ATU in plastic box - UK Vintage Radio Repair and Restoration Discussion Forum

Silicon · 23rd Feb 2014, 4:06 pm

I want to make an Aerial Tuning Unit for reception only.
It will connect simple aerials to a variety of vintage radios and communication receivers.
It will be based on the Pi network from the www.mds975.co.uk website.

Most ATUs are built into metal boxes. Will there be any significant disadvantage in making it in a fully plastic or a metal faced plastic box?

23rd Feb 2014, 4:21 pm

Not much below 30MHz for reception, for transmit a metal box will keep out the RF from your shack.

Biggles · 27th Feb 2014, 5:21 pm

I have a couple of plastic cased Rx only ATUs in the shack and they seem to operate fine. They are commercial units. I suppose if you want improved immunity from local interference it would be better in a metal box but it doesn't seem to be that critical for receiving purposes.
Alan.

G6Tanuki · 27th Feb 2014, 6:45 pm

A plastic case is fine for an ATU - indeed it could work out better than a metal one!

There's a rule-of-thumb that for a linear coil to get high 'Q' you shouldn't have any metal within at least one coil's diameter. Quite a number of commercial ATUs using linear coils in metal cases break this rule - one can only conjecture at the eddy-current losses this causes.
With a plastic case there are no such losses even if things are packed in tightly.

23rd Feb 2014, 4:06 pm	#1
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,169	ATU in plastic box I want to make an Aerial Tuning Unit for reception only. It will connect simple aerials to a variety of vintage radios and communication receivers. It will be based on the Pi network from the www.mds975.co.uk website. Most ATUs are built into metal boxes. Will there be any significant disadvantage in making it in a fully plastic or a metal faced plastic box?

23rd Feb 2014, 4:21 pm	#2
Guest Guest Posts: n/a	Re: ATU in plastic box Not much below 30MHz for reception, for transmit a metal box will keep out the RF from your shack.

27th Feb 2014, 5:21 pm	#3
Biggles Rest in Peace Join Date: Feb 2004 Location: Hexham, Northumberland, UK. Posts: 2,234	Re: ATU in plastic box I have a couple of plastic cased Rx only ATUs in the shack and they seem to operate fine. They are commercial units. I suppose if you want improved immunity from local interference it would be better in a metal box but it doesn't seem to be that critical for receiving purposes. Alan.

27th Feb 2014, 6:45 pm	#4
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: ATU in plastic box A plastic case is fine for an ATU - indeed it could work out better than a metal one! There's a rule-of-thumb that for a linear coil to get high 'Q' you shouldn't have any metal within at least one coil's diameter. Quite a number of commercial ATUs using linear coils in metal cases break this rule - one can only conjecture at the eddy-current losses this causes. With a plastic case there are no such losses even if things are packed in tightly.