Flarm and ADS-B antennas

[Andrzej Kobus]

I am puzzled by what was delivered with my brick. Flarm antenna
ANT-916-MHW-RPS-y and another antenna ANT-916-MHW-SMA-y (this one came
with a note that is was ADS-B antenna and it had a blue heat shrink
close to the connector). I am puzzled that they both are for 916 MHz
frequency. Is something wrong with this picture? Should the ADS-B
antenna be 1090 Mhz? It looks to me that the only difference between
them is a connector one is RPS and the other one is SMA. I can't
believe this is right.

[bumper[_4_]]

Andrzej,

From what I've seen earlier bricks came with the ADS-B/PCAS antennas you discribe. Later bricks are shipping with a shorter dipole that is more tuned for the 1090 Mhz frequency. The only differance in the two antennas is that the radials on the 1090 antenna are a little shorter (gueestimating each radial is 3/16" shorter). Flarm had to special order the higher frequency antennas . . . they are from the same company that makes the 916 Mhz antenna, but are not an off-the-shelf item.

One could heat the little ribber cap to remove them and then lop off a bit of the radial with a Dremmel cut-off wheel after doing the math. But in the real world, the 916 Mhz antenna should work pretty well as receive is much less critical than transmit. That and the fact that the signal you are receiving is being transmitted at >200 watts.

bumper

[Andrzej Kobus]

On Oct 29, 12:37*am, bumper > wrote:
> Andrzej,
>
> From what I've seen earlier bricks came with the ADS-B/PCAS antennas you discribe. Later bricks are shipping with a shorter dipole that is more tuned for the 1090 Mhz frequency. The only differance in the two antennas is that the radials on the 1090 antenna are a little shorter (gueestimating each radial is 3/16" shorter). Flarm had to special order the higher frequency antennas . . . they are from the same company that makes the 916 Mhz antenna, but are not an off-the-shelf item.
>
> One could heat the little ribber cap to remove them and then lop off a bit of the radial with a Dremmel cut-off wheel after doing the math. But in the real world, the 916 Mhz antenna should work pretty well as receive is much less critical than transmit. That and the fact that the signal you are receiving is being transmitted at >200 watts.
>
> bumper

I would not think PowerFlarm would special order anything if it was
not required. Why would they change the antenna later, maybe because
of poor PCAS performance? If PCAS estimates distance through signal
strength (as I was told) then how would they be able to calculate the
strength with two different antennas?

[Andy[_1_]]

On Oct 29, 3:25*am, Andrzej Kobus > wrote:

> I would not think PowerFlarm would special order anything if it was
> not required. Why would they change the antenna later, maybe because
> of poor PCAS performance? If PCAS estimates distance through signal
> strength (as I was told) then how would they be able to calculate the
> strength with two different antennas?

There is provision in the ADS-B module interface for calibrating for
different antenna performance. However, I have no way of knowing if
units delivered with the later antenna are calibrated differently.
( See TRX-1090 Data Port Specification)

Andy GY