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Old 25th Jun 2011, 1:08 pm   #1
Chaparal
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Default EMI RE-983 Push-Pull Distribution Amp

Hi all,

i'm searching for some information, specs, schema etc. for an

RE 983 / EQO Push-Pull Distribution Amplifier 40-270 MHz and
RE 983A Push-Pull Distribution Amplifier 40-270 MHz from
EMI electronics Ltd, Hayes Middlesex.

Build maybe in the 60th.

Circuit with 7 transistors and a 3055 as regulator.

Where and for what was it used ?

What is the AC supply voltage?

Thanks
Peter
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Old 25th Jun 2011, 3:47 pm   #2
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Default Re: EMI RE-983 Push-Pull Distribution Amp

This looks like an Aerial amplifier.Used on Band 1 and 3 etc plus FM.

David GM8JET
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Old 25th Jun 2011, 3:47 pm   #3
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Default Re: EMI RE-983 Push-Pull Distribution Amp

The old 405 line system.
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Old 25th Jun 2011, 8:31 pm   #4
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Default Re: EMI RE-983 Push-Pull Distribution Amp

Maybe for Hotel or small cable system?
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Old 26th Jun 2011, 9:44 am   #5
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Default Re: EMI RE-983 Push-Pull Distribution Amp

Hi.
It will have a high output for large systems and one with a fairly long cable run. The slope and equalisation will be for balancing the gain of the amp at higher frequencies on big systems which would be more noticeable on Band 3.
Probably from a VHF relay system and less likely for a dedicated 405 line system.

Looks early 70's to me.
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Old 26th Jun 2011, 3:09 pm   #6
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Default Re: EMI RE-983 Push-Pull Distribution Amp

Here is a pic from the amplifier Board (front side) and PSU (back side).

The question is, what is the AC supply voltage?
I don't think it's 220V AC.
I looks like, there is also an AC voltage on the output line ?
Maybe for other (remote) Amps ?

Output/input connectors are coax plugs and for coax wire.

Peter
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Old 26th Jun 2011, 5:26 pm   #7
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Default Re: EMI RE-983 Push-Pull Distribution Amp

If this is for UK use,it will be 240 AC mains.

David
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Old 26th Jun 2011, 6:10 pm   #8
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Default Re: EMI RE-983 Push-Pull Distribution Amp

David,
i don't think so, because if you look at the PSU wiring,
there will be then 240V on the coax line ,too

Peter
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Old 26th Jun 2011, 7:50 pm   #9
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Default Re: EMI RE-983 Push-Pull Distribution Amp

Maybe 18V, at most 48V
Very likely part of a distribution system. Need not be anything to do with 405.
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Old 26th Jun 2011, 8:12 pm   #10
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Default Re: EMI RE-983 Push-Pull Distribution Amp

I stand corrected.

David
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Old 28th Jun 2011, 8:45 am   #11
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Default Re: EMI RE-983 Push-Pull Distribution Amp

Some more info,

a quick draw of Input, Output, Amp and PSU

Peter
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Old 28th Jun 2011, 7:26 pm   #12
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Default Re: EMI RE-983 Push-Pull Distribution Amp

Add

I powered the AC line input to reach the +20V supply voltage.

So i think the ext. supply voltage should be 48V AC.

Peter
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Old 28th Jun 2011, 8:23 pm   #13
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Default Re: EMI RE-983 Push-Pull Distribution Amp

So potentially powered on the cable, powering the cable, or via an isolating 48V mains transformer.

It looks very like coax can come in/out via coax or screw terminals.

Powered coax in via screw terminal and non-power connection in via coaxial.
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Old 29th Jun 2011, 5:27 am   #14
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Default Re: EMI RE-983 Push-Pull Distribution Amp

OK, PSU is clear so far.

My question,
what is a Push-Pull Distribution Amplifier ?
Special kind of Amplifier or special kind of distribution ?

The Amplifier has 1 input, 2 outputs (75 Ohm).
An INPUT attenuator (Jumper 6dB - maybe others),
Switchable Equaliser (in/out),
Variable Gain Range 4 dB,
Variable Slope Range (tilt) 6dB,

What is the difference between the RE-983 /EQO and the RE-983A version ?
Both have the equaliser switch.
I can't see main differences.

Peter
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Old 29th Jun 2011, 9:37 am   #15
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Default Re: EMI RE-983 Push-Pull Distribution Amp

A regular mast head amp only needs to amplify maybe 4 channels, and only enough to compensate for cable loss.

On Cable TV systems the "power" of an amplifier for same signal level per channel must be much higher. A modern 110 channel rated amp will carry 110 x 8MHz channels of Analogue, Broadband or Digital with 5MHz to 65MHz amplification or bypass in reverse direction and 88MHz or 110MHz to 862MHz or 1200MHz in "normal" direction.

Cable distribution (for Hotel or for a town) started by using 40MHz to 275MHz approx with maybe as many as 24 TV channels and 10 radio channels.
Then they added 275MHz to 470MHz (cable hyperband) to almost double the channels.
Next was up to 560MHz (77 Channel rated systems), then to 862MHz (110 channel systems).

A regular home mast amp is low power class A. A cable distribution amp as well as more channels has to have enough signal level to drive maybe 20 Trunk tap splitters or more (an ordinary splitter is -3dB if perfect as each gets 1/2 the signal. 3.5dB is common) A trunk tap maybe has household port at -11dB and -1.5dB to trunk output. You might get 4 or 8 in one box with and amplifier to drive an 8 way splitter (over 9dB loss per port).

So for more power you need class AB aka Push Pull. Usually the output transistors are RF transmitter types rather than small signal of a home amplifier.

You need equalisation for the cable length to next amp. On regular TV home amp the channels are all close together so no equalisation needed. But a Distribution system for Hotel or town or community reception (CATV/MATV as well as regular cable TV companies) may have many more channels, and the higher ones attenuated very much. This is a problem for later amplifiers and for RF AGC in TVs.
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Old 29th Jun 2011, 10:20 am   #16
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Default Re: EMI RE-983 Push-Pull Distribution Amp

Thanks neon indicator,
for your explanations.
I have never seen such an amplifier model here in Germany.
Maybe it was used in some (british) MIL facilities
I think i will connect the amplifier to my spectrum analyzer and power meter to see,
what the amp can or not. ;-)
Maybe it's usefull as power amp for a signal gen.
I also didn't find any datasheets for the Texas RF transistors R2249A.

Peter
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