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Listening on the repeater one evening the subject arose as to where you are allowed to transmit SSB signals on 75 meters. A DX station was operating in the DX window (3.795) and was listening up the band at 3.800mhz which is the lower edge of the General Class sub band. The General class license sub band for SSB is 3.800 to 4.000mhz.

Does this mean a General Class licensee can set the dial on 3.800 and transmit a lower sideband signal? (Lower SSB is the de-facto side band used on 75 meters) The answer is NO!!

 There are two problems with a General transmitting SSB on this frequency. The first is that your rig’s actual frequency may not be accurately displayed on the dial. These radios although, very good, may be a few hundred cycles off the actual frequency being displayed on that nice digital readout. You must check the calibration on occasion.

The second and the main reason you cannot operate at 3.800 is that you are operating lower sideband (the de-facto mode on 75 meters) which means that all your sideband energy (RF) is being transmitted from 3.800 down to 3.797mhz which is entirely outside the general sub band.

Remember your are not transmitting a single frequency but a "band" of frequencies that are all lower (when using lower side band) than what is being displayed on your rig.

The same applies if you are an extra class. You may not operate lower sideband on 3.600mhz. A safe bet would be to transmit no lower than 3.604mhz.

To be safe stay away from all band and sub band edges by >3khz when using sideband Also when operating CW you should allow 1khz from the band edges since a cw signal also has band width and your radio dial may be off.

Refer to spectrum display provide by Andy K4SU (Fig 1) showing a SSB signal on 3.800mhz centered on the display. All the squiggles you see below and above the center frequency is where you are actually transmitting. Notice all the energy is below the center(3.8mhz) The frequency displayed on your dial is where the carrier frequency would be “IF” it weren’t suppressed as it is in SSB  mode and you were not talking.  

FIGURE: (1)

Once you start talking your no longer on that dial frequency but spread out over a band of frequencies equal to the voice frequencies modulating your rig. 

This band of energy must stay inside the sub band where you are allowed to operate.

 Likewise when on 20 meters and above where Upper side band is used don’t operate on a frequency closer than 3khz to the upper edge of the band at 14.350mhz.

These edges are watering holes for the FCC monitoring stations. Take if from one who has received the proverbial pink slip from uncle Charlie years ago!

Our equipment is very good and relatively stable and accurate compared to a days of old but by no means are they laboratory quality. Unless you have an oven controlled stabilized master oscillator they can drift a fair amount. Be on the safe side stay clear of the band and sub band edges.

If the DX won’t listen up in your band then get the Extra class license and go in his band where permissible.