[Premium-Rx] RA1792 Front panel removal

[Karl-Arne Markström]

I would first check the spectrum analyzer against a crystal oscillator 
to be sure that you don't have 50 Hz modulation sidebands already in its LO.

Since the RA 1792 LO covers the whole 40 - 70 MHz range in one sweep, without presetting,
it takes only a very minute hum voltage on the VCO tuning voltage to create a 
hum sideband. 

I recall that the total tuning voltage sweep is about  3 - 10 V, which means that creating a 
- 50 dB hum sideband requires a fraction of a microvolt of 50 Hz voltage on the tuning line.
This is easy to get from a ground loop or induction from an outer source.

73/

Karl-Arne
SM0AOM

----- Original Message ----- 
From: "Andrew Holme" <andrew at holmea.demon.co.uk>
To: <premium-rx at ml.skirrow.org>
Sent: Saturday, August 13, 2005 4:18 PM
Subject: Re: [Premium-Rx] RA1792 Front panel removal


Thank you all for the responses.  The job is done!

Whilst I had the set out on the bench, I thought I would take the opportunity to check the LO on the spectrum analyzer.  It looks pretty good, but there are -50 dBc sidebands close-in at a 50 Hz (UK power line frequency) spacing.  Please see http://www.holmea.demon.co.uk/Misc/1792_LO.png  Is this normal?

Thanks,
Andrew.
 
  ----- Original Message ----- 
  From: Andrew Holme 
  To: premium-rx at ml.skirrow.org 
  Sent: Saturday, August 13, 2005 11:59 AM
  Subject: [Premium-Rx] RA1792 Front panel removal


  Hi,

  I recently purchased an original front panel for my RACAL RA1792 which has one of those blue and white Telford Electronics jobs on it.  I was wondering if anyone could give me a few pointers on the dismantling procedure?  I presume I need to disconnect the ribbon cables first, and then undo the four large retaining screws from the front?  Peering in and around it, I don't yet see how the 3 knobs will come off.  Any tips would be appreciated.

  Thanks,
  Andrew Holme.




------------------------------------------------------------------------------


  _______________________________________________

  Premium-Rx Mailing List
  To Post: premium-rx at ml.skirrow.org
  For Info: http://ml.islandnet.com/mailman/listinfo/premium-rx
  Visit the Website: http://kahuna.sdsu.edu/~mechtron/PremRxPage/



--------------------------------------------------------------------------------


> _______________________________________________
> 
> Premium-Rx Mailing List
> To Post: premium-rx at ml.skirrow.org
> For Info: http://ml.islandnet.com/mailman/listinfo/premium-rx
> Visit the Website: http://kahuna.sdsu.edu/~mechtron/PremRxPage/
> 


--------------------------------------------------------------------------------


No virus found in this incoming message.
Checked by AVG Anti-Virus.
Version: 7.0.338 / Virus Database: 267.10.8/71 - Release Date: 2005-08-12



-- 
No virus found in this outgoing message.
Checked by AVG Anti-Virus.
Version: 7.0.338 / Virus Database: 267.10.8/71 - Release Date: 2005-08-12