DIY wire monopole antennas for PowerFlarm?

I have a carbon fuselage, and am considering experimenting with a monopole antenna on each side of the canopy. What I am hoping for is the thinnest wire that will work, taped to the inner canopy wall with clear tape on each side. Hopefully this would provide diversity without FOV obstruction. Can any RF engineer out there suggest length of wire, minimum dia. of wire, etc. that might work? Advice on avoiding nodal interference patterns welcome as well.

Thanks,

Matt

On 12/5/2020 9:11 PM, Matt Herron Jr. wrote:
I have a carbon fuselage, and am considering experimenting with a monopole antenna on each side of the canopy. What I am hoping for is the thinnest wire that will work, taped to the inner canopy wall with clear tape on each side. Hopefully this would provide diversity without FOV obstruction. Can any RF engineer out there suggest length of wire, minimum dia. of wire, etc. that might work? Advice on avoiding nodal interference patterns welcome as well.

Thanks,

Matt

I wonder why you're saying "monopole", Matt? An antenna, like a magnet,
needs two poles. The monopole antennas you may have seen sticking out
of metal airplanes use the metal fuselage as the other "pole". You can
achieve the same using several wires in a plane perpendicular to the
"monopole". Those are called ground radials. If the surface you want
to mount it on is made of carbon fiber, which conducts but not as well
as metal, you may want to add a patch of sheet metal (even aluminum foil
may do), or several ground radial wires, flat on the carbon surface and
connected to the ground side of the cable where its internal wire
connects to the "monopole". If it's flat against the canopy then you
can't have the ground plane extending out through the plexiglass, so
it'll be a compromise, but may work well enough.

As far as dimensions, that ground patch should be at least a
half-wavelength across, and the "monopole" should be 1/4 wavelength tall
(minus about 5%). So for 915 MHz (USA FLARM frequency) you'd compute it
as 0.95*300/915/4 = 0.078 meters, i.e. 7.8 cm, or 3.1 inches. It's OK
if the wire is thin, but a thicker wire would work somewhat better
(wider bandwidth - the signals are in a range, 905-925 MHz or so).
There would be no significant interference with antennas on opposite
sides of the canopy (unless they are way forward where the canopy sides
almost meet).

If you can get the bottom end far enough (say 3+ inches) above any
carbon structure, you can use a dipole instead. Those are available off
the shelf complete with cable and connector. Easier than trying to
build a decent connection yourself at those ultra-high frequencies.
This isn't like my shortwave ham radio days... Be sure to route the
cable away from the dipole in a direction perpendicular to the dipole,
for the first few inches. One good dipole may work better than two
compromised monopoles.

There may be monopole+groundplane antennas available off the shelf too,
look around. The fact that we share this frequency with many other uses
makes for better availability of parts.

I found a major improvement in range when I moved from a single antenna over the glareshield to dual long antennas on the canopy sides of my ASW-27.

I did Range Analysis on six installations and documented the results in the 2019 Free Flight. Look for Antenna Placement:

http://sac.ca/index.php/en/free-flig...ight-vol-libre

On Saturday, December 5, 2020 at 8:11:17 PM UTC-6, Matt Herron Jr. wrote:
I have a carbon fuselage, and am considering experimenting with a monopole antenna on each side of the canopy. What I am hoping for is the thinnest wire that will work, taped to the inner canopy wall with clear tape on each side. Hopefully this would provide diversity without FOV obstruction. Can any RF engineer out there suggest length of wire, minimum dia. of wire, etc.. that might work? Advice on avoiding nodal interference patterns welcome as well.

Thanks,

Matt
Matt,

To do what you are trying to do correctly and well is very complicated. To do it right you would need a network analyzer to ensure that at the operating frequency that the antenna has the correct impedance, otherwise you are likely to get seriously degraded range. (Strictly speaking, unless you are properly licensed by the FCC (in USA) you are not allowed to mess with an antenna like this as it could invalidate the RF certifications of the FLARM and conceivably interfere with other services.)

The wire diameter has only second order effect on antenna performance, so mechanical considerations are probably more important. Good conductivity on the surface of the wire is good, and larger diameter helps as well, to a point. 20 to 22AWG solid copper is probably appropriate. The main thing is that the wire length be about 1/4 wavelength at the frequency used. There are antenna calculators on the web that you can use to get a first guess. After that, carefully verify the range before trusting that your FLARM is working like you think (or hope).

Rich L.

Hello,

what about re-routing the antenna in the tail ?
This part is fiber and not carbon, and there is room to paste an antenna inside the rudder logement.
The hard task is to route a descent coax until there ...

On Saturday, December 5, 2020 at 10:16:08 PM UTC-5, wrote:
I found a major improvement in range when I moved from a single antenna over the glareshield to dual long antennas on the canopy sides of my ASW-27.

I did Range Analysis on six installations and documented the results in the 2019 Free Flight. Look for Antenna Placement:

http://sac.ca/index.php/en/free-flig...ight-vol-libre
Hi George,

I read with interest your FF article on FLARM range analysis. I fly a Discus-2 (carbon fuselage) out of Gatineau Gliding Club. My FLARM gets marginally acceptable range so I am tempted to fit a second antenna as you showed.Â*Â*Before I do this however, I want to ask how you know you are transmitting a uniform pattern?Â* While two antennas improve receiving signals from other aircraft, with only one antenna transmitting, as currently permitted, is it possible that your setup gives uneven transmission range on different bearings around the glider? Glad to hear your thoughts on this.

Ian IN

On Saturday, December 5, 2020 at 6:11:17 PM UTC-8, Matt Herron Jr. wrote:
I have a carbon fuselage, and am considering experimenting with a monopole antenna on each side of the canopy. What I am hoping for is the thinnest wire that will work, taped to the inner canopy wall with clear tape on each side. Hopefully this would provide diversity without FOV obstruction. Can any RF engineer out there suggest length of wire, minimum dia. of wire, etc.. that might work? Advice on avoiding nodal interference patterns welcome as well.

Thanks,

Matt
Matt,

The first question is what range are you presently getting with your present antennas?

Richard
www.craggyaero.com

Hi Ian,

Well transmit from one side obviously favors that side and the opposite side of the cockpit will block signals. Hopefully any other Flarm in that sector will alert you, but yes, the other aircraft might not be receiving you.

I was following an ASW-28 a few years ago when I had a single antenna on my glareshield and didn't see him until we turned into a thermal.

Not too long after we both got an alarm and I decided to rework my antenna placement.

Unfortunately while the Flarm website advertised the Core 1.1 could transmit on both antennas, Flarm did not bother to get their FCC and "Innovation" Canada approvals amended to allow that to happen in North America.

Getting a sufficient (thick) coax to the fin is likely impractical. You can't have improperly secured coax interfering with the elevator linkage and the coax would have to negotiate the transition from the fuselage to the fin.

Maybe buy a wreck where the necessary openings have mostly been made.