What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Dual radio operations question

AX-O

Well Known Member
Guys, have a question regarding radio dual radio operations. Not simultaneously, one at a time.

I have 2 radios (Garmin 430W and SL-40 also a Garmin 240 audio panel) and would like the capability to transmit on either radio without having to select that radio as the transmit radio. Each radio would have its own PTT switch (on the control stick; china hat switch). Has anyone done this with their set-up? If so, how did you wire it? What pins?

All the military stuff I have flown has the capability to transmit on whatever radio you want just by pressing the china hat switch in the appropriate direction. For example, inboard is radio 1, outboard is radio 2 and aft is radio 3.

Any help or guidance would be appreciated.
 
Axel, you helicopter people are weird :). You should placard your airplane for rotorcraft license holders only. Sounds neat though.
 
I have 2 radios (Garmin 430W and SL-40 also a Garmin 240 audio panel) and would like the capability to transmit on either radio without having to select that radio as the transmit radio.

Looking at the GMA 240 installation manual, pin 20 and 21 on the J2402 connector are for the COM swap function. Connect a normally open momentary pushbutton switch between those pins, when pushed it will swap the active COM.

So if you have COM1 selected on the 240, hit that switch and now COM2 is selected. If COM2 is selected, hit the switch and now COM1 is selected.

You'd use just one pilot PTT switch with this, though, and it transmits on whatever COM is selected. But at least with the swap switch on the stick, you don't need to take your hand off to select the other COM.

From your description, it sounds like you want to just choose which COM you're transmitting on, without at the same time choosing that radio for receiving. I don't see that the GMA 240 can do that, but that seems like a bad idea anyway... but maybe I misunderstood you.

Actually, a remote switched full COM swap (like the GMA 240 can do) also is not such a good idea IMO. When we bought our RV-6, a button on the Ray Allen grip was wired as COM swap. It was more trouble than it was worth... hit the button by accident a few times. The results of that are never good. That button doesn't do that anymore :).

This is separate issue compared to a remote button that does frequency swap on one radio with active/standby frequencies. That is somewhat more useful, IMO. With a flip-flop radio as COM 1, I stay on that radio 95% of the time. When I want the other radio, I switch it on the audio panel!

--PK
 
From your description, it sounds like you want to just choose which COM you're transmitting on, without at the same time choosing that radio for receiving. I don't see that the GMA 240 can do that, but that seems like a bad idea anyway... but maybe I misunderstood you.

--PK

Why is it a bad idea? Just trying to figure out the negative aspects. Right now in one of the aircraft I fly, we have 3 radios and we receive on all 3 and transmit on whatever radio we want via the direction of the switch press.

The reason I wanted two radios is so I can listen to multiple freqs at the time. Is that not possible? Do I need to select the radio I want to listen to specifically? One or the other? I thought I could select to listen to both radios at the time via the audio panel.
 
If you just want to listen to multiple channels ...

Not sure if it's the same with GMA 240 & 430 but I've got a GNS 480, SL40 and PS8000B. The 480 let's me transmit and listen on 1 freq while monitoring the standby freq. The SL40 can do this also.

The PS8000B also lets me monitor the non-transmit radio. So if I want, I can monitor 3 frequencies in addition to the one that I'm transmitting on.

I have monitored 2 plus the transmit a few times but I've never tried to listen to 4 at once.:eek:
 
The way I see it....

To do what you are asking would take a switch capable of switching the PTT and the mic audio at the same time.
Unless you are going to use relays, that means that your mic audio circuit would have to go from the mic jacks through your stick and back to the radio.
 
Why is it a bad idea? Just trying to figure out the negative aspects. Right now in one of the aircraft I fly, we have 3 radios and we receive on all 3 and transmit on whatever radio we want via the direction of the switch press.
That's not as bad an idea as transmitting without listening at all, which is what I thought maybe you were suggesting at first! Sorry for the misinterpretation. I guess you're not as weird as people say. :D

In fact if you are good at listening to 3 radios at once and knowing which one is the right one to transmit on at any time... more power to you.

But the downside that I see is that there is no way to tell which radio is selected for transmit without looking at the audio panel. With the GMA 240 the remote switch just toggles between the two radios, and there isn't a pin for a remote switch to force COM 1 vs COM 2, for example. If the panel isn't in your scan, you can't be sure. That's what messed me up a few times and why I disabled the remote com swap switch.

The reason I wanted two radios is so I can listen to multiple freqs at the time. Is that not possible? Do I need to select the radio I want to listen to specifically? One or the other? I thought I could select to listen to both radios at the time via the audio panel.

Yes, on the GMA 240 you can select both radios to listen to simultaneously, just push both of the top "COM" buttons. Then select which one you are transmitting on by pushing one of the "COM MIC" buttons, or hitting your remote com swap switch. You can give the selected-to-transmit radio listening priority with the "Mon Mute" switch if you want.

