[Elecraft] CW Sidetone

[Tom W8JI]

> I am not using such an elaborate sound system,   just 
> running the headphones direct into the rig.  Speakers are 
> SP 20 Icom and the other is a Ten Tec 307B.  Using this 
> method of plugging the headphones into the pnones jack, 
> and using the speaker in put on the rig for output,  there 
> is definitely an audio problem when going from phones to 
> speaker which requires and adjustment of the sidetone. 
> Another way around this is to have an MFJ 784B tunable 
> filter and use it for both  both phones and speakers. 
> This way the volume comtrol on the MFJ unit will equalize 
> all audio and it will work the way I would like it to.

Hi Toby,

Because I use stereo diversity, I also have a set of 784 DSP 
filters in stereo. The frequency and passband controls in 
one adjust both. I used them primarily with my stereo 
modified R4C's, so the DSP filters follow my heavily 
modified R4C's around.

Whether I use the 784's or not, I still mix left and right 
ears into mono because I only have a single speaker. This 
led me to discover an interesting phase effect combining two 
receivers into one channel when the receivers shared the 
same oscillators. When using two antennas that have wide 
spatial separation, and by changing phase lag or lead 
between the two channels (either at RF or at audio), a 
signal can be totally nulled out or directly added.

I had a calibration chart for my antennas. I measured audio 
phase difference between the channels, and by using antennas 
several hundred feet apart I could resolve a difference in 
direction of a few degrees. It was easy to resolve the 
difference between eastern and western Massachusetts  from 
here in Georgia. I found this very useful for locating 
jammers, spurious signals from BC transmitters, or just 
nulling unwanted CW signals out while still hearing other 
much weaker signals on the very same frequency.

DF'ing unfortunately does not work with the K3 because the 
channels rotate phase in relationship to each other as dial 
frequency is changed, so DF'ing is out of the question. 
Nulling signals will work, but maintaining directional 
calibration is impossible. Someday someone smarter than me 
will do this in firmware, where the two receivers in the K3 
can be used to null a CW signal while still passing a weaker 
signal on the very same frequency.

Another interesting effect is nulling one's own transmitter, 
although for maximum dynamic range it has to be done at 
radio frequencies. Even with limited dynamic range it is 
possible to hear stronger signals while the key is 
depressed. The ultimate in QSK. If done properly at radio 
frequencies, it even works on SSB. I can hear stronger SSB 
stations while I am transmitting on the very same frequency. 
My own transmitter is S-9 or so, so I can hear anyone 
stronger than S-9 on my own frequency while I am 
transmitting.

There are many things that can be done with two identical 
receiver channels, or with RF phasing. :-)

73 Tom