Transponder antenna installations

I hate to break it to you, but a Becker 4401-175 installed using RG-58
as an antenna line violates Becker’s instructions. They state in
paragraph 5C that only RG-223 is to be used with the 4401-175. RG-58
can only be used with a 4401-250. Don’t overlook that you also must
comply with paragraph 6E, where you must check the power at the
antenna end of the cable. I’d bet that a 4401-175 using RG-58 will not
meet Becker’s power spec of 18.5 dBW.

As far as the non-mention of LM240 in the Becker manual, I’d bet
you’re allowed as an A&P to attach data showing that LM240 exceeds the
performance of RG-223. This data, combined with the mandatory power
test proving that the 4401-175 installed using LM240 exceeds the
Becker requirement of 18.5 dBW at the antenna end of the cable, would
make you golden.

Unfortunately, you have to buy male BNC and male TNC crimp connectors
when you buy the LM240. They’re a buck more expensive than RG-58
connectors. But your crimper will definitely work.

Your log book entry would simply say that the Becker 4401-175 was
installed in accordance with the manufacturer’s instructions, except
for the use of an antenna cable that exceeds the manufacturer’s cable
specifications which results in greater power being delivered to the
antenna. I guess you could attribute the idea of using a better cable
to RAS, if you liked – humor shouldn’t a violation of the A&P code, is
it?

-John

On Feb 7, 9:18 am, JJ Sinclair wrote:
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

In article jcarlyle writes:
I hate to break it to you, but a Becker 4401-175 installed using RG-58
as an antenna line violates Becker's instructions. They state in
paragraph 5C that only RG-223 is to be used with the 4401-175. RG-58
can only be used with a 4401-250. Don't overlook that you also must
comply with paragraph 6E, where you must check the power at the
antenna end of the cable. I'd bet that a 4401-175 using RG-58 will not
meet Becker's power spec of 18.5 dBW.

Remember to account for the greater loss of the cable after 10 - 20 years.


As far as the non-mention of LM240 in the Becker manual, I'd bet
you're allowed as an A&P to attach data showing that LM240 exceeds the
performance of RG-223. This data, combined with the mandatory power
test proving that the 4401-175 installed using LM240 exceeds the
Becker requirement of 18.5 dBW at the antenna end of the cable, would
make you golden.

Unfortunately, you have to buy male BNC and male TNC crimp connectors
when you buy the LM240. They're a buck more expensive than RG-58
connectors. But your crimper will definitely work.

I doubt it. LMR 240 is larger in diameter than RG-58. The crimper for
RG-59 might be a closer fit.


Your log book entry would simply say that the Becker 4401-175 was
installed in accordance with the manufacturer's instructions, except
for the use of an antenna cable that exceeds the manufacturer's cable
specifications which results in greater power being delivered to the
antenna. I guess you could attribute the idea of using a better cable
to RAS, if you liked =96 humor shouldn't a violation of the A&P code, is
it?


The problem is that "better" isn't just lower loss per foot when the cable
is new. There may be a lot of other factors that the manufacturer took into
account with their cable selection. "Better" needs to be better in all of
these factors.

The transponder may need a minimum amount of loss in the coax to ensure that
the SWR seen by the transmitter is low enough in case something gets near the
antenna. (This would protect both the transmitter, and the receiver, as a mismatch
at the duplexer often reduces the isolation between the transmitter output and the
receiver input.)


-John

On Feb 7, 9:18 am, JJ Sinclair wrote:
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


I suspect it LMR 240 would work better than the other cables, both in loss and
service life, but I don't know it. As JJ notes, he doesn't know it for sure, and
and would need to.

Alan

Alan,

The best way to answer is to quote from section 5.11.2 of the Trig
installation manual. They state that excessive cable loss will degrade
both transmitter output power and receiver sensitivity. Then they
define the three qualities of an acceptable cable:
(1) less than 1.5 dB loss for the run length,
(2) a characteristic impedance of 50 ohms, and
(3) double braid screens, or a foil and braid screen.
They then say that their table of maximum usable lengths for common
cable types is a guide only, and tell you to refer to manufacturer’s
data sheets for your specific chosen cable. This is clearly permission
to choose your cable type, as long as it meets Trig’s three acceptance
criteria above as backed up by specific manufacturer’s data.

As for “knowing” about cables, like anything else you need to do
research and get educated. I’ve tried to let this forum know that
there are much better choices for microwave cable than RG-58 and
RG-400. Naturally, people will do as they wish, even to the extent of
tossing away transponder output power and getting less receiver
sensitivity. It may work out OK, or it might possibly be a link in an
accident chain someday. I have the satisfaction of knowing that in my
transponder installations pilots are getting 175 W transponders that
meet or exceed their performance specifications for just $20 extra in
cable.

-John

On Feb 8, 2:04 am, (Alan) wrote:

The problem is that "better" isn't just lower loss per foot when the cable
is new. There may be a lot of other factors that the manufacturer took into
account with their cable selection. "Better" needs to be better in all of
these factors.

