FLARM dipole mount
The major problem with installing FLARM in a Libelle is
working out how and where to fit the transceiver antenna. I put
the FLARM electronics on the instrument tray, and assume most
people will do the same, but simply fitting the transceiver
antenna there will cause the upper row of instruments to obscure
any gliders that might be lurking behind you. I know of two
- Use the standard LX FLARM dipole antenna but mount it as
high as possible inside the nose, placed roughly half way
between the front of the instrument tray and the rudder pedals
on a non conductive support.
- Fitting a dual antenna is another possibility: one being
fitted in front of the panel and the other in the rear
fuselage. I contacted Glasfaser to find out how other
people had solved this problem. Hansjörg Streifeneder told
me about using a dual antenna system. He knows a German
engineer who can supply them.
I'm using the first of these ideas, which came from Thorsten
Mauritsen, a Danish Libelle pilot. My version is shown below. The
rest of this page should give enough detail for anybody with good
DIY skills to design and make a similar antenna mount.
Construction and setup notes
- Make sure you buy a FLARM unit with some means of
downloading log files. You'll need to analyse them to ensure
that your FLARM installation has adequate detection range in
all directions. My LX Red Box has the vanilla SD card reader
option, which it uses to save non-certified log files and also
provides a convenient way to configure the FLARM or upgrade its
firmware. The IGC logfile option is an additional feature which
may be implemented by a subsequent firmware upgrade. It is not
needed unless you intend to use your FLARM as an IGC-certified
- It is essential that the antenna mount has no metal or
carbon parts near to the dipole, which is why my antenna mount
is made from glass epoxy board, a section of a glassfibre
fishing rod, nylon bolts and a wooden block.
- The fitting that attaches the whole assembly to the Libelle
instrument tray was cut from 1.5mm epoxy board and glued
together with slow setting Standard Araldite. It uses a metal
bolt as a pivot for the rod, since its far enough from the
dipole for this to be OK. It is attached to the instrument tray
by the same steel bolts that were holding the perspex pneumatic
line support when I bought the glider. You can just see a black
M5 nylon screw under the front of the fitting: this allows the
angle of the rod to be adjusted so the dipole is as high as
possible without touching the inside of the glider's nose
- The green tube was cut from one of the butt sections of a
fibreglass fishing rod after I'd measured the distance from the
front of the instrument tray to my usual pedal position. I
drilled a hole through its base end and epoxied in a section of
brass tube that slides over the mounting bolt. I filed the tube
ends flush with the rod's outer surface when the epoxy was set.
This protects the thin walls of the rod section from wear by
the threads and also prevents the rod from being squashed and
the mount fitting being damaged if the pivot retaining nut is
tightened too enthusiastically: fishing rod sections have very
little resistance to being squeezed.
- The block needs to be a fine-grained hardwood, such as
beech, because you'll will be cutting threads into it. Start by
drilling the block to fit on the rod and hold the dipole as
shown above. You want sloppy fits so the rod section and dipole
slide easily into the block. Then drill two further holes,
which will be tapped to take nylon bolts. Any size is fine, but
M4 or M5 are probably best: drill these holes to the
appropriate tapping diameter for the bolts you've selected.
After tapping the holes, harden the threads by wetting them
with cyanoacrylate glue and then clear the threads by
running the tap through again when you're quite sure the
cyano has set: you really, really don't want to find you've
glued the tap into the block. The tapped holes must not be
drilled along the grain or the threads will strip. The photo
shows the rod locking bolt in the underside of the block and
the dipole retention bolt in the front face where it is almost
hidden behind the rod.
- Roughly position the dipole halfway between the instrument
tray and the rudder pedals, reinstall the panel and go flying.
Half an hour or so of local soaring would be a good idea
because that will let the FLARM register more contacts than if
you wander off cross-country. Do this at least two or three
times before downloading the logs and submitting them to the
FLARM range analysis tool to check your installation's
- My installation initially showed excellent range to either
side, poor range in front and barely acceptable to the rear.
So, I moved the dipole about 20mm further forward and tried
again. This time the side range was reduced a bit but the
rearward range was considerably improved and the forward range
was also better. The overall performance is now acceptable, but
I'm still collecting data and fiddling to see if I can get even
- In other words, if your range in some directions is poor,
move the dipole forward or aft a small distance and try again.
If that gives an improvement, try moving it a bit further in
the same direction: if it doesn't help, try in the other
- Don't forget to record exactly what changes you made and
keep screenshots of the range analysis for each setting. You'll
need this data so you can place the dipole at the optimum
position when you've finished the tests.
 Cyanoacrylate is the generic name for a class of
almost instant setting medical glues which set in the presence of
moisture. The best known consumer brand is Superglue, though
there are very much better brands available through your local RC
model shop. These come in different formulations for different
uses, e.g. thin cyano is very runny. It is intended for sticking
close fitting parts and sets fast enough to stick your fingers
together if you aren't careful, while thick cyano sets a lot
slower (10-20 seconds) and is a good gap filler. I recommend thin
Zap or HotStuff for general use as well as for hardening threads
tapped in soft materials.
Coverage after adjusting the antenna