increase or decrease. Now adjust the NOISE PHASE control until you
see the “S” meter dip. If you do not see a dip or rise in the “S” meter
reading, try changing the PHASE RANGE pushbutton to the “OUT”
(“B”) position and readjust the NOISE PHASE control. One position of
the PHASE RANGE pushbutton provides a NOISE PHASE range from
0 to 180 degrees, while the other position provides a NOISE PHASE
range from 180 to 360 degrees. One of the settings of the PHASE
RANGE button will provide the proper phase so that a good null can be
attained. Readjust the NOISE GAIN and NOISE PHASE controls
alternately until the local noise has been cancelled. If you cannot obtain
a null, follow the procedure given in the following paragraphs to
determine if adequate noise is being picked up by the noise antenna. If
you obtain a null of the noise, but it is not as deep as you believe it should
be, try changing the polarity of the noise antenna to agree with the
polarity of your main station antenna. Although the vertical whip may
do a good job of cancelling the noise regardless of the main antenna
polarity, better performance (deeper nulls) can be obtained in some
cases when the main antenna and the noise antenna have the same
polarity. When a null has been reached, you now hear the noise level you
would have if no local noise was present, because you have just
cancelled the locally-generated noise. Now you will hear signals that
you didn’t know were there before. Or you’ll get good copy on signals
that you couldn’t quite hear because they were in the noise level.
If your receiver does not have an “S” meter, listen carefully to the noise
level. When you hear the noise level increase with noise from the noise
antenna, switch to the NOISE PHASE control and listen for the null in
the noise. Switch between the NOISE PHASE and NOISE GAIN
controls to attain the local noise null. The null obtained is normally good
for most of, if not the entire band in which you’re listening. If you go to
a new frequency, you will probably have to readjust the settings on the
NOISE PHASE and NOISE GAIN controls to recancel the local noise.
If you cannot obtain a satisfactory null in the noise, make the following
check to determine if adequate noise is being picked up by the noise
antenna.
(1) Turn both NOISE PHASE and NOISE GAIN controls fully CCW.
(2) Note the S meter reading on noise received from the main antenna.
Also listen to the character of the noise.
(3) Disconnect the main antenna and increase the NOISE GAIN in a CW
direction until the S meter reads the same as it did with noise from the
main antenna. Listen to the noise to be sure it sounds the same as it did
in step 2 above. If you cannot get the S meter reading high enough to
equal the reading taken in step 2, the noise antenna length must be
increased to pick up enough noise to properly cancel that received by the
main antenna.
(4) If the character of the noise is not the same in step 3 as it was in step
4, you may need to place an outside noise dipole to pick up the noise.
Feed the output from this outside probe through shielded wire or coaxial
cable to the NOISE ANT connector on the rear of the ANC-4.
For operation at frequencies above 20 MHz, the FREQ RANGE
pushbutton should be in the “OUT” ( HI) position. This centers the
network so that it will operate properly at these higher frequencies. If you
have trouble getting a good null at high frequencies, try placing the
FREQ RANGE switch in the LO position and readjust the NOISE
PHASE and NOISE GAIN controls. All other adjustments should be
made as noted above to cancel the local noise. The unit will cancel local
noise down to about 100 KHz and up to about 80 MHz.
4
ADJUSTING FOR
MINIMUM NOISE
