I was approached by the owners of an RV-10 who were having problems with their COM 1. In simple terms, the receive performance was poor and the transmit performance was diabolical. There were all kinds of theories; antenna splitters, poor coax cable, defective connections, you name it. How long had the problem persisted? Well they said, at least as long as we have owned the aircraft. COM 2 works fine so we don’t worry too much.
So, the first thing to do was connect up the VSWR meter and see what was happening in the feed line. Answer, not much. The VSWR reading was off the scale on my meter. Not good. So I pulled out the feed line and replaced it with a test-item of known quality direct from the radio to the antenna. No change… I’m thinking it must be the antenna… But it looks fine. Let’s look in the manufacturer’s catalogue to see what they say… Very strange, the antenna looks almost like the one I’m thinking it is, but just not quite.
To cut a long story short, at some point, probably from new, the aeroplane had been fitted with an FM broadcast receive antenna rather than a COM antenna. Sure, they look almost identical but the performance is very different.
A new antenna of the correct specification was ordered, fitted and hey presto, five by five at forty miles.
Simple but not so simple…
Aeroplane Electrical 