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Standing Waves (and Impedance)
Roy,
Plot this on a smith chart program. You are correct, your meter reads close to 2:1, however you know nothing about the phase or resonance of the antenna. It does not tell you if you have a tuned antenna and a poor R match or if your antenna is way out of tune. (Of course neither does the telescope) Dan Roy Lewallen wrote: This is pretty strange. Suppose Reg has a 50 ohm line of some length connected to an antenna whose impedance is 100 + j0 ohms. After putting away his evening's bottle of wine, he climbs the tower and inserts a 50 ohm SWR meter at the antenna. He climbs back down, gets out his vintage brass telescope and keys the transmitter. Then, steadying himself, he peers through the telescope and sees that the SWR meter reads 2:1. (Being a clever person, he mounted the meter upside down so it would be right side up in the telescope, obviating the need for the added challenge of mental inversion.) I have an identical antenna, feedline, and SWR meter. I sit in my warm shack sipping my moonshine, connect the SWR meter to the input end of the line, hit the key, and note that the meter reads 2:1. Or perhaps slightly less if the line is noticeably lossy. Reg says: Placing the SWR meter at the start of the feed-line terminated by the antenna, will tell you NOTHING about the SWR on that line. I guess the 2:1 reading from the meter at the input end of the line is telling Reg nothing, while the 2:1 reading at the antenna is. Strange. The fact is that it's the SWR on the line, and it can be measured at any point along the line. I like my method better, but each to his own. Roy Lewallen, W7EL Reg Edwards wrote: Roy, you surprise me. Try a jug of Moonshine. Placing the SWR meter at the start of the feed-line terminated by the antenna, will tell you NOTHING about the SWR on that line. It is the antenna input impedance which determines the SWR on the line, and the meter doesn't have the foggiest idea what THAT is. The unknown antenna impedance is at the other end of a line of unknown length, unknown impedance and unknown loss. Unknown, that is, to the meter. YOU might have that knowledge. But then you can CALCULATE what the SWR is on the line. Meter readings having been discarded as useless. I repeat - the meter tells you only whether or not the transmitter is loaded with a resistive 50 ohms. No more and no less. If it is not 50 ohms the ambiguous meter will not even tell you the actual value of Z. Intoxicated or not, if you insist on a meter reading, there is no alternative to climbing the antenna mast. ---- Reg, G4FGQ. PS. The use of SWR by American plug and socket manufacturers to describe unrelated characteristics of their products is a small indication of the abysmal depths to which engineering has descended. Technical specifications are reduced to Camm's Comics. But they look good to the uninitiated. ---- Reg. ========================================== |
Standing Waves (and Impedance)
In this day and age, there is only one meter on or associated with a
transmitter. It is the misnamed SWR meter. Consequently and unavoidably, with nothing else left to talk about, the importance attached to SWR becomes exaggerated. It is perfectly natural, for CB-ers and professional engineers alike, to imagine the indicated SWR applies to the one and only transmission line in the system. That is along the line from the transmitter/tuner to the antenna. But the meter does not indicate SWR on any line. It merely indicates whether or not the load on the transmitter is 50 ohms. Which is nice to know. But, nevertheless, you have been fooled! After half a century of being unwittingly misled, it is admittedly difficult to have to suddenly switch one's ideas about what is thought to be an important subject. Carry on arguing! ---- Reg. |
Standing Waves (and Impedance)
dansawyeror wrote:
Roy, Plot this on a smith chart program. You are correct, your meter reads close to 2:1, however you know nothing about the phase or resonance of the antenna. It does not tell you if you have a tuned antenna and a poor R match or if your antenna is way out of tune. (Of course neither does the telescope) What you say is true, but I don't understand what it has to do with the discussion at hand. No one has mentioned phase, resonance, tuning, or R match. An SWR meter isn't a suitable tool for measuring any of these, except that it'll usually indicate the resonant frequency fairly closely for most typical antennas. Roy Lewallen, W7EL |
