[Lowfer] Really easy filters for L.F.

[Art]

Bob and Rich,

I built a 10-12 KHz wide filter centered on 185 KHz with 50 ohms 
in/out using some enormous toroids (unknown parentage) and litz wire 
(thanks K2ORS) with polystyrene caps. It's all basic filter 
technology, and I used the AADE filter software (freeware). I think I 
used 7 or 8 litz wound toroidal inductors, each core is about 1 inch 
in diameter.

I use the softrock receiver with a divided down 12.6 MHz TCXO for the LO.

The filter for the front end is 10 times larger than the softrock, 
but it's sharp....very very sharp.

I did some quick comparisons a couple years ago (unshielded) and the 
little softrock works as well as the full blown ICOM transceiver.

I hope to box it up this year and add a low noise sound card to the 
computer and to run it using Spectrum Lab, which now has excellent 
support for image cancelling direct conversion receivers.

Previous attempts to run the softrock in the lowfer band were 
disasters (using random wire antenna and marginal/quickie front end 
tuning). With such a radio, you can hear every signal known to man on 
every frequency you tune, and this is no exaggeration.

Put a good tuned circuit on the front end with a limited passband and 
a 50 ohm antenna and the softrock turns into a very nice lowfer receiver!

Enjoy.

Art

>   and if you put a hamfest slug tuned coil in series with the toroid you
>can fine tune the
>z to the exact value
>
>Dick
>build a band pass filter centered on 185 and another on 137 Khz
>then only that span of frequencies will pass
>to your raddioi
>
>its called sintony and Tesla had it right
>
>Bob K3DJC
>\\
>On Fri, 22 Feb 2008 21:48:58 -0500 "Richard Goodman" <wa3usg at comcast.net>
>writes:
> > Hey gang,
> >
> >    I've neever really tried building filters before but Bob Riese,
> > K3DJC and
> > I have been playing around with our new little LC meter kits and a
> > really
> > cool filter design program.
>_______________________________________________
> >From the Lowfer mailing list
>Send messages to: Lowfer at mailman.qth.net
>To sub/unsub visit: http://mailman.qth.net/mailman/listinfo/lowfer
>
>
>--
>No virus found in this incoming message.
>Checked by AVG Free Edition.
>Version: 7.5.516 / Virus Database: 269.20.8/1289 - Release Date: 
>2/20/2008 10:26 AM