deffinition in the ARRL handbook. Oh I forgot you don't believe what is in there either. Then try some of the Collins Radio SSB handbooks. Maybe Art Collins didn't know what he was talking about either? How about in the IEEE handbook. Keep in mind when trying to understand PEP that there is no peak power involved. It is all average power. Also when calculating side band power and carrier power that is all average power too. Forget about peak power. Once you understand how this works then you can work from there to figure out the rest. I have eliminated all the other stuff as you seem to be going round and round only for the sake of arguing and not for understanding. I'm sorry but how you can write a sentence, above, like "Keep in mind when trying to understand PEP that there is no peak power involved" when you use "PEP" and "peak power" in the same sentence and say something that sounds like "its there but it isn't there." As I've already said in an earlier post that my problem was the conflict between characteristic curves for tetrodes and pentodes showing no change in Ip for large changes in Vp and the real need for Ip to move in proportion to Vp to get a quadrupling of input power on a modulation peak over an unmodulated carrier. This only can happen if the screen voltage is modulated along with plate--which everyone, including me, knows--but no one pointed out that practically all if not all characteristic curves give only curves for one fixed typical screen voltage. I would encourage you to go to your local library and look at some of Terman's books or get his radio handbook from ebay etc. Also the radiotron designer's handbook is excellent. 73 Gary K4FMX |
Collins 32V-3 HF Transmitter NICE!!!
On Thu, 26 Jan 2006 22:45:57 -0500, Straydog wrote:
On Thu, 26 Jan 2006, Gary Schafer wrote: On Thu, 26 Jan 2006 19:26:21 -0500, Straydog wrote: The PEAK ENVELOPE POWER output will be 4 times the unmodulated output. Re-read the deffinition of PEP which you deleted. Yeah, I read it. Some of us have heard the rumor that the FCC has lawyers write its material, not engineers. I wasn't too impressed with that definition, by the way. Well then if you don't believe anyone you should go and look it up for yourself. You will find that same deffinition in the ARRL handbook. Oh I forgot you don't believe what is in there either. Then try some of the Collins Radio SSB handbooks. Maybe Art Collins didn't know what he was talking about either? How about in the IEEE handbook. Keep in mind when trying to understand PEP that there is no peak power involved. It is all average power. Also when calculating side band power and carrier power that is all average power too. Forget about peak power. Once you understand how this works then you can work from there to figure out the rest. I have eliminated all the other stuff as you seem to be going round and round only for the sake of arguing and not for understanding. I'm sorry but how you can write a sentence, above, like "Keep in mind when trying to understand PEP that there is no peak power involved" when you use "PEP" and "peak power" in the same sentence and say something that sounds like "its there but it isn't there." Let me explain: There is peak envelope power and there is peak power. Peak power is seldom used. Peak power is the instantaneous power at the very peak of the voltage and current. You will see peak currents discussed in tube manuals often. Our 100 watt carrier output transmitter with no modulation is 100 watts average power as we talked about before. The actual peak power is 200 watts output. (nothing to do with modulation right now) This is found by multiplying the 70.7 volts RMS output voltage by 1.414 to find peak voltage. That gives us 100 volts peak. Divide that by 50 ohms and we have 200 watts peak output power. Note that peak power is 2x average power with a sin wave. PEP Peak envelope power does NOT involve peak power as above. It only deals with AVERAGE power. Remember the definition of PEP: The AVERAGE power out at the crest of the modulation waveform. (perhaps the "peak" in peak envelope power is a misnomer) The modulation voltages, that we use to calculate PEP, in each side band are also RMS voltages, they are not peak voltages. In the figures below are typical voltages present in the signals at the output of an AM transmitter modulated 100%. I gave these same figures in another post. 100 watts into 50 ohms = 70.7 volts (carrier) 25 watts into 50 ohms = 35.35 volts (side band) 25 watts into 50 ohms = 35.35 volts (side band) Total voltage = 141.4 volts (which is 2 x carrier voltage) 141.4 x 141.4 = 20000 / 50 = 400 watts PEP. This takes care of our PEP power. The amount of voltage that you see on a scope when looking at this same modulated signal, if we actually measure them with the scope, will be peak to peak voltage as that is what the scope sees. So measuring the composite signal voltage on the scope it will show 400 volts peak to peak. Take ½ that to find peak voltage and you have 200 volts peak. To find RMS voltage multiply that by .707 and that will give you 141.4 RMS volts. This is what is used to calculate PEP. 73 Gary K4FMX |
Collins 32V-3 HF Transmitter NICE!!!
