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my SWR reading
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Hash: SHA1 Hi, I just got my new (used) HF rig, and I strung up a half wave dipole for 10 meters using 28.4 mhz in my calculations. Several hours later I am getting an SWR reading of 2:1 at 28.4mhz. Is that pretty good or should I try to do better? I appreciate any opinions. Jim -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) iD8DBQFHHmVGQuDJiZ/QrH0RAnRNAJ9NcIJ58EeREFNwztYV7nkCSbb+hACcDveD LHfGOxSNluOb7JXvTpx3OLY= =EEQ7 -----END PGP SIGNATURE----- |
my SWR reading
if the radio is happily putting out its rated power then don't touch it,
keep operating! remember, too low an swr can kill you! "James Barrett" wrote in message ... -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi, I just got my new (used) HF rig, and I strung up a half wave dipole for 10 meters using 28.4 mhz in my calculations. Several hours later I am getting an SWR reading of 2:1 at 28.4mhz. Is that pretty good or should I try to do better? I appreciate any opinions. Jim -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) iD8DBQFHHmVGQuDJiZ/QrH0RAnRNAJ9NcIJ58EeREFNwztYV7nkCSbb+hACcDveD LHfGOxSNluOb7JXvTpx3OLY= =EEQ7 -----END PGP SIGNATURE----- |
my SWR reading
"James Barrett" wrote in message ... -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi, I just got my new (used) HF rig, and I strung up a half wave dipole for 10 meters using 28.4 mhz in my calculations. Several hours later I am getting an SWR reading of 2:1 at 28.4mhz. Is that pretty good or should I try to do better? I appreciate any opinions. Jim What are you feeding your dipole with? Coax or ladder line ?I found that if you use 450 ohm ladder line for your feed the length of the feed line can cause you problems . What kind of rig are you using ? BTW welcome to the group ! 73 Will _._ ._ ..._ _ ..._ .. _.. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) iD8DBQFHHmVGQuDJiZ/QrH0RAnRNAJ9NcIJ58EeREFNwztYV7nkCSbb+hACcDveD LHfGOxSNluOb7JXvTpx3OLY= =EEQ7 -----END PGP SIGNATURE----- |
my SWR reading
"James Barrett" wrote in message ... -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi, I just got my new (used) HF rig, and I strung up a half wave dipole for 10 meters using 28.4 mhz in my calculations. Several hours later I am getting an SWR reading of 2:1 at 28.4mhz. Is that pretty good or should I try to do better? I appreciate any opinions. Jim Go up and down in frequency a few hundred KC and see what the swr is in several places. Depending on the feedline and length it should probably be lower at some frequency near 28.4. |
my SWR reading
James Barrett wrote:
Hi, I just got my new (used) HF rig, and I strung up a half wave dipole for 10 meters using 28.4 mhz in my calculations. Several hours later I am getting an SWR reading of 2:1 at 28.4mhz. Is that pretty good or should I try to do better? That's marginally OK. What is the SWR at 28 MHz.? What is the SWR at 29 MHz? -- 73, Cecil http://www.w5dxp.com |
my SWR reading
ahso#1 wrote:
What are you feeding your dipole with? Coax or ladder line ?I found that if you use 450 ohm ladder line for your feed the length of the feed line can cause you problems. Not if your ladder-line is a multiply of 1/2 wavelengths at the frequency of operation. -- 73, Cecil http://www.w5dxp.com |
my SWR reading
"James Barrett" wrote in message ... Hi, I just got my new (used) HF rig, and I strung up a half wave dipole for 10 meters using 28.4 mhz in my calculations. Several hours later I am getting an SWR reading of 2:1 at 28.4mhz. Is that pretty good or should I try to do better? I appreciate any opinions. Jim If you can hear - and be heard and the band is open - then you're ok. If you can't hear or get heard - raise the antenna and try again. Good swr does not automatically mean a good antenna. |
my SWR reading
"James Barrett" wrote in message ... -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi, I just got my new (used) HF rig, and I strung up a half wave dipole for 10 meters using 28.4 mhz in my calculations. Several hours later I am getting an SWR reading of 2:1 at 28.4mhz. Is that pretty good or should I try to do better? I appreciate any opinions. Jim It's probably too long, but check it at 28 & 29 Mhz. If the SWR at 28 is better, it is too long; if the SWR at 29 is better, it is too short. Assuming you are using 50 Ohm coax, no reason you can't get it below 1.5:1. Tam |
my SWR reading
On Tue, 23 Oct 2007 17:19:02 -0400, James Barrett wrote:
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi, I just got my new (used) HF rig, and I strung up a half wave dipole for 10 meters using 28.4 mhz in my calculations. Several hours later I am getting an SWR reading of 2:1 at 28.4mhz. Is that pretty good or should I try to do better? I appreciate any opinions. Jim Nobody else has asked this magic question yet.... How high off of the ground is your dipole? --Teh |
my SWR reading
Try transmitting up and down the band to see where your lowest swr is.
