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.
|