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Transponder Antenna

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VE3LVO(at)rac.ca
Guest

Posted: Mon Dec 18, 2006 7:28 pm Post subject: Transponder Antenna

I see some discussion regarding the subject, and might mention I am using a 

homebrew, with an Aircraft Spruce monopole. This design is about $30US and 

some gash aluminium sheet. It takes about 30 minutes to fabricate and hangs 

by a string from the roof, of course prevented from flailing about.

        I have used this design at other frequencies and it works well in 

signal strength horizontally in all directions. Add it to RG400 or RG58 and 

its UHF connector, and then test for signal strength by alternating with the 

present set-up. If you don't like it, you've wasted 20 quid and half an 

hour.



It is shown in the Europa Forum gallery, third source down, and in album, 

Idjit Builder, item 5.

Happy landings

Ferg Kyle

Europa A064 914 Classic

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nwcmc(at)tiscali.co.uk
Guest

Posted: Tue Dec 19, 2006 12:07 am Post subject: Transponder Antenna

I have an aerial on a homemade groundplane of 'bid' layup/tinfoil

sandwich. It is mounted in the rear fuselage on the fuselage join line.

It works well but sometimes signal is lost when ATC ground station is

straight ahead. I suspect the engine is obstructing the signal. With

that in mind the lower the aerial position the better.



Nigel Charles

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VE3LVO(at)rac.ca
Guest

Posted: Tue Dec 19, 2006 6:16 am Post subject: Transponder antenna

I agree that the average power is less than one usually experiences from the 

ubiquitous cellphone and with the square of the distance is insignificant.

But Nigel is perfectly correct  that the engine and one or two brine-bags 

may hinder signal strength - was just hoping that the ground antenna was 

seldom hiding forward. If this is a problem, just slide the thing sideways a 

bit - it can't always be at one o'clock.......

Cheers

Ferg Kyle

Europa A064 914 Classic

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kpaviat(at)verizon.net
Guest

Posted: Wed Dec 20, 2006 10:23 am Post subject: Transponder antenna

Hello Fergus!

The typical transponder operating frequency is 1030Mhz (if I remember

correctly). This means a very large loss through the typical RG58 cable over

14 feet. (the higher the frequency, the higher the loss) Ideally the x-pndr

antenna should be mounted away from other reflective surfaces, that means

getting it above the engine or propeller face lines. (more distance/length

needed in the Europa installation) I used RG-233/U specified at 14.5 db loss

per 100 feet. Of course, make sure whatever you use it is 50 ohm impedance!

The antenna may be optimal but if there is a large loss of signal

strength/energy getting to it then that transponder system is compromised.

Hope this helps!

kp

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josok-e(at)ukolo.fi
Guest

Posted: Wed Dec 20, 2006 11:27 am Post subject: Transponder antenna

Hi Kim,



The cable length used is probably less then 10 feet? The the loss will be  

1.45 db.

That's neglectible. Even when 0.5 to 1 db per connector is taken in  

account.

It's more important, as you said, to mimimize the blanking effect of  

things like the engine.

While VHF frequency radio signals still bend around objects, Ghz signals  

do not.

As somebody mentioned, far back in the tail, and as los as possible looks  

like the best option.

But, if i have followed this thread correctly, most of the problems are  

caused by having antennas in need of a ground plane without them, and  

groundplanes added to non- groundplane dipoles.

-- 

Kind Regards,



Jos Okhuijsen



workshopcam http://www.okhuijsen.org/plane

http:www.europaowners.org/kit600

mono xs, top on, gear in, tail wheel in, wings set, flapdrive in, tail  

closed, tailwheel in, tail top in, blue stuff filled, sanded and primed,  

fuel system in, doors done, windows in, sanding and filling the fuse and  

wings, engine installation, panel

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