ASW27 Trasponder Antenna Installation Inside Fuselage.

[Paul Birkett]

Hello, my intention is to fit a Transponder Antenna within my ASW27. I was

wondering does anyone know where on the ASW27 Fuselage is not Carbon
or Aramid(conductive) construction, which would allow internal fitting of
an
antenna such as a Dolba BD1, Dolba BD2, FUNKE DP1090-5 or similar?
Schleicher TM/TN 13 “installation of a PCB-transponder antenna in the
vertical tail” doesn’t give a drawing/photo/diagram and I have
requested
additional information from Zulu-Glasstek. If I were to install antenna
within
the vertical stabilizer (Dolba BD1), the coax cable length would be
considerable (6 to 7 metre) and routing-security could be an issue, using
Carlisle ECS P/N 311501 coax cable. However, if the nose (tip area) of the

fuselage was manufactured from GRP as maybe used on other carbon fibre
Schleicher fuselages, then I would endeavour to install antenna within this

area? I have 95% dismissed TM/TN 12, installation of external antenna
alongside undercarriage due to it being ugly and prone to damage. Any
information gladly received. Best regards Paul.

[uncl...@ix.netcom.com]

We have installed the antenna, before TN 12 came out, on the bottom behind the gear. This requires and external ground plane of aluminum formed to match the fuselage contour. It looks better than the TN install and is about 5 times the work. All later ones were done to TN 12.
Nose does not meet required criteria.
FWIW
UH

[John Cochrane]

You can snake a coax cable back through the fuselage to an L2 antenna in the tail battery box. Not easy or fun but possible. UH solution is "easier"

John Cochrane

[Richard Pfiffner]

UH can the ground plane be inside the fuselage and if not why?

Richard

[uncl...@ix.netcom.com]

Carbon fuselage so it will be more effective on the outside.
UH

[JS]

If it's a "27", not a "27B" or "29", there is a place below the seat pan, under your left knee that a ground plane and stubby antenna can be mounted.
It tests fine at TXP certification, is relatively easy to install and connect, and is zero drag.
Jim

[jfitch]

You can often determine what is carbon vs. kevlar or white glass by shining a strong light through it. Carbon is opaque, gel coat/glass less so. On a 26 which has a very similar fuselage, I installed a dipole inside of the nose ahead of the rudder pedals. It tests fine from all angles, and return is reported good from many contacts in the air. No drag, no possibility of breaking it off ground handling. There are some who considered this a heretical install, so you will have to decide for yourself.

[uncl...@ix.netcom.com]

RF transmitting a foot and a half from the family jewels may not be optimum.
FWIW
UH

[Dan Marotta]

My LAK-17a has a carbon fuselage.  I installed a blade antenna aft of the gear doors, at about the 5-o'clock position with a ground plane inside the fuselage.  Transponder checks show well over 200 watts transmitted.  I've got a Trig TT22.

--
Dan, 5J

[Dan Marotta]

The ground plane should take care of that.

--
Dan, 5J

[jfitch]

There's been plenty of tests on that in conjunction with the European personal transponder initiatives. All of my children have had no more that 4 eyes and 3 ears.....

[Paul Birkett]

Hello John, many thanks for the information. Was the L2 antenna mounted
inside the battery box and doesn't the horizontal
stabilizer(carbon-Kevlar-
aramid) structure shadow the antenna? Also, did you have to "Fettle" the
vertical stab to enable coax routing?
Many thanks to all replies.
Best regards
Paul

[Paul Birkett]

At 15:20 28 February 2016, John Cochrane wrote:

[Paul Birkett]

At 15:20 28 February 2016, John Cochrane wrote:

[George Haeh]

I've been looking into ways to secure coax
inside the tailboom. My current avenue of
investigation is using magnetic receptive
rubber sheet.

Wrap a strip of sheet around the coax with
appropriate (suggestions welcome)
adhesive and use magnet on exterior of
tailboom to clamp at appropriate locations
well clear of elevator pushrod.

Times Microwave has a coax cable and
attenuation calculator:

http://www.timesmicrowave.com/calculat
or/?
productId=38&frequency=1090&runLength
=26&mode=calculate#form

Extra coax length is necessitated by tilt up
instrument panel.

I'd also like to to put a PowerFLARM
dipole in the fin, but that would have to be
at least a foot from the xpdr antenna.

The battery box is not big enough for both;
so may need an opening in the box to
achieve enough separation. Once in use
for antenna(s), likely the box would no
longer be available for ballast.

