REFLECTOR: Transponder Signal Strength Anomaly - Recommendations forReplacement

[Ron Brown]

I have had this problem just once - right after take off.   After I got up 
to about 3000 feet, I got "radar contact".

I have one of the little metal rod antennas, 
http://www.aircraftspruce.com/catalog/avpages/ted_transponder.php mounted 
under my battery.  I had to raise my automotive battery up off of the 
Velocity supplied shelf to make some additional clearance from the retracted 
nose gear.  I built an aluminum plate - about the size of the bottom of the 
battery, mounted the antenna to it, then used a couple of 2x2" wooden blocks 
to raise the battery.  The antenna's tip is just above the inside of the 
fuselage.

Other than the one occurrence, I have had excellent results with this 
antenna and location.

(By the way, my experience is that many of the transponder failures appear 
to be ATC equipment related - I recall several instances of ATC telling me 
to recycle my transponder (back when I owned a Cessna 172, but if you listen 
up they are telling several other aircraft the same thing.)

Ronnie



----- Original Message ----- 
From: "Gary T. Ciampa" <gciampa at nc.rr.com>
To: <reflector at tvbf.org>
Sent: Monday, March 14, 2005 9:32 PM
Subject: REFLECTOR: Transponder Signal Strength Anomaly - Recommendations 
forReplacement


> All,
>
> I'd like to describe an anomaly that occurs with my current transponder 
> and solicit recommendations on a solution.
>
> So: I have an epoxy circuit board dipole transponder antenna that is 
> mounted along the right-side of the fuselage, in the nose compartment, 
> about twelve inches foward of the canard bulkhead. The anomaly that I've 
> encountered is when flying directly away from the radar station and 
> somewhere around 40-50NM from the station, the contollers lose my 
> transponder signal. I can change my aspect to the station (turning the 
> airplane about 30 degrees) and the controllers re-acquire my transponder 
> signal. Upon resuming my original course, controllers lose the signal. 
> I've tested this scenario with multiple controlling agencies, in several 
> cases, doing a 360 while the *accomdating* controller keeps me apprised of 
> the transponder status. Additionally, heading towards (or flying abeam) a 
> station, I have never had a problem with the controlling agency picking up 
> the transponder from one-hundred plus miles, which seems to rule out a 
> signal strength problem.
>
> Question:
> Is this a generally known problem with pushers? (I'm assuming the 
> engine/firewall is attenuating the signal aft of the airplane)
>
> Is an antenna such as the AV-22 a suitable substitute?
>
> I was planning to locate the AV-22 somewhere along the bottom of the 
> fuselage, perhaps between the nose-wheel strut and speedbrake. Is this 
> satisfactory? (this location is purely for convenience as I happen to have 
> the canard off for an inspection and sufficient antenna cable length)
>
> Other recommendations?
>
> Thanks in advance for your advice....
>
> Gary
>
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