On Thu, 5 Feb 2004 22:13:05 -0500, "Tom Holden"
wrote:

ARRL Handbook says that the BFO frequency should be at the -20dB point down
the skirt of the SSB filter. Pete, KE9OA, says -24dB.
1. What is the reasoning behind these choices?
2. How critical is it that the BFO be so positioned?
3. Wouldn't the shape factor have some bearing on where it should be?
4. Is linear interpolation between the -6 and -60dB points accurate enough
to determine the BFO freq?

TIA,
Tom



20 db down is where they are usually set. It is not too critical
though. It does provide that much carrier suppression in addition.

The best way is to set it where it sounds the best. Too far down and
you get better opposite side band suppression but it also cuts the low
frequency response of the wanted side band.

Yes it will depend on the shape factor of the filter as to where the
best point on the slope is.

You can easily measure 20 db down or how far you want it by just
measuring the output voltage level from what you get at the center of
the filter. Measuring is much easier than interpolating the correct
point as only a few tenths of a cycle change on the slope will make a
large change in db down.

73
Gary K4FMX