Van's Air Force
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2nd comm
- Thread starter lhawkins
- Start date
vlittle
Well Known Member
Adding a second comm will require a bit of fussing.
First, the audio output from the second comm needs to be mixed into the intercom circuit. Depending on who's intercom you are using, this can mean using an auxiliary input (PS Engineering), or mixing directly into the headphone bus (Sigtronics).
Second, the microphone and PTT circuit needs to be switched between your two comms so that you can select which one you are transmitting on.
Thirdly, you need to install a second antenna for the comm.
There's an application drawing on the Vx Aviation page (follow the link for the AMX-2A, look for the installation guide). While the AMX-2A may be overkill for your application, it takes no panel space and is very compact. http://vx-aviation.com/
Let me know if you have any more questions after reviewing the document.
Thanks, Vern
First, the audio output from the second comm needs to be mixed into the intercom circuit. Depending on who's intercom you are using, this can mean using an auxiliary input (PS Engineering), or mixing directly into the headphone bus (Sigtronics).
Second, the microphone and PTT circuit needs to be switched between your two comms so that you can select which one you are transmitting on.
Thirdly, you need to install a second antenna for the comm.
There's an application drawing on the Vx Aviation page (follow the link for the AMX-2A, look for the installation guide). While the AMX-2A may be overkill for your application, it takes no panel space and is very compact. http://vx-aviation.com/
Let me know if you have any more questions after reviewing the document.
Thanks, Vern
az_gila
Well Known Member
AeroElectric Bob
As always, AeroElectric Bob is a good read...
http://www.aeroelectric.com/articles/Rev11/18Audio_R11.pdf
The simpler mixing schemes at the start of the chapter are probably what you need, with a double pole switch to select COMM1/COMM2 mic and PTT lines. Use the volume controls on the radios to select what you want to hear.
gil A
As always, AeroElectric Bob is a good read...
http://www.aeroelectric.com/articles/Rev11/18Audio_R11.pdf
The simpler mixing schemes at the start of the chapter are probably what you need, with a double pole switch to select COMM1/COMM2 mic and PTT lines. Use the volume controls on the radios to select what you want to hear.
gil A
groucho
Well Known Member
You can solve this one by having two PTTs. Yes, TWO!
That way you can listen to both radios & talk to either depending on which button you push. It does take a bit of wiring to switch what radio you send the mic to, but not horrible. There's probably a solution to that in Aeroelectric - good stuff.
az_gila
Well Known Member
Listening to two channels...
Walt wants an all independent system... but by switching the audio lines, you cannot monitor both radios at once (is the SL-40 a pseudo two channel radio?).
If your radios are dumb single channel units, then the trade off is fiddling with volume controls or on/off switches vs. only listening to one radio at a time.... definitely an individual preference thing...
gil A
PS ... my solution will be an AeroElectric Bob Isolation amp. with switched audio inputs... but I haven't built it yet....
Walt wants an all independent system... but by switching the audio lines, you cannot monitor both radios at once (is the SL-40 a pseudo two channel radio?).
If your radios are dumb single channel units, then the trade off is fiddling with volume controls or on/off switches vs. only listening to one radio at a time.... definitely an individual preference thing...
gil A
PS ... my solution will be an AeroElectric Bob Isolation amp. with switched audio inputs... but I haven't built it yet....
Norman CYYJ
Well Known Member
Using the 4p or a 3p switch you are right you only get to monitor one radio. But if you use a spst switch with a 180 or so resistor in series with it tied across the two audio lines you can monitor both or just one comm. the comm that you are using will be the loudest and the second comm the weakest that way you know which one the traffic is on. When you switch to the other comm then it becomes the loudest and the other the weakest.
gmcjetpilot
Well Known Member
What radio? Intercom? Audio panel?
If you go with DUAL radios, for sure you will for sure need a second antenna. FORGET any kind of antenna switcher manual or auto switching, forget it. TWO RADIOS, TWO ANTENNAS. To not have a second antenna really makes having two Transceivers null and void. Again the Garmin does not need two antennas. It's a pricey little devil but worth it for this little two receiver, one transmitter integration deal.
