[HCDX] Steve Bohac modified HQ-180A

["Robert Foxworth" <rfoxwor1@xxxxxxxxxxxxxxx>]

> I am looking to get some information on a newly acquired HQ-180A, that
> apparently has been modified by or according to Steve Bohac.
> A "mixer trimmer" control has been added to the front panel on a small
> plate where the clock would otherwise be, and a small circuit board is
> mounted under the chassis.
> I would like to get in touch with him and get some more details on it.
> A Rick Shaftan, in the Dec.14 2000 issue mentioned knowing this
> gentleman.
> Any help would be greatly appreciated. Thanks very much.
>
> Al Santangelo VE3 AJM


I am catching up on some old e-mail. I knew Steve a long time ago
and don't know if he is still around in the DX world, but I do know
that the purpose of the modification for the mixer trimmer was to
enhance performance on the MW band by replacing the compression
padder capacitor on the mixer stage, which was adjusted with a
screwdriver and was always a constant value, with a variable cap
which was adjustable from the front panel. The reason for this is
to enhance performance on weak signal reception of MW BC stations
that are close in frequency to strong local signals 10 or 20 kHz away.

Since the three stages (RF, mixer and osc) don't always track linearly,
you can have situations where the mixer actually tunes differently
than the RF stage (and the Osc stage determines the nominal
tuning). The "antenna trim" does this job for the RF stage, and
the newly added "mixer trim" does the same thing for the mixer,
so you can minimize the slight de-sensing from strong locals
on nearby frequencies. A typical value is 100 pF.

SWBC Dxers don't notice this so much as the differential signal
levels are somewhat less, with everything arriving by skywave,
but if you are DXing weak MW, with nearby locals 70 dB louder, it
really does help.

The National Radio Club is the clearinghouse for info of this type.
See  www.nrcdxas.org  (NRC DX Audio Service) website.

Sorry if this was already answered.

- Bob k2euh


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