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LF: Minimum carrier detect level -140 dBm is that good ?

To: <[email protected]>
Subject: LF: Minimum carrier detect level -140 dBm is that good ?
From: "Graham" <[email protected]>
Date: Sat, 20 Aug 2011 22:28:33 +0100
Importance: Normal
Reply-to: [email protected]
Sender: [email protected]
Minimum carrier  detect  level  -140 dBm   is that  good ?
 
Run into  a odd  problem  on 500Khz , neither the RA6790 (with LF front end  / no  rf  pre amp)  or the  RA1778   will  show a  carrier on 504 Khz , that the  Skanti R5003 , shows at 10/20 dB over the  noise  level  using  'spec-lab' as the indicator, R5003 , has  no  pre-amp , direct to  first mixer. same  as the RA 6790
 
Using the  sig-gen  and  60 dB  atten , the  RA1778 minimum  trace level  is  -150 / -155 dBm (has  rf-pre amp) , The  6790, round  -140 / -145.. removing the  rf  cable  and fitting  50  ohm load to  gen o/p with  atten , removes the  trace  from the  rx, so  assume its  not  leakage
 
As  these  levels  are  well below the  ambient  noise  levels, it not a  sensitivity  problem .??. adding a  stepped attenuator  to the  Ae  signal  path , makes  no  difference, other than to  alter the  noise  level..
 
The   500  khz feed is  from the  atu  and the  vswr round 1:1.2 on tx .The  R5003  is the  same  lay-out , 40 meg 1st IF > 1.4 second (rx section  of the  TRP5000)
 
Any  ideas  or  suggestions  as to  'how'  to  solve  the  problem ..

wide band  noise  causing the  roofing filter to  ring may  be?
 
Tnx -Graham


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