I was wondering if anyone has used Pentrox to help provide good electrical contact between antenna/doubler/metal skin. It's a product used to ensure good electrical contact and inhibit corrosion between grounding cables and sections of aluminum cable tray in industrial applications.
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Pentrox for bonding antenna
- Thread starter sjrossi
- Start date
Years ago we used penetrox for the antennas but I think that went out of vogue. It seems that Penetrox as well as many other compounds used for the same purpose are graphite in a petroleum jelly base. Experience showed that graphite, on one end of the galvanic scale, and aluminum towards the other was not a good thing, and dissimilar metal corrosion ensued.
I never saw this for myself, but it makes sense.
There are currently silicone gel gaskets with a wire mesh embedded that eliminate corrosion and ensure a conductive path. The problem with them is the cost- typically around $80 or more depending on antenna base area.
Otherwise, I use the standard gasket and put a bead of proseal around the antenna base.
I never saw this for myself, but it makes sense.
There are currently silicone gel gaskets with a wire mesh embedded that eliminate corrosion and ensure a conductive path. The problem with them is the cost- typically around $80 or more depending on antenna base area.
Otherwise, I use the standard gasket and put a bead of proseal around the antenna base.
Captain_John
Well Known Member
I have used it extensively on power wires in the construction industry. Personally I would never use it on my airplane.
If you are looking to mitigate corrosion underneath the antenna base and between the stiffener and skin, use a conversion product such as alodine.
It offers no resistance because it is wiped away after the conversion process is complete.
If dirt or grime got into the penetrox, it would make a poor connection. Besides, the antenna manufacturers specify alodine if I recall their instructions correctly.
CJ
If you are looking to mitigate corrosion underneath the antenna base and between the stiffener and skin, use a conversion product such as alodine.
It offers no resistance because it is wiped away after the conversion process is complete.
If dirt or grime got into the penetrox, it would make a poor connection. Besides, the antenna manufacturers specify alodine if I recall their instructions correctly.
CJ
Did not use it on antenna but would have had I thought of it. I did use it for any ground connection to the airframe and through the firewall. No ground issues have ever occurred on the 19-year old airplane after more than 3,200 flying hours.
If you use alodine, make sure it is the one that is conductive. Only some of what I have seen in the field is conductive. Most of what I have seen used is non-conductive.
Captain_John
Well Known Member
Carl Froehlich
Well Known Member
The last time I said this I got yelled at - but I'll say it again. DC Resistance is much different than RF impedance. Many people look at a 1/4 wavelength vertical antenna ground plane like it is a battery ground.
So what does this mean:
- View the backing plate function as mechanical.
- Drill your antenna mounting holes and then rivet on the back plate. I prime both the inside of the airplane skin and back plate as my main concern about all this is aluminum corrosion.
- Paint the plane, then install the antenna on top of the paint.
- No reason not to add a star washer on each antenna mounting screw. The rivets will provide DC conductivity between the skin and backing plate so that and the star washers will mitigate the rare issue of RFI.
- Connect the coax.
- Use an antenna analyzer from the radio BNC connection to verify antenna and feed line operation (e.g. you did not screw up when you made up the BNC connectors)
- Done.
Note - for fiberglass airplanes you will need to add a counterpoise on the inside surface of the hull. Various ways to do this.
The point here is the same functioning ground plane for a 1/4 wavelength antenna is provided using the above process as compared to welding the antenna base to the fuselage. I note that if you have the antenna spaced off the ground plane by any distance, and try to compensate by adding a ground strap, you have now changed both the antenna impedance and resonate frequency - even though you have provided a superb DC ground. Example of this is when people try to glass in a wingtip antenna and use a ground strap instead of mounting it on the last wing rib (the wingtip antenna is just another form of 1/4 wavelength antenna). Performance is typically poor.
I would never consider using any compound like Pentrox on an airplane. I have use a similar antenna specific compound for building outside antennas that have telescoping aluminum tubing (the stuff prevents the bare aluminum from corroding together). I also use it for those pesky fat aluminum ground wires to power panel ground block connections as the dissimilar metals will eventually lead to a high resistance ground connection in your home. I can only imagine problems to paint and such if used on an airplane.
Side note - I recall building my first real antenna when I was 14 - and I used some anti-corrosion compound as my old engineer mentor told me to. I assembled the antenna and found to my dismay that using my trusty Heathkit VTVM I measured a high resistance across the antenna element joints . My mentor just shook his head at me - the sign that I was about to learn something.
Carl
So what does this mean:
- View the backing plate function as mechanical.
- Drill your antenna mounting holes and then rivet on the back plate. I prime both the inside of the airplane skin and back plate as my main concern about all this is aluminum corrosion.
- Paint the plane, then install the antenna on top of the paint.
- No reason not to add a star washer on each antenna mounting screw. The rivets will provide DC conductivity between the skin and backing plate so that and the star washers will mitigate the rare issue of RFI.
- Connect the coax.
