Walt,
Not the first time we find ourselves on different pages, on the same issue.
While your reference is exactly correct, it does not reflect reality for our applications and should be viewed as “make it so it can be checked using DC units of measure”. In my previous life we called this “make it sailor proof”. Striving for a perfect DC ground when an RF ground is the objective results in unnecessary bare aluminum being exposed to the elements - even if top coated after installation.
I note that use of nutplates does what you suggest without scraping paint - so that option makes us both right. With the backing plate primed, along with the interior fuselage skin, setting the backing plate rivets will achieve your perfect DC ground. Measure if in doubt.
So if anyone is thinking they need to scrape off paint to mount these antennas, install the antenna as I suggest then check it with an antenna analyzer to verify proper operation. I do this for all antennas and feed lines as standard practice.
Carl
Reality is you can choose to believe what you read on VAF or just go the manufacturer/and or FAA guidance and use that. I'm not making this stuff up. I'm pretty sure Carl or anyone else on VAF doesn't have the testing facilities/equipment to test antennas like the manufacturer does, but may I'm wrong? Or perhaps that's the way you did it, so now you recommend everyone else do it that way because yours works ok?
Will it work if you just bolt it on probably, but maybe not as good as it could... don't forget any receiver/xmtr is only as good as the antenna, the cable and it's installation. I believe we've been down this road before on ignoring antenna ground plane requirements as well if I recall.
I learned a long time ago I'm not the smartest guy in the room so I'm always looking to "experts" on how to do things, the 'expert' in this case is the antenna manufacturer unless someone can prove them wrong.
In case anyone wants to read what Comant has to say (one of the largest aviation antenna manufaturers) review their document in the link or the quick view I copied from it below.
PS: I get the practical aspect of installing on a painted aircraft, but on an unpainted aircraft why not follow best practice.
http://delta-omega.com/download/comant/AntennaInstall.pdf
In short here is what Comant has to say:
Aircraft Skin Surface and Mounting Preparation
The electrical bonding of the antenna to the aircraft ground is highly important. If this is not done properly, antenna performance characteristics may become distorted and nulls may appear in the antenna radiation pattern. This, in turn, may cause erratic navigational readings or signal drop out. The electrical bonding of the antennas to the aircraft skin is best accomplished by direct metal-to-metal contact of the antenna base to the aircraft skin. To accomplish this, the aircraft paint in the mounting area will need to be removed and the surface alodined to protect aluminum against corrosion. An alternate method for providing electrical bonding is through the mounting screws, which attach to a backing plate inside the aircraft skin. Remove any interior paint in the area where the backing plate is placed to assure a good ground. Coat this area with alodine to minimize corrosion. To test the electrical bonding of the blade to the aircraft, a reading of .003 ohms between the antenna base plate and ground should be achieved.
Important Warnings !
Failure to follow Installation Instructions as provided by Comant, and/or supplemental information and guidance provided
by the FAA when installing antennas could result in poor systems performance, a void in warranty, and/or damage to the
aircraft. Comant is not responsible for improper installations