On Fri, 27 Jan 2006, Gary Schafer wrote: On Thu, 26 Jan 2006 22:45:57 -0500, Straydog wrote: On Thu, 26 Jan 2006, Gary Schafer wrote: On Thu, 26 Jan 2006 19:26:21 -0500, Straydog wrote: The PEAK ENVELOPE POWER output will be 4 times the unmodulated output. Re-read the deffinition of PEP which you deleted. Yeah, I read it. Some of us have heard the rumor that the FCC has lawyers write its material, not engineers. I wasn't too impressed with that definition, by the way. Well then if you don't believe anyone you should go and look it up for yourself. You will find that same deffinition in the ARRL handbook. Oh I forgot you don't believe what is in there either. Then try some of the Collins Radio SSB handbooks. Maybe Art Collins didn't know what he was talking about either? How about in the IEEE handbook. Keep in mind when trying to understand PEP that there is no peak power involved. It is all average power. Also when calculating side band power and carrier power that is all average power too. Forget about peak power. Once you understand how this works then you can work from there to figure out the rest. I have eliminated all the other stuff as you seem to be going round and round only for the sake of arguing and not for understanding. I'm sorry but how you can write a sentence, above, like "Keep in mind when trying to understand PEP that there is no peak power involved" when you use "PEP" and "peak power" in the same sentence and say something that sounds like "its there but it isn't there." Let me explain: There is peak envelope power and there is peak power. Peak power is seldom used. Peak power is the instantaneous power at the very peak of the voltage and current. You will see peak currents discussed in tube manuals often. Yes, and I've looked at them very often. The term "instantaneous power" seems more appropriate to me since it implies a time dependent function, but that is just my prefernce. More below. Our 100 watt carrier output transmitter with no modulation is 100 watts average power as we talked about before. The actual peak power is 200 watts output. (nothing to do with modulation right now) This is found by multiplying the 70.7 volts RMS output voltage by 1.414 to find peak voltage. That gives us 100 volts peak. Divide that by 50 ohms and we have 200 watts peak output power. Note that peak power is 2x average power with a sin wave. PEP Peak envelope power does NOT involve peak power as above. It only deals with AVERAGE power. Remember the definition of PEP: The AVERAGE power out at the crest of the modulation waveform. (perhaps the "peak" in peak envelope power is a misnomer) I think it very well is a misnomer, but that is also maybe "my" problem. Defining what we mean, and explaining very technical issues bery accurately is much more difficult than most people realize and sometimes people read things and still don't understand what they are reading. Just about everything you wrote above and below is fine with me except that I've already explained several times in several posts that the problem I always had, for tetrodes and above, is that all the published curves show Ip being independent of Vp and I could not see how, under modulation, there would be enough instantaneous input power to give a 4X instataneous output instantaneous power. Now that I realize that modulating screen voltage can make Ip move in proportion to Vp, and thus give double current at double voltage, my problem with understanding this dissapears. And, this was the major basis for my squabble with the PEP spec on the 32V3 original post. Non linearities are still an issue, but minor. I guess I am just dismayed that nobody is reading what I'm saying to see what I'm saying but they all jump in to talk about everything except the problem that I more or less figured out by myself after re-reading, thinking, and getting some stimulation from the discussions. But, thank you for your time. You need not repeat yourself any more. ===== no change to below, included for reference and context ===== The modulation voltages, that we use to calculate PEP, in each side band are also RMS voltages, they are not peak voltages. In the figures below are typical voltages present in the signals at the output of an AM transmitter modulated 100%. I gave these same figures in another post. 100 watts into 50 ohms = 70.7 volts (carrier) 25 watts into 50 ohms = 35.35 volts (side band) 25 watts into 50 ohms = 35.35 volts (side band) Total voltage = 141.4 volts (which is 2 x carrier voltage) 141.4 x 141.4 = 20000 / 50 = 400 watts PEP. This takes care of our PEP power. The amount of voltage that you see on a scope when looking at this same modulated signal, if we actually measure them with the scope, will be peak to peak voltage as that is what the scope sees. So measuring the composite signal voltage on the scope it will show 400 volts peak to peak. Take ½ that to find peak voltage and you have 200 volts peak. To find RMS voltage multiply that by .707 and that will give you 141.4 RMS volts. This is what is used to calculate PEP. 73 Gary K4FMX |
Collins 32V-3 HF Transmitter NICE!!!