Edit: Mel's short response above is really more to the point of your original question than all my verbiage. To do exactly what you want, you'll want a relay, controlled by the hat switch, that can work around what the GMA 240 is designed to do. A single simple hat switch and the GMA 240 by itself won't do it.

--Paul
 
Last edited:
Actually, a remote switched full COM swap (like the GMA 240 can do) also is not such a good idea IMO. When we bought our RV-6, a button on the Ray Allen grip was wired as COM swap. It was more trouble than it was worth... hit the button by accident a few times. The results of that are never good. That button doesn't do that anymore :).

I did that for about a month. And then I got use to it, and haven't made the "screwup" for quite a while. It did get a bit embarrasing though, as comm 2 was sometimes Class B ATC.

L.Adamson --- RV6A
 
That's what the audio panel does

Any audio panel will have a dedicated on/off switch so you can monitor any audio source connected to the audio panel. In the GMA 240, the top row of buttons turn the receive audios on/off regardless of which radio is selected to transmit. The audio panels also have an auto monitoring function, so if you have the receive for com2 off, and then select com 2 to transmit on, the panel also turns on the receive for that radio.

I like to wire the swap function on the aircraft we work on, because for it allows you to, for instance, tune com 1 to approach and 2 to tower, and hit the swap button to select the appropriate transmitter when needed.
 
Wondering why?

I'm reading this and trying to figure out what problem you are trying to solve. I have the same combination, 430 and SL40. I have a flip/flop on the stick for the 430 and you can listen to two freq's on the 40. Sometimes this can be confusing. I fly in the busy Class Bravo of Phx. I usually have my Comm2 (SL40) programmed with the Atis frequencies I need. The 430 has the two main channels I need on my commute. I use the flip/flop to swap them. This works fine in very busy airspace.

I think having the capability to transmit on two comms will only cause problems as you get them mixed up and hit the wrong one. A busy ATC person will not be happy!!!! For fixed wing I can't see the need to have the ability to transmit on two freq's at once. It is only one button push to change transmit freq's.

On the helicopter I fly I'd love to have this ability. On most flights I have to deal with 5 atc frequencies and 3 bands of emergency service frequencies, sometimes switching and talking in rapid succession. Having this ability would allow me to talk to ATC and then give position reports on the helicopter air to air freq. We've worn out the selector switch on the audio panel!!!!
 
I'm reading this and trying to figure out what problem you are trying to solve.
Not trying to solve a problem, just trying to use an implementation that I like.
-------------------------------------------------------------------------
Let me try to re-cage this thread. I want the ability to talk on radio 1 or 2 without having to select it on the audio panel or hitting a flip/flop switch on the stick.

I am used to flying like this. Please do not assume it will be more difficult if you have never used that type of function. It works for me. It may not work for someone else. The beauty of my airplane is that if I can figure out a way to do what I want, I have the option to implement it or not.

If I can't figure out how to implement the function I want, then the flip/flop will do.

If you can help me figure this one out, I would deeply appreciate it. Thanks to everyone that has taken the time to post a response.
 
Last edited:
Axel, I have no idea how to do it, but that's what I intend to do as well. I'm going to stick a coolie hat switch on the inboard end of the deluxe throttle--push forward with left thumb for comm 1, pull back for comm 2.

Reason--probably won't use comm 2 all the time, but it would be nice when flying in a group or formation to be able to have a dedicated formation freq while monitoring local freqs, atis, atc, etc.
 
Hi Axel,

Just FYI, in my day job, we use a communications panel that allows us to monitor up to 36 comm channels at one time - and it is normal to have about 8 up at once. In order to transmit on one, you have to select it for transmit, and then key your mike - two separate actions - so that you don't end up transmitting on the wrong loop. (The keyset stays "transmit selected" on whatever loop you used last, so it's quite simple, and for a guy in my position it is really simple - 99% of the time, I am on the "Command" loop.)

We do have a feature that allows us to transmit on three loops simultaneously, and it is fraught with peril - or at least the distinct possibility of embarrassment. A day doesn't go by when someone doesn't say something on the wrong loop with that feaeture....;)

I like the "select, then key" philosophy. In my airplane, I can monitor three frequencies at once, and the audio panel flip-flop on the stick allows me to select which Comm I want to be th transmitter.
 
I've done it

I've done something similar. Instead of the hat switch, I used a couple of other stick buttons, one for PTT1 one for PTT2. I'm not using an audio panel, just an aeroelectric mixer to combine the audio outputs, but you could certainly use your audio panel as a mixer on steroids.

