How many PTT's can you have?

I'm very likely to put a PTT on my throttle quadrant, but can I have others too? The Boeing 737 had a PTT switch on the glareshield, and no doubt it was used the vast majority of the time, even though there were others.

If I have a PTT on the throttles, can I also have others?

Yes, assuming all the PTT does is pull the signal to ground. Just wire them up in parallel.

claycookiemonster said:

I'm very likely to put a PTT on my throttle quadrant, but can I have others too? The Boeing 737 had a PTT switch on the glareshield, and no doubt it was used the vast majority of the time, even though there were others.
If I have a PTT on the throttles, can I also have others?

Click to expand...

You can have as many PTT's as your heart desires.... it is just a ground on that pin.

Yes Jets often have PTT on each yoke and sometimes another PTT on glare shield, so pilot not flying does not have to use yoke PTT. There are also the handheld Mic's with PTT, both pilot seats (usually off to the side panel) and another at observer seat. Another PTT or two or three may be located in the audio panel's often located in the center pedestal with radios. So in a two crew plane you may have 4 PTT's at minimum. In a two place RV 3 PTT's would be reasonable.

Caution make sure your PTT's can't be hit accidently. A PTT on top of stick is subject to resting an object on top of stick and keying up the radio accidently. Same with Throttle PTT make sure you can't press it accidently or inadvertently.

I am not an avionics expert but when wiring your PTT's be careful. I would have a shielded wire pair, with ground back at the radio. I recall some weirdness if your PTT ground is acting like an antenna and you ground the PTT locally (especially on the control stick). Basically follow the instructions the radio manufacture provided carefully.

Yes, you can parallel PTT switches. But of course, you need to have a means of directing only one mike to the com at a time, e.g., parallel all the pilot’s switches, feed them into your audio panel/audio switch panel. Do the same for copilot. You (or your audio panel) will have to decide what happens if both pilot and copilot push their PTT. Or what happens if a center-panel PTT is pressed.
I’d use ordinary wire, not shielded. If there was to be a problem with RF pickup on what is a dc circuit I’d say you bought the wrong radio.

BobTurner said:

I’d use ordinary wire, not shielded. If there was to be a problem with RF pickup on what is a dc circuit I’d say you bought the wrong radio.

Click to expand...

Well I said I'm not an avionics expert. You seem so sure one size fits all. Are you an avionics expert? I'm not so dogmatic to say you do or don't need shielding on a PTT. It may be overkill, but I have reasons to suggest it as good practice and has no drawback (except a few grams of weight).

Second you say if a radio specifies shielded wire for PTT (and some do) that radio should not be used as unworthy? That is a strong statement. Up to you.

I will tell you the shield and common ground point to radio is a great way to protect against RFI or EMI. Twisted wire pair is another good practice from common mode.

The PTT circuit provides a ground to an internal DC circuit that controls transmitter operation. PTT is not an audio signal. It likely is a transistor pull down circuit that isolates the PTT ground from radio ground. You would think it doesn't need to be shielded (you would think). However simple GROUND issues have been the bane of many electrical systems.

I'm a big fan of not having different ground potentials in any audio circuit or audio adjacent circuit (like the PTT). My preference and insurance to avoid issues is common ground point to radio. PTT wiring has been known to cause strange things to happen like the radio keying up on it's own for example. Single unshielded wire with local ground for PTT? Up to you. I am sure it is fine with your superior radio model.

When in doubt follow the manufactures recommendation. The Headphone and Mic do of course need shielding and common ground to radio for best performance.

3 PTT in my RV7. The first was the trigger switch on the pilot stick but the one I use 99% of the time is on the throttle quadrant and love it. The 3rd is panel mounted for the co-pilot’s use. There is no PTT on the passenger’s stick as the stick is removable with a quick release button. BTW, The passenger’s stick is out (stowed) 90% of the time and I love that too.

Bevan

claycookiemonster said:

I'm very likely to put a PTT on my throttle quadrant, but can I have others too? The Boeing 737 had a PTT switch on the glareshield, and no doubt it was used the vast majority of the time, even though there were others.

If I have a PTT on the throttles, can I also have others?

Click to expand...

My 24-year old RV-6 has a PTT on the stick and on the arm rest both sides. There are TWO (2) for the left seat and two (2) for the right seat. Total four (4). I used two single strand wires for each switch. Has worked great for 24-years except for one (1) broken switch that was replaced.

Third way which will probably cause debate

Reference GMCpilot and Bobturner’s exchange above. I installed a PTT in my short bodied Mooney. I f’ing HATE exposed wires, temporary looking installations, etc. basically the approach the avionics shop was going to do.

Mooneys of that era had a vacuum relief button for wing leveler relief. It utilized 1/8” tube embedded in the yoke casting. That was my natural choice for a “conduit”. Anyway, they let me spot face the yoke and install a micro PTT in the yoke.

They had me run a single shielded wire to the switch. The shield was connected to one side of the switch and ground so it completed the circuit. Was small enough allow the system to break vacuum. Worked that way going on a few decades.

Why the short story, long? Most anything unshielded can resonate or pick up interference under the right conditions. The most knowledgeable and experienced in the art will still get surprised from time to time. Would have never guessed such a stone simple wiring approach would have provided as elegant a solution as it did for me.

Keep an open mind. Build safe.