VENOM 1/2 WAVE SILVER ROD HI GAIN AERIAL

Just acquired a venom hi-gain 1/2 wave silver rod thru Amazon. Delivered very quickly and no probs erecting same two days ago. Came to it tonight and used the multi 2 and Binatone on it for about two hours. Started off as I left it with a SWR of 1.2:1. Max power (measured with SWR/Power meter so know it probably won't be that accurate) of 10 watts output. Realised that when I keyed mike(s) (both radios) no reaction on SWR meter or power indication. Checked all patch leads - OK. Went to isolated aerial and checked for continuity between 259 centre connection and ground and got a direct short. Can anybody help as to what has happened and if any possible damage to rigs/aerial?

I'm not familiar with that particular make of antenna but many 1/2 waves (and nearly all 5/8s) have a matching coil across the coax at the antenna feedpoint for matching purposes which will look like a DC short. If there was a fault at the antenna end (eg if the vertical element has somehow been disconnected from the feedpoint - this has happened to me before) you will still see some power going up the coax through the power meter, but your SWR will look very high.

There are a couple of suspects - one is that the antenna is faulty, but also that the SWR/power meter is playing up. You could try a few things - dummy load on the back of the meter and see what it indicates when you key up; try a different meter; check DC continuity between the antenna element and the middle of the coax socket. And still the most common issue of all with SWR meters, check you've got the radio and antenna plugged into the correct sockets on the meter!

Thank you for that. Checked for correct coupling to SWR meter on 3 separate ones and all correct and showed no movement. Showed a mate today and fired it up to find a very high SWR that I was able to bring down to 1.5 with a tuner. I'm still waiting to hear from Sigma/Amazon as to what they want me to do. Don't fancy sending the unwieldy lot back but I suspect that the coil has become detached somehow. Can't understand the varied performance though. Checked the radios used on a mag mount on my car and they were working OK. I was worried that with a 'dead short' I'd blown the output but it seems OK. Thank you again for your response - wait for developments from suppliers... (New to the forum and CTDX so can't find your name/call sign to mention you)

I can only say I was very impressed with Sigma. Technician rang me and went thru what had happened and I included the fact that I had actually opened the bottom cover where there is a balancing coil. I couldn't find anything wrong but the technician was excellent. He told me to send the bottom section back to Sigma where he would examine it and if necessary make repairs. I sent it off at my own expense and included return postage - altogether £6. Within four days of sending the technician got back to me on mobile and said that he had found the coil to be damaged. He couldn't make out what had damaged it (delivery or me - which I can rule out) but he had replaced it with a complete new coil and housing. Sigma were not going to make a charge. I got it back within two days of him contacting me and immediately erected it - perfect SWR on 19. Also 'getting out' OK. Farthest under the conditions was about 10 miles - FM @ 4 watts. Thank you Sigma credit where credits due