[Heathkit] HR-10B LATTICE FILTER?

[Rodger]

I think Tom's suggestion about the audio filter is an excellent one, 
especially for the HR-10 series since as I recall this receiver is meant 
to operate CW with AGC off.  A common complaint about audio filters 
involves signals outside the AF filter passband (but still in the IF 
passband) causing AGC action but if operating with AGC off then there is 
no problem.  I also highly recommend the Autek QF-1 and 1A filters as 
being very useful, particularly on CW.  I have found the QF-1A helpful 
on 160 and 80 CW even when operating my Drake R-4C with the narrow 
Sherwood CW filter selected as its audio peak function further helps 
bring weak signal up out of the noise.

Rodger WQ9E

Tom NØJMY - AAR7FV wrote:
> Ed,
>
> I had an HR-10 that a previous owner had narrowed the width down to 
> about 400 Hz. using crystals.  I've since sold it and can't remember 
> the frequencies, but I do remember that I was not impressed.  You see, 
> the -6 db width is narrow, but the half-lattice filter's skirts are so 
> wide that if plotted, the response curve would surely look like a 
> circus tent.  It just didn't do much to alleviate interference at all.
>
> A much simpler and exponentially more effective alternative is to pick 
> up a MFJ CWF-2 audio filter (usually $10 - $15 used and common at 
> hamfests).  It's even authentic for that HR's time period, having come 
> out in the late sixties.  You can run one outboard or take the little 
> circuit board out and put it inside the HR, with input from the 
> detector.  You can then install a switch to kick it in or out.  I 
> replaced the RF gain pot on my HW-16 with another one that had a 
> push-pull switch on the back and I used it for that purpose.  I'm sure 
> something similar could be done on the HR-10B.
>
> I also believe the CWF-2 is still available as a kit from 
> Vectronics(?).  It just has a different part number.  It's still 
> pretty reasonable price-wise, I think.
>
> If you decide to go the audio filter route and can't find a filter, 
> let me know, as I'm sure I can come up with one from somewhere.
>
> 73,
> Tom
>
> Ed - K9EW wrote:
>> Hello to The List,
>>
>> I see this question has been asked before, but I haven't come across
>> an answer...
>>
>> I just acquired an HR-10B, and I'd like to narrow-up the crystal
>> half-lattice filter.  It looks like it's about 2000 Hz wide as built,
>> but I'd like to narrow it up to around 500 - 700 Hz for CW operation.
>> Installing a couple of new crystals seems like the way to go, but it
>> would be much easier if someone has already done this and could
>> provide the necessary information.
>>
>> Has anyone out there already invented this wheel?
>>
>>
>>   
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