Some years ago I developed a switchable cutoff frequency set of low pass
filters to go in the speaker line. The lowest cutoff was in the 400 -
500 Hz range. CW was erie with that lowest one in the circuit, really
single signal and NO receiver stage noise. Circuit is at:
http://www.geraldj.networkiowa.com/papers/speakerfilter.pdf these days.
Places that deal in sound systems still handle the line to voice coil
transformers that make using a single set of coils at many different
frequencies possible.
73, Jerry, K0CQ
On 12/14/2010 11:18 AM, Neal Laugman wrote:
> Rick,
>
>> Neal, where can I get one of those "Money Trees" you have?
>
> Hmmm - like all of us, they eventually wither away and die ... hi - and
> rodger on the KVG filter. Maybe Mike is right; just add on an audio
> filter. Even a passive LPF like KK7B designed for his High
> Performance DC receiver (think it cuts off at (1000 hz with a very
> sharp skirt). Bill Kelsey at:
>
> http://kangaus.com/r2pro.htm
>
> sells the single board + components for $15. I built one and it's
> unbelievable and not much insertion loss. I'd rather do that than mess
> around with op amps (again). There was some serious engineering that
> went into those LPFs.
>
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