If the front of the nose cone, would work
for an L2 antenna, the problem would be
much simplified.

Any interference with the comm coax
and/or antenna would mess things up.

[Andrzej Kobus]

George, I am afraid the coax cable losses for Flarm antenna would be too high if you run it from the tail of your glider to the instrument panel. Flarm is a very low power unit and the cable length is very important. Also if the horizontal stab is carbon that would not work very well either.

[George Haeh]

LMR-300 would do the job for a price:

COAXIAL CABLE - ATTENUATION POWER
HANDLING CALCULATOR

Coaxial Cable Data
Product:
Frequency (MHz): 968
Run Length (Feet): 26
« Reset Calculate »

PRODUCT PERFORMANCE PARAMETERS
Attenuation: 6.3 db/100ft 20.6 db/100mtr
Average Power: 0.35 KW
Cable Vg: 85 %
Nominal Td: 1.2 nSec/ft 3.92 nSec/mtr
Capacitance: 23.9 pF/ft 78.4 pF/mtr
Typical Connector Loss: 0.06 dB/pair

CABLE ASSEMBLY PERFORMANCE
Cable Run Attenuation: 1.6 dB
Total Cable Assembly Loss: 1.9 dB
Cable Run Efficiency: 68.6 %
Cable Run Time Delay: 31.08 nSec


As far as RG 58 is concerned, forget it for
that length.

At 13:13 05 March 2016, Andrzej Kobus
wrote:

>On Friday, March 4, 2016 at 8:30:10 PM
UTC-5, George Haeh wrote:
>> I've been looking into ways to secure

coax=20

>> inside the tailboom. My current avenue

of=20
>> investigation is using magnetic
receptive=20
>> rubber sheet.=20
>>=20

>> Wrap a strip of sheet around the coax

with=20
>> appropriate (suggestions welcome)=20

>> adhesive and use magnet on exterior

of=20

>> tailboom to clamp at appropriate

locations=20
>> well clear of elevator pushrod.=20
>>=20

>> Times Microwave has a coax cable

and=20
>> attenuation calculator:
>>=20
>>
http://www.timesmicrowave.com/calculat
>> or/?
>>
productId=3D38&frequency=3D1090&runL
ength
>> =3D26&mode=3Dcalculate#form
>>=20

>> Extra coax length is necessitated by tilt

up=20
>> instrument panel.=20
>>=20

>> I'd also like to to put a

PowerFLARM=20

>> dipole in the fin, but that would have to

be=20

>> at least a foot from the xpdr

antenna.=20
>>=20

>> The battery box is not big enough for

both; =20

>> so may need an opening in the box

to=20

>> achieve enough separation. Once in

use=20

>> for antenna(s), likely the box would

no=20
>> longer be available for ballast.=20
>>=20

>> If the front of the nose cone, would

work=20

>> for an L2 antenna, the problem would

be=20
>> much simplified.=20
>>=20

>> Any interference with the comm

coax=20

>> and/or antenna would mess things up.
>
>George, I am afraid the coax cable losses
for Flarm antenna would be too

>hi=

>gh if you run it from the tail of your glider
to the instrument panel.

>Flar=

>m is a very low power unit and the cable
length is very important. Also if

>=

[Andrzej Kobus]

George, transponder installations usually call for total loss not higher than 2 dB with a practical allowance for a connector of 0.25 dB on each end, leaving 1.5 dB for coax.
Your connector allowance is really low.

For example Schleicher uses Aircell 7 and total coax length and connectors are just about at max allowance for a Class 1 transponder.

I doubt that such loss will be tolerated by PF. I actually discussed this with Schleicher and I was told it will not work in practice.

[Darryl Ramm]

Yes to all that. Trig for example assumes 0.5dB connector losses (thats for the pair of connectors at the RF unit and another pair that joins to the coax to the antenna), but even that may be low vs. what what people will achieve assembling these connectors in practice. And you can get less lossy coax that LMR-300 if you really needed to.

You really don't want the PowerFLARM antenna that close to the Transponder antenna. And I'm not comfortable with a FLARM antenna being close below the RF opaque and reflective horizontal stabilizer. not sure if test flying a mock-up is an option or not but something I'd consider.

