Fw: Heathkit Crystal Rcvr CR-1

Steve Byan stevebyan at MAC.COM
Mon Feb 7 13:54:02 EST 2005

On Feb 7, 2005, at 10:15 AM, Linden, Jerome wrote:

> Before moving to AZ, I was really getting into xtal radio rcvrs but
> after I moved here, I found that I lived about 5 miles from a 50kw am
> radio station.  I can receive them on my telephone.  I get them on xtal
> radios with out any ant or ground hooked up.  Whether tuned by cap or
> coil, it comes in across the board.  Is there anything I can do about
> them? ..... JR

You need a QRM coil. See the description in the National Radio Club's 
publication "The Challenging Crystal Set" by Ray Cole, available at 
<http://www.nrcdxas.org/catalog/books/>. Basically you loosely couple 
another high-Q tuned-circuit to the tuned-circuit(s) of your crystal 
set. The QMR-coil tuned circult isn't electrically connected to 
anything - it just magnetically couples in to the crystal set's tuned 
circuit and adds another pair of poles. If you get the coupling just 
right, you get a response curve that has a peak next to a sharp notch. 
Put the notch on your local pest station, and you should be able to 
knock it down quite a bit.

The same principle is used in VHF cavity duplexers on receivers; the 
peak is set on the receive frequency and the notch set on the transmit 


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