novel.jpg (28146 bytes)inovel.jpg (1353 bytes)n the November 1998 issue of antenneX, the ability to "turn off " the reception of international AM broadcasting stations, operating in the single sideband portion of the 40-meter amateur band, was discussed in the article entitled SSB "Q" Channel Communications.

In essence, when you are trying to listen to a SSB station "sharing the frequency" with an AM station, it is much easier to listen to the SSB station on that frequency if the AM station is "turned off" by using a feature available on an advanced synchronous demodulation receiver or adapter.

In addition to this very advantageous feature, I would be remiss if I failed to discuss some of its other "features" I observed and enjoyed while using advanced synchronous demodulation. Some of these novel features are discussed in this article. It is suggested you become familiar with the previous article before reading this article.

NOVEL RESPONSES WITH LSB AND USB RECEPTION MODES
An interesting effect can be observed when listening to music being received from an AM broadcast station if the input to a headset is toggled, or switched, between the LSB ("reject USB") and USB ("reject LSB") output positions of an advanced synchronous demodulator system when the AFC is turned off. (This is assuming that a very slight r-f VCO oscillator phase error rate will exist when the AFC is off.)

In one position the music seems to be very "light and lively!" While in the other output position the music seems to be "slow and dragging." Yet, the music being broadcast had not changed its musical beat or character! This is because the incoming r-f signal’s LSB and USB signals are actually two distinct sets of signals, even though they are generated, or developed, from a common audio modulating signal at the AM transmitter. The greater the error, or off-set in tuning, the more pronounced these extremes will be.

Expand this experiment to use a stereo headset, or even better, include two audio amplifiers with speakers. With the left hand input being connected to the LSB (reject USB) output position and the right hand input being connected to the USB (reject LSB) output position, the results can also be impressive. The "lively" music is heard on one side and the "slow" music is heard on the other side!

A SPATIAL SPECTRUM ANALYZER
In addition to the above observations, any interference, or signal, existing on the lower frequency side of the signal being received will come out of the left-hand side, while those higher in frequency will be heard on the right side.

When receiving CW, two CW signals can have the same tone, but are not as difficult to copy when one is heard on the left side and the other is heard on the right side. (Of course, when this occurs, the receiver can then be retuned slightly to cause one to give a slightly lower audio pitch while the other one shifts to a slightly higher note.)

This system configuration gives the effect of having the room become a spatial spectrum analyzer. This permits a person’s brain to use its ability to sort out a desired signal, from a crowd of signals, that the ears hear in a way that is very helpful, especially when receiving CW.

As the receiver is being tuned higher in frequency, the signals can be heard "panning", or shifting, from the right side of the room, through the center, and then move on to the left side of the room. The signal that seems to be straight ahead is the one in the center of the receiver’s band-pass.

When operating SSB, as adjacent channel signal chatter occurs, or another signal pops-up, its "direction" (in frequency) can be immediately determined. Also, a very weak signal that is "straight ahead" of the listener can much more easily be picked out of a "crowd" of signals in the room. (This is similar to what psychologists refer to as the "Cocktail Party Effect" where one can hear his own name being mentioned in a busy crowded room, even though the noise level in the room is much greater than that of his name being spoken.)

NOVEL RESPONSES WITH "I" AND "Q" CHANNEL RECEPTION MODES
mmc-1.gif (7681 bytes)With an "I" channel output being fed to the left channel of a stereo headset, and the "Q" channel being fed to the right channel, while receiving an AM signal, the result is that everything is heard on the left side only. Then, by turning off the AFC, the oscillator will drift slightly, and the sounds will start "swishing" back and forth through the head! The rate of swishing is a function of twice the oscillator’s phase error rate. This is impressive when receiving music.

Carrying this a step farther, replacing the headset with a pair of amplifiers with speakers, putting one in front and to the left side and placing the other in front and to the right side, creates an effect more impressive, and more comfortable. The music is now "panning" from left to right in front of me, rather than going through my head!

Then by expanding this idea even more, I conducted an experiment using four audio amplifiers with speakers, and a speaker being placed in each of the four corners of a room. Each of the speaker amplifiers were fed from one of four product demodulators, with each of these demodulators being fed from one of four unique sequential phases from an r-f phase delay network which was, in turn, being fed by the common r-f VCO oscillator.mmc-2.gif (9884 bytes)

When receiving music the results were astounding! Instead of going back and forth in front of me, the music was now filling the room and swirling all around me in 3-D!

Demonstrating this to one young man, to test his reaction to the experiment, I had him stand in the middle of the room with his eyes closed. (This was done to reduce his sensory references to vertical. Vertical references include sight, sound, and touch, in addition to the Eustachian tubes sensing gravity.) Then I switched on the system with the resulting music swirling and rotating around the room at an accelerating spiraling rate.

He was so startled that he quickly grabbed onto a chair to keep from losing his balance! He shouted, "What are you doing to my mind?!! I can’t stand it!!!" This resulted from receiving an AM broadcast station on the new system. (I developed and conducted this experiment in 1960, a long time before any four-channel FM stereo stations were even thought of.) By the way, the young man returned many times after that. He was always anxious to experience more of those "mind boggling psychedelic sounds." (These experiences did not blow out his brain. On the contrary, he became very interested in science and went on to become a doctor.)

AN INVITATION
Please share some of your novel amateur related experiences with us and have a HAPPY NEW YEAR ! ! !
w4mmc@antennex.com  & a_scientist@rocketmail.com -30-


Click to Print/Save Article

Send mail to webmaster@antennex.com with questions or comments.
Copyright © 1988-2000 All rights reserved worldwide - antenneX©
Last modified: March 23, 2005