To All from PA0SE
Narrow bandwidth filters do not have to ring provided they are of the
phase-linear
type (constant group delay in the passband).
I use a home made passive phase-linear filter with a bandwidth of 30Hz and
centre frequency of 1000Hz. It can pass up to 24 wpm without trouble
(unfortunately the operator can't ...) The filter has four tuned circuits
with coils in large ferrite potcores.
Harry, PA0LQ, has designed a similar filter of the active type using 4
opamps. If you are interested in his design write to:
H.A.A. Grimbergen, PA0LQ
Lijtweg 1202
2341 HE Oegstgeest
The Netherlands
73, Dick, PA0SE
----- Oorspronkelijk bericht -----
Van: Andre' Kesteloot <[email protected]>
Aan: <[email protected]>
Verzonden: vrijdag 12 mei 2000 22:24
Onderwerp: Re: LF: Optimal width for LF?
Petr Maly wrote:
> Hello all
> I am just designing a new RX for 136 kHz band. It will have IF on 1 MHz
with
> high quality x-tal filter with bandwidth 200 Hz. The main selectivity
will
> by obtained on AF with passive filter with coils on pot cores. Till now
I
> used similar filter with bandwidth about 50 Hz and it seems to be still
too
> wide for LF. I was about to make it new with 15 Hz width. Somebody here
> mentioned 1 Hz wide filter which seems to me to be too narrow. At least,
the
> filter cannot be narrower than obtainable osc stability. Can we make a
> little questionnaire here? What bandwidth do you use and what is the
> experience?
>
> 73, Petr, OK1FIG
My own experience is that your narrow-band filters, if physical filters
(i.e,
coils and capacitors, or crystals), are very liklely to ring. How about
using
software filters?
73
Andre' N4ICK
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