- Use an antenna analyzer from the radio BNC connection to verify antenna and feed line operation (e.g. you did not screw up when you made up the BNC connectors)
- Done.
Note - for fiberglass airplanes you will need to add a counterpoise on the inside surface of the hull. Various ways to do this.
The point here is the same functioning ground plane for a 1/4 wavelength antenna is provided using the above process as compared to welding the antenna base to the fuselage. I note that if you have the antenna spaced off the ground plane by any distance, and try to compensate by adding a ground strap, you have now changed both the antenna impedance and resonate frequency - even though you have provided a superb DC ground. Example of this is when people try to glass in a wingtip antenna and use a ground strap instead of mounting it on the last wing rib (the wingtip antenna is just another form of 1/4 wavelength antenna). Performance is typically poor.
I would never consider using any compound like Pentrox on an airplane. I have use a similar antenna specific compound for building outside antennas that have telescoping aluminum tubing (the stuff prevents the bare aluminum from corroding together). I also use it for those pesky fat aluminum ground wires to power panel ground block connections as the dissimilar metals will eventually lead to a high resistance ground connection in your home. I can only imagine problems to paint and such if used on an airplane.
Side note - I recall building my first real antenna when I was 14 - and I used some anti-corrosion compound as my old engineer mentor told me to. I assembled the antenna and found to my dismay that using my trusty Heathkit VTVM I measured a high resistance across the antenna element joints . My mentor just shook his head at me - the sign that I was about to learn something.
Carl
+1
Yes, I've seen photos of Archer style wingtip antennas mounted well away from the rib. And then the owner reports poor performance. I've also seen one where the radiating element was attached to the rib, and the ground arm was free standing. So I guess if there's a way to screw up, someone will find it!
Yes, I've seen photos of Archer style wingtip antennas mounted well away from the rib. And then the owner reports poor performance. I've also seen one where the radiating element was attached to the rib, and the ground arm was free standing. So I guess if there's a way to screw up, someone will find it!
Are you thinking about anodizing? Anodizing is non-conductive.
Not sure why you are confused.
Only thing I had anodized on my airplane is the custom alternator pulley that I had made. Anodizing makes the surface of aluminum harder and will shorten its life because of bending fatigue.
Alodine is typically non-conductive unless you get the one that is conductive.
I used PENTROX every place that a ground is connected to my airframe. Unlike your recommendation, I recommend Pentrox everywhere that an electrical connection to aluminum is needed.
Have not seen any problems with airframe grounds that used Pentrox but have seen lots of problems on airframe grounds that did not have it.
Captain_John
Well Known Member
Gary, what confuses me is your statement about a conductive and non-conductive alodine.
Alodine is a conversion process. The alodine doesn't remain on the aluminum.
All that is left is an aluminum chromate layer which IS conductive. It converts the surface of the aluminum. It doesn't coat it at all.
CJ
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rv7charlie
Well Known Member
Is this the product series being discussed?
https://objects.eanixter.com/PD372804.PDF
If so, I don't see any mention of carbon in the description of ingredients. It would seem highly unlikely that there would be, since the point of using it is to prevent corroded joints, and carbon would cause corrosion on aluminum house wiring/products just like aircraft products.
Charlie
https://objects.eanixter.com/PD372804.PDF
If so, I don't see any mention of carbon in the description of ingredients. It would seem highly unlikely that there would be, since the point of using it is to prevent corroded joints, and carbon would cause corrosion on aluminum house wiring/products just like aircraft products.
Charlie
That is a different product than I used in the past. You are correct, no graphite- If that is the product being discussed
Gary, what confuses me is your statement about a conductive and non-conductive alodine.
Alodine is a conversion process. The alodine doesn't remain on the aluminum.
All that is left is an aluminum chromate layer which IS conductive. It converts the surface of the aluminum. It doesn't coat it at all.
I am extremely familiar with Alodine. Almost all of the Alodine and or Iridite I have use is NON-CONDUCTIVE Class 1A. IF one wants a conductive Alodine, they need to make sure that it is Class 3 so that it will conduct some electricity.
For the average homebuilder, it is better to stay away from Alodine when you want an electrical connection on aluminum. Most homebuilders will not know about Class 1A and Class 3. Alodine 1001 is Class 3 and conductive. Alodine 1201 is Class 1A and non-conductive.
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Penetrox A is the product that I have been using for decades.
At the last 2 helicopter MROs I worked for, we used Penetrox A and a bead of proseal around the antenna base, for antenna installs where the customer was too cheap to spring for the Av-DEC conductive gaskets.
fl-mike
Well Known Member
Gary,
The data I have read indicates that Class 1A is less conductive, but not non-conductive. Class 3 is preferred for applications requiring low-conductivity, but conductivity is proportional to film thickness and class 1A will still be conductive enough for our purposes. All of my samples (Iridite 14-2) are conductive and I would have to break out the milliohm meter to see any appreciable difference between the coated and un-coated condition. If the average builder stays with a light iridescent gold finish, they'll be fine.
