Transponder Antenna Location

I am going to install a transponder in my Ventus and struggling with
the decision on where to locate the antenna.
Any comments on installing the antenna on the forward portion of the
glare shield...inside the cockpit?
Scott

One thing that concerns me is that the transponder frequency is
centered at 1060 MHz. A microwave oven frequency is close by, centered
at 2450 MHz. The power output of a transponder is about half that of a
microwave oven, but still, I don't want the transponder antenna close
to my body. I'll be mounting my antenna as far back in the tail boom
as I can get it.

-John

On Jan 16, 10:39 am, wrote:
I am going to install a transponder in my Ventus and struggling with
the decision on where to locate the antenna.
Any comments on installing the antenna on the forward portion of the
glare shield...inside the cockpit?
Scott

I followed Tom Knauff's lead with my Discus 2cT, and mounted it on the
outside, on top of the turtle deck. The fuselage is carbon fibre
there, which is opaque to the radiation, shielding me, - and the
antenna is not vulnerable to vagaries of landing as when mounted
behind the gear doors.

While this position will also shield the signal from a receiver
directly below, that is not much of a concern; ATC and onboard TCAS
systems in approaching commercial traffic will have a good signal. To
a large extent it makes one of my concerns, - a mid-air with a jet
whose pilots have their heads down on checklists and approach
frequencies, much more of their concerns.

BTW, I also use a Zaon PCAS on my glare shield for added protection.
Like all the other pilots to whom Tom lent one last winter, I bought
one. I had no idea there was so much traffic out there!

I installed one on my Discus 2 in the factory-recommended position,
offset just behind the gear doors (the factory will send you photos if
you ask). It seems to work fine there, but you have to be careful
rigging and de-rigging as you can easily damage it on the trailer
ramp.

I know of a couple of successful installations on the upper fuselage
turtle deck, where performance is also reported to be good.

I would be disinclined to mount it too close to my head.

Mike

The antenna on my V2C was mounted in the factory-recommended position
that Mike mentions. It worked great and the rigging/de-rigging issue
wasn't a big deal. The antenna lead will be shorter and easier to
route in that position, where on the turtle neck you'll probably be
hitting the cable every time you try to futz with your O2 or stow
something above the wing spars.

John

On Jan 16, 7:50 am, jcarlyle wrote:
One thing that concerns me is that the transponder frequency is
centered at 1060 MHz. A microwave oven frequency is close by, centered
at 2450 MHz. The power output of a transponder is about half that of a
microwave oven, but still, I don't want the transponder antenna close
to my body. I'll be mounting my antenna as far back in the tail boom
as I can get it.

-John

On Jan 16, 10:39 am, wrote:

I am going to install a transponder in my Ventus and struggling with
the decision on where to locate the antenna.
Any comments on installing the antenna on the forward portion of the
glare shield...inside the cockpit?
Scott

I'm not sure where the "about half" power ratio you mention is coming
from. Radiated power specs for a microwave oven would claim something
like "1,200 watts", a transponder something like "175 watts" and an
(incorrect) naive ratio there is 1,200/175 = ~7%. That is wrong
because the specs on radiated power for a transponder is pulse power,
while that of a microwave is average power (the microwave oven may
still pulse the RF signal, especially at less than full power
settings). If you want to compare the two devices without worrying
about the duty cycles, etc. and converting to equivalent power a
simpler crude comparison would be to compare the power consumption of
a microwave oven (typically ~1.5 to 2 killowatt) and the typical spec
power consumption of a transponder, say ~5 watts (Becker 175 Watt mode
C). The power consumption of the transponder is obviously dependent on
the interrogation rate. Still instead of "half" as claimed a better
simple guesstimate is a ratio of 5/2,000 = ~.2%. A better analysis of
actual radiated power would show an even smaller ratio (the cavity
magnetron in the microwave oven will be more efficient than the
transponder at converting power into RF signal).

Still I agree with not getting too close to the antenna and I would
not put the antenna close to my eyes, head or other parts I care
about. But "mounting as far back as I can get" may not a good
optimization either. You want to avoid long cable runs and for
standard quarter wave antennas you want a part of the fuselage that
allows the mounting of a ground plane, i.e. a large area of the
fuselage that does not have too an extreme curvature. Carbon fiber
fuselages will shield the pilot very well from RF exposure but you
still need a proper ground plane for the antenna, usually adhesive
metal foil or aluminum sheet inside the fuselage wall and of radius at
least about the length of the antenna. In a fiberglass (RF
transparent) fuselage mounting the antenna inside may be a good idea,
you need to avoid metal parts close to the antenna and provide a good
ground plane.

