[Premium-Rx] Racal RF preamp

[Carcia, Frank A. HS]

http://www.qrp.pops.net/default.htm <http://www.qrp.pops.net/default.htm> 
 
Enclosed is a cool web site with Norton amplifier design. Look at preamps.
I have been playing with Nortons and they work very well. I'm presently
using a
push pull Norton as my first IF in my hot rod 6830. I tried it on the front
end and it
improved the MDS by about 7 dB. My amplifier measures about 10 dB of gain.
I wanted it crunch proof so biased the transistors at 40 ma each.  My
transformer ratio is 1: 15 tap at 11 turns. It is easy to push pull them
with a 1:1 transformer
in and out. 
Yes the Racal front end increases gain but I heard that the MDS doesn't
change very much. I would convert it to Norton feed back. Somebody on
Premium RX sent me the spec and schematic but don't have it here at work.  
I use a pair of 2N5109s with top hats. 
Also I suspect the low frequency limit on the Racal unit is about 500 KHz.
My Norton with type 43 cores ran 100 KHz to almost 40 MHz.  
  fc

-----Original Message-----
From: GandalfG8 at aol.com [mailto:GandalfG8 at aol.com]
Sent: Monday, February 17, 2003 12:01 PM
To: francis.carcia at hs.utc.com; 103360.2133 at compuserve.com;
premium-rx at ml.skirrow.org
Subject: Re: [Premium-Rx] Racal RF preamp


Hi All 
It was suggested in a previous posting that I ask Gary Wingerd for his
comments on this one. 
I did that earlier today and his reply was as follows.... 
---------- 
The RA6790/GM RF amp is the same as the RA1792 amp, both are metric screws,
The only difference might be in the Relay that is inside on the PCB, the
case construction is a folded metal case on both. 
The 1792 was first, then the RA6790, then the RA6790/GM, this was a total of
about 5 years. 
----------- 
At least we know now that the amps are the same but it does still seem to me
that the 1792 with it's amp bypassed is not as sensitive as the 6790/GM.. As
far as I can tell there is very little difference, if any, between the A4
455Khz IF in both sets so still not sure if the 6790 has extra gain
elsewhere. 
Of course, it might just be that my 1792 is a bit deaf anyway:-) 

I think now that I will fit my spare preamp to the 6790 when I get round to
fitting the LF ROMs and will look seriously at the idea I mentioned earlier
of fitting a couple of relays inside the preamp to replace the bypass links
so that it can be switched in and out as necessarry. 
There's nothing like having the best of both worlds:-) 

regards 

Nigel 




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