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How to Test New Com Transmitter

R

rgmiller1974

Member
Hello Everyone,

I'm working on my panel and am at the point where I'd like to test the comm transmitters. I'm not too worried about the transmitters themselves, but I want to make sure the wiring is correct and I've got a good, clean signal from the microphone all the way to the transmitter.

AC 43.13 just says to test "...in accordance with the procedures appropriate for the airport and area..." That's not a lot of help. I'm not even at an airport; I'm still in my garage.

The best plan I can think of is to pick an unused frequency, connect the transmitter to a dummy load and then hold a hand-held receiver next to the dummy load. That said, dummy loads aren't perfect - which is why I think holding a handheld radio right near it will work - and that means I will be radiating some signal into the air.

So, my question is: Is there a better way to conduct this sort of test?

Thanks,
-Ross
 
Test with antenna

I recently installed and tested a comm radio by connecting it to the aircraft antenna and testing two-way communication with a hand-held. I used the designated pilot-pilot frequency 123.45 (Australia; may be different at your location) for testing and it was done in the shop so it's unlikely anyone else would have picked up the brief "radio check" transmission, which is legit anyway. I think it's worth testing the complete installation including the antenna and coax, with other equipment turned on (to check for interference), rather than with a dummy load.
 
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PaulvS said:
I used the designated pilot-pilot frequency 123.45 for testing and it was done in the shop so it's unlikely anyone else would have picked up the "radio check" transmission, which is legit anyway.
Click to expand...

Just a side note for those in the USA: At least in the USA, the frequency 123.45 MHz (aka 'fingers') is not a designated air-to-air communications frequency (Yes, I know everyone uses it. I may have also :eek:). The frequency 123.45 MHz is assigned for flight test uses and transoceanic communications.

The frequency 122.75 MHz is the only assigned fixed-wing air-to-air communications frequency. For general aviation helicopters, 123.025 MHz. Gliders and hot air balloons share 123.3 and 123.5 MHz.



Several years ago I lobbied AOPA and EAA to ask the FCC for additional air-to-air frequencies since 122.75 MHz is always quite busy, but no obvious action was taken.
 
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If you already have an antenna installed, then just use a handheld and 122.75 (as Carl described). Your Comm checks shouldn’t take more than a couple of seconds, and the guys chatting away shouldn’t mind…..
 
RV8JD said:
Just a side note for those in the USA: At least in the USA, the frequency 123.45 MHz (aka 'fingers') is not a designated air-to-air communications frequency (Yes, I know everyone uses it. I may have also :eek:). The frequency 123.45 MHz is assigned for flight test uses and transoceanic communications.

The frequency 122.75 MHz is the only assigned fixed-wing air-to-air communications frequency. For general aviation helicopters, 123.025 MHz. Gliders and hot air balloons share 123.3 and 123.5 MHz.



Several years ago I lobbied AOPA and EAA to ask the FCC for additional air-to-air frequencies since 122.75 MHz is always quite busy, but no obvious action was taken.
Click to expand...

I've amended the post... I'm in Aus!
 
RV8JD said:
Several years ago I lobbied AOPA and EAA to ask the FCC for additional air-to-air frequencies since 122.75 MHz is always quite busy, but no obvious action was taken.
Click to expand...

When I was doing my primary flight training in the '90's, the local folks in conjunction with some FCC types had convinced themselves that 122.85, 122.9 and 122.925 could also be used, as those frequencies are reserved for "secondary noninterference aeronautical utility 'mobile' stations"

An aeroplane is pretty mobile after all....

(ducking)
 
I waited until the project was at the airport for final assembly before testing the comm system end to end. Luckily I had line of sight from my open hangar door to a tower so a regular “radio check” from both seating positions was sufficient.

Or so I thought. My coax connection to the antenna was evidently flaky, and just happened to work that one time. On my first real taxi test, with real motion and engine vibration, my Tx failed all the way across the other side of the airport so I got some light gun practice. So lesson learned: don’t assume anything you test while stationary also works in motion or in flight!
 
RV8JD said:
Just a side note for those in the USA: At least in the USA, the frequency 123.45 MHz (aka 'fingers') is not a designated air-to-air communications frequency (Yes, I know everyone uses it. I may have also :eek:). The frequency 123.45 MHz is assigned for flight test uses and transoceanic communications.

The frequency 122.75 MHz is the only assigned fixed-wing air-to-air communications frequency. For general aviation helicopters, 123.025 MHz. Gliders and hot air balloons share 123.3 and 123.5 MHz.


Several years ago I lobbied AOPA and EAA to ask the FCC for additional air-to-air frequencies since 122.75 MHz is always quite busy, but no obvious action was taken.
Click to expand...

FWIW; as per FAA AC90-50d, para 6 you can also use 122.825 and 122.875 for this kind of testing. :cool:
 
I knew some ham radio guys a long time ago who were sticklers for the FCC rules. That got me thinking about the rules as they affect builders since I'm going to be in the same position soon and I live in NYC where unauthorized radio transmissions may get me in hot water. I know the FCC has some crazy rules so I thought I'd dig into this a bit. I'm making this post just because I find this stuff interesting and I have some time to waste waiting for replacements of my laser cut parts, not because I'm a stickler about these things.

It looks like your ability to operate an aircraft radio without a license depends on whether you qualify as an "aircraft station", which is defined as a "mobile station in the aeronautical mobile service ... located on board an aircraft." This was a change from previous rules that required pilots to have a radio license (I have my grandpa's from the 40s). The change came about through a notice of proposed rule making (WT Docket No. 96-82) in which the FCC decided "to amend ... the Rules to remove the individual licensing requirement for recreational vessel and aircraft stations operating domestically." Aircraft stations may be exempted from licensing, but they can't use the radio for just anything, they "must limit their communications to the necessities of safe, efficient, and economic operation of aircraft and the protection of life and property in the air" 47 CFR § 87.185.

It sounds like builders testing equipment may have issues qualifying as "aircraft stations" exempted from licensing because we aren't operating aircraft or using the radio for permitted purposes. You can also argue that we don't even have aircraft yet if the build is not complete and we aren't registered.

I dug a little deeper and found a category called "flight test stations", which can transmit "information or instructions relating directly to tests of aircraft or components thereof." 47 C.F.R. § 87.299. Amongst those eligible to be a flight test station are "Manufacturers of aircraft or major aircraft components." 47 C.F.R. § 87.301. It seems like we would fall into that category. The problem is that 47 C.F.R. § 87.18(a) requires flight test stations to have a license.

Another issue--if you want to transmit from a handheld radio to test your radio, it turns out that you need a ground station license for that.
"You may only use your hand-held aircraft VHF radio in your aircraft under the terms of your aircraft license. You are required to have a separate Ground Station license to operate your radio on the ground." (https://www.fcc.gov/aircraft-stations under "Operations").

So what does that mean? I think technically we have to have licenses to test our radios during the build. Having said that I seriously doubt any builder has ever followed the rules. ;)
 
FWIW an aircraft with an FAA registration (tail number), flying or not, is an "aircraft station". :cool:
 
Thank you

Thanks everyone for the replies and advice. My wife helped me test the transmitters last night and the signals picked up by the handheld sounded just fine.

(And to address PaulvS's concern: yes, I absolutely will do more testing with the complete system once it's installed in the plane. This initial test was just to make sure the wiring was correct while everything was still on my workbench and the wiring was easily accessible.)

-Ross
 
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