[ARC5] Easy selectivity increase for receivers.

[Bill Cromwell]

On Fri, 2013-05-03 at 04:46 +0000, Fuqua, Bill L wrote:
> If I recall the low frequency receiver IF transformers are constructed
>  differently than the higher frequency  ones. I'll have to take a look.
>  Reducing the coupling should increase the selectivity somewhat.
>  Perhaps even putting a shorted copper strap turn between the two
>  coils. Sounds likes there could be some experimentation here. However,
>  I don't expect a lot of improvement  at MHz IF frequencies. I liked
>  the regeneration approach, Q multiplier more or less. Worked well for
>  me in the 60's. Maybe after Dayton Hamvention and after I get some
>  other projects finished, such as my completely restored1970 hot rod VW
>  Beetle. And my two Berkeley's. Never ending.     73 Bill wa4lav

Hi,

What about moving the coils apart as described and then adding a
Q-multiplier - also described? An additional bit of help sorting contest
weekend signals would be a NEScaf audio filter (or similar). It has a
variable passband from under 100 cps (CW) to about 1.8 kc (SSB) and a
variable center frequency over that same range.

So..choke the IF down as much as you can and then use that tunable scaf
filter to tune across the range selected by the *fast* main tuning dial.
Something like the dual dial receivers with a bandset and a bandspread
dial. Just a thought. I haven't tried it - yet. I HAVE used the tunable
audio filter to sweep for signals coming through a wider I.F. (3 kc) and
THAT works. The CW tone of course varies across the tuned bandwidth. If
you can tolerate that it will work. If you prefer an all tube lineup put
a "Select-O-Ject" in the audio filter position. The functions are the
same.

73,

Bill  KU8H