[Premium-Rx] Alignment test points in Racal 6790

[Carcia, Francis A HS]

-----Original Message-----
From: Carcia, Francis A HS 
Sent: Tuesday, December 06, 2005 2:32 PM
To: 'premium-rx at ml.skirrow.org'
Subject: RE: [Premium-Rx] Alignment test points in Racal 6790

 

-----Original Message-----
From: Carcia, Francis A HS 
Sent: Tuesday, December 06, 2005 2:30 PM
To: premium-rx at ml.skirrow.org
Subject: RE: [Premium-Rx] Alignment test points in Racal 6790

 
The Radio should increase audio 3 dB RMS with about -130 dBM input with a
300 hZ filter selected in Cw mode. If that works and the S meter is off the
next thing to look at is the 3 pots that set up the AGC which are probably
way off. This procedure is critical for the S meter to work properly. The
D/A should be at 10 VDC with no signal going into the radio. That will screw
up bite if that is off.  fc  


-----Original Message-----
From: premium-rx-bounces at ml.skirrow.org
[mailto:premium-rx-bounces at ml.skirrow.org] On Behalf Of Paul
Sent: Tuesday, December 06, 2005 10:38 AM
To: premium-rx at ml.skirrow.org
Subject: [Premium-Rx] Alignment test points in Racal 6790

Hi Group,

I think I have determined that the RA6790 first mixer FETS are actually ok.
I turned on the radio the other day and had a good listen to it and it was
right in there with the 6793. Maybe only 1/2 and LCD segment lower than the
6793 for a given station. I don't know why it was way down 2 weeks ago. Mood
swings? 

Anyway, I would like to do a proper alignment on the A1 filter and A2 mixer
as I have played with the slugs. Question is, am I correct in assuming when
testing the levels in the various modules, I should be using a high
impedance RF probe when on the internal test points, and a terminated 50 ohm
RF probe when measuring at the SMB output connectors like J2 etc.?
Also when measuring relative levels as in figure 5-2 in the receiver block
diagram in the manual, would those levels indicated, like -21dBm out of A2,
assume using a 50 terminated RF probe as well?

Finally, when I put in -50dBm, which I think is about 300uV, out of my
IFR-1500 or 8640B into the antenna input of the RX, I don't see any LCD
segments lit up on the 6790, but I see about 5 or 6 on the 6793. Then as
mentioned above, if I connect to an antenna and listen to a station, they
actually read the same RF level. Is there an alignment for the D/A driver
for the LCD? I didn't see anything in the schematics or alignment manual.

Thanks again boys for your help.

Kind regards

Paul
VE7KHz


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