User manual

C. USEFUL ADJUSTMENTS
See Tables 1 and 2.
D. IN CASE OF TROUBLE
We carefully test all filters. Most problems occur
when first used due to improper connection (read
instructions again) or misunderstanding of operation.
The following are most common:
HUM OR DISTORTION WHEN USING
HEADPHONES
Hum generated in the QF-1A is normally barely
audible with a speaker unless you place your ear
within a few inches of the speaker. However, hum and
distortion may be troublesome if you use 4-8 ohm
“Hi-Fi” headphones, which are much too sensitive. To
cure this (and improve “Hi-Fi” listening as well!)
connect a 47 ohm resistor in series with this type of
headphones.
HUM WITH SPEAKER.
Usually this comes from your receiver. The QF-1A
loads the receiver output much less than a speaker or
phones. Therefore, you may find that switching the
filter “on” produces hum, although no hum is heard in
the filter “off” (bypass) position. This may simply be
because the filter is not loading down the receiver as
much. To see if the filter is really causing the hum,
pull the filter input jack out of your receiver (not the
same as switching to bypass!). If the hum goes away,
or is reduced to nothing, with the filter input jack
lying on the table, then the hum is coming from the
receiver, and being emphasized because of the light
loading by the filter input. Several solutions are
indicated: 1) Check for good contact between the filter
input plug and receiver jack. 2) Especially if the
receiver phone jack is on an auxiliary speaker, try
connecting some hookup wire between the speaker
case and the receiver/transceiver chassis, or between
the filter chassis. 3) Try connecting a 10 to 47 ohm
resistor across the receiver phone jack or other output
to load it down.
PICKUP OF YOUR TRANSMITTED SIGNAL
This should be extremely rare with the QF-1A, as
layout and RF bypass caps are excellent, and show no
sign of RF at 2 KW with the antenna 20 feet away and
the cover off, in our tests. However, some shacks,
especially using end-fed antennas in the shack, and/or
extreme RF on the 115 VAC AC line may possibly
interfere with any audio gear. Solutions in this case
are: 1) Plug the filter into an outlet away from the
transmitter. 2) Move the filter physically a few feet
away from the strong RF source; experiment. 3) Try
connecting pieces of hookup wire between various
units in the shack to eliminate ground loops, e.g.,
transceiver/linear, linear/filter, speaker case/filter, etc.
until all possible combinations have been tried. 4) Use
a good water pipe ground to your rig. 5) Try an L/C
RFI AC line filter available at (most) electronic
distributors. 6) Read more in radio handbooks. The
above measures are rarely necessary as the QF-1A has
been designed for use in high-power transmitting
stations. So, if you have a problem, you must solve it
in your shack; and all shacks are different.
BATTERY OPERATION DESIRED
Locate the rectifier diodes, D1 and D2, on the
schematic. These are directly forward of the right
transformer screw (as viewed from the front of the
unit). Connect +12 to +14 VDC to the right side of
either diode (the side with the band on the diode).
Connect the battery ground to the filter chassis
ground. Note: reversal of battery polarity, even for an
instant, will burn out the filter -- not covered by
warranty.