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fklein(at)orcasonline.com
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 Posted: Sat Mar 14, 2009 5:22 pm Post subject: transponder antenna wiring |
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Hi All,
I'm in the midst of locating antennae and attempting to zero in on
avionics selection.
I find in the Garmin Installation Manual for their 320A transponder a
max. length for the RG-400 coax to be 8.8 feet, 12.5 feet for RG304 (a
coax which I've yet to see for sale anywhere, and 17.0 feet for "ECS
Type 311601 sold by Electronic Cable Specialists in Wisconsin (again,
a product which I haven't seen in any of our wiring discussions). This
may be a moot point as I expect to use the Narco 165 (Value Series, to
save a few bucks [unless the consensus might be that doing so would be
pennywise/pound foolish].) I can't seem to find a downloadable
installation manual for the Narco, so I'm not sure that Garmin's 8.8
foot max would still apply.
On our forum, I've only found folks using RG-400. I don't see how I
can get the distance down to an 8.8 foot run from antenna to the
panel, unless I bring the transponder antenna forward to just aft of
the baggage bay (close to strobe power supply; however, it seems many
guys have put the transponder as far aft as possible abeam the rear
bulkhead.
Any advice and counsel to this electronic neophyte would be much
appreciated...don't want to get anal, but don't want to create
problems either,
Thanks,
Fred
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fklein(at)orcasonline.com
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| Posted: Sat Mar 14, 2009 11:17 pm Post subject: transponder antenna wiring |
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Spent the evening at Europa University scrolling thru the archives on
this subject...thanks for all the input assembled when these issues
have been previously discussed so thoroughly!
Fred
On Mar 14, 2009, at 6:22 PM, Fred Klein wrote:
| Quote: | I'm in the midst of locating antennae and attempting to zero in on
avionics selection.
|
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frans(at)paardnatuurlijk.
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| Posted: Sun Mar 15, 2009 2:18 am Post subject: transponder antenna wiring |
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Fred Klein wrote:
| Quote: | I find in the Garmin Installation Manual for their 320A transponder a
max. length for the RG-400 coax to be 8.8 feet, 12.5 feet for RG304 (a
coax which I've yet to see for sale anywhere, and 17.0 feet for "ECS
Type 311601 sold by Electronic Cable Specialists in Wisconsin (again, a
product which I haven't seen in any of our wiring discussions). This may
be a moot point as I expect to use the Narco 165 (Value Series, to save
a few bucks [unless the consensus might be that doing so would be
pennywise/pound foolish].)
|
This is one of the reasons why I choosed a transponder where the actual
transmitter and the panel part are separate. There is just a very thin
and light weight data cable in between; I will mount the antenna
directly onto the transmitter part, which will be located somewhere in
the tail section. Another reason for this is of course that mode-S is
mandatory here.
You might consider doing the same, especially if mode S requirements are
foreseen in the near future. It saves you some headaches now and maybe
in the future if mode S is coming your way ultimately.
If you choose to go for the coax routing, keep in mind that the 8.8 foot
is an arbitrairy value. You won't notice much difference between 8.5
foot of cable or 9 foot of cable. The whole point is that the high
frequencies attenuate very fast in coax cable, so the shorter the
better. In fact, a less optimal antenna location but with a shorter
cable is preferable over a better antenna location but with a much
longer cable. All this has nothing to do with the transponder
manufacturer but with the signals used by the transponder, and is equal
for Garmins and Narco's.
Thicker, heavier cables have less attenuation than standard size coax,
so these bulky cables can be used for longer distances. However, more
length of a cable which is also heavier by itself, comes with a
substantial weight penalty, and these cables are difficult to route.
Bends need a large radius; a little bit to tight and the attenuation
comes up again spoiling the advantages of the expensive heavy cable. Oh,
and they often forget to tell you, but these cables "age" and losses
build up year after year. A tiny amount of moisture in the cable kills
the signals. All with all, I think I wouldn't go for low loss cables.