Then you can shorten or lengthen the antenna a bit to get a low swr in the 28.4 mhz range. If you can't quite get it to 1:1, coiling the coax at the feedpoint, 4 or 5 turns about 6 inches in diameter can get you pretty close to 1:1. 2:1 isn't bad, but you're probably not getting full power output if your rig is solid state. ================================= When SWR is 2:1 the reflected power is only 11% of the tx output power, which will hardly be noticeable at the receiving end . Even when SWR would be 3:1 only 25% of the transmitter power would be reflected , still resulting in only a fraction of an S-point at the receiving end. But a low SWR will make the solid state PA of your radio feel happier ! Frank GM0CSZ / KN6WH |
my SWR reading
Highland Ham wrote in
: Try transmitting up and down the band to see where your lowest swr is. Then you can shorten or lengthen the antenna a bit to get a low swr in the 28.4 mhz range. If you can't quite get it to 1:1, coiling the coax at the feedpoint, 4 or 5 turns about 6 inches in diameter can get you pretty close to 1:1. 2:1 isn't bad, but you're probably not getting full power output if your rig is solid state. ================================= When SWR is 2:1 the reflected power is only 11% of the tx output power, which will hardly be noticeable at the receiving end . Even when SWR would be 3:1 only 25% of the transmitter power would be reflected , still resulting in only a fraction of an S-point at the receiving end. But a low SWR will make the solid state PA of your radio feel happier ! Frank, your analysis ignores the fact that the PA may deliver other than its rated power into the actual load, it could be higher or lower power, but in radios that incorporate VSWR protection of the PA, it is most likely to be lower, and at 3:1, substantially lower. VSWR protection helps protect radios operated by operators with the view that 'anything works'. To me, 2:1 seems a bit poor for such a simple antenna and probably readily capable of improvement to 1.5:1 or better. More importantly, the OP might expand their knowledge in the process. The original description was scant on information about the configuration, and I guess that sometimes, knowing how to describe the configuration / problem is the first step of knowing how to solve it. Others have identified missing elements of the description, the use or otherwise of a balun is relevant in indicating the extent to which common mode feed line current plays a part in determining the load presented to the feedline. Owen |
my SWR reading
2:1 isn't bad, but you're probably not getting full power output if your rig is solid state. ================================= When SWR is 2:1 the reflected power is only 11% of the tx output power, which will hardly be noticeable at the receiving end . But a low SWR will make the solid state PA of your radio feel happier ! Frank GM0CSZ / KN6WH Frank, I know that you know this, but I want to comment to the group... Assuming the transmitter does not fold back, the 11% reflected power will not change the signal strength... The reflected 11% will be 88% radiated on the return trip (minus any line losses) and 88% of that on the next round trip, etc... So, in the end the decrease in transmitted power is only a fraction of 1% for feedlines with low losses to start with... W2DU's very readable book REFLECTIONS, would be a good place to start for those who are a bit hazy on transmission lines, reflections, conjugate mirrors, etc.... Now, if we take transmitter foldback into consideration, we will need a lot of information about the various rigs before we can even begin to discuss how much a 2:1 SWR will change radiated power... Personally, for a situation where there is SWR on the line, I prefer a DX100B - it's pi-net could not care less and will still put out full power into 2 or 3 to 1... As well as some more modern rigs such as TS-830, etc... Tubes have a lot going for them... The Omni series of solid state rigs from Ten Tec also do not fold back under 2:1, though 3:1 does have some effect... cheers ... denny / k8do |
my SWR reading
Assuming the transmitter does not fold back, the 11% reflected power will not change the signal strength... The reflected 11% will be 88% radiated on the return trip (minus any line losses) and 88% of that on the next round trip, etc... ] That will only be true IF the Tx output stage has an infinite SWR looking back in to it, AND the reflection is in phase with the forward signal. In practice this will not happen. In fact the re-reflected signal may be 180degrees out of phase and so diminish the signal by its total value. The real story is that a much smaller proportion of the reflected signal will be re-reflected and the phase will depend on the system in use. In reality the impedance of a transistor o/p stage looking back in will not be too far away from 50 ohms due to the broadband matching networks.Some transmitters that I have worked on even had a spec on the impedance looking back in, a real pain to measure under full power conditions. 73 Jeff |
