COM antenna question

[piperboy84]

In your average spamcan with 2 COM radios, does each radio have it's own antenna or is a splitter used to share a single antenna?

[glendalegoon]

Ideally it would have two antennas.

Amazingly enough, the reason is that at times (more in the past), you could fly over the top of an ATC antenna and be using your TOP SIDE antenna and the wings/fuselage could block the signal to the ground.

So, you switched to the OTHER radio which had the antenna on the bottom and would have a good signal to the ground.

I can't tell you for your plane, but count the number of com antennas!

[BEagle]

Individual radios with independent antennae. Otherwise there would be a risk of single point failure if either an antenna coupler or sole antenna should fail.....:uhoh:

[piperboy84]

And while im asking, same question for the VOr/ils/gs antenna is it acceptable to share the signal with a splitter or is one antenna for each vor the norm

[Mark 1]

Diplexers are more common on the Nav side.

They do attenuate the signal slightly, but that's often an acceptable trade-off with less external hardware. They also don't have to deal with transmitter power as they are only using the aerial to receive.

[jollyrog]

Aerial. It's an aerial.

Insects and Americans have antenna.

[tecman]

Communications engineers the world over have antennas these days, according to our professional style manuals. Insects have antennae, presumably because entomologists are a better class of scholar.

[ChickenHouse]

Two COM, two aerials [british] = antennas [aviation] = antennae [US]. For redundancy this is the golden rule, while for NAV it is quite common to use one antenna setup and Multiplexer (don't forget Glideslope GS, my day2day plane has one antenna and a Triplexer).

[sapperkenno]

Aerial/antenna... My understanding was aerial is receive only, and antenna can send and receive?!

[tecman]

Sap, that's never been the case. Since the earliest days of the technology the term "aerial" was used for both transmitting and receiving installations. Check out some of the very early Marconi literature. And, actually, it was Marconi who later brought the term "antenna" into common use.

One of the fundamental tenets of antenna engineering is reciprocity: an antenna can be used interchangeably between transmitting and receiving. In practice, passive or active means are sometimes used to restrict operation to one or other application. But the antenna itself is completely reciprocal.

The US IEEE style of "antenna" and "antennas" is universal in professional international use and, indeed, the British IET journal (which is also widely read internationally) is called "IET Microwaves, Antennas and Propagation".

Popular usage does vary a bit, with older folks in the UK, Australia and a few other places still using "aerial" - most often for the wire style of HF antenna in my observation.

On the substantive question by the OP: go for 2 antennas!

[IFMU]

piperboy84,
I have seen first hand a com installation that used two Garmin radios, one antenna, and a diplexer. The goal was low drag. It worked poorly. We ditched the diplexer and went with a second antenna. That was much better.
Bryan

ps sorry for veering back onto topic, won't happen again.