The wiring. Not a problem you will need a switch to select which radio the PTT switch will KEY. That is easy, a simple toggle double pole, single throw DPST switch will do. Just put a label on it "TX select" COM #1 and #2.
As far as audio you can do that with out an audio panel. All you have to do is turn up or down the volume as you desire. Now you want to make sure you are not transmitting on the radio that the volume is down on. That is where an "audio panel" comes in with basic logic. It know if you want to TX on radio #1 you want to listen.
How do you mix two radio audio? Easy but need to know what you have now. For some radios like ICOMS A200 you can just feed the second COM into the AUX input of the ICOM.
If you don't have a COM with AUX inputs you can make a little hidden fixed (adjustable) mixing circuit behind the panel.
The next step is an audio panel. The problem with audio panels is overkill for a homebuilt with two Coms. Audio panels often have COM 1 & 2, NAV 1 & 2, ADF, DME, MB........
New audio panels are expensive new. Old audio panels off of eBay might work, King, Narco & Terra. The latter two have thin profile versions that can be had for a few bills. If they are not beat up they look OK. You can even make a "DIY" RST audio panel.
PS engineering make a very simple intercom with selector buttons for COM and NAV 1 & 2 in a no nonsense design. It's not cheap but integrates all the functions.
As other mentioned the Garmin SL30 and SL40 is a true two receiver in one radio, that does not need an audio panel or second antenna. The new ICOM that has "traffic watch" is a joke. Its really a scanner that goes back and forth between two freqs but never at the same time. In other words it has one reciver.
If you go with DUAL radios, for sure you will for sure need a second antenna. FORGET any kind of antenna switcher manual or auto switching, forget it. TWO RADIOS, TWO ANTENNAS. To not have a second antenna really makes having two Transceivers null and void. Again the Garmin does not need two antennas. It's a pricey little devil but worth it for this little two receiver, one transmitter integration deal.
The wiring. Not a problem you will need a switch to select which radio the PTT switch will KEY. That is easy, a simple toggle double pole, single throw DPST switch will do. Just put a label on it "TX select" COM #1 and #2.
As far as audio you can do that with out an audio panel. All you have to do is turn up or down the volume as you desire. Now you want to make sure you are not transmitting on the radio that the volume is down on. That is where an "audio panel" comes in with basic logic. It know if you want to TX on radio #1 you want to listen.
How do you mix two radio audio? Easy but need to know what you have now. For some radios like ICOMS A200 you can just feed the second COM into the AUX input of the ICOM.
If you don't have a COM with AUX inputs you can make a little hidden fixed (adjustable) mixing circuit behind the panel.
The next step is an audio panel. The problem with audio panels is overkill for a homebuilt with two Coms. Audio panels often have COM 1 & 2, NAV 1 & 2, ADF, DME, MB........
New audio panels are expensive new. Old audio panels off of eBay might work, King, Narco & Terra. The latter two have thin profile versions that can be had for a few bills. If they are not beat up they look OK. You can even make a "DIY" RST audio panel.
PS engineering make a very simple intercom with selector buttons for COM and NAV 1 & 2 in a no nonsense design. It's not cheap but integrates all the functions.
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MontanaMike
Well Known Member
Handheld Second Com -Antenna
What do you think about wiring in a feed from the Vertex to the main antenna, to use if my single com goes paws up? Any issues, except never use both at the same time? Would a T fitting suffice, or would I need a splitter?$$?
I have the aux plugs installed thru the PM501 harness, would that work for a handheld interface if the single com fails?
"Am I making myself clear?" Cone of confusion reappears.
What do you think about wiring in a feed from the Vertex to the main antenna, to use if my single com goes paws up? Any issues, except never use both at the same time? Would a T fitting suffice, or would I need a splitter?$$?
I have the aux plugs installed thru the PM501 harness, would that work for a handheld interface if the single com fails?
"Am I making myself clear?" Cone of confusion reappears.
