[R-390] R-390A Audio hiss

Tue, 2 Sep 2003 21:13:42 -0400

All: For those who are also LMR types, I wonder if using a SINAD meter and a
signal generator that does AM would allow us to do this just as well?  Seems
to me (but I could be wrong) that checking SINAD at reference sensitivity
would allow the IF gain to be set quite accurately.  What does anyone else
think?

Dave Maples

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Roy Morgan
Sent: Tuesday, September 02, 2003 12:52 PM
To: [email protected]; [email protected]
Subject: Re: [R-390] R-390A Audio hiss

At 11:04 AM 8/30/03 -0400, you wrote:
..  I have a very
>objectionable hiss from the spkr constantly.  Can
>anyone tell me what I'm doing wrong??

Joe,

Adjust the IF gain setting..

It is very common for folks who don't understand to set the IF GAIN
adjustment too high. They think it "makes the receiver hotter."  It is a
mistake. (It is also a mistake to put higher gain tubes in place of the
normal ones..Check that you have the correct tubes installed, especially
the 6DC6 in the first RF amplifier.)

Here is the IF Gain set procedure:

IF GAIN SETTING

Here is Chuck's procedure:
From: http://www.R390A.com/html/gain.html>
Text in brackets [ ... ] is mine (Roy, K1LKY)
*********************
Procedure to set R390A IF Gain:

  Once the receiver has been fully mechanically and electrically aligned,
the final procedure to perform before "buttoning it up" is to set the IF
gain control. [This means that you should have done the mechanical
alignment - set the cams properly and so on.]
  Many otherwise very sensitive R390A's are thought not to be due to weak
signals being covered by noise generated by excess IF deck gain.

  Allow the receiver to warm up for at least 1 hour then:

  1- Terminate the antenna input [This means unhook any antenna and put a
50 ohm resistor,or a 125 ohm resistor, on the balanced antenna input, no
signals from any antenna or signal generator.]
  2- Set receiver for 15.2 mHz
  3- Set the "FUNCTION" control to MGC
  4- Select the 4kc filter with the "BANDWIDTH"
  5- Set "RF GAIN" control to 10 or maximum [If your receiver goes whacko
at this point, reduce the IF gain setting as in step 9 till it behaves
right.]
  6- Peak the "ANTENNA TRIM" for maximum noise as indicated on the "LINE
LEVEL" meter [If you do not get a noticeable peak, your receivers front end
and rf amplifier stages are not working right.]
  7- Set "Line Meter" switch to -10db scale [minus 10 db]
  8- Set "Line Gain" control to full CW or "10." [Local Audio gain 0 or low
if you are listening to it.]
  9- Adjust IF gain control, R-519 to cause "Line Level" meter to indicate
between -4 to -7 VU.
  10- Re-zero the carrier meter control, R-523 [This can be a touchy
adjustment.]
  11- Set controls above for normal operation and reconnect antenna.

Roy

- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
7130 Panorama Drive, Derwood MD 20855
Home: 301-330-8828 Work: Voice: 301-975-3254,  Fax: 301-948-6213
[email protected] --

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