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Powering avionics w/o antennas (ADSB, transponder, ec)

Steve Crewdog

Steve Crewdog

Well Known Member
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Ready to start applying power to my system, obviously there won't be antennas attached to the gizmos (comm radio, ADSB, transponder, GPS). Should I leave them unplugged/off the main bus, a freind said it was Ok as long as I don't transmit on the comm radio. Thinking it through, the comm radio would be in receive only as long as I don't transmit, but unless I leave them unplugged I have no control over the ADSB, transponder, & GPS, soooo....


If I have to leave them unpowered, how do you test to make sure they're working ok until you have an antenna? Do you make a temporary antenna plane to mount them on?


TIA
 
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I'm assuming the reason for this is to see if 'things work'.
Trouble is... can you be SURE that there isn't a mistake that will activate the PTT line on the radio? If you have an antenna connected, fine, spot the issue and resolve it.

If no antenna connected... you run the risk of blowing the transmitter section.

At that point you will have discovered things aren't right, and have an expensive repair bill.
 
Dummy load

Buy a dummy load. It's the correct impedance so the device won't be harmed if it transmits. Better yet, buy a watt meter and or SWR meter. Hook up in line to check the coax up to the dummy load.
 
You will toast the transponder if you power it up without an antenna or dummy load.
 
Walt said:
You will toast the transponder if you power it up without an antenna or dummy load.
Click to expand...

That just peaked my curiosity, does the transponder transmit only when queried or does it always transmit as soon as it starts up?
 
Pilot135pd said:
That just peaked my curiosity, does the transponder transmit only when queried or does it always transmit as soon as it starts up?
Click to expand...

It depends. If you have a mode S-ES transponder (adsb data sent out) it will transmit without a query. Otherwise, it only replies to queries. But remember most airliners, as well as faa radar, send out query pulses.
 
Dummy Load - caution

I didn't bring up the dummy load idea deliberately. It is easy to find a 5 or 10 watt rated dummy load... but https://www.trig-avionics.com/product/compact-transponder/ indicates the transponder puts out over 100W peak.

Blowing out the dummy load will then (likely) damage the radio, and leave you with a dummy load that you think is good, allowing you to put it on some other radio.

You are better off getting an antenna and connecting it as a load.
 
blaplante said:
I didn't bring up the dummy load idea deliberately. It is easy to find a 5 or 10 watt rated dummy load... but https://www.trig-avionics.com/product/compact-transponder/ indicates the transponder puts out over 100W peak.

Blowing out the dummy load will then (likely) damage the radio, and leave you with a dummy load that you think is good, allowing you to put it on some other radio.

You are better off getting an antenna and connecting it as a load.
Click to expand...

Some of the better ones can put out 250 watts, however because these are pulse systems the average power is very low so a 10W load is fine.
 
Dynon tech support recommends not powering them up unless there is an antenna connected, so I will unplug them.
 
The installation manuals that I've read all recommend NOT powering up without the antenna(s). Check your manuals.

Dave
 
Antenna load

David Paule said:
The installation manuals that I've read all recommend NOT powering up without the antenna(s). Check your manuals.
Click to expand...

I've never installed any CB/two way radio/transponder/ADS-B that didn't recommend having the antenna attached before powering up. Some even recommend putting the SWR meter between the radio and the antenna. ......BOOOOOF.......(insert smoke emoji here) :eek::eek:
 
*sigh*.... sometimes your purpose in life is to serve as the bad example. I'll send everything back and have it bench checked.
 
Need more info

Steve Crewdog said:
*sigh*.... sometimes your purpose in life is to serve as the bad example. I'll send everything back and have it bench checked.
Click to expand...

Why? Do you believe you damaged something? As others pointed out, you can get inexpensive dummy loads to plug in. And as Walt said, it’s average power (heat load) that counts for these things, so a 10 watt unit is fine.
 
BobTurner said:
Why? Do you believe you damaged something? As others pointed out, you can get inexpensive dummy loads to plug in. And as Walt said, it’s average power (heat load) that counts for these things, so a 10 watt unit is fine.
Click to expand...

Yes, before I knew what I was doing in the past I powered up my system, so I figure I might have damaged something. I have some down time now, it's easier to send them in for a quick check now than find out later when I'm in final assembly that I broke them.

The antennas are in the wings, which are one of the final things to put on. When the wings go on you shift from 80% done/80% to go to 95% done/75% to go.
 
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Dynon says the ADSB is a receiver only and should be ok, they're willing to bench test the transponder for a fee but suggest I wait until I have it mounted and can test it myself, then send it in if it's broke. If I choose to send it in and they find that it works fine there would be no fee beyond freight.

Think I'll wait, since I won't be ready for it until next year.
 
Just to let you know, I have the Trig TT-22 transponder, which is basically the same as yours. I inadvertently screwed up the TNC connector (the center pin wasn’t fully seated, on insertion into the jack it was pushed backwards and failed to make a connection). I tested it, ‘no signal out’, hunted down the problem, fixed it, tested again with my fingers crossed. While I don’t recommend this, my TT22 did survive transmitting into an open circuit. I would keep my hopes up!
 
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