[ARC5] Using SCR-274N

[Geoff]

----- Original Message ----- 
From: "Bill Cromwell" <wrcromwell at gmail.com>
To: "ARC-5 Maillist" <arc5 at mailman.qth.net>
Sent: Friday, March 29, 2013 1:53 PM
Subject: Re: [ARC5] Using SCR-274N


> On Fri, 2013-03-29 at 09:54 -0700, Dennis Monticelli wrote:
>> I have fancied going the crystal filter route with the BC-453 (with
>> converter ahead for the ham bands).  Unfortunately, 85KHz resonators
>> are not only hard to find, then are very high in impedance. The hi-Z
>> makes them hard to graft into the IF chain without a lot of loss.  It
>> can be done, but it takes more work to do it in such a manner that it
>> is easily reversible.  A better route is probably using a fast op amp
>> configured as an active filter.  You can use a modern hi-speed op amp
>> these days at 85KHz and still get good Q.  It would be small and could
>> run off a step-down from the DC filament voltage.  I would experiment
>> with this if I had the time.
>>
>>
>> Dennis AE6C
>
>
> Hi Dennis,
>
> The IF strip in a BC-453 or R-23 is already pretty narrow with the tabs
> pulled all the way up..their narrowest setting. I get single signal
> reception and when I plug in the NEScaf filter is chokes right down to
> narrow CW bandwidths - less than 100 hurts. I am thinking of the xtal
> filters (or Q-multipliers) for the 80 and 40 meter receivers. A guy on a
> Harley rode right through on my 40 meter receiver (evil grin). He passed
> a VW bug that was already coming through the IF.
>
> 73,
>
> Bill  KU8H

For the high IF's you might also want to consider dropping down to 455 in a 
single IC, toss in a sharp filter and then to the detector if there is 
enough gain available.

I dont like audio filters altho many do.

Carl