PowerFLARM antenna separation

[kirk.stant]

I just looked at the latest PF manual and it recommends 5 ft of separation between the PF A (xmit/rec) and B (rec only) flarm antennas. The older antenna installation documentation stated that a minimum of 1 ft was needed.

What gives?

I have the A and B flarm antennas just over a foot apart in the nose of my LS6, wondering if I need to rethink the setup.

Havn't any flight with other PFs around to use the range estimating tool.

My earlier install had the A antenna in the nose cone and the B about 3 ft away on the side of the instrument panel cluster, and it had pretty good numbers for range and coverage.

Kirk
66

[bumper[_4_]]

On Tuesday, June 2, 2015 at 10:37:03 AM UTC-7, kirk.stant wrote:
>
>
> I have the A and B flarm antennas just over a foot apart in the nose of my LS6, wondering if I need to rethink the setup.
>
> Kirk
> 66

Kirk,

Not meaning to second guess you, but as you say, the Flarm A antenna is both send recieve, while the Flarm B (optional to use) antenna is for Flarm receive only. There would be no logical reason to co-locate these two antennas in the nose of a glider as the Flarm B antenna, if used, is typically located so as to cover a null or blind spot in the Flarm A antenna's location.

Now the ADS-B IN antenna is another thing entirely. It is also a dipole and it makes a lot of sense to have it up in the nose with the Flarm A. One foot of separation is more than enough, but both antennas want to be vertical and both want to be, within reason, a good distance from other vertical metal which would cause nulls - even the coax wants to run back away from the dipole antenna at least a few inches.

I'm thinking you may be confusing Flarm B with ADS-B???

bumper

[kirk.stant]

On Tuesday, June 2, 2015 at 2:32:58 PM UTC-5, bumper wrote:
> On Tuesday, June 2, 2015 at 10:37:03 AM UTC-7, kirk.stant wrote:
> >
> >
> > I have the A and B flarm antennas just over a foot apart in the nose of my LS6, wondering if I need to rethink the setup.
> >
> > Kirk
> > 66
>
> Kirk,
>
> Not meaning to second guess you, but as you say, the Flarm A antenna is both send recieve, while the Flarm B (optional to use) antenna is for Flarm receive only. There would be no logical reason to co-locate these two antennas in the nose of a glider as the Flarm B antenna, if used, is typically located so as to cover a null or blind spot in the Flarm A antenna's location.

[bumper[_4_]]

On Tuesday, June 2, 2015 at 1:53:56 PM UTC-7, kirk.stant wrote:

> But before I go stringing antenna coax aft to stick my Flarm B on my gear box, I just wanted to know why... ;^)
>
> Kirk
> 66

Kirk,

I'd guess as the Flarm A side is a transceiver, it disconnects its receive circuit while its transmitter is sending. This is commonly done in transceivers to prevent the transmit power going into the receiver as that would overload things and shut down the AGC (automatic gain circuitry). If the Flarm A antenna was located too close to the "always on" Flarm B antenna (which is a separate receiver from the A side), it is possible that the transmission would overload the B receive circuitry, or at the least turn the AGC way down. There is typically a slight delay as receive AGC ramps back up, and this would result in degradation of B receive function.

[John Carlyle]

Kirk,

I've got a PowerFlarm mounted in an LS-8. I sort of mounted the Flarm A antenna in the traditional location, and I'm getting pretty circular coverage out to about 6 km. I don't use a Flarm B antenna.

"Sort of" means that you can only see one arm of the dipole above the glare shield; all the rest is below. The canopy with glare shield comes off freely, leaving the Flarm A antenna behind. The ADS-B antenna is about 6 inches away horizontally, and some 6 inches below the Flarm A antenna.

By the way, my original PowerFlarm (s/n 117) had to be replaced (s/n 3217). I notice that my range analysis plots now have a more circular shape plus about 2 km more range. It's all due to the new core, everything else is the same.

-John, Q3

On Tuesday, June 2, 2015 at 4:53:56 PM UTC-4, kirk.stant wrote:
> No confusion, bumper. The Flarm A is mounted as far forward as possible, but that puts it next to the nose Tost hardware, so the Flarm B is mounted in a position to see where the A may be blocked.
>
> ADS-B is supposedly not very sensitive to location (again, per the PF manual).
>
> The reason for all this playing around with antenna locations is that the LS6 (and I assume 7, 8, and 10) do not have room between the glare shield and canopy to mount in the "traditional" location, and anyway the glare shield goes with the canopy so is a really poor choice of location.
>
> But before I go stringing antenna coax aft to stick my Flarm B on my gear box, I just wanted to know why... ;^)
>
> Kirk
> 66

[[email protected]]

Strange, I never noticed that change in the manual but it's right there in black and white. The only reason I can think of is that presumably the second Flarm antenna would be enabled and installed in order to cover a blind spot in the primary antenna so placing them close together would be kind of pointless.

So far the coverage of my Flarm installation seems good with just the one Flarm antenna judging by the range tool results. Good thing as on my ASW-15 the only place to put the primary was as far forward into the nose as possible since there's nowhere near enough room between the glare shield and canopy to fit it there. I was concerned that the rudder pedals might cause a blind spot but it seems to have decent range even straight back. If that weren't the case I would have to get a long cable because a secondary antenna would probably have to go back behind the trailing edge of the wing on the rear most bulkhead.