Weak Comm Transmit

I'm getting a weak transmit on my comm and need some assistance in troubleshooting the system.

Equipment:
ICom A200
Flightcom FC-130 intercom.
Commant Bent whip 122

Receiving communications is fine.
The transmit seems to be degrading over time.

I've checked my grounds and all seems well.
The antenna mount is clean strong.

I suspect my coax cable center lead has a weak connection on the connection side at the rear 90* connection to the A200.
I remember this as being suspect when I installed it.
The multi-strand conductor had to be soldered into a slotted bushing.

Am I on the right track here?

Try another headset before going to far with this.

Good luck,

Good Start

It's hard to narrow it down from your description, but check the easy stuff first. Swap headsets or clean the plugs, remove and re-seat the radio, pull and reset the circuit breaker (if it has one). If it's still broke, it could be the radio, the antenna, the coax, or the power supply.

Since its working ok on receive, I would imagine it is, a resistive connection in the power supply circuit, a high SWR situation, or a factory defect.

It is possible that you could have a resistive connection in either the power lead, or ground connection that would cause an excessive voltage drop when you go to transmit (I've even seen a bad circuit breaker drop a couple of volts) The best way to eliminate this is to measure the voltage right at the tray while transmitting. While you're there, check the PTT circuit. Make sure the PTT line is going all the way to ground. Failing PTT switches make for scratchy transmitters.

A high SWR will lead to eventual transmitter failure and could be caused by anything from the tray to the antenna itself. About all you can do for the tray and coax is visually inspect it and use an ohmmeter to check it out. Visually, if it looks suspicious, it's worth fixing. The usual culprits are radios not fully seated in the tray, cold solder joints, broken wires and a single strand of shield touching the center conductor. While it is doubtful that your coax is shorted (your receiver would be suffering also), it is possible that the center conductor has broken. I'd use an ohmmeter to verify continuity of both the center conductor and shield from the tray to antenna (this might take a helper and a couple of pieces of wire.). You'll have to disconnect the coax from the antenna, and remove the radio from the tray. If it passes the ohmmeter check and it's not smashed or frayed, then chances are the coax is OK.

The only real way to check out the antenna is to use a SWR meter or antenna analyzer. If you don't have a buddy with one, it's probably going to cost you around $70 for a meter, adapters and a patch cable. Don't go out and buy a CB meter, most of them are worthless at VHF.

Of course, the way to rule out the radio is to swap it out.


Hope this helps,

Paige
RV-8A

The Icom A200 is common enough, you might find someone at your field who has one that you could borrow for a few minutes?

If you use an ohm meter on the coax and find that it is grounded it may not be the antenna. Not all antenna have an open circuit. If the reception is good then the antenna and coax are most likely good. Check your mic and power connections. Clean the mic jacks.

Craig is right on - see if you can borrow another unit and slide it in your rack - this will cut your troubleshooting in half. It's what i did this week when my 430 stopped "comming" - borrowed one for two minutes to figure out I had a disconnected antenna.

Paul

Thanks guys.
I've swapped headsets.
I'll try swapping the radio next, you're correct in that I should be able to find one locally.

Troubleshoot coax.
Troubleshoot PTT.

weak radio performance

You mentioned that you were not real happy with a 90 degree connectors solder joint.

I had an intermittent transmit problem that was caused by a bad solder joint on a cables coax connector. Flying cross country with an intermittent radio is an "adventure" I will never repeat.

My desparate fix was have an avionics shop shot gun my antique antenna and cabling (1960 Tri-Pacer). When I saw how easy the crimp-on coax connectors worked and experienced the quality of the radio link; I bought crimpers and use them on all my coax cabling now. The $600 shop bill was expensive but well worth the final result.

You might try wiggling the cable during radio useage and see if there is a change. Replacing the suspect connector (if sensible) will be a way to rule it out or if your lucky fix it.