You will need a relay controlled by your #2 PTT switch. Wire your mic through the normally closed position to the intercom / audio panel. Don't connect your #2 radio to the audio panel, instead connect it to the normally open position of the relay. I also used another normally open contact to switch the PTT line on the #2 radio so that the radio only transmits after the relay has pulled in, and the mic is connected.

Your first PTT switch will work for any radios connected to the audio panel, and the second switch will work for com 2. If you bypass all the mic lines around the audio panel, you would lose your intercom functionality.

Hope this helps.

-Paige

 
Last edited:
Swap Feature

On my RV7, I had a GNS480 and SL40 tied into a PMA7000 audio panel. On my stick I had both a flip/flop button (one for comm the other for nav) and comm swap button. I could easily be listening to 4 frequencies at one time if I had the monitor function selected on the 480 and SL40. Depending on which radio was primary I could flip/flop the frequency from the stick. The swap button on the stick allowed me to select which radio to transmit on. There was never a need to touch the audio panel except the initial turning on of which comm(s) to receive on. It sounds like this is what you are trying to achieve. You can listen to multiple frequencies and have the option of transmitting on any three of them by hitting the swap button. A quick glance at the audio panel will tell you if you are "swapped" so you can keep track of which frequency you are set up to transmit on.
 
Last edited:
Let me try to re-cage this thread. I want the ability to talk on radio 1 or 2 without having to select it on the audio panel or hitting a flip/flop switch on the stick.

I'm with you Axel. When I am leading a formation flight I want the ability to talk on either of two frequencies (flight descrete or air boss) without looking inside the cockpit or taking my hands off the throttle or stick. A "swap" button would be a partial solution, but this requires that I visually confirm which frequency I have selected and could cause confusion and require me to take my eyes off the formation. I would like to have the PTT for comm-1 on the stick and the PTT for comm-2 on the throttle. You need two radios for this to work properly as the "monitored" frequency on the SL-30 is cut out when there is incoming audio on the primary frequency, and that isn't good.
 
Not a problem at all. Just use 3 double pole relays. Your coolie hat will then be used to select which relay will pull up. Run each radio ptt and mic hi to a relay. Tie the ptt from each relay to ground and each mic hi to your mic jack. Then run 12dc to each relay coil and the other side of the coil to the coolie hat. Should work just fine.
 
Not a problem at all. Just use 3 double pole relays. Your coolie hat will then be used to select which relay will pull up. Run each radio ptt and mic hi to a relay. Tie the ptt from each relay to ground and each mic hi to your mic jack. Then run 12dc to each relay coil and the other side of the coil to the coolie hat. Should work just fine.

Man, you just scrambled my brain! :confused: Can you put all those words into a schematic for a 2-radio setup for us non-EE majors?
 
If I knew how to draw on here I would it would save a lot of words. I'll try again.

Each relay will have 6 contacts on it. 2 are for the coil which is used to activate the relay. Run a wire from one of these coil contacts to 12 volts, do the same for each relay. The other coil contact will go to the coolie hat switch. There are two contacts for each switch. One contact will go to the relay the other to ground. When that coolie switch is pressed the appropriate relay will operate.

The other contacts will control the switch of the MIC HI and the PTT from each radio.

From each radio wire the ptt to one of the relay contacts the opposite contact will then be wired to ground. Then wire the MIC HI wire from the radio to the other contact and the opposite contact to the mic jack. Make sure that the number one radio is wired to the number one relay and the second radio to the second relay etc. Then on the opposite contact of the MIC HI run this to the mic jack. There should be a wire from each relay going to the MIC HI of the mic jack or in other words this contact on the relay should be in parallel to the other relays MIC HI contacts.

Relay # 1
____
Radio # 1 PTT_______________________O O________________ground

____
Radio # 1 MIC________________________O O______________ mic jack

Relay Coil
12 volts DC ________
________________________________@@@@@_____________Coolie Hat


Ground_________________________________________________Coolie Hat

Repeat for each radio that you use.

Hope this helps.
 
If you only have 2 radios, here's a way to do it with one relay (and a diode):
2COMPTT.png

Possible advantage is that it is fail-safe in that if the relay coil opens, you still have COM1 capability. Possible disadvantage is that when keying COM2, COM1 might get keyed for a few milliseconds before the relay switches.

--Paul
 
Last edited:
Simpler way?

Garage guy,

I certainly don't object to a catch diode, but you don't need a diode to make the circuit work. Here's a repost of my original schematic (original imageshack link appears to be broken):

PTTswitch.png


It doesn't have your temporary key up problem, and you don't need to worry about a spike from the relay coil going into your radio.

I used the audio panel PTT / Mic vs. your use of COM 1 PTT / Mic so that intercom functionality would still exist. If you really must have a dedicated hard wired PTT button for each radio that isn't affected by the Com panel, you could daisy chain a couple of these relays as Norman suggested.

