You won't like this.
If changing the jumper length changes the SWR, then one of two things is the problem. Either the antenna's input impedance is not 50 ohms, or the amplifier's output impedance is not 50 ohms. That's where the problem is, one or the other.
If removing the amplifier completely, hooking the antenna directly to the SWR meter, then using a short jumper to the radio produces something not close to that 1.2:1 (anything less than about a 1.5:1 is fine), then I'd say the antenna needs to be looked at/tuned. If the SWR is acceptable though, then putting the amplifier back in line but still using that short jumper between meter and amp, should yield the same SWR, -if- the output impedance of the amplifier is reasonably close to that of the radio, which ought'a be close to 50 ohms. If the SWR isn't at least fairly close, then that amplifier's output impedance is off. Some difference is normal, a big difference isn't. That's a fairly common reason with something like this happening. That reason being the 'no-tune' feature of the typical CB amplifier, one size does NOT fit all, they do have to be adjusted for individual circumstances. You have a choice of fixing the problem where the problem actually is, or 'rigging' it so that you just don't see the problem anymore, which is what you are doing by adjusting jumper/feed line lengths to some 'magic' number. (Sort of like adjusting water pressure by squeezing the pipe instead of just turning the knob.) Your choice.
- 'Doc
