flarm internal antenna

[rg]

Is this sort of thing likely to be any good on the ARF side of things?  http://www.air-store.eu/1000027

Looks like it could be a neat solution allowing PAW to be safely stowed.

[Mig29fuk]

I purchased one of these a few days back along with Puck Aerial.
Both ara being assessed by a very knowledgeable Radio HAM at this time.
The Puck aerial claims 2.5 dBi gain. The Dipole is unknown.
I have lent the Aerial boys two PAW's with ARF's and hope to have some information by weekend.

[Richard]

Just for info. I have both the FLARM internal antennas connected to the PAW. The ADSB antenna performs much better than the one supplied with the DVBT. I still have to test the 868mhz antenna, but this is already tuned and ready to use. The other advantage is if you put a suction cup on it it simply sticks to thr window. They have to be vertical but are very small and neat. You can get them from http://www.lxavionics.co.uk/collision-warning-systems.htm the disadvantage is the price, but your transmitter is only as good as your antenna.

[rg]

Thanks

[The Westmorland Flyer]

The Puck aerial claims 2.5 dBi gain. The Dipole is unknown.

A resonant dipole has 2.15dBi (isotropic) gain. Most of the system gain will come from the ability to put the dipole (or other antenna) somewhere where it has a clearer view of the sky. Antenna gain is less relevant.

[rg]

Did you get any feedback from the radio hams on that antenna?

I haven't purchased one yet.  What sort of connection does it have?  Any adapters required to hook it up to the ARF?

[Mig29fuk]

Should get feedback this weekend on Puck and dipole.
Also need to 'fly' them and that too is on the programmed but not today. Wind 340 20 knots gusting 31.
G

[neilmurg]

the FLARM dipole is 145mm, I thought the best length for PAW was 164mm?
(from http://www.csgnetwork.com/antennaedcalc.html)

[The Westmorland Flyer]

the FLARM dipole is 145mm, I thought the best length for PAW was 164mm?

It depends what velocity factor (VF) you use. VF varies, amongst other things, with the aspect ratio of the antenna - thickness of elements vs. length, the conductor material/plating and the type of insulation, if any.

The free space half wavelength for 868MHz is 173mm. The calculator you're using supposes a VF of ~0.95 (164mm), which I would say is a bit high. The VF could be as low as 0.85 (147mm). I tend to the view that the Flarm antenna is slightly short and that the calculator value is somewhat too long. I find a VF of around 0.9 (155mm) is usually about right when designing VHF/UHF antennas. Won't make a great deal of difference in the grand scheme of things.

[Richard]

Hi,
  I have both FLARM Antennas. The wire is raped around in a spiral and then it is covered with heat shrink to seal them up. They are very simple. The length is probably tuned correctly, the range of ADS-B out performs any thing I have tried so far. Sorry I cant comment on the other antenna as I still have to test it.

[The Westmorland Flyer]

Forming the antenna elements into a spiral is a well known way of reducing the overall length of the antenna. There's no such thing as a free lunch, however - the resultant antenna is less efficient than the full sized, straight wired dipole. To be honest, I am a little surprised that Flarm has resorted to this technique as the full-sized antennas at these frequencies are pretty small anyway.