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Old 22nd Apr 2019, 8:26 am   #1
its ur aerial
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Default Home brew ATU

I intend to build a home brew aerial tuning unit for my home brew 80M AM TX O/P about 13 watts max.
I cant, find any suitable metal cases for it under £28, would it be acceptable to use plastic,or is screening of the ATU that important? I vaguely remember the ATU for the Joystick aeril in the 60`s being plastic.

73`s Ken G6HZG
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Old 22nd Apr 2019, 9:15 am   #2
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Default Re: Home brew atu

THe ATU can be an easy ingress route for domestic interference on receive. A metal case is wanted more than ever nowadays.

On transmit, to keep losses low, the cabinet needs to be big enough to be well spaced from inductors.

Balanced antennae are better for dodging interference, and they work best with a dedicated balanced ATU. Be sure you build an ATU suited to your antenna (I got this wrong and built a tour-de-force ATU that would win any construction competition, and I've never used it in anger!)

David
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Old 22nd Apr 2019, 6:51 pm   #3
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Default Re: Home brew ATU

I think, buying some aluminum sheet and making a case is the way to go.
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Old 22nd Apr 2019, 7:20 pm   #4
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Default Re: Home brew ATU

A big biscuit tin?
 
Old 22nd Apr 2019, 7:41 pm   #5
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Default Re: Home brew ATU

In the past I've used large plastic industrial IP68-rated enclosures but had them 'metal-sprayed' inside for screening [this is the modern version of the metallising used on valve-envelopes in the 30s and 40s].

The metal-spraying provides electrostatic screening but by virtue of being both non-magnetic and of a relatively high resistance it avoids the whole 'shorted-turn' or 'ferrite slug' detuning effects (which can sometimes be rather spectacular if you're running a couple of Kilowatts of RF up the spout).
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Old 23rd Apr 2019, 7:16 am   #6
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Default Re: Home brew ATU

Did think about a Biscuit Tin,but all this years Xmas assortment came in plastic containers.
I was also thinking about a IP65/68 enclosure and lining it with thin aluminium or tin plate.
Once upon a time, 10/6d in your pocket and a little swaray down Tottenham Crt Rd or Soho`s Lisle Street, had your chassis and cabinet sorted.
You could even purchase one of those Artistic Magazines for the more discerning Gent, while there.
Ken, G6HZG.
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Old 23rd Apr 2019, 4:15 pm   #7
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Default Re: Home brew ATU

I have N.O.S steel case 12" x 7" x 8" w x h x d if not too big.

Mike
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Old 24th Apr 2019, 7:13 am   #8
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Default Re: Home brew ATU

Mikeymusyradio,
metal box on offer sound ok, I have sent you a private message, thanks Ken
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Old 25th Apr 2019, 11:27 am   #9
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Default Re: Home brew ATU

Hi Ken

No P.M. at this end yet, just spotted your response.

Mike
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Old 3rd May 2019, 7:47 am   #10
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Default Re: Home brew ATU

I use 50mm adhesive copper tape for screening and veroboard ground plane..about £3.50 per roll
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Old 3rd May 2019, 1:38 pm   #11
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Default Re: Home brew ATU

Make the entire box out of ds copper clad board?
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