Don ... you are correct!
73, Lee ZL2AL (Old AMer of the 50s) "Don Bowey" wrote in message ... On 1/24/06 12:57 PM, in article 6xwBf.11951$bF.2404@dukeread07, "Uncle Peter" wrote: "Straydog" wrote in message My understanding of AM transmitter technology would estimate that a 32v3, with ~120 DC input (two 6146s, or were they still using one 4D32?) would have at most (class C, plate modulated) 70% X 120 = 80 watts of CW carrier output. 60 watts of audio on that final tube (as a non-linear high level mixer) will at best, double the _instantaneous_ (peak) input voltage, therefore power to 240 watts (plate current will _not_ double even if the plate voltage doubles on peak audio cycle [look at your tube curves again of iP vs vP at constant biases]) which you could only attempt to measure with an oscilloscope. Peak output? Could it be more than 240 x 0.7 = 168 watts? I doubt it (unless he's got something like "super-modulation" in the rig). Without delving into the limitations of the 32V3, according to the info from an ARRL publication: "..since the amplitude at the peak of the upswing is twice the unmodulated amplitude, the power at this instant is four times the unmodulated, or 400 watts." Average power, on the other hand, will be 1.5 times carrier. A Class C amplifier with high level modulation should produce an instaneous PEP of 4x carrier power. Pete Getting back to basics: A 120W (input) power, class C stage, will require 60W of audio (using a high-level, e.g. plate, modulator) for 100% modulation. If we assume 85% efficiency, then the output will consist of a Carrier of 102W and two sidebands of 25.5W each. In my opinion, any other explanation is useless. Do remember that the carrier amplitude does NOT vary with modulation. Don |
Collins 32V-3 HF Transmitter NICE!!!
Don ... you are correct!
73, Lee ZL2AL (Old AMer of the 50s) Getting back to basics: A 120W (input) power, class C stage, will require 60W of audio (using a high-level, e.g. plate, modulator) for 100% modulation. If we assume 85% efficiency, then the output will consist of a Carrier of 102W and two sidebands of 25.5W each. In my opinion, any other explanation is useless. Do remember that the carrier amplitude does NOT vary with modulation. Don Wohoooo here, maybe, since I caught this thread in mid stream, I am out of place, but Don, your last sentence, "Do remember that the carrier amplitude does NOT vary with modulation." doesn't sound like high level amplitude modulation. When I was young(er), amplitude modulation meant exactly that: carrier amplitude varying with modulation. In fact, when working out the bugs of home designed and built AM transmitters, one favorite test was with an oscilloscope, measuring the amplitude of the carrier, making sure that the carrier amplitude did actually approach zero and rise to twice the unmodulated carrier level. (voltage, not power, of course) Now, for sure, the carrier average POWER didn't vary (much), but the audio power was added. Now, PEP, peak envelope power, is a whole different thing for us old timers, and maybe that's what is being discussed here. In that case, please excuse Mr. Buttinski! Old Chief Lynn, W7LTQ |
Collins 32V-3 HF Transmitter NICE!!!
Hi, Lynn
The oscilloscope monitor on an A.M. transmitter output doesn't show the carrier (except during periods of no modulation). The scope shows the resultant of the carrier and both sidebands added together vectorially. A spectrum analyzer would show a constant amplitude carrier in the center of the A.M. spectrum. There is a good description of the process at the Agilent site. Google a.m. phasor diagram Click on "Spectrum analysis AM and FM HP T&M Application Note 150-1" Beginning on page 48 of the pdf file is a description of the a.m. spectrum, based on phasor diagrams. 73, Ed Knobloch Lynn Coffelt wrote: Wohoooo here, maybe, since I caught this thread in mid stream, I am out of place, but Don, your last sentence, "Do remember that the carrier amplitude does NOT vary with modulation." doesn't sound like high level amplitude modulation. When I was young(er), amplitude modulation meant exactly that: carrier amplitude varying with modulation. In fact, when working out the bugs of home designed and built AM transmitters, one favorite test was with an oscilloscope, measuring the amplitude of the carrier, making sure that the carrier amplitude did actually approach zero and rise to twice the unmodulated carrier level. (voltage, not power, of course) Now, for sure, the carrier average POWER didn't vary (much), but the audio power was added. Now, PEP, peak envelope power, is a whole different thing for us old timers, and maybe that's what is being discussed here. In that case, please excuse Mr. Buttinski! Old Chief Lynn, W7LTQ |
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