In all fairness I re-read the trafficscope manual, and I think what
they are suggesting is that they only approve of certain antenna
models.

My thought is they didn't want to give a "blanket approval" for just
any antenna on the market. This is understandable, considering
transponder-only antennas have smaller bandwidths than the broadband
DME antennas.

I used to work bench test transponders (in my much younger years) and
when I used the broadband antennas the power loss was much higher than
in the dedicated transponder antennas. The typical broadband antenna
had a VSWR of around 1.5, where the transponder antenna had a 1.2 In
Lamens terms, this COULD mean a difference of several dB depending on
ground-plane arrangements.

I have two of the commant blade antennas installed, one above just
rear of my comm, another forward of my transponder antenna, and
trafficscope functions flawlessly. One consideration I noticed is
that you do need to place the antennas 27 cm apart in a vertical
plane. When I asked them about this they explained that it helps their
splitter maintain phase balance.

In reading their publications, it appears that Surecheck gives more
attention to detail. They specify cable type, and antennas. This can
mean a major difference in range, especially if you took the monroy
advice and just wired up some lossy RG-58 and an unknown DME antenna.
At the frequency these guys operate at, a few extra feet of RG-58
could mean a range difference on more than a mile.


"Jon S" wrote in message ...
Thomas --

Just spoke to Paul about this. Turns out you're right -- there is no
difference. Paul checked with his radio person and was told it's exactly the
same part number. Interesting because SureCheck was adamant that a DME
antenna won't work and a transponder antenna will.

JonS


"Thomas Borchert" wrote in message
...
Jon,

We tried both the Monroy and the SureCheck units with a
DME antenna (because it was on the plane and not being used) and neither
one
worked at all.


There is a difference between DME and Transponder antennas? I was told
there
isn't.

We use ours with a cheapo single-stick transponder antenna on the belly
(see
http://www.aircraftspruce.com/catalo...ransponder.php - it's
listed as suitable for DME and transponder). Didn't work at first - which
turned out to be faulty antenna wiring. I would suggest your failure to
use it
with a mounted antenna might be because of problems with the antenna.

--
Thomas Borchert (EDDH)