my SWR reading
"Denny" wrote:
Assuming the transmitter does not fold back, the 11% reflected power will not change the signal strength... The reflected 11% will be 88% radiated on the return trip (minus any line losses) and 88% of that on the next round trip, etc... So, in the end the decrease in transmitted power is only a fraction of 1% for feedlines with low losses to start with ... Now, if we take transmitter foldback into consideration, ... ____________ If, as reported, more than 99% of the output power of a transmitter ultimately is absorbed/radiated even by a mismatched antenna system, then why would a transmitter need power foldback for such loads? RF |
my SWR reading
Denny wrote:
Assuming the transmitter does not fold back, the 11% reflected power will not change the signal strength... True if a match has been achieved by a network. A 100 watt source will provide 112.4 watts of forward power with 12.4 watts of reflected power. Power delivered to the load is 112.4w - 12.4w = 100w Not true where a 100 watt 50 ohm source is not matched and provides 100 watts forward with 11 watts reflected. Power delivered to the load is 100w - 11w = 89w -- 73, Cecil http://www.w5dxp.com |
my SWR reading
Jeff wrote:
Assuming the transmitter does not fold back, the 11% reflected power will not change the signal strength... The reflected 11% will be 88% radiated on the return trip (minus any line losses) and 88% of that on the next round trip, etc... ] That will only be true IF the Tx output stage has an infinite SWR looking back in to it, AND the reflection is in phase with the forward signal. In practice this will not happen. How about this? 50 ohm 100w TX-------1/2WL Z0=100 ohm feedline--------50 ohm load -- 73, Cecil http://www.w5dxp.com |
my SWR reading
On Oct 25, 11:11 am, Cecil Moore wrote:
Denny wrote: Assuming the transmitter does not fold back, the 11% reflected power will not change the signal strength... True if a match has been achieved by a network. A 100 watt source will provide 112.4 watts of forward power with 12.4 watts of reflected power. Power delivered to the load is 112.4w - 12.4w = 100w Not true where a 100 watt 50 ohm source is not matched and provides 100 watts forward with 11 watts reflected. Power delivered to the load is 100w - 11w = 89w -- 73, Cecil http://www.w5dxp.com Ahhh, ya namby pambys... My open wire feed line can lick your coax! And the tuner is a conjugate mirror to boot... nyaa, nyaa, nyaa... denny / k8do Oh yeah, and to add something constructive for the one questioner: Foldback on transistor amps is to prevent RF voltages rising high enough to puncture the transistor junction... Tube radios with pi-net or pi-L tanks had enough matching capability to handle significant impedence mismatch compared to broadband transistor amps... Today, that function is served by autotuners, etc... |
my SWR reading
My homebrew Field Day rig monitors only the "forward power" with a
single directional coupler and adjusts the output level to keep the "forward power" constant. That rig delivers 83% of the power into a 2.38:1 SWR load as it does into a 1:1 SWR. This represents a 0.8 dB power reduction. Big deal. But my 25 year old Icom 730 delivers a full 100 watts to the output regardless of the SWR up until it starts shutting down at around 3:1. For example, with a 2.38:1 SWR, the "forward power" is 120 watts and the "reverse power" is 20 watts. Aren't modern rigs able to do this, or have they gone to the simpler system like I use in my homebrew rig? Roy Lewallen, W7EL |
my SWR reading
Roy Lewallen wrote in