Standing Waves (and Impedance)
Reg Edwards wrote:
. . . But the meter does not indicate SWR on any line. It merely indicates whether or not the load on the transmitter is 50 ohms. Which is nice to know. But, nevertheless, you have been fooled! . . . Let's not be fooled by these contrived misstatements. An SWR meter tells us the SWR on a transmission line to which it's connected, providing that the line and meter impedances are the same. This can easily be verified with a couple of simple experiments. So it does indeed indicate the SWR on a line. It will, of course, still give a reading under other conditions, such as when the line and meter Z0 are different or when there's no line at all, in which cases it means only what Reg says(*). But I'm afraid that the effort to leave a legacy of a new TLA (three letter acronym) for SWR meters is causing Reg to adopt an increasingly distorted view of what SWR meters can and can't indicate. (*) Any kind of test equipment can be misused or the results misinterpreted. For example, anyone using a 1000 ohm/volt voltmeter to read voltage in a high-impedance circuit will not see the voltage which is there when the meter is disconnected. Likewise, measuring high frequency waveforms with a 10 pF scope probe, even at moderate impedances. The list is endless. But this doesn't justify renaming each of those pieces of test equipment to accommodate the most naive user. Roy Lewallen, W7EL |
Standing Waves (and Impedance)
The so-called SWR meter is just a resistance (not impedance) bridge. The bridge is at balance and indicates SWR = 1:1 when a resistance of precisely 50 ohms is connected to its output terminals. It is arranged within the meter that this 50-ohm resistance, or whatever is connected to the output terminals, is the transmitter load. With the meter in its normal location, the load is the input impedance of the transmission line to the antenna. So when the input impedance of the line, as determined by Zo of the line and the antenna input impedance, is 50 ohms then the meter indicates SWR = 1:1 regardless of Zo, line length and antenna impedance. As Roy says, in the special case of line Zo being precisely 50 ohms it so happens that the meter will correctly indicate SWR along the line. For any other value of line Zo the meter will indicate varying degrees of nonsense. At HF, line Zo is frequently anywhere between 50 and 600 ohms and a tuner is used to transform line input impedance, either up or down, to the 50 ohms required by the transmitter. But Zo is not affected and the SWR meter indications remain in error. Whatever Zo and antenna impedance may be, the meter always indicates whether or not the transmitter is correctly loaded with a resistive 50 ohms. Note that the circuit operates independently of transmitter internal impedance whatever that may be. ---- Reg. |
Standing Waves (and Impedance)
Owen Duffy wrote:
There is nothing in what you have said that suggests to me that VSWR is the cause of TVI (or feedline radiation in the more general case). Please reference "Baluns: What They Do and How They Do It" by W7EL. VSWR causes impedance transformation. Impedance transformation varies the impedance. Baluns work better with some impedances than they do with others. Therefore, VSWR can cause balun malfunction accompanied by feedline radiation. All it takes is one time. And a possible cause is not necessarily a probable cause. There is nothing to suggest that you will be injured every time you ride your motorcycle at 120 mph. All it takes is one time. -- 73, Cecil http://www.qsl.net/w5dxp |
Standing Waves (and Impedance)
Crazy George wrote:
Those antennas aren't flat, and there are 2 transmitters, visual and aural. The audio is not mixed with the main carrier? -- 73, Cecil http://www.qsl.net/w5dxp |
Standing Waves (and Impedance)
On Sun, 25 Dec 2005 22:24:20 GMT, Cecil Moore wrote:
