Re: [IRCA] TP 11 Nov + Phasing

[Rick Kunath <k9ao@xxxxxxxxxxx>]

Walter Salmaniw wrote:

> This is fascinating, Rick.  You're absolutely right.  In your
> preferred method, watching the meter is of no use, and it's simple by
> ear alone.  In fact this may indeed be the preferred method of using
> a phaser effectively.  I'm experimenting now nulling 1200 CJRJ to
> hear a Gospel program underneath without any difficulty.
> Thanks!........Walt.

I'm glad to be of help Walt.

One other thing about DXing with the AGC off and the receiver set up as 
I described is that the receiver will no longer adjust the AGC to follow 
the level one of the stations on the channel, causing the others to 
decrease in volume as one of the stations rises and lowers in signal 
level. This makes for easier listening to stations on the channel. 
Additionally, sub-audible heterodynes on a channel can also cause this 
effect, and at times when these are present the AGC will sometimes try 
to follow these hets and add an additional layer of volume variations or 
fluttery sound to the audio. Sometimes the effects of turning off the 
AGC on a channel with or without sub-audible hets can be startling.

You do naturally have to adjust the RF gain control up and down 
occasionally to keep the volume where you want it and to compensate for 
slow signal variations over long periods of time, but usually this does 
not require much attention. The band can be surprisingly stable lots of 
times.

One other thing I have found effective at times, is to have the ability 
to reverse the phase of one of the earpieces in a pair of headphones. 
Adding a switch to reverse the phase of one earpiece is the easiest, but 
there is also a way to place the two earpieces in series and effect the 
same phase shift. The audible effect of putting the phase of one 
earpiece 180 degrees out of phase from the other is to cause the audio 
to sound like it originates inside the head rather than in front of it. 
Sometimes this causes a jumble on a channel to seem to be easier to 
understand. Other times it either makes no difference or makes things 
worse. It is handy to have the ability to flip a switch and see if 
flipping the phase makes a difference on a particular channel. I've 
managed to get some IDs this way that I would never have been able to 
pull out normally.

You can disassemble one of the earpieces on a pair of headphones and add 
a miniature double-pole double-throw switch to do the phase reversal.

Alternately, or to try this out, if you use a pair of jumper clips and a 
bare plug into the radio, you can connect the sleeve and tip of the 
radio plug to the tip and ring of a set of stereo phones, thus placing 
the two sides of the phones in series and out of phase with each other. 
The sleeve is not connected in this way of reversing phase. I built a 
switchable box to do this a few years ago and it works nicely, though 
there is a slight decrease in volume level when series connecting the 
phones to achieve the out of phase condition. It's better to add the 
switch to the headphones, if possible.

I may build a phase reversal box using a pair of transformers to do the 
job someday, and reverse one of the secondary windings to reverse audio 
phase to one side of the headphones.

I believe that Heil or one of the other headphone makers offers a pair 
of headphones already fitted with a phase reversal switch.

Any tool you can use to make intelligibility better is worth 
experimenting with.

Rick Kunath






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