[Heathkit] HR-10B LATTICE FILTER?

[Tom NØJMY - AAR7FV]

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?
>
>
>