: .... But my 25 year old Icom 730 delivers a full 100 watts to the output regardless of the SWR up until it starts shutting down at around 3:1. For example, with a 2.38:1 SWR, the "forward power" is 120 watts and the "reverse power" is 20 watts. Aren't modern rigs able to do this, or have they gone to the simpler system like I use in my homebrew rig? Roy, Modern rigs often employ a range of protective devices that influence the power delivered to the load. Many of the modern Icom HF radios control: - 'maximum output power' using either the forward output of a directional coupler or a non directional sample of output; - VSWR protection to limit maximum reflected power indicated by the directional coupler, typically to a value that is equivalent to the reflected power at rated output and specified maximum VSWR (eg 11W for a transmitter rated at 100W and max VSWR=2:1); - maximum collector current. The actual power delivered to a severely mismatched load is affected by all of these. It is likely for such a radio that with a 5 ohm load, the radio will level 'reflected' power to 11W, 'forward' power would be 16.5W, output power would be 5.5W. Depending on the way in which maximum output power is detected / controlled, it is indeed possible to get more than rated output power, so mismatch doesn't necessarily result in lower radiated power (despite popular opinion). Owen |
my SWR reading
Richard Fry wrote:
If, as reported, more than 99% of the output power of a transmitter ultimately is absorbed/radiated even by a mismatched antenna system, then why would a transmitter need power foldback for such loads? Egad, here we go again. Foldback has nothing to do with "reflected power". It's simply that a mismatch results in higher voltage or current at the output which could damage the output device or circuitry. That's why foldback is used. And, for that matter, "reflected power" isn't radiated *or* absorbed by the transmitter. The transmitter produces power which is sent to the antenna. All the power produced by the transmitter arrives at the antenna less whatever is lost as heat in the transmission line. There are no waves of average power bouncing back and forth on a transmission line. Mathematically separating the power moving down the line into "forward" and "reverse" components doesn't mean that waves of average power actually exist. Roy Lewallen, W7EL |
my SWR reading
Roy Lewallen wrote:
Foldback has nothing to do with "reflected power". It's simply that a mismatch results in higher voltage or current at the output which could damage the output device or circuitry. That's why foldback is used. If the source is connected to a transmission line, the mismatch results from a virtual impedance other than the one for which the transmitter was designed. The virtual impedance seen by the source is (Vfor+Vref)/(Ifor+Iref) where Vfor is the forward voltage phasor and Vref is the reflected voltage phasor. |Vfor|*|Ifor|=Pfor and |Vref|*|Iref|=Pref If it were not for reflections, the source would see Z0. DEVIATIONS AWAY FROM Z0 ARE *CAUSED* BY REFLECTIONS! Deviations away from the design impedance are what causes foldback. There are no waves of average power bouncing back and forth on a transmission line. One way for that to be true is for reflected energy waves to contain zero energy but any rational person knows that cannot be true. Reflected waves consist of an E-field and an H-field whose ratio is Z0. ExB is watts. Watts are the unit of power. Do you really think that the EM waves bouncing back from your mirror into your eyeballs while you shave contain ExB = zero watts? -- 73, Cecil http://www.w5dxp.com |
my SWR reading
"Roy Lewallen" wrote:
All the power produced by the transmitter arrives at the antenna less whatever is lost as heat in the transmission line. There are no waves of average power bouncing back and forth on a transmission line. Mathematically separating the power moving down the line into "forward" and "reverse" components doesn't mean that waves of average power actually exist. ____________ Roy, I have been involved with the evaluation and repair of FM and TV broadcast antenna systems where the initial problem was a failure in the antenna, which then produced a high mismatch between it and the main transmission line. The allegedly non-existent nodes along the transmission line for this condition did a fine job of melting holes in the inner conductor and Teflon insulators of 3-1/8" OD (and larger) rigid transmission line, at 1/2-wavelength intervals over a considerable length of that line. What other phenomenon do you believe caused such a result? RF |
my SWR reading
There
are no waves of average power bouncing back and forth on a transmission line. ************************************************** ******* You really mean that Roy, or am I misreading? I agree that no 'average' value of power is reflecting, but with a mismatch at the antenna terminals, voltage/current is definitely sloshing back and forth on the line making standing waves at .25L intervals that we can physically probe and measure... denny / k8do |
my SWR reading
Correction: substitute the word "loop" for "node."
