Geico266

Geico266

Well Known Member
Now this might not be the most exciting thread, but it is something that I "discovered" about antennas and I thought I would pass it along, and start a thread about antenna also.

I installed a new XCOM radio in my old -3. The reception was great, I could pick up transmissions 100's of miles away, but I could not transmit to them. I could only "get out" about 50 miles and even that was "grainy".

I was just about to replace the antenna & coax. When I took a close look at the old antenna. I noticed it was pretty gunked up being near the exhaust. Bugs, oil, dirt, corrosion, etc., your basic neglected antenna.

I decided to take a Scotch brite pad and WD40 and polish it up. I really cleaned it up good and went flying (my favorite part ;)) It was bright & shiney as new. The 1st transmission was to a guy in the pattern 165 miles away, and I was 1,500' AGL! :eek:

My next project is to find a avionics guru with an VSWR meter and calibrate the antenna & coax, but with the transmission range I'm getting now it should be good?

Keep your antenna clean shiny clean!

Any other tips on keeping your radio & antenna healthy?
 
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And very important...

Mel said:
This is especially important for your transponder antenna.
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...for SS "rod" type antennae where the transmitting surface is exposed to the elements.

Since WD-40 and scotchbrite were involved in the original post, it's easy to surmise that this was a metal rod type antenna... Grease/oil/gunk will form a somehat conductive path shorting out the RF to the ground of the airframe...:(

In the transponder case, the "blade" type antennae where the transmitting element is encased in a plastic cover would be a little less immune from these effects.... a good argument for using this type.

But as Mel says... keep them all clean... noting that a reduction in transponder antenna performance will significantly reduce your TCAS detection range.
 
Wow...I had no idea that crud on the antennas could have such an effect on them. I'm no radio geek, but I assume it's the metal deposits that creates the problem?

Learned something new today. Thanks for sharing!
 
I second that

Had no idea either..i do know the transponder don't work when you snap the anntenna off...Of course it was 500 miles from home...:)

Frank
 
frankh said:
Had no idea either..i do know the transponder don't work when you snap the anntenna off...Of course it was 500 miles from home...:)

Frank
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I know this one too well. Broke mine the other day while washing my plane. Thank goodness it was at my home airport located in the DC ADIZ or it would still be grounded somewhere else. Easy fix but had to wait a few days for a new one to arrive.

To the antenna cleaning....especially when flying a CAP plane I always clean off the DF (direction finding) antennas as part of my pre-flight. Amazing how those things get dirty so quickly and really degrade performance of the DF unit. I'd hate to be the one flying and not able to DF an ELT then have to explain that it was not possible to locate it because the antennas were dirty.
 
frankh said:
Had no idea either..i do know the transponder don't work when you snap the antenna off...Of course it was 500 miles from home...:)

Frank
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If you weren't inverted all the time maybe you would be snagging your antenna on stuff. ;)

Gil, I know what you mean about grounding out, but I think the metal being dirty / corroded insulates it from the air? Does that make sense or am I thinking too much again?
 
It should not be...

Geico266 said:
If you weren't inverted all the time maybe you would be snagging your antenna on stuff. ;)

Gil, I know what you mean about grounding out, but I think the metal being dirty / corroded insulates it from the air? Does that make sense or am I thinking too much again?
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...corrosion, since the antenna would work perfectly if you insulated it with shrink tubing (at least at VHF frequencies)

I think the oil and grime is somewhat conductive and provides a RF short across the insulator at the base of the antenna.

At the 1 GHz frequency of the transponder, other effects (that's why it's sometimes refered to as "black magic"...:)...) may come into play though...
 
Larry has clearly hit upon the importance of keeping contacts free and clean from non-conductive material and it is apparent that he hit on the right materials to use to clean his particular antenna's.

I would caution however, that there are some antenna's out there that use various non-conductive material for strength, and then coat those materials with a nice sheet of copper.

That copper tends to turn dark after a while as it oxidizes. The appearance may be that it is "dirty" and needs to be cleaned. A good session with a green pad will get that nasty dirty old copper right off there....and eliminate the conductivity at the same time.

So, you will have a nice, bright and shiny, non-tranmsitting antenna. That will become evident when the reflect power back into the radio eventually burns the transmitter out.

Just be sure you know what material you are working with. I'm sure various manufacturers of antenna's can recommend the best way to clean them up.
 
Aviation or not?

TeaSea said:
Larry has clearly hit upon the importance of keeping contacts free and clean from non-conductive material and it is apparent that he hit on the right materials to use to clean his particular antenna's.

I would caution however, that there are some antenna's out there that use various non-conductive material for strength, and then coat those materials with a nice sheet of copper.

That copper tends to turn dark after a while as it oxidizes. The appearance may be that it is "dirty" and needs to be cleaned. A good session with a green pad will get that nasty dirty old copper right off there....and eliminate the conductivity at the same time.

So, you will have a nice, bright and shiny, non-tranmsitting antenna. That will become evident when the reflect power back into the radio eventually burns the transmitter out.

Just be sure you know what material you are working with. I'm sure various manufacturers of antenna's can recommend the best way to clean them up.
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TeaSea (?)

...are you talking about any of the aviation antennae we normally use on our RVs?

I can't recall any that have externally exposed shiny copper when new...
 
No, not all of them, but you have to be careful.

Also, copper coating on antenna leads is often the color of steel, so it's hard to tell.

I think Larry's absolutely correct in keeping his leads clean but a green pad can be very destructive on the wrong part. I just urge caution until you're sure what you're scraping away at.
 
Any....

TeaSea said:
No, not all of them, but you have to be careful.

Also, copper coating on antenna leads is often the color of steel, so it's hard to tell.

I think Larry's absolutely correct in keeping his leads clean but a green pad can be very destructive on the wrong part. I just urge caution until you're sure what you're scraping away at.
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Are any aviation ones built like this?

I think you might be talking about antennae for other purposes....
 
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