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Comm Antennae

ColoCardinal

ColoCardinal

Well Known Member
If a duplexer is used to split one antennae to be used by two radios can they both be used at the same time? I assume that no problems would arrise from listening on two at once but what about pilot speaking to tower on one radio while Co-Pilot speaks to FSS?
Is there a well writen treatise on this subject any of you would recommend? I'm like a "babe in the woods" when it comes to this.
Thanks!
 
Carl:

Typically the cost is such that it is cheaper and easier to use two antennae.

Here is a link to Duplexer and one to Diplexer.

The explanation is better than I can provide here in a short period of time.

Yes it is possible to listen on two radios from one antenna but you end up with 1/2 the signal strength you would if you had an antenna for each radio. Another problem is transmitting in the same frequency band on two radios to one antenna is where your problem will occur. You do not want one radio transmitting into the other radio and that is what you would have. Your diplexer would need to be tuned to reject the frequency that is being transmitted on the other radio. Since both radios are in the same frequency band and frequency will change on each radio at different times, it is not practical to have a tuned diplexer that will work. If both radios were limited to one frequency, yes you could get a circuit tuned that would work but the cost is going to be greater than a 2nd antenna.
 
Thanks guys. This Grasshopper has much to learn, especially proper terminoligy, eh?
My main focus for asking is in trying to avoid a flying antenna farm. I already have 5 GPS antennas. Two will be hidden under the cowl but 3 will llikely land on the glare shield. There's a VOR antenna in the right wing; one for the VHF Comm and one for the Transponder on the belly; an ELT antenna on the top of the empenage and I still need a Glide Slope or two, a Marker Beacon and second Comm antenna. Yikes.
Maybe I can combine the GPS and Comm antenna or some other combination?
 
ColoCardinal said:
Thanks guys. This Grasshopper has much to learn, especially proper terminoligy, eh?
My main focus for asking is in trying to avoid a flying antenna farm. I already have 5 GPS antennas. Two will be hidden under the cowl but 3 will llikely land on the glare shield. There's a VOR antenna in the right wing; one for the VHF Comm and one for the Transponder on the belly; an ELT antenna on the top of the empenage and I still need a Glide Slope or two, a Marker Beacon and second Comm antenna. Yikes.
Maybe I can combine the GPS and Comm antenna or some other combination?
Click to expand...

Marker Beacon? You can get rid of that by putting one in the wingtip (or forgetting it altogether - not needed anymore).

Having a second Comm radio with a poor antenna is a waste of money for the second Comm - take it from someone who has a lousy wingtip Comm antenna on #2 (on one airplane) - put two good Comm antennas on the airplane. You can put GS in the gear leg fairings, in the cowl, or in front of a roll bar - pretty simple to make.
 
a different opinion

Marker Beacon's are going away, I wouldn't install a new one, but if you have one then as mentioned above almost any wire in the wingtip will work.

GS: You can put in your own dipole, or use a splitter on the VOR cable. If you have an SL-30 it has its own internal splitter, no option there. Splitters aren't cheap (like $100) but good coax isn't cheap either.

#2 Com: Unlike other reports, I am satisfied with my wing tip Archer-clone wing tip antenna for the #2 com. It is not as good as a "real" antenna, but not too bad, either. Ground stations regularly report it as "a little weaker than #1, but readable". I can get the ATIS above the static on #1 (external antenna) a few miles earlier than I can on #2 (wingtip). I have made no effort to swap radios to do a proper test. I will say that installation is important. I have a -10 so my wingtip is relatively thick. The leading edge of the antenna (where the feedline is attached) is placed at the thickest part of the wingtip, mounted as high as possible and then bent diagonally downward as much as possible. This is important as com's are supposed to use vertical polarization. Sometimes on the ground my belly whip is blocked by the airframe, and the wingtip works better! (but I view this as unimportant).
 
I guess there's some antenna construction in my future. Thanks again. Has anyone tucked their ELT antenna into some hidden recess?
 
ELT antenna. Yes, some builders have tucked the ELT antenna under the fairing between the horizontal and vertical stabilizers.
Con: much poorer location electronically, wrong polarization, doesn't meet TSO.
Pro: more likely to survive crash, less drag, not ugly.
 
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