RD |
my SWR reading
Denny wrote:
There are no waves of average power bouncing back and forth on a transmission line. ************************************************** ******* You really mean that Roy, or am I misreading? I agree that no 'average' value of power is reflecting, but with a mismatch at the antenna terminals, voltage/current is definitely sloshing back and forth on the line making standing waves at .25L intervals that we can physically probe and measure... It depends upon one's definition of "power". A purist will argue that it is not power until it is dissipated and steady state reflected power is not dissipated until power is removed from the source. The question is: Are the ExB watts associated with a reflected energy wave defined as "power" or not. -- 73, Cecil http://www.w5dxp.com |
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Richard Fry wrote:
Correction: substitute the word "loop" for "node." "Anti-node" will also work. -- 73, Cecil http://www.w5dxp.com |
my SWR reading
"Richard Fry" wrote in message ... "Roy Lewallen" wrote: All the power produced by the transmitter arrives at the antenna less whatever is lost as heat in the transmission line. There are no waves of average power bouncing back and forth on a transmission line. Mathematically separating the power moving down the line into "forward" and "reverse" components doesn't mean that waves of average power actually exist. ____________ Roy, I have been involved with the evaluation and repair of FM and TV broadcast antenna systems where the initial problem was a failure in the antenna, which then produced a high mismatch between it and the main transmission line. The allegedly non-existent nodes along the transmission line for this condition did a fine job of melting holes in the inner conductor and Teflon insulators of 3-1/8" OD (and larger) rigid transmission line, at 1/2-wavelength intervals over a considerable length of that line. What other phenomenon do you believe caused such a result? RF Hi Richard I recognize that you address your question to Roy, so forgive me for breaking in. It seems clear that the power is generated at the "source" and disipated at the "load" and that between the source and the load, only disipative components will exist. I would ask "what component along the transmission line between the source and load can *inrease* power?". As for the melting of condutors at 1/2 wave intervals, I attribute that to high current density related to a low impedance at that point. The damage may actually be related to the high impedance on the line which caused the voltage to rise too high. Jerry |
my SWR reading
Denny wrote:
There are no waves of average power bouncing back and forth on a transmission line. ************************************************* ******** You really mean that Roy, or am I misreading? I agree that no 'average' value of power is reflecting, but with a mismatch at the antenna terminals, voltage/current is definitely sloshing back and forth on the line making standing waves at .25L intervals that we can physically probe and measure... Waves of voltage, yes [1]. Waves of current, yes [1]. Waves of average power, no. History repeats itself in this discussion, so someone is sure to come up with that snappy line about: "Feel the dummy load on the reflected power port of a broadcast TX! If there's no such thing as reflected power, how come that load gets hot?" That's sloppy thinking. You are not looking directly at the main transmission line - you're looking at the output of a directional coupler that has been inserted into that line. Without the coupler, there's nowhere to connect that load. That coupler is a transducer. It samples signals from the main line, and then it does things to them. A directional coupler does NOT sample waves of power from the main line. It samples the voltage and current on the main line, adds the reflected components in phase, and delivers them to the output port labeled 'Reflected'. Connect a dummy load there, and sure enough it will get hot... but that's only through the action of the coupler. The challenge is still on the mat from several previous rounds: can anyone provide a fully detailed description of the operation of a directional coupler, circulator or similar device, based ONLY on waves of forward and reflected power? It can be done easily using forward and reflected waves of voltage and/or current, but that approach is off-limits for this challenge. Believers in waves of power shouldn't need it. [1] Real hams can blow their own holes in the side of the coax - we don't need no broadcast TX :-) -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
