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I’m just getting more into airplanes and trying to do a project on antennas. This airplane example is a enter image description herePiper PA-28-181 Archer II. I’ve labeled all the antennas, and I’ve noticed there’s a lot!

I’m specifically curious about #1. I know it looks more like a com antenna, but it also doesn’t look like most antennas I’ve come across. Any insight on why antenna #1 looks different than other com antennas and/or if there’s a more specific purpose for it?

Also, I’d love to learn more, so if someone is willing to label what each one does to confirm what I’m researching, I’d really appreciate it. Thanks!

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    $\begingroup$ Welcome to aviation.SE! This question might be helpful. $\endgroup$
    – Pondlife
    Jun 1 at 15:20
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Its a comm antenna, Belly mounted antenna have a few purposes

Worth mentioning is properly planning the antenna placement for modern audio panels, especially if you are installing antennas before you get into the audio panel wiring. Both Garmin and PS Engineering panels have a split-com mode. This is where the pilot can transmit on one radio and the copilot on the other simultaneously. While most com radios should be wired for transmit interlock (another reason to carefully follow the wiring schematics), for the split mode to work, one antenna should be mounted on top of the aircraft and the other on the bottom. That should be enough separation for closely tuned frequencies on both radios.

Since you are flying and generally controllers/towers/centers etc are below you it can be advantageous to have the antenna on the bottom of the aircraft so it's in a direct line to the receiver.

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Note: I'm not exactly an expert in this, so it's possible I've made some mistakes. I'm sure someone in the comments will correct me if that's the case.

#1: As the other answer says, this is the antenna for one of the two-way VHF radios. It's on the bottom because airplanes are typically above the ATC facility they're talking to, and so putting the antenna on the bottom may give it a better line of sight.

#2: This is the antenna for the marker beacons, part of ILS.

#3: This is the UHF antenna, used for both the transponder and DME (if installed).

#4: This is one of two navigation antennas (the other one is on the other side of the tail, not visible in this photo). They're mounted at a 45 degree angle to the aircraft centerline, and are typically used to navigate via VORs. They may also feed other navigational equipment.

#5: I'm not sure about this one. I think it might be the ELT antenna.

#6: This is the antenna for the other two-way VHF radio. It's mounted on top on the theory that, if you can't get a good signal on one radio, another radio with an antenna in a different position might give you better reception.

#7, #8, and #9: These are all satellite receivers for stuff like GPS and satellite weather, though you can't tell from the outside which is which.

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