[Premium-Rx] Preselectors

[Tim Shoppa]

KA5QEP writes:
> He may have found it acceptable, but I have a problem with the
> NRD-525,535,545 preselectors.  I have a 525 and 545.  The design of the
> preselector is very clever and is similar on both.  There are 5 switched
> bands covering the medium and short wave bands, and in each band a voltage
> is supplied by the tuning logic to voltage variable capacitor diodes to 
> tune
> the preselector through that band.  Very nice design except for one 
> problem:
> When a strong broadcast station's voltage hits those tuning capacitors it
> sets up cross modulation of that station on all the other signals.  I have
> that situation here

For me, a varactor-tuned preselector sounds like a disaster too.
I mean, in different applications varactors and switching diodes
are used in mixers! With 50V of RF on the front...

Been a while since I looked at new rigs, but don't some of the new
super-high-end ham transceivers have tracking preselectors that move
slugs up and down with little motors as an option?

Tim.