Owen Duffy wrote: There is nothing in what you have said that suggests to me that VSWR is the cause of TVI (or feedline radiation in the more general case). Please reference "Baluns: What They Do and How They Do It" by W7EL. VSWR causes impedance transformation. Impedance transformation varies the impedance. Baluns work better with some impedances than they do with others. Therefore, VSWR can cause balun malfunction accompanied by feedline radiation. Your example depends on the (mis)behaviour of a component (the balun) external to the feedline as a vital link in the asserted relationship between high VSWR and feedline radiation (both properties of the feedline itself). As you describe it the balun was not suited to the application, and it is the interaction of the unsuited balun in the whole topology that gives rise to feedline radiation. In addressing the suitability issue, you could: - change the environment external to the balun until the balun was suitable; or - replace the balun with one that suits the external environment. If the balun were replaced with a balun that was effective, then feedline radiation would be reduced sufficiently, without needing to reduce the high VSWR on the feedline. Excessive feedline radiation is not a necessary outcome of high VSWR, high VSWR does not, of itself, cause feedline radiation. If high VSWR does not, of itself, cause excessive feedline radiation, then finding the root cause of feedline radiation means looking beyond the myth that high VSWR feedlines radiate. Owen -- |
Standing Waves (and Impedance)
Owen Duffy wrote:
In addressing the suitability issue, you could: - change the environment external to the balun until the balun was suitable; or - replace the balun with one that suits the external environment. So if TVI can be fixed, it never existed in the first place? -- 73, Cecil http://www.qsl.net/w5dxp |
Standing Waves (and Impedance)
On Sun, 25 Dec 2005 22:31:09 GMT, Cecil Moore wrote:
Crazy George wrote: Those antennas aren't flat, and there are 2 transmitters, visual and aural. The audio is not mixed with the main carrier? It can be either way. If you choose to use separate transmitters the demands on antenna bandwidth are greatly reduced. John Ferrell W8CCW |
Standing Waves (and Impedance)
John Ferrell wrote:
Cecil Moore wrote: The audio is not mixed with the main carrier? It can be either way. If you choose to use separate transmitters the demands on antenna bandwidth are greatly reduced. John Ferrell W8CCW Thanks John, my IC-706 will receive the TV frequencies, but since I have never heard any audio, I assumed the audio and video were mixed to an IF frequency and then mixed to the TV frequency. (I have a reference book on TV but haven't looked at it in a long time). -- 73, Cecil http://www.qsl.net/w5dxp |
Standing Waves (and Impedance)
No. They are separate. Audio is FM and video is AM. Dan
Cecil Moore wrote: John Ferrell wrote: Cecil Moore wrote: The audio is not mixed with the main carrier? It can be either way. If you choose to use separate transmitters the demands on antenna bandwidth are greatly reduced. John Ferrell W8CCW Thanks John, my IC-706 will receive the TV frequencies, but since I have never heard any audio, I assumed the audio and video were mixed to an IF frequency and then mixed to the TV frequency. (I have a reference book on TV but haven't looked at it in a long time). |
Standing Waves (and Impedance)
dansawyeror wrote:
No. They are separate. Audio is FM and video is AM. Dan I can receive the commercial FM band just fine on my IC-706. Why can't I receive TV audio on it? -- 73, Cecil http://www.qsl.net/w5dxp |
Standing Waves (and Impedance)
If the meter is misapplied, it's misapplied. If my transmitter is
designed to operate optimally into a 300 ohm load and I use an "SWR" meter calibrated to 50 ohms, it's not going to do any better job indicating proper transmitter matching than indicating SWR on a 300 ohm line. I will continue happily to call my SWR meter an SWR meter, and know enough about what's going on inside it to apply it appropriately--whether it's to the task of giving me an indication of SWR on a transmission line or the task of indicating proper loading on a source. I suppose there are many who will continue to happily call them SWR meters and NOT understand how to properly apply them. I'd much rather work on educating them to understand how the meter works and how to apply it properly than to insist they call it by some other name. I've been at the task since B.R.E. But of course, not everyone sees it that way. Cheers--and Merry Christmas, Tom |
Standing Waves (and Impedance)
You can if you tune to the audio offset.
