[R-390] R-390 Visual Alignment

[Kenneth G. Gordon]

> Ken, I have never heard of a visual alignment procedure for a multi-stage
> transformer I.F. strip. Where can I find out more about this? Thanks, yours
> truly, Todd Roberts WD4NGG.

For those who are not familiar with this method, it consists of using a sweep 
generator covering the IF frequency, and an oscilloscope, preferably with a 
triggered sweep and blanking on re-trace. It would also help if the o'scope 
had a long persistence phosphor on the screen.

For a single-conversion receiver with a 455 Khz IF, you connect the sweep 
generator through a DC blocking capacitor at the plate of the 1st mixer tube. 
Set the sweep genny frequency so that it sweeps from 440 to 460 Khz, and 
set the sweep rate as slow as it will go. 

Connect the output of the sweep generator also to the scope so that it 
controls the horizontal sweep and in synchronized with it.

Connect the vertical input of the scope to the plate of the detector tube. You 
may find that connection to the grid of the detector tube makes a slight 
difference so try it both ways. I prefer the plate. Again, I use a large value 
capacitor.

With the lights dimmed so you can see the trace, start your sweep generator.

When you have everything set right, you will see, on the scope screen, a 
visual representation of your receiver's IF passband.

If your scope doesn't blank on re-trace, you will see two images. By proper 
manipulation of the controls, you can separate the two traces.

Now, when you make any adjustment to any transformer in the IF strip, you 
will instantaneously see the effect. You may have to adjust the sweep 
generator amplitude until you get a large enough trace.

Once you figure out how to use this method, it is REALLY NEAT and makes 
perfect adjustment of IF strips really easy.

I hope this helps.

Ken W7EKB