If you are installing a TRIG transponder mount the RF box somewhere other than the panel, ideally behind the cockpit area, so there is no coax flexing to the panel and the coax is shorter/straighter to the antenna location. For an ASW-27 the old-safe simple external antenna behind the gear doors with a short coax from a nearby TT-22 transponder would be my first (and last) choice. If ordering a new Schleicher from the factory, sure I might go for a tail hinge mounted transponder antenna.

I'm not sure why all the complex approach of vertical fin mounted transponder and FLARM antennas is needed in the first place. The transponder antenna behind the gear door works fantastically well, is really not a hassle unless you are stupidly careless.. and then it's easy to replace anyhow). People are getting good performance of FLARM antennas mounted in the cockpit area, including the nose cone area of ASW-27.

[t...@serkowski.com]

Another option is to install the antenna on top of the fuselage just behind where the cockpit vent exhaust would be. I think it was Andy Durbin that posted many years ago that he did some research which involved talking to people actually involved in building ATC radars, and the consensus was that the top of the fuselage is just as good as the bottom.

Install a pretty blade antenna on top and paint some cool lightning bolts on it, just put a sticker like this on it:
http://static.seton.ca/media/catalog/product/canada/international-symbols-s2283-ba.jpg

[OHM Ω http://aviation.derosaweb.net]

I am resurrecting this old post as some pilots I know are installing transponders this winter. The key questions are the location of the antenna and the type to use.

1) Does the blade type antenna provide "better" coverage than the rod type? What about aerodynamics between the two?

2) Potentially dumb question - Ground Planes - It was mentioned above by UH that the ground plane should be on the outside of a CF glider. As carbon blocks RF transmission is it considered conductive? If conductive, and grounded to the avionics, can the CF constitute a ground plane? I saw another RAS thread on this same subject without a clear consensus given.

Thanks, John

[stu8...@gmail.com]

> 1) Does the blade type antenna provide "better" coverage than the rod type? What about aerodynamics between the two?

I happen to have checked the pattern at 1M over the transponder band on a rami blade versus a simple 1/4 wave. They both seemed pretty close in gain and (non)directionality.

>
> 2) Potentially dumb question - Ground Planes -

Actually an really interesting question.

An outside ground plane should be ideal from an RF standpoint, but how would you do it from a low drag standpoint, and is it worth it?

I don't have CF there, but would still want to put the ground plane inside and hope it was good enough. Officially, it seems like it ought to be up to the av tech signing off on the install, but finding one that has a clear understanding of this seems unlikely. I guess you could try to measure the installed antenna pattern, but even if you did, what is good enough? Maybe a VSWR spec on the transponder, but CF seems likely to make loss which would make that ok. It comes down to antenna system loss. For the places you plan to fly, is it good enough so the transponder does it's job of keeping you safe. I would do what is easy, (inside ground plane) and then try it out and see if it works. Not sure if the FAA's ADSB report includes signal strength information. It ought to.

[Dan Marotta]

I installed a blade type antenna on the belly of my LAL-17a several
years ago and installed an aluminum ground plane cut to the
specifications in the Trig-22 Installation Manual.  I installed the
ground plane inside the fuselage and the system always showed over 175
watts during transponder tests.  It may have been higher power, but I
know it was at least that.

--
Dan, 5J

[Darryl Ramm]

On Saturday, December 30, 2017 at 2:58:29 PM UTC-8, OHM Ω http://aviation.derosaweb.net wrote:
> I am resurrecting this old post as some pilots I know are installing transponders this winter. The key questions are the location of the antenna and the type to use.
>
> 1) Does the blade type antenna provide "better" coverage than the rod type? What about aerodynamics between the two?
>

The blade antenna is a rod antenna encased in plastic, they all have the same RF performance.

> 2) Potentially dumb question - Ground Planes - It was mentioned above by UH that the ground plane should be on the outside of a CF glider. As carbon blocks RF transmission is it considered conductive? If conductive, and grounded to the avionics, can the CF constitute a ground plane? I saw another RAS thread on this same subject without a clear consensus given.
>

Follow the directions of your glider manufacture. A proper aluminum grounding plane behind the carbon fiber will provide a better ground than relying on the carbon fiber alone, and manufacturers will be recommending to do that. "Considered conductive" and actually how good a connection to the ground you can make and the impedance of/to that ground at 1GHz you don't know...

Stop trying to overthink stuff, just crack open a manufacture's TN (or one close) and follow the instructions. In the case of an A&P IA signing off on any work I would hope they expect that to have been done.

Installations of antennas requiring ground planes in a carbon fuselage without a separate ground plane is counter to guidance provided in AC No: 43.13-2B. Your A&P, or anybody else working on an aircraft, should be aware of this.

