Transponder antenna installations

I am installing a new vane style antenna for my transponder. My
original antenna was located where the cg hook used to be on my
discus. This location often tangled with the trailer ramp when
loading the glider. Next I tried a whip style on top of my instrument
panel cover. All of the self proclaimed experts said that was a
terrible place. Much to much power too close to the rest of my
avionics and electronics. I now intend to place it on the underside
of the fuselage as far aft of the main gear housing as I can reach.
My question is, does it have to be mounted near the centerline, I'd
rather not tangle with the overlap of the two fuselage halves. How
far off the center line can I go before the biannual inspector will
object or I will lose effectiveness? IT

Dick,

Have a look at the glider manufactures website or contact the dealer
as many have very specific directions for transponder antenna
location. On the Ventus 2b there is an engineering drawing showing the
location which puts the antenna is substantially off centerline on the
right side. This works well as it clears the trailer easily and is
generally out of the way.

John Seaborn (A8)

On Feb 5, 10:26*pm, Dick wrote:
I am installing a new vane style antenna for my transponder. *My
original antenna was located where the cg hook used to be on my
discus. *This location often tangled with the trailer ramp when
loading the glider. *Next I tried a whip style on top of my instrument
panel cover. *All of the self proclaimed experts said that was a
terrible place. *Much to much power too close to the rest of my
avionics and electronics. *I now intend to place it on the underside
of the fuselage as far aft of the main gear housing as I can reach.
My question is, does it have to be mounted near the centerline, *I'd
rather not tangle with the overlap of the two fuselage halves. *How
far off the center line can I go before the biannual inspector will
object or I will lose effectiveness? *IT

We've use the Advanced Aircraft Electronics L2 antenna on several
installations, with excellent results. This antenna mounts
internally in the fuselage tail boom. (won't work with carbon fiber
in the fuselage though...)

On gliders with carbon fiber, we used typical stub antenna, mounted
per manufacturer's drawings....we fabricated a "ground plane" plate to
go inside the fuselage......you need some space for this.

The antenna can be quite far off center line...but I would worry about
not going too far off vertical orientation.

Cookie

We've use the Advanced Aircraft Electronics L2 antenna on several
installations, with excellent results. * This antenna mounts
internally in the fuselage tail boom. *(won't work with carbon fiber
in the fuselage though...)

I second the L-2, di-pole antenna suggestion, all inside with nothing
sticking out to get ripped off. Carve a1"X 1"X4" balsawood block so
that it matches the inside curve of your non-carbon fuselage, then
glue the antenna vertical to the flat side and the curved side to the
inside aft fuselage. Keep it about 6" away from metal objects like
your elevator push-rod, etc. Secure the RG-58 lead so that it can't
get tangled with controls and you're good to go.
Hope this helps,
JJ

First of all: what kind of a glider are you installing the antenna in?
If it is carbon with enough conductivity in the fuselage then you have
to go outside, but if not, you can install the antena inside.

Installing antenna on top of the panel cover was probably a bad place,
but primarily because with proper ground plane primary emission would
be up, rather than down towards radar station.

Cheers,
Henryk

On Feb 5, 7:26*pm, Dick wrote:
I am installing a new vane style antenna for my transponder. *My
original antenna was located where the cg hook used to be on my
discus. *This location often tangled with the trailer ramp when
loading the glider. *Next I tried a whip style on top of my instrument
panel cover. *All of the self proclaimed experts said that was a
terrible place. *Much to much power too close to the rest of my
avionics and electronics. *I now intend to place it on the underside
of the fuselage as far aft of the main gear housing as I can reach.
My question is, does it have to be mounted near the centerline, *I'd
rather not tangle with the overlap of the two fuselage halves. *How
far off the center line can I go before the biannual inspector will
object or I will lose effectiveness? *IT

JJ, please don't use RG-58 for a transponder cable - it has very high
attenuation per foot. Times Microwave LM240 is a much better choice,
with only 1/3 of the attenuation of RG-58 at 1 GHz. I usually use
Times Microwave LM300, with only 1/4 the attenuation of RG-58, but it
has double the diameter. Both of these cables have a greater than 20
year life outdoors.

-john

On Feb 6, 9:07 am, JJ Sinclair wrote:
I second the L-2, di-pole antenna suggestion, all inside with nothing
sticking out to get ripped off. Carve a1"X 1"X4" balsawood block so
that it matches the inside curve of your non-carbon fuselage, then
glue the antenna vertical to the flat side and the curved side to the
inside aft fuselage. Keep it about 6" away from metal objects like
your elevator push-rod, etc. Secure the RG-58 lead so that it can't
get tangled with controls and you're good to go.
Hope this helps,
JJ

Correcting myself - the 1/4 and 1/3 figures were a straight comparison
of the dB loss per 100 feet, which is wrong. The correct figures are
that LM240 has 20% of the attenuation of RG-58 at 1 GHZ, while LM300
has 13% of RG-58.

-John

On Feb 6, 12:57 pm, jcarlyle wrote:
JJ, please don't use RG-58 for a transponder cable - it has very high
attenuation per foot. Times Microwave LM240 is a much better choice,
with only 1/3 of the attenuation of RG-58 at 1 GHz. I usually use
Times Microwave LM300, with only 1/4 the attenuation of RG-58, but it
has double the diameter. Both of these cables have a greater than 20
year life outdoors.

I installed an L-2 antenna with my transponder. While my wings and tailboom
are carbon fiber, the nose of my glider is fiberglass. I installed the L-2
vertically on the bulkhead that closes off the nose ahead of my feet. I've
not noticed any effect on my other instruments in the panel or on my GPS
(CA302). I have noticed that my feet still get cold at altitude, so I don't
think the power output is a problem. The vertical orientation means my
glider is at the center of a very fat horizontal donut.

John Scott

On Feb 6, 9:57*am, jcarlyle wrote:
JJ, please don't use RG-58 for a transponder cable - it has very high
attenuation per foot. Times Microwave LM240 is a much better choice,
with only 1/3 of the attenuation of RG-58 at 1 GHz. I usually use
Times Microwave LM300, with only 1/4 the attenuation of RG-58, but it
has double the diameter. Both of these cables have a greater than 20
year life outdoors.

-john

On Feb 6, 9:07 am, JJ Sinclair wrote:



I second the L-2, di-pole antenna suggestion, all inside with nothing
sticking out to get ripped off. Carve a1"X 1"X4" balsawood block so
that it matches the inside curve of your non-carbon fuselage, then
glue the antenna vertical to the flat side and the curved side to the
inside aft fuselage. *Keep it about 6" away from metal objects like
your elevator push-rod, etc. Secure the RG-58 lead so that it can't
get tangled with controls and you're good to go.
Hope this helps,
JJ- Hide quoted text -

- Show quoted text -

The instructions from Advanced Aircraft Electronics call for RG-58A/U
unless wire bundle size is critical where the smaller RG-174/U may be
used if length is held to 20 feet or less.
JJ

I understand your point - I saw those suggestions on my L2
instructions, laughed, and pitched it. Why should you pay for
transponder output just to heat up the antenna cable with outdated
RG-58, when low loss LM240 is only $0.70 more per foot? And if RG-58
is bad, RG-174 is 4 times worse...

-John

On Feb 6, 1:27 pm, JJ Sinclair wrote:
The instructions from Advanced Aircraft Electronics call for RG-58A/U
unless wire bundle size is critical where the smaller RG-174/U may be
used if length is held to 20 feet or less.
JJ