Do not use a "T" fitting. The transmission line is impedance matched. A "T" will screw this up. I don't recommend a splitter. Either use a separate antenna or swap out the coax when you plan to use the second radio.
MontanaMike
Well Known Member
Handheld Antenna Interface
If I follow you Mel, it would be best to put in two bulkhead fittings...one to disconnect the RG cable from the antenna-main radio interface, and another to re-connect the RG cable from the antenna to the handheld. STOP.
I am answering my own question here, sir. Just put in a second "emergency" antenna for the handheld and be done with it. Duh.
Cone of confusion dissipated. Thank you!
If I follow you Mel, it would be best to put in two bulkhead fittings...one to disconnect the RG cable from the antenna-main radio interface, and another to re-connect the RG cable from the antenna to the handheld. STOP.
I am answering my own question here, sir. Just put in a second "emergency" antenna for the handheld and be done with it. Duh.
Cone of confusion dissipated. Thank you!
rvmills
Well Known Member
I looked at the PS Eng PMA-4000 in my panel upgrade planning, to add a second radio like you are doing. That may be the unit gmcjetpilot was referring to.
I ended up grabbing a full audio panel via a buddy at SnF (fit my stack well), but the 4000 looked like a good unit, and is pretty small (1.7" X 2.435" rectangle, or 2.25" round) and looks pretty simple (Comm 1/2, Nav 1/2).
As mentioned above, more expensive, and maybe less fun to put together than a DIY, but maybe an option. Best price I could find on it was mid-700's (Gulf Coast has a $749 special on it now). Checked e-bay today after I read this but came up empty. I did see one go for about $500 in the VAF Classified several months ago, so who knows, might be another source if you go that direction.
Just wanted to pass what I learned as I explored the same area!
Cheers,
Bob Mills
"Rocket" RV-6
N600SS
4SD
I ended up grabbing a full audio panel via a buddy at SnF (fit my stack well), but the 4000 looked like a good unit, and is pretty small (1.7" X 2.435" rectangle, or 2.25" round) and looks pretty simple (Comm 1/2, Nav 1/2).
As mentioned above, more expensive, and maybe less fun to put together than a DIY, but maybe an option. Best price I could find on it was mid-700's (Gulf Coast has a $749 special on it now). Checked e-bay today after I read this but came up empty. I did see one go for about $500 in the VAF Classified several months ago, so who knows, might be another source if you go that direction.
Just wanted to pass what I learned as I explored the same area!
Cheers,
Bob Mills
"Rocket" RV-6
N600SS
4SD
mandm1516
Well Known Member
Warning: Possible dumb question ahead!
I've considered a second comm radio, probably the remote behind the panel one MGL is working on for backup. I'd like to have the PTT on the upgraded throttle quadrant--as Groucho pointed out, having 2 PTTs for 2 separate radios could work. Wondering if you could mount a coolie hat type switch as a PTT on the throttle--connecting 2 of the 4 points. Push forward to talk on Comm 1, pull backward to talk on Comm 2. Comm 1 for local area freq, Comm 2 for inter-flight freq if out flying with buds.
I've considered a second comm radio, probably the remote behind the panel one MGL is working on for backup. I'd like to have the PTT on the upgraded throttle quadrant--as Groucho pointed out, having 2 PTTs for 2 separate radios could work. Wondering if you could mount a coolie hat type switch as a PTT on the throttle--connecting 2 of the 4 points. Push forward to talk on Comm 1, pull backward to talk on Comm 2. Comm 1 for local area freq, Comm 2 for inter-flight freq if out flying with buds.
Actually this CAN be done. Our old C-124s used a similar setup. You push the cooley hat forward to transmit and push it back for intercom.
Also on some open cockpit aircraft where VOX doesn't work well, we use 2 buttons. One for radio and one for intercom.
The same thing can be done between 2 radios.
Just remember, you will need to switch the "mic audio" at the same time.
Also on some open cockpit aircraft where VOX doesn't work well, we use 2 buttons. One for radio and one for intercom.
The same thing can be done between 2 radios.
Just remember, you will need to switch the "mic audio" at the same time.
