+ THE BAND EDGE, HOW CLOSE IS TOO CLOSE?
by Ed Ewell, K7DXV - Associate Editor for Training - ewell@e-isco.com
Suppose I am a general class operator and I'm operating on a net on
7227kHz LSB. Is this operation legal? No. What if I am
operating on 7228kHz LSB? Am I "legal"? Probably...if all
technical requirements are met and the SSB is 3 kHz wide (or less). (3 kHz is
considered normal for SSB). However, if you are operating a linear
amplifier that has typical intermod distortion, your signal may be 5 kHz wide.
So beware, if you are using high power you must take extra care not to go beyond
a band edge.
Let's take a look at the rules. The core of this matter is found in
FCC part 97.307 which reads (in part): "Emissions resulting from modulation
must be confined to the band or segment available to the control operator."
The rule is saying that we are not allowed to have ANY emissions at ANY
level outside the band or segment you are allowed to operate on. If you do, you
are in violation.
The same is true about harmonics that cause interference. What may get
someone "busted" is if ANYTHING can be heard outside the band or
authorized segment. 7225kHz is the lower band edge for General Class licensed
operators.
Suppose you are getting interference from a station a few kHz away. First
of all, don't "jump" on that station! Secondly, do you really know
what is happening? Is the station overloading your receiver? If the
signal is S9 or better it could be. Is the station running a linear
amplifier? Your receiver will possibly be overloaded.
As I mentioned earlier, an amplifier can produce a signal 5 kHz wide
because of intermodulation, and there is no specific rule that says a signal has
to be only 3 kHz wide on SSB. Good engineering and operating practice
warrants that a narrow signal is desirable. If a station's SSB
signal is heard up and down the band, (sometimes called
"shot-gunning"), or produces spurious side bands, then the operator is
over driving his/her amplifier in the transmitter, or the linear amplifier; then
the transmitter is not "linear" in it's operation. This is a
violation as your signals are
not confined to your operating frequency.
Most modern transceivers have an ALC meter that will help you "stay
linear", just follow the manual. However, linear power amplifiers do have
automatic ALC circuits, but they are not normally used with the modern
transmitters.
If you have a linear amplifier use a peak reading watt meter and do not
over drive the amplifier beyond the power the amplifier will handle, or the
maximum authorized power for which you are licensed. Make sure that your
amplifier is heavy loaded to keep it linear, this will keep your signal
narrow. You should know how to do that.
The last tuning step with a linear amplifier is to heavy load it.
When a signal is monitored, use your attenuator, move the filters to wide and
listen outside of the band. I often hear signals that are over 2 kHz out of
band. If you switch your filter to narrow, you will not hear the signals, but
they are still there.
So in review, pay attention to the band edges. Remember that your dial
only indicates your transmitter frequency. A side band has your voice on
it...about 3 kHz away.
Official Observers monitor signals. OO's follow special guidelines, and
if you receive an advisory notice take it as a positive guide to help solve a
problem with your signal. You may not be aware of the problem. The bottom line
is, nets probably should not be closer than 5 kHz from the band edge.
Older transceivers with out digital frequency read outs can easily be off
frequency. In the example given above do not do down 5 kHz to handle traffic,
you will be in the Extra Class sub-band and the station you are in contact with
may not have privileges there. Remember to be careful in net operations near
band edges. Stay at least 3 kHz from the edge of the band or sub band. If
you are using high power, a good rule of thumb is 5 kHz. Ed Ewell, K7DX