Van's Air Force
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Question about antennas inside landing gear fairing
- Thread starter AX-O
- Start date
Norman CYYJ
Well Known Member
Not a good idea unless you are only wanting a highly directional receive and transmit pattern and short range. The transmitter will also not like the high VSWR and will cut back on the power.
Brantel
Well Known Member
There was a guy that put a APRS J pole in there but I have not seen someone try a COM antenna there.
I doubt seriously that this would work out very well. Normal ones need a good ground plane and having that steel gear leg that close to the antenna will definately impact the signal pattern around the aircraft.
Some antennas do not need a ground plane...but having that much steel mass in close proximity would trash any normal expectations for such antennas.
I doubt seriously that this would work out very well. Normal ones need a good ground plane and having that steel gear leg that close to the antenna will definately impact the signal pattern around the aircraft.
Some antennas do not need a ground plane...but having that much steel mass in close proximity would trash any normal expectations for such antennas.
rzbill
Well Known Member
NFG
I few years ago I posed the hair brained idea to actually use the mains as antennas. My dad (long time Ham and electrical genius) and I did the calcs and found the legs the be pretty much exactly the worst length selectable for the frequencies involved. The above comments about locating an antenna very close and parallel to the gear legs will be quite true. Pi$$ poor SWR, low range and highly directional.
I few years ago I posed the hair brained idea to actually use the mains as antennas. My dad (long time Ham and electrical genius) and I did the calcs and found the legs the be pretty much exactly the worst length selectable for the frequencies involved. The above comments about locating an antenna very close and parallel to the gear legs will be quite true. Pi$$ poor SWR, low range and highly directional.
Yeah, I tried it and the antenna is still there. I got the super cheap copper foil strip from Vans (I think) and used a layer of fiberglass to make sure it stayed stuck to the inside leading edge of the left leg fairing. Even made a point on the leg for connecting the coax cable to the antenna so the fairing can be removed with the antenna but still leave the cable in the plane. It works, its cheap and I don't seem to have any problems with it though I've never measured its output and compared it to a more proper installation. My main reason for doing this was that I couldn't see building a super slick aircraft and then have all these bug-like antennas sticking out of it.
Alan
RV-4 N7028K 60 hours and counting
Alan
RV-4 N7028K 60 hours and counting
rvmills
Well Known Member
I'm the knucklehead with the j-pole in my right gear leg fairing. I have a 6, but I have the Harmon titanium Rocket struts, FWIW.
My APRS and my SAR radio (a 137-174 MHz transmitter) are switchable between the j-pole and a second bent whip I have on the belly (its an old Loran antenna that has been trimmed).
Both transmitters work on either antenna, but performance for each is degraded on the j-pole. For instance, the APRS tracks go to the ground on the belly whip, but stop at about 1000' agl on the j-pole. The SAR radio is for shorter range work with ground crews or an airborn control plane, and has worked with the j-pole at relatively short ranges of 5-10 miles or less. No real opportunities to test it at longer ranges so far.
I've considered testing the comm 1 on the j-pole, but don't want to fry my SL-40 along the way! Anyone know if I can do harm to the SL-40 with a higher SWR set up (my tests showed about 3:1 to 3.5:1 at 50 ohms IIRC). Doc's EI issue just got my attention on this one too, but I doubt the SL-40 power-out is higher than the SAR radio...not sure if its higher than the MT-8000FA I have. Not sure I want to make the mic switch a mag-check button!
Pete Howell and I have discussed trying to tune the j-pole for the APRS when he comes to see the races sometime, to see what we can do, but we concur that its pretty much an SWR and signal propagation nightmare in the leg fairing. OK for APRS, not sure for Comm 1.
Might be other places to hide it too...John Huft, if you're reading, where did you hide your comm antennae in your blazing fast 8? (That is, if you're telling!)
Cheers,
Bob
My APRS and my SAR radio (a 137-174 MHz transmitter) are switchable between the j-pole and a second bent whip I have on the belly (its an old Loran antenna that has been trimmed).
Both transmitters work on either antenna, but performance for each is degraded on the j-pole. For instance, the APRS tracks go to the ground on the belly whip, but stop at about 1000' agl on the j-pole. The SAR radio is for shorter range work with ground crews or an airborn control plane, and has worked with the j-pole at relatively short ranges of 5-10 miles or less. No real opportunities to test it at longer ranges so far.
I've considered testing the comm 1 on the j-pole, but don't want to fry my SL-40 along the way! Anyone know if I can do harm to the SL-40 with a higher SWR set up (my tests showed about 3:1 to 3.5:1 at 50 ohms IIRC). Doc's EI issue just got my attention on this one too, but I doubt the SL-40 power-out is higher than the SAR radio...not sure if its higher than the MT-8000FA I have. Not sure I want to make the mic switch a mag-check button!
Pete Howell and I have discussed trying to tune the j-pole for the APRS when he comes to see the races sometime, to see what we can do, but we concur that its pretty much an SWR and signal propagation nightmare in the leg fairing. OK for APRS, not sure for Comm 1.
Might be other places to hide it too...John Huft, if you're reading, where did you hide your comm antennae in your blazing fast 8? (That is, if you're telling!)
Cheers,
Bob
Last edited:
pierre smith
Well Known Member
You need practicality..
....as well as low drag. A belly mounted antenna won't even cost you 1/2 a MPH. Do you really want to sacrifice clear communications for that little gain?
Same thing applies to having steps on BOTH sides of the airplane,
Best,
....as well as low drag. A belly mounted antenna won't even cost you 1/2 a MPH. Do you really want to sacrifice clear communications for that little gain?
Same thing applies to having steps on BOTH sides of the airplane,
Best,
