Transponder antenna installations

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

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.

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

On Feb 6, 11:12*am, jcarlyle wrote:
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- Hide quoted text -

- Show quoted text -

You're right John.................I'll disregard the manufactures
instructions and go with something I heard on ras.............
Yeah, right!
JJ

Good point - everything on RAS is always suspect.

Would you believe an attenuation calculator from Times Microwave? See
http://www.timesmicrowave.com/cgi-bin/calculate.pl
Another option is to look up attenuation values on Newark and Allied,
since a manufacturer has a vested interest in lying. Oh, wait -
Advanced Airborne Electronics is a manufacturer...

-John

On Feb 6, 2:18 pm, JJ Sinclair wrote:
You're right John.................I'll disregard the manufactures
instructions and go with something I heard on ras.............
Yeah, right!
JJ

On 2/6/2011 11:18 AM, JJ Sinclair wrote:
On Feb 6, 11:12 am, wrote:
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...



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- Hide quoted text -

- Show quoted text -

You're right John.................I'll disregard the manufactures
instructions and go with something I heard on ras.............
Yeah, right!

JJ, call AAE and ask about the LM240 cable. It might be their
recommendation was aimed at airplanes carrying 200+ watt transponders
and using shorter cable runs, compared to gliders that might using units
with 150 watts or less and long cable runs. Also, looking at the
transponder manufacturer's recommendation is probably a better
indication of what's needed than the antenna manufacturer. My Becker
instructions made quite a fuss about which cable to use.

Generally, I like to go the "good stuff" for transponders, as
attenuation per foot is much higher at transponder frequencies than our
communication radios frequencies (factor of 8).

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

Hi,

The Trig TT21 and TT22 manual is also quite fussy about transponder antenna
cable. But it important to note that many of the "long run" antenna cables
they recommend are extremely expensive.

I recommend mounting the transponder unit (it is separate from the control
head) as close to the antenna as possible. When that is done I have
received customer feedback that RG-58 cable works fine - with all required
tests passed with flying colors.

Paul Remde

"Eric Greenwell" wrote in message
...
On 2/6/2011 11:18 AM, JJ Sinclair wrote:
On Feb 6, 11:12 am, wrote:
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...



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- Hide quoted text -

- Show quoted text -

You're right John.................I'll disregard the manufactures
instructions and go with something I heard on ras.............
Yeah, right!

JJ, call AAE and ask about the LM240 cable. It might be their
recommendation was aimed at airplanes carrying 200+ watt transponders and
using shorter cable runs, compared to gliders that might using units with
150 watts or less and long cable runs. Also, looking at the transponder
manufacturer's recommendation is probably a better indication of what's
needed than the antenna manufacturer. My Becker instructions made quite a
fuss about which cable to use.

Generally, I like to go the "good stuff" for transponders, as attenuation
per foot is much higher at transponder frequencies than our communication
radios frequencies (factor of 8).

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email
me)

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 Becker 4401-175 manual does say that RG-223/U is preferred over
RGU-58, but it doesn't mention LM-240? As a mechanic I am bound to
follow the appropriate tech data. Does LM-240 use the same BNC
fittings I have in stock? Can I use my crimper? What would my log book
entry say? Installed Becker 4401-175 transponder in accordance with
opinions found on ras?
:) JJ