[R-390] IF sweep alignment

[rbethman]

The R-390 series has NO crystal filters at all.  The R-390s used pure 
circuitry to achieve the end, while the R-390As use the mechanical filters.

Bob - N0DGN

On 2/26/2011 6:43 PM, Bill Hawkins wrote:
> Haven't seen any mention in this thread of the mechanical filters
> in the A version.
>
> You may recall that there was a hybrid combination of the A and
> a non-A IF deck (R-725) because the mechanical filters prevented
> fine direction-finding operation. Ringing mechanical filters,
> IIRC.
>
> There was also at least one thread in the good old days of this
> list that strongly advised against trying sweep alignment of the
> IF strip, because the ringing filters distorted the wave form.
>
> Perhaps you could use a wide band 455 KC receiver before the
> filters to see the response curve of the IF transformers before
> the filters. You can't align the filters anyway. What you do is
> find the center of the 100 Hz filter (does an A have that crystal
> filter?) and use that as the base frequency of the sweep generator.
>
> Hope this stirs someone's memory.
>
> Bill Hawkins