An option would be to mount the transponder antenna under the radiator
cowling. There is already metal there that can double duty as a ground
plane, and as a shield/reflector, so the signals go to the ground
instead of to your head and nearby avionics.  And this allows for a
very short cable run.
And of course, it all depends about how much you care about transponder
performance.
--
Frans Veldman
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ptag.dev(at)tiscali.co.uk
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| Posted: Sun Mar 15, 2009 2:33 am Post subject: transponder antenna wiring |
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Hi! Fred
Mine has worked with the Garmin 320A with the antenna located on the
belly about 12" behind the enlarged baggage bay couldn't begin to tell
you what standard wire or length it is. I hope I don't pick up any
difficulty with the existing Gold Wing Strobe kit mounted about 24"
further aft but I'm holding my breath with the Garmin 328 now fitted and
the Skyflash strobe currently being fitted in identical locations.
Regards
Bob H G-PTAG
--
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fklein(at)orcasonline.com
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| Posted: Sun Mar 15, 2009 8:21 am Post subject: transponder antenna wiring |
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On Mar 15, 2009, at 3:14 AM, Frans Veldman wrote:
| Quote: | This is one of the reasons why I chose a transponder where the actual
transmitter and the panel part are separate.
|
Thanks Frans...and who makes such a transponder?
Fred
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frans(at)paardnatuurlijk.
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| Posted: Sun Mar 15, 2009 2:15 pm Post subject: transponder antenna wiring |
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Fred Klein wrote:
| Quote: | Thanks Frans...and who makes such a transponder?
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Have a look at
http://www.aircraftspruce.com/catalog/avpages/garrechttransponder.php
They are somewhat more costly than "standard" transponders, but if mode
S becomes mandatory (like it is in Europe already in many countries) it
saves you from buying a transponder twice. I believe it is just a matter
of time before it becomes mandatory in the US as well.
The good thing is that mode-S can be linked to the GPS, enabling TCAS
for General Aviation.
For my 914 powered ship an additional advantage is that the most heavy
part of the transponder can be mounted aft, and only a very light weight
control unit has to be mounted in the instrument panel.
Anyway, I hate the costs, but as I said, in the Netherlands we have no
other choise than mode-S, unless one wants to limit himself to a maximum
of 1200 feet, and stay entirely out of controlled airspaces.
--
Frans Veldman
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Rowland_Carson
Joined: 04 Jul 2008
Posts: 155
Location: Cheltenham, England
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| Posted: Sun Mar 15, 2009 3:51 pm Post subject: transponder antenna wiring |
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At 2009-03-15 09:21 -0700 Fred Klein wrote:
| Quote: | On Mar 15, 2009, at 3:14 AM, Frans Veldman wrote:
>This is one of the reasons why I chose a transponder where the actual
>transmitter and the panel part are separate.
Thanks Frans...and who makes such a transponder
|
Fred - have a look at the Trig TT21 - see:
http://www.trig-avionics.com
I think maybe Becker do a separate-head version too.
regards
Rowland
--
| Rowland Carson http://home.clara.net/rowil/
| <rowil(at)clara.net> ... that's Rowland with a 'w' ...
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paul.the.aviator(at)gmail
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| Posted: Sun Mar 15, 2009 5:12 pm Post subject: transponder antenna wiring |
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If the price of 1300 pounds is correct, this is $1800 US... not bad for a mode S !
[quote][b]
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rparigor(at)suffolk.lib.n
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| Posted: Sun Mar 15, 2009 8:49 pm Post subject: transponder antenna wiring |
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Hi FredI went with a long run of RG142A cable.See:http://www.europaowners.org/modules.php?set_albumName=album272&op=modload&name=gallery&file=index&include=view_album.phpfor information on cable and my plan. I went with a Becker 250 watt unit, not their 175 watt unit. If performance is poor, I have notes on RG213 equivilent from ECS.I have quote for them making up a cable with a BNC and TNC connector, a few hundred dollars. My run is from a bit forward of stabilator spar (torque tube) through tunnel and into Transponder.Going to have it checked before I bond top of fuse on. Boy is that RG142A thin and light.Ron P. [quote][b]
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