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comm radio wiring question
https://www.warbirdinformationexchange.org/phpBB3/viewtopic.php?f=26&t=21201		 Page 1 of 1
Author:  snj5 [ Sun Apr 13, 2008 10:29 pm ]
Post subject:  comm radio wiring question
This is about a VHF radio in a plane with a headphone and microphone jack.

I currently have one comm radio with a harness to the pilot mike and headphone jacks as shown, with a standard separate push to talk (PTT) to the throttle handle. One of the goals was to be able to listen to both at the same time. I did find this on a cursory internet search:


Quote:
The outputs of two pieces of audio gear cannot be combined directly without circuitry to prevent loading of one by the other. If you are trying to combine the headphone outputs of two pieces of portable gear, you can make a mixer yourself by running each channel of both devices through a 10ohm resistor of 1/2 watt or more. You can place the resistors in-line with the "hot" leads of the wires of a "Y" adapter if you're in a DIY kind of mood.

So if I added the 10 ohm resistors to the headphone input of each radio afterwhich combining them, then used HF's schematic for the rest, would that work with the switch choosing which radio was primary and which was listen only?

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Author:  b17engineer [ Sun Apr 20, 2008 2:10 pm ]
Post subject: 
I'll probably get roasted for this, but I think your best solution would be to install an audio panel. That wya, you can select one or both of the radio's audio without mixing them. In addition, with some of them you get a built in intercom.

RICK
Author:  LadyO2Pilot [ Sun Apr 20, 2008 2:55 pm ]
Post subject: 
taking this on a side trip....how is the cylinder stuff coming along????
Author:  snj5 [ Sun Apr 20, 2008 7:15 pm ]
Post subject: 
LadyO2Pilot wrote:
taking this on a side trip....how is the cylinder stuff coming along????

Cylinders are on -
just waiting to upgrade to the Airwolf oil filter and an oil tank shut-off valve to keep the sump and lower cylinders from filling.

Finished the cockpit, new radios, hoses and wiring - looks terrific - come over Monday and have a look.
Author:  snj5 [ Sun Apr 20, 2008 7:19 pm ]
Post subject: 
b17engineer wrote:
I'll probably get roasted for this, but I think your best solution would be to install an audio panel. That wya, you can select one or both of the radio's audio without mixing them. In addition, with some of them you get a built in intercom.

RICK

I appreciate the suggestion, but every audio panel I find is such overkill.
I have two coms, and use the sidetone intercome feature on one of them as a ptt intercom between seats. It just seems like there should be something simpler if all you have is two coms and NO navs. For me, as simple as I can make this plane the better.
thanks
Author:  CAPFlyer [ Sun Apr 20, 2008 7:28 pm ]
Post subject: 
Have you looked at the PMA-4000s or other similar "gauge-mount" audio selectors/panels? They seem to be pretty straightforward to use and able to be hidden away with a true intercom inbuilt.
Author:  skymstr02 [ Sun Apr 20, 2008 7:34 pm ]
Post subject: 
I don't think that you will get the Federales to buy off on your alteration, have you approached them on this for preliminary approval?
Author:  snj5 [ Sun Apr 20, 2008 7:35 pm ]
Post subject: 
CAPFlyer wrote:
Have you looked at the PMA-4000s or other similar "gauge-mount" audio selectors/panels? They seem to be pretty straightforward to use and able to be hidden away with a true intercom inbuilt.

No - I have not seen them. Will search around now - thanks

Edit - add

It looks good - it's also $900 + a new harness. I wish they had a "PS 2000" with half the seat positions for $400. :D

Will keep looking, but this is a nice unit, and still overkill for my simple application. Perhaps I will call PS and see if they can custom build something.
Author:  LadyO2Pilot [ Sun Apr 20, 2008 8:48 pm ]
Post subject: 
snj5 wrote:
LadyO2Pilot wrote:
taking this on a side trip....how is the cylinder stuff coming along????

Cylinders are on -
just waiting to upgrade to the Airwolf oil filter and an oil tank shut-off valve to keep the sump and lower cylinders from filling.

Finished the cockpit, new radios, hoses and wiring - looks terrific - come over Monday and have a look.


hey, that's great...look forward to seeing it all !!!!

I'll be out next weekend for polishing detail on the black one....<pppsssssttttt I have a day job during the week :lol: :twisted:>
Author:  snj5 [ Sun Apr 20, 2008 8:55 pm ]
Post subject: 
skymstr02 wrote:
I don't think that you will get the Federales to buy off on your alteration, have you approached them on this for preliminary approval?

Thanks for the advice;
All is common standard T-28 stuff, and all are certificated experimental -
Author:  markcia [ Wed Apr 23, 2008 9:05 pm ]
Post subject: 
I think your Push to Talk (PTT) label is in the wrong place. It should be the switch that is closer to the mic. The switch you currently have labeled PTT is really the active/standby switch for the radios. By switching that you can make one or the other radio the one that you want to transmit on. The switch near the mic should be a momentary SPST. The other active/standby switch should be a DPDT. Currently most modern radios (even some older ones) will allow this circuit quite readily. Given that most headphones in aircraft are >32 ohms the series resistors from each radio audio output will be fine. You may have to turn up the volume a little more than you currently do but I can tell you from experience that my radio (Icom A200) can do it as I have a very similar circuit.

Mark
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