UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - President Lincoln SWR issue "only" when meter inline.

SiriusHardware · 14th Jun 2021, 9:10 pm

I remember a number of historic instances where problems of unexpectedly bad SWR on half-wave vertical CB antennae were solved by substantially altering the length of the coax going to the aerial, hence my earlier suggestion to Damo.

However one thing which was always a given even on a working setup was that the higher the output power, the higher the indicated SWR even after the meter had been appropriately readjusted for FSD in the 'FWD' direction, so Damo's situation where turning the power UP makes the SWR BETTER is highly unusual, and lends weight to the idea that the radio may be going unstable and generating other frequencies (to which the aerial would present a bad SWR) when running at low power. Unfortunately the only thing which would show this properly would be a spectrum analyser, or possibly an SDR if anyone nearby has such a thing.

The question is, why does this only happen when the external meter is inline? I'm assuming that the bad SWR Damo sees is being indicated by the radio's onboard meter.

Damo, I think it's definitely worth (experimentally) changing the length of the coax on the aerial side if you can find a joiner.

14th Jun 2021, 9:10 pm	#11
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,560	Re: President Lincoln SWR issue "only" when meter inline. I remember a number of historic instances where problems of unexpectedly bad SWR on half-wave vertical CB antennae were solved by substantially altering the length of the coax going to the aerial, hence my earlier suggestion to Damo. However one thing which was always a given even on a working setup was that the higher the output power, the higher the indicated SWR even after the meter had been appropriately readjusted for FSD in the 'FWD' direction, so Damo's situation where turning the power UP makes the SWR BETTER is highly unusual, and lends weight to the idea that the radio may be going unstable and generating other frequencies (to which the aerial would present a bad SWR) when running at low power. Unfortunately the only thing which would show this properly would be a spectrum analyser, or possibly an SDR if anyone nearby has such a thing. The question is, why does this only happen when the external meter is inline? I'm assuming that the bad SWR Damo sees is being indicated by the radio's onboard meter. Damo, I think it's definitely worth (experimentally) changing the length of the coax on the aerial side if you can find a joiner.