I was contacted by Barry A., a local ham radio operator, a few days ago. Barry had taken an interest in my RV-8 project years ago, and he happened to check my blog and see that I was having radio problems. He offered to bring a bunch of his gear to the hangar to check out the COM antenna.

Saturday morning I removed the front seat and floor yet again, and fixed the problem of the COM 1 antenna coax connector hitting the doubler at the antenna mount. I removed the antenna, and enlarged the hole where the connector comes through the floor to make room for the connector. My current theory is that the original radio problem was due to the coax connector working itself loose at the antenna - it was found to be loose last weekend when I went under the floor. During my initial troubleshooting, I managed to create a wring issue when I replaced a questionable intercom connector. So I was dealing with two problems, one of my own making.

Saturday afternoon Barry came by. First he checked the antenna Standing Wave Ratio (SWR). The SWR was about 1.3 at 127 MHz, and 2 to 2.1 at 118 and 136 MHz. The antenna impedance was about 41 ω, a bit lower than the ideal 50 ω. The return loss was about 15 dB. The aft tip of the antenna is a few inches from the lower surface of the flaps when the flaps are down. I raised the flaps, and he checked again - the return loss improved 2 to 3 dB. Next he checked the transmitter power - it was cranking out a bit more than 10W (the spec is 10W). Bottom line - I don’t understand the significance of all the numbers, but Barry says the antenna and coax between the radio and the antenna are both in good shape.

Out of curiosity, I also had him check the COM 2 antenna, which is a Bob Archer internal wing tip antenna. I expected that it would be less optimized than the Comant external antenna, but the Archer antenna produced numbers that were slightly better. Its SWR was 1.3 at 126 MHz, increasing to about 2 at the upper and lower ends of the frequency range. The impedance was about 54 Ω, not too far off the ideal 50 Ω. The return loss was about 16 dB. He also offered to check out the NAV antenna, which is another Bob Archer internal wingtip antenna, but it proved to be too hard to get to the connector on the back of the GNS 430.

I really appreciated Barry taking the time to help me. Thanks Barry!

After Barry left I reinstalled the floor, then spent some time reworking wiring harness position to gain a bit more slack at the intercom connector. I rechecked all wiring, then tried some transmissions, listening for the speaker output from the ICOM A6 portable VHF COM I bought last week. I could hear the audio, but it was a bit broken. This is a bit improvement over earlier tests where nothing was heard at all. I suspect the audio may have been broken because the high power transmitter was overpowering the ICOM receiver at such short range (it is not at all uncommon to read reports of aircraft in close formation who are unable to communicate with each other due to this problem).

I need to check out a brake leak before I fly again and I ran out of time to do that this weekend. I hope to get a test flight off next weekend, and I think there is a chance the radio problem is solved. But, I won’t know for sure until I fly and can do some radio checks with stations a long way away.