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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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25th Jun 2021, 7:49 pm | #1 |
Diode
Join Date: Jun 2021
Location: Selkirk, Selkirkshire, Scotland, UK.
Posts: 8
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Aerial attenuator?
Hi Guys, I'm quite new to amateur radio and have bought some 70's equipment i intend refurbishing in my retirement the item in the pic was with the rest of the gear and I'm not quite sure exactly what it is, i think its an aerial attenuator but not sure. i would appreciate any comments, cheers
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25th Jun 2021, 8:08 pm | #2 |
Moderator
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,288
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Re: Aerial attenuator?
Looks more like an aerial matching unit to me.
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25th Jun 2021, 8:23 pm | #3 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,876
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Re: Aerial attenuator?
It's a variable inductor of a type called a "Roller-Coaster" and is used in aerial matching units on the outputs of transmitters. It's a medium sized one likely to be 20 to 50uH at the maximum end and suited to a transmitter of up to a few hundred watts, though the power depends on the ATU settings.
They're quite sought after. Good ones have silver plated wire and a silver plated contact wheel. Very good ones have a sintered metal contact block like yours. It looks to have been made into a low power aerial tuning unit. Those transistor radio variable capacitors will limit the whole thing to a few watts. David
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26th Jun 2021, 10:34 am | #4 |
Diode
Join Date: Jun 2021
Location: Selkirk, Selkirkshire, Scotland, UK.
Posts: 8
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Re: Aerial attenuator?
Hi David, Thanks for the info. It came in a bundle with a Codar AT5 and power supply, a K.W. communications KW 204 and a Trio 9R-59DS receiver. Does it make sense that the modified inductor fits in with this rig?
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26th Jun 2021, 10:06 pm | #5 | |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,715
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Re: Aerial attenuator?
Quote:
The roller-coaster itself is a good one, I had the exact same one many years ago, and I no doubt bought it from one of the government surplus stores in and around Shudehill Manchester, but other than that, I can't tell you what original equipment it was made for. By coincidence I have just re-discovered another roller-coaster in in the garage that is part of an original ATU of some kind, does anyone recognise it?
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27th Jun 2021, 12:15 am | #6 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,340
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Re: Aerial attenuator?
This little poly VC's will handle up to 10W in most cases - although personally I don't think they should be used in any transmitting application.
As for is it an attenuator - definitely - if it is adjusted incorrectly. |
27th Jun 2021, 11:35 am | #7 |
Hexode
Join Date: Mar 2006
Location: Helston, Cornwall, UK.
Posts: 303
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Re: Aerial attenuator?
Hi, just so you know there is a very active KW group on groups.io, they have a lot of knowledge on the 204 if you need any assistance
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27th Jun 2021, 6:25 pm | #8 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,998
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Re: Aerial attenuator?
The 'roller-coaster' looks rather like a 'tunable HF choke' that I came across in a few valve-based military transmitters late last century [RACAL cunningly combined the anode-choke and first-stage RF matching into one component!].
Polyvaricons - yes they can deal with 10 Watts or so of RF in a pi-tank ATU provided that the circulating currents [which get greater with higher impedance-matching ratios] are not too high. Wouldn't want to push a Polyvaricon beyond 10 Watts of RF, though we happily used 'close-spaced' 500+500pF broadcast-radio-type airspaced capacitors in the pi-net of two-6146-in-parallel linear amps on 80M and they never flashed-over... |