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  #1  
Old 07-15-2010, 02:36 PM
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AX-O AX-O is offline
 
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Default Dual radio operations question

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.
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  #2  
Old 07-15-2010, 03:39 PM
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Default

Axel, you helicopter people are weird . You should placard your airplane for rotorcraft license holders only. Sounds neat though.
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  #3  
Old 07-15-2010, 04:12 PM
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Default

.............
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Last edited by AX-O : 04-09-2012 at 07:08 PM.
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  #4  
Old 07-15-2010, 05:02 PM
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Garage Guy Garage Guy is offline
 
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Default

Quote:
Originally Posted by AX-O View Post
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
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  #5  
Old 07-15-2010, 07:12 PM
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Quote:
Originally Posted by Garage Guy View Post

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.
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  #6  
Old 07-15-2010, 07:30 PM
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Default 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.
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  #7  
Old 07-15-2010, 07:36 PM
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Default 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.
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  #8  
Old 07-15-2010, 07:40 PM
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Garage Guy Garage Guy is offline
 
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Quote:
Originally Posted by AX-O View Post
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.

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.

Quote:
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 by Garage Guy : 07-15-2010 at 11:08 PM.
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  #9  
Old 07-15-2010, 08:12 PM
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L.Adamson L.Adamson is offline
 
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Quote:
Originally Posted by Garage Guy View Post
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
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  #10  
Old 07-15-2010, 09:58 PM
fmarino1976 fmarino1976 is offline
 
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Default 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.
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