Question with swr

Yeah, I'm at a loss on this one as well. In the many years i have been in this Hobie,with a correctly setup antenna,i have never seen the SWR rise when power levels increase. Even when i used over 2kw,my SWR would stay constant whether it was being measured on a Bird meter or a cheap Dosy meter. I have friends that run considerably more than 2kw and i have never seen an increase of SWR with there setups. The only time it would ever increase would be if there was a problem. Also. I have always been told to measure SWR at a higher carrier versus a lower one because the higher carrier would show a truer reading of reflection.

 

Every time I've checked SWR while the linear is on, it has been higher than when it is off. Was always told not to check it while the linear was on as the reading wouldn't be true. As far as too low of power, yeah that is what I've found. I have to turn my power up on high, on the radio, to calibrate the SWR meter. Just won't do it when in the low position.

I've run all kinds of mobile linears from little 100 watters up to the Texas Star 667V and several different base, tube type linears, the biggest being a Maco 750.

 

"i have never seen the SWR rise when power levels increase"

Neither have I as reading my posts carefully would have explained. Helps not to skim text quickly when you are talking technical theory. The SWR is not rising the meter is becoming less accurate as return current on the shield rises. Simple OHMs law involving non perfect conductors. As current on the shield rises a voltage drop occurs from the finite resistance of the shield braid between the meter chassis and the antenna feedpoint. This places the meter chassis at a higher voltage than the antenna feedpoint. Unless of course you are one of the fortunate few who can afford liquid Helium cooled superconducting coax.

 

withit,

My 4300/300 does the same thing. If your SWR is low with the power down, you are good with the power up. I use a different "barefoot" radio to check and calibrate SWR and then hook up the "good un"

 

helium cooled liquid conducting super cool coax!!!!

Yeah, that's what I got. Bought me some at the Petro!!!!

 

That "someone" knows what he is talking about, and I thought explained it. Ohms law etc..........

 

An SWR of zero is impossible since it would require an infinity in the equation. SWR is a RATIO! Enough of the kindergarten math around here. 1/0 = infinity. 0/1 = 0. Non sequitur. Here is a link. Don't want anyone to break their brain.


http://en.wikipedia.org/wiki/Non_sequitur_(logic)

 

....

 

Better watch out...... The way you smoke pills, you might start a fire-or worse.........

 

Everything that AB7IF is true.

If you use an antenna analyzer connected to the antenna's feedpoint, you don't have to worry about coax length at all.

If you insist on measuring SWR at the radio end of the coax:
A. Determine the wavelength of your favorite frequency, and divide by 2.
B. Multiply the answer you got above by the velocity factor of your coax. The resulting length is the exact length to which your coax must be cut in order for a radio's SWR meter to read correctly. Any other length will cause an incorrect reading.