[stu8...@gmail.com]

AC 43.13B 308d says you need a backing ground plane.
But I didn't see any special details for CF versus other composites?

Following the instructions from the glider manufacturer seems smart.

[Scott Williams]

My std Cirrus has a schempp-Hirth TN that clearly spells out the installation
of the blade antenna. but it allows either aluminum or copper for a ground plane.
I chose a copper plate 0f .043 thick.
Trigg 22 has good output, but the 'sensitivity' was right on the low tolerance.
Any thoughts or insights?
thanks,
Scott

[Darryl Ramm]

On Sunday, December 31, 2017 at 5:33:39 AM UTC-8, stu8...@gmail.com wrote:
> AC 43.13B 308d says you need a backing ground plane.
> But I didn't see any special details for CF versus other composites?

The big note in plain English and bolt text staring you in the face in AC 43.13-2B: "NOTE: Carbon Fiber composite material, while conductive has not been found to be adequate as a ground plane."

[Darryl Ramm]

What did the technician doing the test recommend? If there was a doubt why did they not direct connect test the transponder?

These measurements are not highly precise. If its within tolerance then go fly. If not then get a different avionics technician to repeat the test if possible and if its bad then direct connect test the transponder to see it is likely the transponder or cable/antenna..

[Scott Williams]

in short,
New trig tt22, new only 14 inch antenna coax, new antenna, copper ground plane, trig authorized shop doing test, fresh battery with good voltage.
Tech reports using two different 'test rigs' , also report "sensitivity is on the low tolerance, but I'll pass it" with no other suggestions.
I followed up with Trig factory tech line, maybe have to send it in for a factory check. Factory rep had on suggestions.
I have no idea just what 'sensitivity is. factory was helpful, but I think maybe "sensitivity" may be outside of the influence of installation variables.
I was hoping for someone to have an insight.

Thanks,
Scott

[Darryl Ramm]

Did they direct connect test the transponder?

Sensitivity is the transponder sensitivity to interrogation. A poor antenna or coax install will affect that the same as it will affect the transmitted power. You can compare the radiated power measurements and guess the loss, but you don't know with much precision what that is if measured by a radiated test. The radiated tests are pretty imprecise, they are not done in free space, they have reflections and lots of stuff going on. If a direct connect test to the transponder with a different coax shows a marginal result then the Trig agent/test shop would hopefully be discussing that for you with mid-century.

The proper thing to do here if in doubt was just direct connect the transponder to a test kit. Did the technician do that? If not was the test kit not capable?? (I can't recall one that isn't but could be wrong)? He didn't have a coax or adapters with him? He really though it was just not an issue to waste time on? The shop/technician should have been able to answer all the questions you seem to have here questions and do more troubleshooting (maybe for a fee) especially after discussion if you still had concern.

[Scott Williams]

the tech did not directly connect, he also admitted that the steel hangar door and wall 18 feet away "could influence" the tests, he had never done a glider and was really friendly, but only did tests with a tripod mounted radiated device. The first device only reported "failed" the second device reported the Sensitivity as a number, 68 or 69 I believe. all other aspects passed.
Initially he was willing to do a "benchtop"? but said he did not have the correct harness.

This is my first experience with transponders and I am just learning.
Scott

[Dan Marotta]

If it's not too much trouble, try a coax cable length of 21 11/16 inches
which would be 2 wavelengths at 1090 MHz (assuming my arithmetic is
correct).  You may have reflected power in your coax which will reduce
performance.

--
Dan, 5J

[Steve Koerner]

On Sunday, December 31, 2017 at 3:13:42 PM UTC-7, Dan Marotta wrote:
> If it's not too much trouble, try a coax cable length of 21 11/16 inches
> which would be 2 wavelengths at 1090 MHz (assuming my arithmetic is
> correct).  You may have reflected power in your coax which will reduce
> performance.

Dan: I'm not jumping into the real technical matters here but its pretty obvious that you're neglecting the fact that waves travel slower in coax.

[Scott Williams]

Hey Dan,
I think you may be correct about Too short,
I googled this and there is a couple of opinions that seem to originate
with Garmin, I doubt very many transponders are installed with coax runs
less than 15 inches, maybe this particular problem is rare?
I'm using rg400, and may try a longer coax run.
Thanks,
Scott.