"Cecil Moore" wrote in message t... dansawyeror wrote: No. They are separate. Audio is FM and video is AM. Dan I can receive the commercial FM band just fine on my IC-706. Why can't I receive TV audio on it? -- 73, Cecil http://www.qsl.net/w5dxp |
Standing Waves (and Impedance)
On Sun, 25 Dec 2005 22:59:49 -0500, "Fred W4JLE"
wrote: You can if you tune to the audio offset. "Cecil Moore" wrote in message et... dansawyeror wrote: No. They are separate. Audio is FM and video is AM. Dan I can receive the commercial FM band just fine on my IC-706. Why can't I receive TV audio on it? Fred, is the correct answer because although analogue TV sound in frequency modulated on a sub carrier of the composite signal, the sub carrier is not transmitted in the "commercial FM band". Cecil's IC-706 may not cover the entire TV broadcast bands, he only asked why, when he can receive the commercial fm band just fine, can he not receive TV sound in general. Cecil probably knows the answer. Owen -- 73, Cecil http://www.qsl.net/w5dxp -- |
Standing Waves (and Impedance)
Fred W4JLE wrote:
You can if you tune to the audio offset. I have run the IC-706 all up and down the channel 3 60-66 MHz frequencies while in College Station, TX and cannot hear the audio anywhere. -- 73, Cecil http://www.qsl.net/w5dxp |
Standing Waves (and Impedance)
Owen Duffy wrote:
Cecil probably knows the answer. Actually, I don't. My IC-706 certainly covers 60-66 MHz which is channel 3 in College Station, TX. I jumped to the conclusion that since I couldn't hear WFM audio anywhere on that band, that the audio wasn't detectable until down-converted to the intercarrier. It is possible that I hit some dead air time and gave up too soon. I just cracked open my TV reference book and it indicates there are two ways to detect the sound, split IF reception and intercarrier reception. What now seems most likely is that I didn't tune high enough up to the 65.75 MHz sound carrier frequency or if I did tune that high, I hit some dead air time with no modulation. Next time I'm over there, I will try again. -- 73, Cecil http://www.qsl.net/w5dxp |
Standing Waves (and Impedance)
On Mon, 26 Dec 2005 06:06:08 GMT, Cecil Moore wrote:
Fred W4JLE wrote: You can if you tune to the audio offset. I have run the IC-706 all up and down the channel 3 60-66 MHz frequencies while in College Station, TX and cannot hear the audio anywhere. Is the sound subcarrier supposed to be at 65.75MHz for your Ch3? -- |
Standing Waves (and Impedance)
In article ,
Cecil Moore wrote: I have run the IC-706 all up and down the channel 3 60-66 MHz frequencies while in College Station, TX and cannot hear the audio anywhere. For what it's worth, I'm able to use my Kenwood TS-2000 to tune in the audio carrier of our local Channel 2 station. According to my cheat sheet, 2's video carrier is at 55.25, with audio carrier 4.5 MHz higher... hence 59.75 MHz. It seems to tune in best on my radio at 59.745. Your channel 3 audio carrier ought to be at 61.25 + 4.5 = 65.75 MHz. I don't have my service monitor handy so I can't tell for certain what the peak FM carrier deviation is, but it's definitely broad enough to cause serious distortion on my TS-2000 (which is set up for ham FM deviations of around 5 KHz). My recollection is that TV audio carrier deviation is similar to that of commercial FM broadcasts. It's possible that your IC-706 isn't willing/able to lock onto a carrier with such a high deviation, perhaps? or perhaps it needs to be switched manually to a "wide FM" mode to do so in this frequency range? -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Standing Waves (and Impedance)
Owen Duffy wrote:
Is the sound subcarrier supposed to be at 65.75MHz for your Ch3? I think that's a valid assumption. It's possibly a cockpit error of some kind. I will have to try again. -- 73, Cecil http://www.qsl.net/w5dxp |
Standing Waves (and Impedance)
Dave Platt wrote:
It's possible that your IC-706 isn't willing/able to lock onto a carrier with such a high deviation, perhaps? or perhaps it needs to be switched manually to a "wide FM" mode to do so in this frequency range? It's also possible that I am senile and need to try again. -- TNX & 73, Cecil http://www.qsl.net/w5dxp |
Standing Waves (and Impedance)
Dave Platt wrote:
It's possible that your IC-706 isn't willing/able to lock onto a carrier with such a high deviation, perhaps? I just drug out the IC-706 manual. It receives channel 2 on the HF antenna and channel 3 on the VHF antenna. :-) -- 73, Cecil http://www.qsl.net/w5dxp |
Standing Waves (and Impedance)
"John Ferrell" wrote
