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Avidyne TAS600 Traffic Advisory System

Minimum antenna cable length for Avidyne 605

Here's a nice tech question

I am getting this done by a good UK avionics installer who has previous experience with the system though not AFAIK on the actual airframe type.

Concurrently, and before I selected the installer, I've been trying to check with Avidyne the proposed antenna locations.

After weeks and weeks of painful and slow "tooth extraction" I now have verification of the proposed antenna locations, but they say the minimum antenna cable length (RG400) is 5m. If it is less then one needs to put inline attenuators in there.

Ideally, given the location of the box, we would prefer 3m (all cables have to be the same length). For 3m, they say 2db attenuators are needed.

Is this "minimum cable length" what other installers have found?

The "genuine RG400" cable spec (there are various cheaper copies) is here and at 1GHz it is 1.2db/m, so perhaps what they are thinking is that 3m, over 5m, needs 2.4db of attenuation to be artifically inserted, hence their 2db attenuator suggestion.

Luckily the system isn't going in till December...

Administrator
Shoreham EGKA, United Kingdom

Update: it turns out that this is a requirement in the TAS 605 installation manual, of which some kind chap sent me a copy.

The IM specifies minimum attenuation of 3db for the antenna cables. It does make one wonder what the hell this is required for. The cable required to meet that attenuation costs about £150 and for many installations one needs about 50% more to meet the figure, which needs to be "hidden" somewhere in the aircraft. And simply coiling it up all together is not allowed either. You can coil it up but the four coils have to be separated from each other

What is unclear is whether one needs the length (the four cables must be very closely matched in length), the attenuation, or both...

Apparently, the Garmin version doesn't have these limitations. But it is a much bigger and heavier box, and is probably a "bizjet" product that has been stripped down for light GA use.

Administrator
Shoreham EGKA, United Kingdom

Avidyne TAS605 installation done - TB20GT

Report here.

Administrator
Shoreham EGKA, United Kingdom

Wow, thanks Peter ;-) You should write for a magazine.

YSS
EGBJ

Sounds like it was a real mess. Sorry about your problems.

EGTK Oxford

Thanks for the write-up Peter - glad it's finally sorted!

EGBJ / Gloucestershire

You will now have to suffer loads of posts from me telling you all to get proper transponders, so I can avoid you with this mega expensive piece of kit

Administrator
Shoreham EGKA, United Kingdom

Thanks for the writeup.

It is really scary though. I keep hearing and reading stories about bad maintenance. And I am pretty sure that few owners can inspect the work like you do. As they say, the worst time to fly an airplane is the first hour after a maintenance.

It's funny that I resisted doing a TCAS install for best part of the 10 years I've had the TB20 - simply because I did not know an installer who had a consistently good user feedback (from people I know and trust personally) and who I could trust to do this job well.

In a perverse sense, installing avionics and wiring is not hard, but removing and refitting interior trim without bodging everything in sight is hard. And that makes a difference between an aircraft which after 10 years looks like new, and one which is shagged because everything rattles and stuff keeps coming loose because somebody stripped the threads.

So I went to an installer who had a good reputation

Administrator
Shoreham EGKA, United Kingdom

You will now have to suffer loads of posts from me telling you all to get proper transponders, so I can avoid you with this mega expensive piece of kit

Peter, you and I can spend the fly-in mutually avoiding each other.

EGTK Oxford
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