[Scott Williams]

In addition,
So does anyone willing to suggest a coax length if not 21 11/16 inches?
maybe tree foot? is there a non critical length range?
Scott.

[Dan Marotta]

You're correct, Steve.  Better knock off a millimeter or two from the
length although the length I quoted was not precise.  Maybe 3 mm... :-D

Happy New Year!

--
Dan, 5J

[Darryl Ramm]

Just leave it alone and go fly.

[Scott Williams]

On Sunday, December 31, 2017 at 8:02:08 PM UTC-6, Darryl Ramm wrote:
> Just leave it alone and go fly.

Fundamentally I agree with you, but if my new expensive transponder installation fails recert in the future, I would have wished to correct it being only a couple of months old. rather than close to the end of the warrantee period. And I must admit to being pretty obsessive compulsive on subjects like this.
thanks,
Scott

[Darryl Ramm]

C'mon you are wasting time, you didn't even know what the guy was talking about but that did not stop you trying to talk to the manufacturer... . He's signed off on the install. These tests are very imprecise (third time I've said that), as you should have taken away from the technician's comments and very likely don't show anything worth worrying about. If you don't trust the avionics tech who signed off on it then go elsewhere. I've already told you what the test to ask for... but given how busy shops are with ADS-B installs I expect many of them would have low tolerance for things that look like they might be wasting time, or maybe they'll be willing to charge you well for farting around with somebody else's transponder install. You are wasting time...

[Scott Williams]

On Sunday, December 31, 2017 at 10:45:56 PM UTC-6, Darryl Ramm wrote:
> On Sunday, December 31, 2017 at 6:25:04 PM UTC-8, Scott Williams wrote:
> > On Sunday, December 31, 2017 at 8:02:08 PM UTC-6, Darryl Ramm wrote:
> > > Just leave it alone and go fly.
> >
> > Fundamentally I agree with you, but if my new expensive transponder installation fails recert in the future, I would have wished to correct it being only a couple of months old. rather than close to the end of the warrantee period. And I must admit to being pretty obsessive compulsive on subjects like this.
> > thanks,
> > Scott

> As an admitted inexperienced guy about transponders, this is why I asked for input. I value your comments, and if the tech had not been so wishy washy and just said "It's fine, let me sign it off" I would not have been concerned.
Thanks again,
Scott.

[Darryl Ramm]

Scott

Thanks for installing a transponder, I expect it will be trouble free, modern solid state transponders like your TT22 are pretty damn reliable.

One thing to mention is since you have a Trig Transponder you can add ADS-B Out, specifically the simpler to adopt TABS version, by adding a ~$350 TN72 GPS Source. Maybe you've already done that, but if not that should be a simple add-on install once you have a TT22 or TT21 installed. How useful that add-on is to you depends on what you are doing, but it will make your glider visible to the increasing number of ADS-B In systems used in GA, visible at longer range (that FLARM) to PowerFLARM, etc.

[Scott Williams]

That capability is why I chose the trig tt22, I plan on adding that functionality in the future, But I'm going to wait a little bit for the surge to subside. also I would like to be less ignorant of the ads-b system.
As a transponder novice, the complexities are intimidating and I usually fly standard type certificated gliders, including my cirrus, possibly complicating my selection of equipment.

Thanks,
Scott

[Eric Greenwell]

The coax is a transmission line, and good quality, undamaged coax does not produce
reflections. If the antenna is not properly constructed, it will produce
reflections, and the coax will carry them back to the transmitter (transponder in
this case).

So, with a good antenna and good coax, variations in length will make no
difference. Go fly, as Darryl says.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/Guide-to-transponders-in-sailplanes-2014A.pdf

[Dan Marotta]

EE school was a very long time ago.  Yes, a coax is a transmission line
and, properly terminated, will not produce reflections.  If you're
cutting your own line to length, make sure you make a good connection
with the connector on the end.  I always preferred the screw together
BNC connectors.  The crimp on connectors take a bit of practice to get
right.

Dan, 5J

[Scott Williams]

Well,
It's easy enough to have a longer coax on hand for a recheck of the trig TT22,
also a 'direct hookup' request if the sensitivity is still low, also, the antenna is a comant CL105 with a copper ground plane per schempp-hirth drawing.
Continuity and resistive tests of the coax and harness were conducted at the time of installation, Rg400 by the way.
I must admit to being much more confident in the system because of all your input!
I could not have spent these cold winter moments any better, Thanks everyone,
And please feel free to add anything,

Much appreciated,
Scott, N8915