my SWR reading
Jerry Martes wrote:
As for the melting of condutors at 1/2 wave intervals, I attribute that to high current density related to a low impedance at that point. Because that impedance is virtual, it is a *result* and not a *cause*. The *cause* of the melting is the in-phase addition of the forward current and reflected current whose phasor sum is a maximum at points 1/2 WL apart. Denying that reflected energy exists will not keep the wire from melting. The low virtual impedance mentioned above is the *result* of: Z = (Vfor+Vref)/(Ifor+Iref) at the points where the two voltages are out of phase and the two currents are in phase. -- 73, Cecil http://www.w5dxp.com |
my SWR reading
Ian White GM3SEK wrote:
Waves of voltage, yes [1]. Voltage is proportional to the E-field. Waves of current, yes [1]. Current is proportional to the H-field Waves of average power, no. ExH = joules/sec = watts. Are watts the the dimensions of power? Are the E-field and H-field usually given in RMS (average) values? Can ExH be considered as the average power in an EM wave? Are you arguing that watts are not necessarily power? Are you arguing that it is not power until it is dissipated? It can be done easily using forward and reflected waves of voltage and/or current, but that approach is off-limits for this challenge. Believers in waves of power shouldn't need it. "Waves of power" is just a semantic strawman designed to elicit an emotional response. Anyone using the term loses technical credibility. It is akin to using the 'N' word to describe race. How about believers of EM waves containing energy passing a point? e.g. joules/sec = watts measured at a point? All this is explained in joules/sec = watts without referring to volts or amps in my energy analysis article at: http://www.w5dxp.com/energy.htm Note that I do not mention "waves of power" anywhere in my article. What I do talk about is forward energy waves and reflected energy waves the average value of which can be measured at a point in joules/sec, i.e. watts. -- 73, Cecil http://www.w5dxp.com |
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Cecil Moore wrote:
Ian White GM3SEK wrote: Waves of voltage, yes [1]. Voltage is proportional to the E-field. Waves of current, yes [1]. Current is proportional to the H-field Waves of average power, no. ExH = joules/sec = watts. Are watts the the dimensions of power? Are the E-field and H-field usually given in RMS (average) values? Can ExH be considered as the average power in an EM wave? Are you arguing that watts are not necessarily power? Are you arguing that it is not power until it is dissipated? It can be done easily using forward and reflected waves of voltage and/or current, but that approach is off-limits for this challenge. Believers in waves of power shouldn't need it. "Waves of power" is just a semantic strawman designed to elicit an emotional response. Anyone using the term loses technical credibility. It is akin to using the 'N' word to describe race. How about believers of EM waves containing energy passing a point? e.g. joules/sec = watts measured at a point? All this is explained in joules/sec = watts without referring to volts or amps in my energy analysis article at: http://www.w5dxp.com/energy.htm Note that I do not mention "waves of power" anywhere in my article. What I do talk about is forward energy waves and reflected energy waves the average value of which can be measured at a point in joules/sec, i.e. watts. Cut the other person's text, pepper with strawman questions, throw in a very ugly smear, and dodge the challenge. Same old Cecil. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
my SWR reading
Ian White GM3SEK wrote:
Cut the other person's text, pepper with strawman questions, throw in a very ugly smear, and dodge the challenge. Same old Cecil. Why must you resort to an ad hominem attack instead of a point by point technical discussion? What are you afraid might be revealed by such a technical discussion? You know and I know that if we polled the readers of this newsgroup, no one believes in "waves of average power". Why you guys feel the need to crucify that old strawman yet one more time just indicates how devoid your arguments are of any valid technical content related to reality. Since it allows you guys to avoid the actual technical issues, the purpose is obvious: "Since we are such gurus, blindly believe what we say." Here are questions for you and the newsgroup: 1. Who believes in "waves of average power"? Please don't be shy. 2. Who believes that reflected waves do not exist? 3. If reflected waves exist, who believes they can actually exist if they are devoid of joules/sec, i.e. ExH = zero? -- 73, Cecil http://www.w5dxp.com |
