Comm Antennas

[Brandontwalker]

I have had some intermittent comm reception issues. Radios have been gone through and tagged. My avionics guy recommended removing the cork gasket that is under the antennas to create a better ground plane. The back antenna will be easy, but we will have to remove the interior to access the front one. Also, it appears that the antennas were painted and I was advised by another avionics shop that this could affect reception. Two questions for you fine folks: 1) Anyone have experience with removing the cork and did it help?; 2) Thoughts on painted antennas. Can they be stripped if that is an issue?  Thanks for the feedback. 

[Yetti]

Are the antennas through bolted? The bolts will create the contact with the skin which is the ground plane.   Paint is probably more your issue.  Stripping paint off plastic is going to be a challenge

[M20F]

Is this a recent problem?  I assume the antennas and gasket were there when you purchased so if this just started occurring recently, probably isn't the issue.  Some more details would be helpful in trouble shooting.  

[jetdriven]

you may be able to strip a painted antenna with Tolulene, MEK, or Acetone. Get it wet and cover with saran wrap a few minuntes, when it wrinkles, rub vigorously with a rag.

Regarding antenna mounting, to get a better ground plane, remove the antenna, scrub the metal under the antenna until it is very bright and clean, and clean the bottom of the antenna really good, especially pay attention to the metal around where the screw comes through the base.  Its a small raised ring. Then reinstall with stainless screws and stainless star washers. Put a thin bead of PRC aound the perimeter of the antenna to seal it, and wipe it with a wet finger to get a really nice bead.

 

You need a really good electrical connetcion to get a good ground plane. Also antennas form corrosion under them. In my case, it ruined one of the "7" antennas. The new Comant version that replaces it is straight and is over 400$

[Brandontwalker]

This is not a new issue. It has been ongoing since I've had the plane. The antennas are through bolted. I loosened and re-tightened the screws on the antenna I could access yesterday to see if there was possibly some corrosion that could be broken free. We will see how that works out. As for the problems, they are definitely intermittent. The biggest issue is when flying under lower-level clouds.

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[Yetti]

Coax and connectors?  Did they SWR meter it?

 

Edited November 1, 2015 by Yetti

[bonal]

Coax and connectors?  Did they SWR meter it?

 

+1. Also when they had them out did you clean the contacts in the treys 

[Brandontwalker]

you may be able to strip a painted antenna with Tolulene, MEK, or Acetone. Get it wet and cover with saran wrap a few minuntes, when it wrinkles, rub vigorously with a rag.

Regarding antenna mounting, to get a better ground plane, remove the antenna, scrub the metal under the antenna until it is very bright and clean, and clean the bottom of the antenna really good, especially pay attention to the metal around where the screw comes through the base.  Its a small raised ring. Then reinstall with stainless screws and stainless star washers. Put a thin bead of PRC aound the perimeter of the antenna to seal it, and wipe it with a wet finger to get a really nice bead.

 

You need a really good electrical connetcion to get a good ground plane. Also antennas form corrosion under them. In my case, it ruined one of the "7" antennas. The new Comant version that replaces it is straight and is over 400$

Good info. I am buying a new Comant com/gps combo antenna, but would like to salvage at least one of the old boomerangs. Did modifying the ground plane help you?

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[Brandontwalker]

+1. Also when they had them out did you clean the contacts in the treys 

Didn't do this. Do you just spray contact cleaner in the tray contacts and slide the radio in and out a couple of times?

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[carusoam]

Sunday spelling review for MSers...

Tray- the thing Mooney radios slide into...

Trey- the guy MAPA members know...

Best regards,

-a-

[M20F]

The biggest issue is when flying under lower-level clouds.

I would test the cables but given you have the same issue with both antennas my suspicion would be more towards the paint being an issue as that is what is common between both of them and it is the same issue with both antennas.  Beyond that you can check anything else common to the two radios (do you use an adapter in your cigar lighter?).

Do you have static wicks?  A lot of debate on the value of them but give the one thing you wrote here they might be something to consider.  If you notice the static in flight in only specific weather conditions you could try turning off one radio for awhile and see if after turning it back on the static goes away as it discharges off the antenna.

As you are already going to buy one new antenna would put that on first and see where things go as opposed to spending a lot of time trouble shooting.

 

 

[bonal]

damn IPad auto spell. Yes some contact cleaner and a few times can help.

Sunday spelling review for MSers...

Tray- the thing Mooney radios slide into...

Trey- the guy MAPA members know...

Best regards,

-a-

darn Ipad auto correct. Yes a little cleaner and a few times can help and about the simplest thing to try.

[Brandontwalker]

I do have an iPad charger connected. May be worth a try to pull it out on the next flight to see if it is causing interference.

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[takair]

Bond path can be your problem. The screws are often relied on for the bond to ground plane, but do not always do a great job, especially after years.  Even a little corrosion will cause issues.  Best ground path I have found is antenna mounted directly to clean skin.  if you do this you have to do a good job of sealing the base.  Their are conductive gaskets available, which are the best compromise.  The paint on the antenna may or may not degrade performance, metallic paint likely will.  My guess, paint got stripped and painted a few years ago.  The stripper wicks under the antenna and through the cork, over time.  Ground plane and mounting hardware are lightly corroded and performance compromised. High humidity seems to accelerate the mode...I suspect the stripper absorbs moisture. Likely, when flying below the clouds you have many of the scenarios that provoke the failure mode, high humidity, low altitude, and possibly some static build up.  I don't think wicks would help in this case, but good bonding may.  Ultimately, the antenna may be compromised as well.  Other advice regarding the coax is good as well, but usually that those issues are obvious at the connector or if the coax was damaged through other maintenance.  

[Brandontwalker]

An update here.  I made a 500 mile cross country last night and the radios performed very well.  I only had one spot where transmission seemed to be an issue and I flipped to the other radio and it was resolved.  I did a couple of things.  First, I ran the screws in and out a couple of times on the antenna I could access in hopes of breaking up any corrosion that may have formed and getting a better ground (not enough time to find new screws).  Second, I unplugged the ipad charger.  I am ashamed to admit that it was probably the charger.  However, in my defense, it never caused any issue in my other plane.  If this is it, it will be my cheapest fix yet.

[ArtVandelay]

On my plane, the 12v outlet is literally within a few inches of the radios. If you need the charger, buy a 12v extension cable (a few $) so you can move the charger away from the radios, see if that helps.

[OR75]

An update here.  I made a 500 mile cross country last night and the radios performed very well.  I only had one spot where transmission seemed to be an issue and I flipped to the other radio and it was resolved.  I did a couple of things.  First, I ran the screws in and out a couple of times on the antenna I could access in hopes of breaking up any corrosion that may have formed and getting a better ground (not enough time to find new screws).  Second, I unplugged the ipad charger.  I am ashamed to admit that it was probably the charger.  However, in my defense, it never caused any issue in my other plane.  If this is it, it will be my cheapest fix yet.

I had com issue with a cigarette charger as well. See attached link. 

One usb charger would create issue on some frequencies but not others . 

I changed to a higher quality charger and so far , no problem 

 

 

 

[WardHolbrook]

I've never experienced this with a Mooney, but I flew a Lear for several years that started to give us a problem. In our case, over the years, there had been a bit of corrosion build up between the base of the antenna and the aircraft skin and some bonding straps had broken. All of the connectors and coax were in good shape. It took a while to check out all of the bonding straps and that helped a lot, but the problem didn't go completely away until we installed a new antenna. I guess nothing lasts forever.

I've experienced cellphone induced static before, but never had a problem with a charger, but it wouldn't surprise me at all.