[R-390] sweep alignment

Kenneth G. Gordon [email protected]
Sun, 12 Jan 2003 17:45:23 -0800


> What type/brand of sweep gen would be good? What is the hook-up? How would one
> install markers at 447 and 463kc? Thanks ......Steve....KJ8L

I suppose you have had answers to this question by now, but I 
thought I might add my experiences with this method and make a 
few suggestions:

First of all, for 455 KHz IFs, I use a cheap B&K Sweep/Function 
generator, and an old Tektronix 7000 series scope. YMMV.

1) I connect the output of the sweeper to the input of the 1st mixer 
in single-conversion sets. In the R-390, you should connect it to the  
input of the mixer stage which feeds the IF strip.

2) Connect the sawtooth output of the sweep generator to the 
external horzontal input of the scope.

3) Connect the receiver's output (usually either the detector output 
or the 1st audio output) to the vertical input of the scope.

4) Set the SWEEP RATE of the sweep generator to as slowly as it 
will go.

5) Adjust sweep generator output level, receiver output levels, and 
scope controls to get as clear a visual representation of the IF 
passband as possible.

If the scope persistence is not very long, you will probably have to 
set the scope brightness to a fairly high level and turn out the room 
lights. You can use a small spot light or goose-neck desk lamp set 
to shine into the receiver so you can see what to adjust.

If your sweep generator puts out a triangle wave instead of a 
sawtooth, you will get a double mirror image of the IF passband. 
MOST modern sweep generators do a pretty good sawtooth.

Lastly, for markers, you will have to build or otherwise aquire either 
a crystal controlled oscillator with crystals for the two marker 
frequencies you want above, or an extremely accurate signal 
generator (HP-8640-B or similar) and connect it to the input of the 
first mixer stage simultaneously with the sweeper.

However, since the actual IF frequency is a function of either the 
crystal filter crystal frequency, or the mechanical filter center 
frequencies, crystal markers are kinda moot.

Ken Gordon W7EKB