My general advice on these is to follow the manufactures
recommendation on antenna placement, if they did not have something
specific then look at what manufactures are recommending for similar
gliders.

Personally I'd mount the antenna below (where all manufactures
recommend AFAIK) for better RF exposure to ground based radar. On my
ASH-26E I have the antenna in the factory recommended location below
the fuselage behind and to the side of the gear, rigging and handling
are not an issue.

Darryl

The DG website has good info re the fitting of transponder
antennas to their gliders,including drawings - good
for guidance.

http://www.dg-flugzeugbau.de/index-e.html

Pete

The DG website has good info re the fitting of transponder
antennas to their gliders,including drawings - good
for guidance.

http://www.dg-flugzeugbau.de/index-e.html

Pete

On 16 jan, 16:39, wrote:
I am going to install a transponder in my Ventus and struggling with
the decision on where to locate the antenna.
Any comments on installing the antenna on the forward portion of the
glare shield...inside the cockpit?
Scott

Hi,

I used the shark antenne on my ventus ct. I decided to do it on top
of the fuselage to avoid damage during riggin-derigging.

It's installed after the doors of the engine so its 1.5 m away from me
with a engine, fuselage, the wing and a fuel tank between me and the
antenna

Due to that i needed an 'minor change modification' at easa , that
cost +/- 300 Euro

It's not the most pretty solution but it's the best one

If you want I can send you some pictures

Darryl,

Thanks for the power calculation. My microwave says 350w, so I just
did the 175/350 ratio. It appears I left out a few
considerations...grin

My glider is a fiberglass ASW-19, and Schleicher has not responded to
my request for guidance on antenna installation. I did see their write-
up for the ASH-26, but I want an internal installation. The DG service
info note 53/04 issue 3 shows a diagram for an internal mounting, but
it neglects to show the ground plane that is required with the type of
antenna they use.

I'm thinking of using an Advanced Aircraft Electronics L-2 transponder
antenna. It's a dipole, doesn't require a ground plane, claims to have
more gain than normal antennas, and can be installed by simply gluing
it onto a vertical surface.

One pilot I'm aware of who used the L-2 antenna made a simple stand
out of 1/4" balsa wood, with a 6" vertical run and a small cruciform
base. He glued the L-2 to the vertical member, and glued the cruciform
base to the bottom center of his tail boom, as far back as he could
reach. The cable he used was RG-213, to minimize losses.

-John


On Jan 17, 2:39 am, Darryl Ramm wrote:
I'm not sure where the "about half" power ratio you mention is coming
from. Radiated power specs for a microwave oven would claim something
like "1,200 watts", a transponder something like "175 watts" and an
(incorrect) naive ratio there is 1,200/175 = ~7%. That is wrong
because the specs on radiated power for a transponder is pulse power,
while that of a microwave is average power (the microwave oven may
still pulse the RF signal, especially at less than full power
settings). If you want to compare the two devices without worrying
about the duty cycles, etc. and converting to equivalent power a
simpler crude comparison would be to compare the power consumption of
a microwave oven (typically ~1.5 to 2 killowatt) and the typical spec
power consumption of a transponder, say ~5 watts (Becker 175 Watt mode
C). The power consumption of the transponder is obviously dependent on
the interrogation rate. Still instead of "half" as claimed a better
simple guesstimate is a ratio of 5/2,000 = ~.2%. A better analysis of
actual radiated power would show an even smaller ratio (the cavity
magnetron in the microwave oven will be more efficient than the
transponder at converting power into RF signal).

Still I agree with not getting too close to the antenna and I would
not put the antenna close to my eyes, head or other parts I care
about. But "mounting as far back as I can get" may not a good
optimization either. You want to avoid long cable runs and for
standard quarter wave antennas you want a part of the fuselage that
allows the mounting of a ground plane, i.e. a large area of the
fuselage that does not have too an extreme curvature. Carbon fiber
fuselages will shield the pilot very well from RF exposure but you
still need a proper ground plane for the antenna, usually adhesive
metal foil or aluminum sheet inside the fuselage wall and of radius at
least about the length of the antenna. In a fiberglass (RF
transparent) fuselage mounting the antenna inside may be a good idea,
you need to avoid metal parts close to the antenna and provide a good
ground plane.

My general advice on these is to follow the manufactures
recommendation on antenna placement, if they did not have something
specific then look at what manufactures are recommending for similar
gliders.

Personally I'd mount the antenna below (where all manufactures
recommend AFAIK) for better RF exposure to ground based radar. On my
ASH-26E I have the antenna in the factory recommended location below
the fuselage behind and to the side of the gear, rigging and handling
are not an issue.

Darryl