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Re: LF: decca

To: [email protected]
Subject: Re: LF: decca
From: "Walter Blanchard" <[email protected]>
Date: Sun, 12 Aug 2001 18:28:54 +0100
In-reply-to: <[email protected]>
Reply-to: [email protected]
Sender: <[email protected]>
At 08:49 12/08/01 Sunday, GII3kev wrote:

Does anyone have the in/out connection for the decca amp.assy 80355/cf
and what is the frequency range. (small rf preamp)
This was used at Decca transmitter sites for reception of the other TX in
chain.
Antenna in is the floating Faston connector
Ground is TB1/2 and TB1/4
Power in (was designed for 26v but works OK at 12v) depends whether you want to feed it up the inner of the coax output or not.
If yes, connect coax outer to ground and inner to TB1/3. Check Link B made.
If no, disconnect Link B, feed power to TB1/1, take output from TB1/3.
TB1/5 can be used as separate ground for static discharge off antenna if Link A disconnected. Gain and frequency response can be altered by adjusting R9 but should not go below 500 ohms otherwise will oscillate. If R9 is missing then voltage gain is nil but power gain is maximum i.e. maximum impedance transformation. Bandwidth is then something like 10-500 kHz. If R9 made 1k or so voltage gain will be 30 dB and bandwidth 50-150 kHz.
I think some are using these amps and wonder if anyone has discovered
the optimum antenna whip length for best match and avoiding overload.
They were designed for use with a "barrel" antenna (about same size and
shape as a small beer barrel) but work OK with ants up to 1m.
I have another cct board and not sure what it is, but looks like some
interface to the aerial/coil control.
The terminals are marked on one side as AE -CL+ K2 K1 G2 G1 and opposite
terminals ST F 1 2 3 4 5 6 7 A B C D P and L N (expect this is mains in
at live and neutral) The board is about 170 x 120 mm. I have 2 of these
cct boards and each one has a small grey box. On one cct board the box
is marked 27.24v and 28.8v and the other cct board box is marked 72v and
68v.
Don't know what this is. Main power around Tx ccts was 65-70v but 28v was
used to drive auxiliaries.
The interface cct board that fed the preamp has eight screw terminals
marked AUX, RX, AE, POWER (26v)., two pot cores and a transformer.
Where did you get them? Looks like some Decca surplus is getting on the market.

Walter G3JKV.




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