L

LarryT

Well Known Member
Got my Icom A200 back from the repair center. According to them, they found little wrong with it.

I have received transmissions from as far as 120 miles away. Two Sundays ago I flew up to Toledo, WA to practice landings. Flying back to W52 I tuned and could receive the ATIS from PDX from about 55sm away. I then made a radio call to PDX Approach for a radio check that went unanswered.

This is perplexing to me. It is my impression that the receive/transmit signals come in/out through the same coax and antenna. Why such a big difference in performance?

Larry
 
Larry,
Easy test.
Might try changing headsets.
Some headsets have a mic gain adjustment. Yours might be set too low.
Good luck.
 
It can also be the antenna and/or antenna connections.
Receive is much less dependent on impedance matching.
 
Antenna is RA bent whip on belly

Mel said:
It can also be the antenna and/or antenna connections.
Receive is much less dependent on impedance matching.
Click to expand...

What is the best way to check the antenna and/or antenna connections? I am electrically challenged.
 
LarryT said:
What is the best way to check the antenna and/or antenna connections? I am electrically challenged.
Click to expand...

First look at both ends of the antenna cable and see that there are no loose connections, frayed shields, etc. If everything looks secure, find someone with an SWR meter and measure the SWR.
 
LarryT said:
Got my Icom A200 back from the repair center. According to them, they found little wrong with it.

I have received transmissions from as far as 120 miles away. Two Sundays ago I flew up to Toledo, WA to practice landings. Flying back to W52 I tuned and could receive the ATIS from PDX from about 55sm away. I then made a radio call to PDX Approach for a radio check that went unanswered.

This is perplexing to me. It is my impression that the receive/transmit signals come in/out through the same coax and antenna. Why such a big difference in performance?

Larry
Click to expand...

Larry,
I have the A200 and have the same problem & have gone thru the same exercises as others have recommended.
One suggestion I have not tried yet is to add solder to the crimped connections. I intend to do this the next time I do panel work.
My backup on the transmit is my handheld and have had to use at times when I'm holding short and it's a long distance to the tower. Inbound, eights miles out I have a weak transmit and use the handheld as well.

You should also try swapping out the A200 with another one.
 
Last edited:
Perhaps the ground-based stations transmit with more power. More power will give a greater range of reception.
 
Did a swap w/ FrankH

DanLandry said:
Larry,
I have the A200 and have the same problem & have gone thru the same exercises as others have recommended.
One suggestion I have not tried yet is to add solder to the crimped connections. I intend to do this the next time I do panel work.
My backup on the transmit is my handheld and have had to use at times when I'm holding short and it's a long distance to the tower. Inbound, eights miles out I have a weak transmit and use the handheld as well.

You should also try swapping out the A200 with another one.
Click to expand...

FrankH was already gracious enough to devote time to the swap-out. In his plane the tranmisssion was also weak, which is why it went back to ICOM, who found nothing wrong.

I must acknowledge that I have some level of frustration about this. I upgraded the panel in my previous aircraft (Cherokee 180) with a KLX 135A and a PSE audio panel. They were professionally installed by a terrific A&P from Idaho (Neil Stone) who specializes in avionics installation and systems repair. In ten years I never had a lick of trouble - reception and transmission from both the 135A and the back-up KX170B were always 5 x 5. That sure spoiled me. I guess I will be flying over to the "Last Resort" airstrip in Weippe, ID next spring to let a real expert, Neil Stone, figure things out.

Thanks for everyone's suggestions.

Larry
 
Un-do the antenna cables at both ends, and test for continuity (volt/ohm meter) between the center post & outside shield. There should be none. When I installed a Garmin SL-40 to replace an A200, I ran into the problem you're decribing. A new cable I put together, had one sliver of a wire that was touching the center lead.

L.Adamson --- RV6A
 
The best way to tell if you have an antenna/cable issue is to put an SWR meter on the unit.

Put it inline as close to the transmitter as possible. Tune the radio to the center of the frequency range that your antenna is rated for.

You should have a reading that is close to or lower than 1.5:1 or at least as low as the spec for your antenna and if not, you have an antenna/cable issue.

Some SWR meters also have a power meter built in. At 1:1 SWR you should be close to full rated power of your transmitter and if not, you have a transmitter issue.
 
Modern radios tend to use integrated RF power models in the transmission side and unlike the former descrete designs have VSWR detection built in and protect against a missmatched load by reducing the power output. Knowing Icom but without any knowledge of the A200 I suspect they would have used such a RF PA module.

In my experience 99% of radio issues are antenna and feedline (co-ax) related, and given that Icom has OKed the unit I think you can be pretty confident with focusing on the co-ax and antenna.

First check the co-ax with a multmeter - disconnect both ends and test for continuity and shorts - BNC to BNC. No continuity between the conductors is acceptable (impedance greater than the limit of most commonly available multimeters, say 2Mohm) and the resistance end to end of the conductors should be no more than the Copper resistance for the length. If there is any doubt replace the co-ax and reterminate with new connectors (and recheck). (You do have the correct crimp tool - right?)

Has the co-ax been damaged during installation? Check its entire length - visually if possible.

If you can - try by-passing the co-ax with a known good length.

Second - check the antenna - ensure it is grounded to the airframe at its base. A multimeter check should indicate zero resistance between the antenna base and the airframe. Check the condition of the BNC socket - is dirt, moisture or corrosion an issue, has the pin socket been damaged?

If the connections seem sound and the co-ax is good - replace with a known good antenna.

Doug Gray
 
Last edited:
You must log in or register to reply here.