receiver alignment info needed
gschafer at MEDIAONE.NET
Fri May 19 12:10:22 EDT 2000
Set the sweep width to show a convenient picture of the pass band. The sweep
speed is the most critical. As a rule of thumb, run the sweep speed at the
slowest rate that will show you the desired picture. The narrower the filter
that you are sweeping or the wider the frequency you are sweeping, the slower
the sweep speed required. If the sweep speed is too fast the curve of the
signal will start to distort and the amplitude will start to sink. Back of
the sweep speed until you notice no sinking or distortion of the curve. With
very narrow filters this speed may have to be very slow, even to the point of
needing a storage crt to view it. Always remember, if increasing the sweep
speed causes the curve to start to sink or distort slightly, the sweep speed
is to fast for the amount of spectrum you are trying to look at.
Stagger tuning is done to broaden the band pass of the IF. If all of the
transformers were peaked at the same frequency you would end up with a band
pass with a narrow peak at the top. Stagger tuning makes the top of the band
pass wider and flatter. When you have the sweep setup on the IF you will also
need a marker generator or a calibrated variable frequency source to use as a
marker. I have not been into an SX28 so I don't know the alignment procedure
but usually one coil of the transformer is tuned to peak near the low
frequency side of the IF and the other coil is tuned to peak near the high
side of the IF frequency. (or one whole IF transformer may be peaked at the
low side and the next one peaked at the high side)
The trick is to get the top of the curve to the proper width at the high and
low frequency limits (This is usually measured at 3 or 6 db down from max.)
without having the middle of the curve droop too much. In other words, you
want as flat a top on the curve as can be had while still maintaining the
maximum amplitude and having the high and low edges on frequency.
"Richard E. Robinson" wrote:
> I recently purchased an HP-8601A RF/sweep generator. I plan on using it
> align my boatanchors, but I have a couple of questions.
> 1. How wide and fast should the sweep be around the IF freq?
> 2. I've seen references to "stagger tuning". What is it and how is it
> done? I've been told that my SX-28s need to be stagger tuned and aligned
> with a sweep generator.
> Thanks in advance and 73,
> Rick Robinson kf4ar
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