Fw: Selectivity enhancements

Floyd Sense sentek at SPRINTMAIL.COM
Mon Nov 29 10:34:46 EST 1999

The best and most flexible solution that I've found is the use of a good
external DSP unit, such as the Timewave DSP-599ZX.  I know - audio
selectivity is no substitute for selectivity in the IFs, but there are many
other advantages that you don't get with any of the IF selectivity
improvements, such as: auto Tone notch, random noise filter, continuously
variable audio bandwidth.  The AGC function is very useful for those old
receivers that did not allow the AVC to be active on CW.  Also, the Timewave
accomodates inputs from two separate receivers, switchable from the front

----- Original Message -----
From: talen <talen at inetport.com>
Sent: Monday, November 29, 1999 8:09 AM
Subject: Selectivity enhancements

> I'd like to see some views on "selectivity" in these old tube
> receivers and tradeoffs for the various methods from those
> who have been there, especially with homebrew equipment.
> Bandwidth data, insertion loss data, effectiveness, retrofit
> difficulty, cost, etc...... if available, would be very interesting.
> For example.........
> * Iron core vs Air core IFs (higher "Q" with iron core)
> * Multiple IF transformers...several 50s articles had series IFs
> * Lower frequency IFs....going from 455Khz to 100/50Khz IFs
> * Various Crystal filters to enhance and null signals....lots of
>     articles in the 50s and 60s on this because it's cheap
>     and adaptable to existing receivers (had one on my S40B).
> * Q-multipliers, Select-O-Jects, etc.
> * Mechanical filters
> * and ???
> 73s  Kees K5BCQ

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