[CQ-Contest] 2-radio 'noise canceling' ?
k1ttt at berkshire.net
Wed Nov 4 00:36:22 EST 1998
you have to watch out, there are 2 very different effects at work
here that should probably be addressed separately.
1. diversity reception by use of physically and/or polarization
separated antennas going into one or more receivers then being
combined to extract the desired signal.
2. taking one signal and processing it different ways to make it
easier for your brain to lock on to the desired signal.
the first one is a measureable and fairly commonly used method of
improving the reliability of circuits subject to fading, phase
shifts, selective fading, or other phenomena that distort the
desired signal. this can also be used in cases where interference
is polarization sensitive or fades at different rates than the
signal source, such as noise that is generated nearby the receiver
or at a different distance from the receiver so it fades in a
different pattern than the desired signal. for this you can either
combine the antennas before the rx or use two separate rx's and
then combine the extracted signals. for most amateur use its
proably easier and cheaper to combine the antennas first.
the second one i think is harder to quantify, but some amazing
effects can be created. i have played with a couple different
things along this line on cw:
1. split audio from one rx into stereo equalizer, set one channel
for high pass the other for low pass and then feed stereo headset.
as you tune past a signal it seems to move across from one side
to the other and when it is in the middle of the passband it is
right in front of you. very amazing effect, but didn't seem to
make signals easier to copy... but it was interesting to listen
to the spatial separation in a pileup. someone with more skill
at copying with wide filters may get more use out of this.
2. use 2 radios or a 2 vfo radio. set one vfo to usb the other to
lsb. this doesn't seem as useful, but it is interesting as a
properly tuned signal is the same frequency in each ear, but one
off frequency is higher in one ear and lower in the other.
3. again with 2 vfo radio set both vfo's to same frequency but
select different filter widths for each ear. it is interesting
to hear how you can pick out the signal that is in the narrower
filter from both ears, but still kind of track the farther out
signals that are only in the ear with the wider filter. this one
also works on ssb unless the band is busy.
how your brain combines the sounds from your ears is amazing at
times, just how useful it is in a contest situation probably
depends a lot on how good the operator is.
Jim White, K4OJ wrote:
> ....a lot of guys are doing this, my most interesting discussions on this
> were with GM3POI who is using a FT1000D on 160 meters. One RX is on the
> transmitting antenna, and the second RX is on a beverage farm. By having
> these two totally different types of RX antenna Clive is able to maintain
> an average higher copiability (does this word exist???????
> The downside is that to do this you need a rig capable of this feat, i.e.
> an expensive one!
> I have heard of other hams taking the rcvr audio out and splitting into two
> channels, then putting one channel through a processor and feeding the raw
> audio in one ear and processed into the other - again to get a different
> feel for it.
David Robbins K1TTT (ex KY1H)
k1ttt at berkshire.net or robbins at berkshire.net
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