my SWR reading
Cecil, W5DXP wrote:
"Waves of power is just a semantic strawman designed to elicit an emotional response." It worked. I like the word power. Ronald W.P. King uses it in "Transmission Lines, Antennas and Wave Guides" on page 245 for example: "Important properties of transmission circuits (wave guides) of all types include the following: 1. Low power loss (a) due to heating the conductors and dielectrics of the circuit itself, and (b) due to radiation. 2. Sufficient power capacity. This implies sufficient spacing of conductors and adequate dielectric strength of insulating media to prevent spark discharge; it presupposes conductors with enough surface to carry large high-frequency currents. 3. An adequate frequency range and a useful frequency response. 4. Physical availability. 5. Special features such as rotational symmetry for swivel points, invariance in polarization of flexible construction." Best regards, Richard Harrison, KB5WZI |
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Richard Harrison wrote:
Cecil, W5DXP wrote: "Waves of power is just a semantic strawman designed to elicit an emotional response." It worked. I like the word power. Richard, what would be the dimensions of flowing power? Wouldn't power flowing past a point be watts/sec or joules/sec/sec? Have you ever heard of such? Wave energy flows. The power in the wave is measured at a fixed point, i.e. the measurement point is NOT moving. A Bird wattmeter is indirectly measuring the power in joules/sec *at a fixed point* on the transmission line. The joules are flowing past a fixed point but the joules/sec power exists at the measurement point which is NOT moving. Reflected energy is the energy flowing in the reflected wave. Reflected power is a measure of that energy flowing past a fixed point, i.e. the power itself is NOT moving. "Waves of Average Power" is an oxymoron since waves move and power doesn't. Be aware that "Waves of Average Power" is an expression designed to sucker the unsuspected into a losing argument. -- 73, Cecil http://www.w5dxp.com |
my SWR reading
Richard Fry wrote:
"Roy Lewallen" wrote: All the power produced by the transmitter arrives at the antenna less whatever is lost as heat in the transmission line. There are no waves of average power bouncing back and forth on a transmission line. Mathematically separating the power moving down the line into "forward" and "reverse" components doesn't mean that waves of average power actually exist. ____________ Roy, I have been involved with the evaluation and repair of FM and TV broadcast antenna systems where the initial problem was a failure in the antenna, which then produced a high mismatch between it and the main transmission line. The allegedly non-existent nodes along the transmission line for this condition did a fine job of melting holes in the inner conductor and Teflon insulators of 3-1/8" OD (and larger) rigid transmission line, at 1/2-wavelength intervals over a considerable length of that line. What other phenomenon do you believe caused such a result? Let's suppose for a moment that the holes were melted by reflecting waves of average power. Why do they repeat every half wavelength? Do the waves of average power have a phase angle such that they reinforce periodically? As an engineer, you of course know that the average of a periodic function is the integral of that function taken over one period, divided by the period. How then can average power have a phase angle? Or do the waves not have a phase angle but rather change amplitude as they travel? If so, what is the mechanism by which they do? Can you write the equations showing the power at each point along the line and how it can be greater at half wavelength intervals? In contrast, the existence of traveling and standing waves of voltage and current have long been established. You can find a rigorous analysis of their behavior in a vast number of textbooks. Given the load and transmission line impedances, you can very quickly calculate, even by hand and without the use of a computer, the current and voltage at any point along the line. Unless the line is perfectly matched, there will be repeating points of high current and of high voltage. Depending