On 7/3/17 11:03 AM, Richard (Rick) Karlquist wrote:
On 7/3/2017 9:13 AM, Jim Thomson wrote:
From: Grant Saviers <grants2@pacbell.net>
We experience lot's of buzz from cw into ssb, need to get as far up the
band as possible. Reverse also true. About the same level of trouble
Grant KZ1W
## band pass filters, each being 7000-7300, probably are not going to
do much good,
if 2 x xcvrs used on the same band, say 40m cw..and 40m ssb. Heres a
thought though.
I see ICE and others make band pass filters for the warc bands, like
100 khz wide for 17+12M,
and only 50 khz wide for 30M band. If they can make a 50 khz wide
band pass filter for 30M
band, they, or somebody should be able to make any BW filter you
want. IE: say 7000-7050,
Jim VE7RF
I am extremely skeptical that any off the shelf filter for 30 meters is
only 50 kHz wide, simply based on the fact that the band is 50 kHz wide.
That is only 1/2%.
It is worth reading "Field Day Filters" (April 1973 QST, page 18).
The authors made a fairly serious attempt at building helical resonator
filters. Even with this technology, the authors state that the
filters they built are not sufficiently selective to do much good
in terms of separating the phone and CW sub-bands.
A better strategy is to use separate receive antennas (as opposed
to receiving on the transmit antennas). That gives a lot of flexibility
to combat interference in its own right. We had a lot of success with
this at K6AO ten years ago.
These days, with inexpensive microcontrollers and vector mods, how about
adaptive cancellers - feed a Tx sample in, adjust the phase and
amplitude with the vector mod driven by a pair of DACs, and notch that
transmit signal right out.
I do it at 3GHz and get a >30-40 dB null in 3 seconds using a not very
sophisticated algorithm.
The nice thing is that it's all low power stuff - you'd collect a low
power sample of the tX signal (<1 mW would be a lot), whether from a
pickup antenna, or some sort of resistive T coupler. It would be single
band: you'd need a canceller for each Tx band; but theyre low power, so
band select could be simple LC lumped filters.
It would be a bit of a rats nest of cables: N*(N-1) cables for N
stations. OTOH, maybe you could do it with some clever processing and
two pickup antennas for each receiver?
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