Powerflarm transmit antenna defect

A big Thanks to Rex Mayes at Williams Soaring Center for a replacement Plarm A antenna. I installed the new one and TG reports now seeing me at 6nm! instead of less than 1nm.

The original antenna delivered with the unit actually had a short, unknown to me as others reported actually being able to see me at short distances despite this flaw(found at the crimp of the SMC connector). If others have transmit range issues, then consider ohming out your antenna and check for a short.

Darren

On Thursday, May 19, 2016 at 1:34:45 AM UTC-4, wrote:
If others have transmit range issues, then consider ohming out your antenna and check for a short.


What should the ohm readings be for healthy Flarm antennas?

On Thursday, May 19, 2016 at 7:06:35 PM UTC-7, son_of_flubber wrote:
On Thursday, May 19, 2016 at 1:34:45 AM UTC-4, wrote:
If others have transmit range issues, then consider ohming out your antenna and check for a short.


What should the ohm readings be for healthy Flarm antennas?

Measuring from the coax connector center pin to the outer housing, should read open or infinite ohms.

To check the antenna without an RF type SWR meter, you would need to either remove the vinyl caps on the radials (if it's a dipole antenna) and measure those. One should read a short to either the coax center pin or outer housing, and the other radial should be a short to the other part of the coax fitting. It's a simple antenna with no loading coils or baluns etc.

If working on avionics a lot, there are testers like this available: http://www.mfjenterprises.com/

bumper
MKIV & QV

I suspect this may be a common problem with the stock antennas. In my case it was a bad ADS-B antenna.. I heard of others with antenna issues.
I recommend folks who have poor range issue with antennas that are installed properly to simply try with another antenna.

Ramy

Yep, simply check for open. This coax has no characteristic impedance unlike other coax types used for video, for example.

Also for the PF designers if they are reading, would be good to sense this case as is done on the Becker Transponder and issue an error. I imagine there a number of ways to do it, like a self test during boot.

On Friday, May 20, 2016 at 12:52:11 PM UTC-7, wrote:
Yep, simply check for open.

scratch that comment about the coax impedance. Darryl rightfully pointed out it will have a characteristic impedance. But we are interested in whether the core and shield have been bridged here.

I have very poor forward performance from my powerflarm, who could I send photos of the install and range analysis image to get some suggestions?

In the mean time I should test the flarm antenna if i can figure out the correct procedure.

Chris

On 5/20/2016 3:52 PM, wrote:
Also for the PF designers if they are reading, would be good to
sense this case as is done on the Becker Transponder and issue an
error. I imagine there a number of ways to do it, like a self test
during boot.

Unfortunately an automated antenna self-test would not be as simple as
simply checking the antenna for a DC short, because some antennas are
purposely designed to incorporate a DC short. It's possible to check a
transmit antenna by sensing the reflected power using a bridge
arrangement, but that requires extra components and (therefore) extra
expense. Building a circuit to automatically check a receive antenna
would be even more difficult.

but that requires extra components and (therefore) extra expense.

Probably right. Simplest solution is for them to do a QA check on the antennas before delivery with the unit.

So easiest way to check the Pflarm A antenna, if you have access to the box itself is simply unscrew it from port A. And get out an ohm meter and carefully probe the inner core socket(middle of the white nylon bush) vs the outer "nut" which is tied to the shield. It should read infinite. If using the continuity feature of your multimeter it should NOT sound the high pitched beeeeep. verify again. if good, carefully screw the antenna back onto the proper/same port A and careful not to cross-thread. do not attempt to attach to any other port.

I should point out that this will detect only one type of failure. Another one could be a disconnect which make the antenna similarly useless. There could be other failure modes. So if you still have issue try to borrow an antenna from someone else or just spend the $30 or so for a new antenna. Another option is to swap the antennas for testing (they are almost identical) but this will require a reverse gender adapter.

Ramy