Crazy George wrote: The audio is not mixed with the main carrier? It can be either way. TV aural uses a separate transmitter from TV visual, because the visual amplifier in a TV tx is not linear enough to amplify both the aural and visual waveforms while maintaining r-f intermods sufficiently low (to FCC spec). The aural and visual signals are combined with mutual isolation of the txs, and radiated by a single antenna, typically. In an emergency, TV stations sometimes combine A&V at exciter level and pipe them through the visual PA, which is operated at reduced power to minimize r-f intermods. Typically the TV station is not meeting spec then, however. If you choose to use separate transmitters the demands on antenna bandwidth are greatly reduced. Reducing antenna bandwidth needed also would require separate antenna systems for the aural and visual transmitters. That is done, occasionally - but not often. This doesn't reduce the bandwidth needed by the visual tx by very much, however. Generally it's more cost-effective to use a single antenna to radiate both A&V. RF (RCA Broadcast systems field engineer, 1965-1980) |
Standing Waves (and Impedance)
US TV aural is frequency modulated, with +/-25 kHz deviation defined as 100%
modulation. Pre-emphasis of 75 microseconds is applied to program audio. It is transmitted as a discrete r-f waveform about 250 kHz below the upper edge of the TV channel. TV receivers typically demodulate it using an FM detector tuned to the 4.5 MHz intercarrier product present in the output signal of its video detector. Therefore if the TV visual carrier (only) goes off the air, no audio will be heard at the TV set, either. Any communications-type receiver capable of tuning to, and demodulating the TV aural carrier will enable listening to it. Even some little "pocket" AM/FM radio receivers have that ability. RF |
Standing Waves (and Impedance)
"Reg Edwards" wrote
Who cares what is the SWR on the transmission line provided the transmitter is loaded with its correct load resistance? ____________ Probably most people who don't want to destroy their transmission line. Apparently this does not include your esteemed self. RF |
Standing Waves (and Impedance)
In article ,
Cecil Moore wrote: It's possible that your IC-706 isn't willing/able to lock onto a carrier with such a high deviation, perhaps? I just drug out the IC-706 manual. It receives channel 2 on the HF antenna and channel 3 on the VHF antenna. :-) #splorf# Well, I suppose it does make sense in a way, but it sorta seems to violate the Law of Least Astonishment! -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Standing Waves (and Impedance)
65.75 is the magic frequency. It does appear the WFM mode can not be used on
this frequency on the 706 MKIIG I have. In the FM position, while distorted it is copyable. The radio shows WFM mode, but it certainly isn't in the wide mode. Now I have to get in the circuitry and see why the WFM is not operable on this band. "Cecil Moore" wrote in message et... Fred W4JLE wrote: You can if you tune to the audio offset. I have run the IC-706 all up and down the channel 3 60-66 MHz frequencies while in College Station, TX and cannot hear the audio anywhere. -- 73, Cecil http://www.qsl.net/w5dxp |
Standing Waves (and Impedance)
Fred W4JLE wrote:
65.75 is the magic frequency. It does appear the WFM mode can not be used on this frequency on the 706 MKIIG I have. In the FM position, while distorted it is copyable. The radio shows WFM mode, but it certainly isn't in the wide mode. My original problem was with an original IC-706 which I sold. I'm now mobile with an IC-706MKII with DSP. But my mode switch switches from FM to AM to FM ... and never shows WFM at all, not even when tuned to 88-108 MHz so commercial FM or TV is not worth listening to. I have a Sony Walkman that does receive VHF TV audio and my CCRadio+ does also. -- 73, Cecil http://www.qsl.net/w5dxp |
Standing Waves (and Impedance)
In the setup menu, you can disable unused modes. Go back in and turn it on.
"Cecil Moore" wrote in message ... Fred W4JLE wrote: 65.75 is the magic frequency. It does appear the WFM mode can not be used on this frequency on the 706 MKIIG I have. In the FM position, while distorted it is copyable. The radio shows WFM mode, but it certainly isn't in the wide mode. My original problem was with an original IC-706 which I sold. I'm now mobile with an IC-706MKII with DSP. But my mode switch switches from FM to AM to FM ... and never shows WFM at all, not even when tuned to 88-108 MHz so commercial FM or TV is not worth listening to. I have a Sony Walkman that does receive VHF TV audio and my CCRadio+ does also. -- 73, Cecil http://www.qsl.net/w5dxp |
Standing Waves (and Impedance)
Fred W4JLE wrote:
In the setup menu, you can disable unused modes. Go back in and turn it on. Thanks Fred, success at last. I don't remember ever disabling WFM mode and, to the best of my memory, I had never accessed the Q0 setting before. I think I liked my Hallicrafters S-53A better. -- 73, Cecil http://www.qsl.net/w5dxp |
Standing Waves (and Impedance)
You guys are testing my gray matter today...
