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....if already going into it, a little bit of history.
when the cows had bigger heads and the air was greener, there was no such thing as coax. what we used was the ubiquitous ladder wire, with an unknown impedance and with a frequency response depending on what the Gods ate at lunch! the VSWR story was not invented yet. What we did was one of two things: either tune the system for maximum current in the line or else used a light bulb in conjunction with a small light bulb and tuned for maximum brilliance. in neither case was SWR involved in the mess. the whole SWR uproar began after WW2 with the advent of coax and the new fangled theories. that was also the time when all kind of directional couplers came up.in due time a few wise guys developed all kinds of theories on the subject, and manged to convey the impression that SWR is king! nothing further from truth. what's really true is that reflections can cause the apparent impedance at the network's input to differ from Zo. SO WHAT? if you can adjust your matching network between the transmitter and the line for a match what do you care? actually the hitch is that, with a high SWR on the line, the losses go up. if the cable can take it, without melting no harm's done: whatever remains will get radiated. this was the good pint of open feeders: the losses were very low. an SWR fo 10 and more was insignificant from the losses' point ov view. Guys, leave it alone! Just make sure that the SWR is a reasonable value, something that the transmitter can handle and leave it at that. Saandy 4Z5KS Reg Edwards wrote: "Saandy wrote you can't measure SWR. ========================================= I am pleased you agree with me. ========================================= You can CALCULATE the SWR using the formula. ========================================= But of what use is the SWR it after you have calculated it? To what transmission line does it apply? Where is it? What are the locations of max-volts and min-volts? It does NOT apply to the line between transmitter and antenna. I suggest it exists only in your imagination. ;o) It is the name of "SWR Meter" which leads to confusion, misunderstandings and arguments. The name says the instrument does something which it does not do. With the help of old-wives, novices are led astray and are stuck with incorrect ideas about standing-waves for the rest of the lives. Just change the name to TLI (Transmitter Loading Indicator) which is what it is and does very well. The true meaning and associations of SWR will then emerge and all will be flooded with the light of reason. ---- Reg, G4FGQ. |
#2
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Saandy , 4Z5KS wrote:
What we did was one of two things: either tune the system for maximum current in the line or else used a light bulb in conjunction with a small light bulb and tuned for maximum brilliance. in neither case was SWR involved in the mess. It was around 1949 when I started hanging out at W5OLV's shack. He had a homebrew 1625 transmitter with a parallel tank circuit. The plug-in tank coil had a few turns of wire wrapped around the bottom and that was the transmitter output. He didn't use a tuner. He had a pickup loop that he slid up and down the line until he located a current maximum point. He cut the line at that point and fed it directly from the transmitter. He added or subtracted turns on the plug-in coil until he was satisfied. I didn't really understand what he was doing until I studied the Smith Chart in college almost ten years later. I now use that same basic technique with my 50 ohm SGC-500 amplifier. -- 73, Cecil http://www.qsl.net/w5dxp |
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