The transponder may need a minimum amount of loss in the coax to ensure that
the SWR seen by the transmitter is low enough in case something gets near the
antenna. (This would protect both the transmitter, and the receiver, as a mismatch
at the duplexer often reduces the isolation between the transmitter output and the
receiver input.)

I suspect it LMR 240 would work better than the other cables, both in loss and
service life, but I don't know it. As JJ notes, he doesn't know it for sure, and
and would need to.

Alan

A bit off topic but when I bought my glider the transponder antenna (flat L2 type) was mounted under the seatpan on the "floor" of the fuselage. After reading some links in this thread I see that, according to the manufacturer, the antenna should be mounted vertically. Where would one typically do this? There aren't many flat vertical surfaces other than the main bulkhead. Glass, not carbon fiber, ship. This is my first glider with a transponder and I admit ignorance on the topic.

On Tuesday, December 31, 2019 at 10:04:40 AM UTC-8, wrote:
A bit off topic but when I bought my glider the transponder antenna (flat L2 type) was mounted under the seatpan on the "floor" of the fuselage. After reading some links in this thread I see that, according to the manufacturer, the antenna should be mounted vertically. Where would one typically do this? There aren't many flat vertical surfaces other than the main bulkhead. Glass, not carbon fiber, ship. This is my first glider with a transponder and I admit ignorance on the topic.

Yep, wrong polarization orientation, and the testicle thing.

As you likely are working out there often is no *great* place to mount an antenna.

Many people would make up a vertical mount out of plywood or fiberglass or just a block of balsa and find a place on one side of the fuselage to mount this down the tail boom to mount this. You want to avoid the antenna being near conductive components and that is often a problem finding space away from control linkage and other hardware, and you have rudder cables and elevator etc. running down the fuselage. Have a look around and see. It may be better to mount an external 1/4 wave antenna with internal ground plane.....

If you end up with longer coax runs pay attention to using a correct high-spec cable, especially with Trig transponders. And secure the cable well so there is no movement.

I cut a piece of balsa wood that matched the curve of the fuselage, aft of the landing gear. I bonded the L2 to the wood and then the wood to the fuselage. The biggest challenge was getting the antenna cable routed, and then plugged into the antenna.

Mike

Further up the thread:

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

I'll agree with Darryl that the rear fuselage / tail cone is a good place to mount an L2 antenna – provided that you can reach the area
AND get an adequate coax there. See

https://www.timesmicrowave.com for a coax calculator.

Do make very sure that nothing will come loose and interfere with the elevator pushrod, or anything else.

Darryl and I disagree on mounting an L2 antenna in the forward fuselage.

That said, my installation forward of the rudder pedals in my previous ASW-20 passed the transponder test and ATC had no complaints.

To shape the balsa, stick 80 grit sandpaper on the site with double sided tape and sand away.

On Sunday, February 6, 2011 at 7:55:37 PM UTC-8, Paul Remde wrote:
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)

I installed an antenna as recommended by SH on my Ventus 2c, down by the wheel. Drilling the hole was traumatic. SH recommended carefully drilling a small hole then using a fine file to gently enlarge it, and that worked well. I installed an aluminum sheet ground plane inside the fuselage, since I could find no clear advice on whether carbon fiber is or is not an adequate ground plane. Even though I only had about a 5ft cable run to the antenna, I used low-loss coax cable recommended by Trig, and got the cable custom cut to length with the proper connectors attached. Its important that the coax connectors are properly fitted, and I didn't have the proper crimper. I also looked up the coax cable specs and found that there was a limitation on the radius that the cable should be bent, and I kept within that bend spec. Its not only that cable and connectors and bends can cause attenuation, they can cause reflections back to the transponder which can upset it's operation.

On Tuesday, December 31, 2019 at 4:43:49 PM UTC-8, wrote:
On Sunday, February 6, 2011 at 7:55:37 PM UTC-8, Paul Remde wrote:
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)

I installed an antenna as recommended by SH on my Ventus 2c, down by the wheel. Drilling the hole was traumatic. SH recommended carefully drilling a small hole then using a fine file to gently enlarge it, and that worked well. I installed an aluminum sheet ground plane inside the fuselage, since I could find no clear advice on whether carbon fiber is or is not an adequate ground plane. Even though I only had about a 5ft cable run to the antenna, I used low-loss coax cable recommended by Trig, and got the cable custom cut to length with the proper connectors attached. Its important that the coax connectors are properly fitted, and I didn't have the proper crimper. I also looked up the coax cable specs and found that there was a limitation on the radius that the cable should be bent, and I kept within that bend spec. Its not only that cable and connectors and bends can cause attenuation, they can cause reflections back to the transponder which can upset it's operation.

Trig specifies that the cable loss must be no more than 1.5 dB. They have a table of acceptable cables in their installation manual. RG304 is ok for runs up to 3.8 m (12.5 ft).

Tom