lars wrote:Thanks. I guess I need to try a new antenna cable. Rather irritatingly, it's all one piece with the antenna mount, so I will probably have to replace the whole thing.
This is why I was wondering about a dummy load -- if the cable imedance is no longer 50 ohms because it is damaged, then (I'm guessing) I would still see poor SWR if I replaced the antenna with a 50 ohms dummy load, right? Or are things not as simple as that?
Yes, but you will need the relevant adaptors to connect the dummy load to the mag mount & don't forget a dummy needs to be a good one to take the load, so avoid anything CB.
A change in the impedance in the coax, would alter the SWR that you are seeing, but that antenna is clearly not very good if it's got a big disparity across just a few khz of spectrum at around 27.5 MHz.
What you are seeing would be normal at a much lower frequency, or across a big chunk of spectrum at around 27 MHz, but it should not be happening with your set up.
If you were trying to use say 26 to 28mhz & not seeing a difference in SWR, then the antenna would be a dummy load. But if you are just covering the few 100 khz of legal band then it should not be showing more than the smallest difference, or with a competently designed antenna.