What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Bob Archer comm antenna work in an RV?

blueflyer

blueflyer

Well Known Member
will a bob archer comm antenna work in our aluminum RVs? If so, where is the best mounting location?
 
This antenna must be internally mounted where the radio waves can ‘escape’. They are also designed to work against a ‘ground plane’, e.g., a significant piece of metal at the base of the antenna. For our all-metal RVs, that pretty much means the fiberglass wingtip. The issue with the wingtip is that com frequencies use vertical polarization, while an Archer laying flat will radiate horizontally polarized radiation. (For nav reception-which uses horizontal polarization-Archers work quite well). The trick is to tip the antenna’s leading edge-where most of the signal comes from-as vertical as possible. e.g., I mounted the ground leg as high as possible inside the tip, then allowed the leading edge of the antenna to slope down until it hit the bottom of the tip. This is in a -10 which has a thicker wingtip than the -7 or -9. Is it as good as the belly whip? No. In uncontrolled tests (different radios) I’d say my wingtip com has about 75% of the range as the belly whip. For my purposes (ATIS and backup) I think that’s acceptable. YMMV.
 
Even the best radio is only as good as it antenna, are you willing to give that up for 0.1 kts?
Do yourself (and everyone that tries to hear/communicate with you) a favor and install a 'real' com antenna.
 
Last edited:
mounting directions

BobTurner said:
This antenna must be internally mounted where the radio waves can ‘escape’. They are also designed to work against a ‘ground plane’, e.g., a significant piece of metal at the base of the antenna. For our all-metal RVs, that pretty much means the fiberglass wingtip. The issue with the wingtip is that com frequencies use vertical polarization, while an Archer laying flat will radiate horizontally polarized radiation. (For nav reception-which uses horizontal polarization-Archers work quite well). The trick is to tip the antenna’s leading edge-where most of the signal comes from-as vertical as possible. e.g., I mounted the ground leg as high as possible inside the tip, then allowed the leading edge of the antenna to slope down until it hit the bottom of the tip. This is in a -10 which has a thicker wingtip than the -7 or -9. Is it as good as the belly whip? No. In uncontrolled tests (different radios) I’d say my wingtip com has about 75% of the range as the belly whip. For my purposes (ATIS and backup) I think that’s acceptable. YMMV.
Click to expand...

I recently purchased an RV7 and it has a Bob Archer COMM in one wing tip and a NAV on the other wing tip. These are installed at angles and are not completely horizontal. They start at the bottom of the wing tip and angle up about a 30-40 degree angle. The plans I received do not have the installation instructions and the previous owner said that he installed them exactly as the plans said too. But all the pictures I look at, and the mechanic I am working with, said that they are usually installed completely horizontal. Can anyone confirm this or even send me a copy of the installation instructions. The other question is can I use the COMM as a NAV antenna or will I need to replace it with a new one? I did notice that the two antennas are different lengths.
 
philsurette said:
I recently purchased an RV7 and it has a Bob Archer COMM in one wing tip and a NAV on the other wing tip. These are installed at angles and are not completely horizontal. They start at the bottom of the wing tip and angle up about a 30-40 degree angle. The plans I received do not have the installation instructions and the previous owner said that he installed them exactly as the plans said too. But all the pictures I look at, and the mechanic I am working with, said that they are usually installed completely horizontal. Can anyone confirm this or even send me a copy of the installation instructions. The other question is can I use the COMM as a NAV antenna or will I need to replace it with a new one? I did notice that the two antennas are different lengths.
Click to expand...

For the Nav, which wants horizontal polarization, the antenna should be horizontal, e.g., flat in the tip. However, a 30 deg tip will only slightly degrade theoretical performance. The com, which should be vertically polarized, will theoretically have zero performance if installed flat; every degree of tip toward the vertical for the leading edge will help. I recommend installing the ground leg high, bending the antenna down, because the asymmetric tips allow more vertical throw going high to low. If you want to use an Archer com as a nav, you should rivet an extension (about 3.5”) to it, as you already noted. In principle you should also adjust the feed leg but that takes some specialized equipment. Are you saying you would like to have two nav antennas? Try it as-is, see how well it works. As far as installation, make sure the ground leg is as close as possible to the end rib, and that there is good (no paint), as short as possible, electrical connection between the ground leg and the end rib.
 
Last edited:
Works for me...

I have one for a NAV radio in my left wing. Seems to work fine. I don't use it a lot as so many airports have RNAV approaches. But I do the occasional ILS and I do the required VOR check for the record and it seems to pick them up at 40 miles fine...
 
Take Walt's advice, we did not, and

ended up replacing the Archer comm with a "real" comm antenna. Nav worked "OK".

Ron
 
BobTurner said:
For the Nav, which wants horizontal polarization, the antenna should be horizontal, e.g., flat in the tip. However, a 30 deg tip will only slightly degrade theoretical performance. The com, which should be vertically polarized, will theoretically have zero performance if installed flat; every degree of tip toward the vertical for the leading edge will help. I recommend installing the ground leg high, bending the antenna down, because the asymmetric tips allow more vertical throw going high to low. If you want to use an Archer com as a nav, you should rivet an extension (about 3.5”) to it, as you already noted. In principle you should also adjust the feed leg but that takes some specialized equipment. Are you saying you would like to have two nav antennas? Try it as-is, see how well it works. As far as installation, make sure the ground leg is as close as possible to the end rib, and that there is good (no paint), as short as possible, electrical connection between the ground leg and the end rib.
Click to expand...
Thanks for the information. Yes I wanted to NAV antennas. I installed to COMM antennas on the bottom of the fuselage and not longer need the COMM in the wing. Here is what I am planning, and let me know if I am doing anything I shouldn’t. I am going to take both wind antennas and lay them flat. They are only attached with some fiberglass and will come off easy. Then I will reattach them in a horizontal position and add, rivet, another 3.5” to the COMM. Thanks for the information Bob and I will see how that works.
 
You must log in or register to reply here.
Back
Top