Transponder Antenna & Battery Placement Nimbus or DUO

Andy wrote:
On Feb 19, 10:25 am, wrote:

Hate external antennas on Composite aircraft. Having worked on a lot
of homebuilts, thought someone else might have come up with an
alternative mount.

I won't help solve your problem but I noted that the Schleicher
ASH31Mi will have a transponder antenna mounted inside the fin as
standard equipment.

Andy


This is interesting as it will probably require some large coax to keep
the antenna loss to less than 1.5 db which is what was recommended in
the microair transponder install manual I have. The RG-58 is limited to
10 ft of coax length and that sure isn't going to get you to the fin
from the instrument panel...

A transponder, such as the Trig Avionics TT21, that has the operating panel
separate from the transmitter/receiver box, will allow the
transmitter/receiver to be installed behind the pilot and thus
considerably reduce the required cable length (and hence losses) to a
tail-fin antenna.

At 03:10 20 February 2009, Gary Emerson wrote:
Andy wrote:

This is interesting as it will probably require some large coax to keep
the antenna loss to less than 1.5 db which is what was recommended in
the microair transponder install manual I have. The RG-58 is limited to

10 ft of coax length and that sure isn't going to get you to the fin
from the instrument panel...

On Feb 20, 7:00*am, Big Wings wrote:
A transponder, such as the Trig Avionics TT21, that has the operating panel
separate from the transmitter/receiver box, will allow the
transmitter/receiver to be installed behind the pilot and thus
considerably reduce the required cable length (and hence losses) to a
tail-fin antenna. *

At 03:10 20 February 2009, Gary Emerson wrote:

Andy wrote:

This is interesting as it will probably require some large coax to keep
the antenna loss to less than 1.5 db which is what was recommended in
the microair transponder install manual I have. *The RG-58 is limited to
10 ft of coax length and that sure isn't going to get you to the fin
from the instrument panel...



I was about to suggest the same thing.

In the ASH-26E/ASH-31Mi fuselage there is a likely location to mount
the RF unit in the just behind the engine. With access though a nice
large opening provided originally for a barograph and now often used
for storage. In that location it should be possible for the factory to
relatively easily install something as large as RG-6 or similar cable
(~5dB/100' vs. ~14 dB/100' for RG-58).

Doing this also ensures that RF coax is not going up to the
transponder mounted on the panel and going though a wiring harness
that is flexing as the canopy is raised and lowered. And I don't know
about others but Becker head units use differential signaling and long
cable runs between the head unit and RF unit should not be a problem.

Another option would be to join some thick coax to RG-58 under he
cockpit floor to handle the transition to the panel, and although the
insertion loss of that connection might be 0.1 dB or so on paper I'd
want to avoid it. Routing say RJ-6 that far forward may be also
difficult.

As I mentioned on r.a.s. before the 1.5dB cable loss budget for the
Microair transponder is because Microair is trying to meet the TSO-
C47c Type 1A (for use above 15,000') transponder specs with a
transponder with only 200W output while other manufactures usually
have a bit more cable loss budget, using a 250W or more transponder
for this. They will typically have at least 3dB cable loss budget (for
250W transponders meeting TSO-C47c Type 1A (use above 15,000') or
3.9dB for 175W transponders meeting TSO-C47c Type 1B (use below
15,000'). There might also be an option of checking with whoever is
doing the install and sign off on say havng a 250W transponder install
as a having say a 250W transponder install as meeting TSO-C47c Type 1B
(below 15,000') and therefore having a 5.5 dB cable loss budget. it's
not like we really need the above 15,00o' specs - the important thing
is to have a transponder at all in high traffic areas.

So bottom line, finding an RF coax solution should not be a issue.

A more interesting question to me is the close proximity of the VHF
and transponder antennas. It is hard to see how you get a large enough
ground plane in there for a 1/4 wave stub antenna and some shielding
between the antennas. If a 1/2 wave or similar antenna is used then
there would obviously be no shielding between antennas (but trying to
line them up exactly co-linear will help.


Darryl

On Feb 18, 8:06*pm, wrote:
Looking for some suggestions on location of Transponder antenna from
people who have them mounted on their Nimbus or DUO.

Looking for area for placement of a 3rd Battery. Do you have a
location that works well?

Thanks in advance for the suggestions.
Mark Mahan
2K

This is not likely helpful for you Mark, sorry but for the non-carbon
types this little gem worked like a charm on my ASW20b, inside the
fusalage, out of sight, no drag & very easy to produce and install.

http://www.as-segelflugzeuge.de/tm/2...2020%20001.pdf

Rick
21