Re: VFR audio panel? DO IT YOURSELF
There are several ways to take audio from several sources and isolate them from each other going into a common amp.
What you are talking about is a simple audio mixer. Before I explain how to make your own, most comm. radios have several aux audio inputs. My icom A200 has several inputs for aux audio. It is very basic; you have no control over selecting what aux source to listen to or volume, except at the source. That would work fine for a handheld (to listen only) and aux inputs from warnings and alarms. If you want you could add extra switches to select or deselect input and add resistors to adjust volume.
To make your own audio mixer there are many electronic kit companies that make little mixers and preamps. Bob of Aeroelectric has one such design on his web site.
http://www.aeroelectric.com/Catalog/AEC/9009/9009-700E.pdf
He sells the printed circuit board for $28 on his site, or you could use a generic board for cheap.
http://www.aeroelectric.com/Catalog/AECcatalog.html
(scroll towards the bottom of the page, makes the project real easy to assemble and look better)
I am pretty sure the $28 is just the board, but he does list all the part numbers and source. The parts would cost another $10-$20? Basically it mixes all the audio and has a small preamp. It is nothing special single OP amp (dual for stereo) mixer. This or one of the kits below will work fine.
Here are some cool kits that will work. If your radio has no aux inputs you can add a small mixer. They cost as little as $10 and come with everything, circuit board and components. One of these electronic kits has 4 channels - 3 mic + 1 music). You could feed two comms, a nav and an alarm. Hide it under the panel. You can get more fancy with base/treble control if you want. Also there is a basic mono mixer with out any controls. They are all cheap. Here are three kits in order of complexity (if you want stereo they make those kits also.)
http://www.electronic-kits-and-projects.com/1054.htm
http://store.qkits.com/moreinfo.cfm/FK652
http://www.electronic-kits-and-projects.com/1052.htm
(note: all you electronic gurus, I know this is overkill but I think it would work. If your audio input (gain) is too high you may need to add a dummy resistor like a 10ohm-1watt?. Also some operate on 9 v and will need a small regulated power supply. Little single chip LM317 voltage regulator kits will take any input volts up to 30 volts down to 1.2 - 25 volts for $3.50 to $6.00)
If you wanted to talk with the second comm (handheld) you could wire in a mic switch to select which radio to transmit from. This is all quick and dirty to get away from an expensive audio panel that takes up space. As a secondary suggestion, you can check out eBay for used audio panels. Often they go cheap. Myself, I will have one comm, a handheld (listen only) and may be an alarm or two. With the Icom A200 Aux inputs and the DRE intercom with Aux stereo input, I don't want or need an audio panel myself.
Cheers George
