[HBR] Look Ma, no I.F. cans!

[Peter Bertini]

I've managed to acquire a few crystals that were used in the Heathkit HR-1
IF filter; my plans are to use them in a lattice roofing filter at the 1st
IF in a HBR project. The original Heathkit design used two rocks in a half
lattice filter, which gave pretty mediocre performance for a Novice CW rig.

I think I would still stay with trying to achieve the sharpest selectivity
at the lower IF. Not the best for dynamic range, but more in keeping with
the original design.  I'd also be tempted to emulate the variable
selectivity system used in the Hallicrafters SX-101, where the coupling can
be varied to control the IF bandwidth.

Pete

On Thu, Mar 26, 2015 at 1:25 PM, Brian Burns <brian at lessonsinlutherie.com>
wrote:

> Hello All,
>
>
>
> In browsing back issues of  73 magazine I came across an article on
> selectivity in the April 1961 issue entitled "Take Your Pick". It's about
> filters in all their various permutations. Here is the link to the on-line
> back issues:
>
>
>
> https://archive.org/details/73-magazine
>
>
>
> It's an excellent article, and about halfway through is the description and
> schematic for a "crystal coupled I.F. amplifier"---no I.F. transformers,
> just crystals. The author says just add RF stage, mixer, detector, and
> audio
> stage, and you have a "good receiver". He says the selectivity is equal to
> that of a mechanical filter.
>
>
>
> My only reservation is that Carl, KM1H, says that selectivity gotten with
> coils and capacitors sounds better. All those super high Q crystals look
> likely to ring a good deal.
>
>
>
> Cheers,
>
>
>
> Brian
>
>
>
> ---
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