on the nature of the conductor and insulator, either or both of these can cause localized heating. In the example you gave, the damage is almost certainly caused by high current rather than high voltage. If you'll provide me with the impedance of the load and the impedance and velocity factor of the cable, I'll show that the high current points fall at the points where the damage occurred. If you tell me the transmitter power output, I'll also tell you what the current was at those points. Can you do the same for your theory of power nodes resulting from bouncing waves of average power? Anyone else having a basic understanding of transmission line operation can explain your cable damage without any necessity to imagine bouncing waves of average power. If you insist on believing that the damage was caused by traveling waves of average power, please provide an explanation of how these waves interact to create more power at some points than others. Because power is the rate of transfer or dissipation of energy, the power into any point has to equal the sum of the power dissipated at that point and the power leaving that point, unless that point contains some mechanism to store energy. Your analysis has to be consistent with this in order to avoid violating the law of conservation of energy. I can provide a detailed mathematical quantitative analysis of the nature of traveling voltage and current waves which explain the phenomenon you cite. I'm looking forward to your corresponding mathematical explanation of the phenomenon using traveling average power waves. Roy Lewallen, W7EL |
my SWR reading
Denny wrote:
There are no waves of average power bouncing back and forth on a transmission line. ************************************************** ******* You really mean that Roy, or am I misreading? Yes, I mean exactly what I said. I agree that no 'average' value of power is reflecting, but with a mismatch at the antenna terminals, voltage/current is definitely sloshing back and forth on the line making standing waves at .25L intervals that we can physically probe and measure... Then we agree on both points. Roy Lewallen, W7EL |
my SWR reading
Cecil Moore wrote:
Here are questions for you and the newsgroup: 1. Who believes in "waves of average power"? Please don't be shy. 2. Who believes that reflected waves do not exist? 3. If reflected waves exist, who believes they can actually exist if they are devoid of joules/sec, i.e. ExH = zero? Cecil, If you ever come to the realization that there is a difference between transient conditions and steady-state conditions, along with the realization that standing waves are actually useful, then all of this mumbo-jumbo about energy coursing back and forth along the entire transmission line would disappear. No waves of power needed, average or not. :D 73, Gene W4SZ |
my SWR reading
Cecil, W5DXP wrote:
"Waves of Average Power is an oxymoron since waves move and power doesn`t." OK, I`m a sucker. I apply power to one end of a transmission line and power results at the opposite end of the line. Power did not exist at the far end of the line until it was transported there by the line. The line moved the power from the 1st place to the 2nd place. It moved! Best regards, Richard Harrison, KB5WZI |
my SWR reading
Roy Lewallen wrote:
In contrast, the existence of traveling and standing waves of voltage and current have long been established. How can those waves exist without energy? In particular, how can those waves exist without their energy components passing a point and being measured in joules/sec? I can provide a detailed mathematical quantitative analysis of the nature of traveling voltage and current waves which explain the phenomenon you cite. What happens when you calculate ExH in watts? Is it zero? If not, your whole argument falls apart. -- 73, Cecil http://www.w5dxp.com |
my SWR reading
Gene Fuller wrote:
If you ever come to the realization that there is a difference between transient conditions and steady-state conditions, along with the realization that standing waves are actually useful, ... Please explain how those waves can exist without energy, i.e. without joules/sec passing a point. No waves of power needed, average or not. Please stop doing that, Gene. You know that I don't believe in "power waves". What you are trying to deny is that EM waves contain energy that can be measured at a point in joules/sec = watts. That argument just won't fly. -- 73, Cecil http://www.w5dxp.com |
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