PTTswitch2relay.png


FWIW,
Paige
 
Last edited:
Here is another idea, but it would rely on a part that may or may not exist. If you can find a make some sort of 3-way mike splitter (there has to be something out there that does this), connect an output directly to each radio (rather than through the aido panel) and one to the audio panel. Then connect a separate PTT to each radio (either separate switches or a coolie hat).

This will allow pasengers to hear all comms via the audio panel / intercom and give you the option to trasmit on either of the radios.

To make this an optional functionality, you could put a switch on the panel. If the switch is on then you can use the multi-trasmit PTT. With the switch off, it could re-route the PTT through the audio panel and back to the radios so that the selected comm is the only one that will trasmit, just like a "normal" setup.
 
Garmin 340

I have the Garmin 340 audio controller installed in my panel. Two years ago I installed Tosten military style grips. Going through the 340 I use ?ground to activate? momentary switches on those grips to swap between comm freq 1 & 2 on the top Garmin 430 and radio transmit frequency on Garmin 1 and 2. I constantly monitor both Garmin 430s on my headset. Works great!
 
The intent is to not have a swap switch. But the ability to talk on either radio by selecting the position on a hat switch.
 
AX-O, any luck with this. I am trying to to the exact same thing as you.

I passed. I did not have the knowledge to do this and did not want to take the chance on burning something up. Those radios were expensive. I wired the flip/flop function of the 240 on the stick and I hate it. Have to look inside for a green light (feedback) in the sun to determine if i am transmitting on comm 1 or 2. so I don't even use it.

I was surprised on how many folks were against this. Specially from folks that have never used the capability.

Would love to wire #1 and #2 comms independently. If you have a working example, please post it. Thank you and good luck.
 
Coupled with directional audio

Separate com ptt switches coupled with radio specific directional audio like the IntelliAudio feature PS Engineering has would be really quite awesome at times. May even be a game changer
 
The T-6 Texan II has this capability, it is provided via a rocker switch on the throttle, up is Comm 1, down is Comm 2. If I'm understanding correctly what your setup is, you may have to bypass the audio panel since most commercial audio panels aren't setup to be configured this way. The rocker switch is a DPDT switch. I think if you were to connect radio 1 to the "top side" and radio 2 to the "bottom side" neutral will allow the intercom to function as normal. Then split your mic audio input to both radios. The issue then will be removing intercom audio while you are transmitting.
 
.... I wired the flip/flop function of the 240 on the stick and I hate it. Have to look inside for a green light (feedback) in the sun to determine if i am transmitting on comm 1 or 2. so I don't even use it.
....Would love to wire #1 and #2 comms independently. If you have a working example, please post it. Thank you and good luck.

Axel,
Stay tuned... My project this week is to do exactly this using an Arduino microprocessor (very inexpensive). It will monitor the Comm1 and Comm2 push buttons on both sticks and the PS-8000 intercomm Comm1 Comm2 output pins (to the radios) and will generate a quick "swap" pulse to my PS-8000 unit if it attempts to transmit on the wrong radio. No relays involved. This design also allows the radio/intercom panel to function normally like you are used to. Relays add way too much mechanical complexity, especially if you need duplicate operation on both sticks in your airplane.
I agree with your comment about flying formation.... Having a dedicated push button that always goes to your flight is a good safety enhancer. I'll let you know when I have the unit installed and tested.
Cheers,
Waldo
 
Interested...

Axel,
Stay tuned... My project this week is to do exactly this using an Arduino microprocessor (very inexpensive). It will monitor the Comm1 and Comm2 push buttons on both sticks and the PS-8000 intercomm Comm1 Comm2 output pins (to the radios) and will generate a quick "swap" pulse to my PS-8000 unit if it attempts to transmit on the wrong radio. No relays involved. This design also allows the radio/intercom panel to function normally like you are used to. Relays add way too much mechanical complexity, especially if you need duplicate operation on both sticks in your airplane.
I agree with your comment about flying formation.... Having a dedicated push button that always goes to your flight is a good safety enhancer. I'll let you know when I have the unit installed and tested.
Cheers,
Waldo

I am interested and will follow. My past aviation experience used this capability routinely. When building my RV-8 it seemed to get complicated quick, so I resorted to a pushbutton flip-flop adjacent to the throttle. The pushbutton does not require visual id to operate, but you're gambling if you don't visually check the audio panel
that the flip actually happened.
 
It is crazy how 10 years later this resurfaces and people now support the original function requested.

Let me see what happens with this request in 10 years.
To radio manufactures, please implement this. Would give you the upper hand in the market for sure. And if you name the function after me even better.

Dedicated pin to XMIT on primary Freq.

A different dedicated Pin to XMIT on STND BY Freq.

Primary freq has priority over secondary freq for deconfliction.

Mic drop... Let the money pour in.
 
Back
Top