The question: Is it possible to detect an FM subcarrier without receiving the base carrier? Perhaps another cup of coffee will help... On Mon, 26 Dec 2005 18:05:38 -0500, "Fred W4JLE" wrote: 65.75 is the magic frequency. It does appear the WFM mode can not be used on this frequency on the 706 MKIIG I have. In the FM position, while distorted it is copyable. The radio shows WFM mode, but it certainly isn't in the wide mode. Now I have to get in the circuitry and see why the WFM is not operable on this band. "Cecil Moore" wrote in message . net... Fred W4JLE wrote: You can if you tune to the audio offset. I have run the IC-706 all up and down the channel 3 60-66 MHz frequencies while in College Station, TX and cannot hear the audio anywhere. -- 73, Cecil http://www.qsl.net/w5dxp John Ferrell W8CCW |
Standing Waves (and Impedance)
"John Ferrell" wrote
The question: Is it possible to detect an FM subcarrier without receiving the base carrier? ______________ If you are still thinking of the broadcast television signal, the audio portion is not a subcarrier -- it is a discrete carrier whose modulation can be detected by any receiver capable of FM demodulation, and able to tune to its r-f center frequency. RF |
Standing Waves (and Impedance)
Richard Fry wrote:
If you are still thinking of the broadcast television signal, the audio portion is not a subcarrier -- it is a discrete carrier whose modulation can be detected by any receiver capable of FM demodulation, and able to tune to its r-f center frequency. The confusing part, at least for me, was that the entire passband *can be* downconverted and then demodulated assuming 4.5 MHz separation. That doesn't imply a *necessary* condition for demodulation. -- 73, Cecil http://www.qsl.net/w5dxp |
Standing Waves (and Impedance)
TV audio is not a sub-carrier. The audio is an independent transmitter from
the aural transmitter. They may have come up with some other way since I worked at WXEL in the fifties, but as a fifty's TV set still works today, I suspect the result is the same. "John Ferrell" wrote in message ... You guys are testing my gray matter today... The question: Is it possible to detect an FM subcarrier without receiving the base carrier? Perhaps another cup of coffee will help... |
Standing Waves (and Impedance)
Richard Fry wrote:
If you are still thinking of the broadcast television signal, the audio portion is not a subcarrier -- it is a discrete carrier whose modulation can be detected by any receiver capable of FM demodulation, and able to tune to its r-f center frequency. You've described how it's commonly generated. But is the end result any different than if it were generated instead by modulation of the main carrier by an ideal modulation system not having the practical problem of intermodulation distortion? That is, isn't the end result identical to a subcarrier? When I worked in radio broadcasting in the '60s, we generated an FM (SCA) subcarrier in addition to the stereo subcarrier by modulating the transmitter. Some stations had multiple SCA subcarriers. Roy Lewallen, W7EL |
Standing Waves (and Impedance)
"Roy Lewallen" wrote
Richard Fry wrote: You've described how it's commonly generated. But is the end result any different than if it were generated instead by modulation of the main carrier by an ideal modulation system not having the practical problem of intermodulation distortion? That is, isn't the end result identical to a subcarrier? ____________ No, in that an aural subcarrier would disappear without a visual carrier to convey it. TV aural via a standalone r-f transmission system would not. RF |
Standing Waves (and Impedance)
I like your answer best, probably because I understand how it works!
On Tue, 27 Dec 2005 13:46:45 -0500, "Fred W4JLE" wrote: TV audio is not a sub-carrier. The audio is an independent transmitter from the aural transmitter. They may have come up with some other way since I worked at WXEL in the fifties, but as a fifty's TV set still works today, I suspect the result is the same. "John Ferrell" wrote in message .. . You guys are testing my gray matter today... The question: Is it possible to detect an FM subcarrier without receiving the base carrier? Perhaps another cup of coffee will help... John Ferrell W8CCW |
Standing Waves (and Impedance)
Richard Fry wrote:
"Roy Lewallen" wrote Richard Fry wrote: You've described how it's commonly generated. But is the end result any different than if it were generated instead by modulation of the main carrier by an ideal modulation system not having the practical problem of intermodulation distortion? That is, isn't the end result identical to a subcarrier? ____________ No, in that an aural subcarrier would disappear without a visual carrier to convey it. TV aural via a standalone r-f transmission system would not. Sorry, I obviously failed to communicate my question. Let me try again. With no information other than looking at the composite signal including video and audio, would you be able to tell if it was generated by two separate transmitters or by modulation of a single transmitter by the video and an audio subcarrier? That is, if you could do the modulation without generation of intermodulation products. Roy Lewallen, W7EL |
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