manpack mic cable interacting with antenna???

[VK4FLYN]

I've made a little manpack out of a Dragon 485. I haven't touched my radios for a while and decided a tune was in order. Long story short - with an antenna attached my mic position seems to affect the SWR on HF. Tuned the antenna to a low SWR on 28.800 and when checking power I noticed the needle jumping around, and in some cases the radio couldn't put out even 2 watts. I thought it must be a patch lead or bad connection but all seem fine. The problem disappears when I Tx into a dummy load but is present on 2 different antennas. I'm not running a counterpoise and wonder if this may be part of the problem. Link below has a pic of the radio - using 2 different antennas to the one pictured. Any advice would be appreciated.

http://vk4radio.blogspot.com.au/2013/12 ... ished.html

[VK2ZRH]

The problem disappears when I Tx into a dummy load but is present on 2 different antennas. I'm not running a counterpoise and wonder if this may be part of the problem.

There's the clue to your problem.

The feedline (however short, or long) should be decoupled from the antenna; either by a "choke balun" (a stack of toroids slipped over the coax immediately behind where the feedline connects to the antenna feedpoint), or by a counterpoise system connected to the coax outer conductor at the antenna feedpoint.

From your description, the feedline + radio is acting as the 'other half' of your antenna and RF is coupled everywhere, creating the problems described.

I hope the above helps.

[VK4FLYN]

Thanks for the tips Roger, I'll have a look and see if that improves it.