Hi, Ramy,
Thanks for posting those configuration values. The important PCAS parameters to which you are defaulting a
Modesalt - default is 1 (get altitude from Mode S signal)
Ownmodec - default is 0 (aggressive mode used with Mode C transponder)
Modec - default is 1 (enable processing of Mode C targets, ie, PCAS)
Since you don’t get false alerts from your own transponder you probably don’t want to “fix” things. But you really should put the command $PFLAC,S,MODESALT,0 into your configuration file, since you have a Mode C transponder. This will not only read altitude values from the PF internal pressure sensor, the altitude will be much less quantized than the 100 foot intervals in a Mode S signal. Right now you are configure to sometimes getting an altitude value from a stray Mode S signal.

-John, Q3

On Friday, July 21, 2017 at 1:20:39 AM UTC-4, Ramy wrote:
On Friday, July 14, 2017 at 7:31:21 AM UTC-7, John Carlyle wrote:
Many thanks, Ramy. What you have doesn't seem too different from my set-up, except I have about 8 feet separation between the transponder antenna and the Flarm ADS-B antenna in a fiberglass fuselage ship. Perhaps the 27's carbon fuselage does some helpful attenuation of your own transponder signal?

I look forward to seeing your configuration file. OWNMODEC in my configuration file is set to Aggressive (= 0). I don't know whether this is the default value.

Do other 27/29 owners who are seeing false Mode C alerts have their transponder and Flarm antennas mounted similarly to Ramy's?

-John, Q3

On Friday, July 14, 2017 at 2:14:58 AM UTC-4, Ramy wrote:
1- Both powerflarm antennas in the nose (no carbon in the nose section of my 27a).
2- transponder antenna under the seat pan in front of the stick (so not far from the powerflarm antenna, maybe 3 feet at the most.
3 - configuration file may need to wait until next week or so. BTW I recall there is an option to suppress own transponder more aggressively, I just used the default.

I really never had false alert from my own transponder, no kidding. And my mode C alert is working very well.

Ramy

Here is the relevant part of my config file. The rest is default.

$pflac,s,acft,1
$pflac,s,xpdr,1
$pflac,s,id,XXXXXX
$pflac,s,pcasvrange,600
$pflac,s,pcasrange,5000

Ramy