Band limits

[k4zmi]

Ok, this one should be easy but I don't know.

How close to the end of a band can I get? Often, some interesting CW dx will be as low as .5 khz to the edge. For instance, I often hear ZS stations on 40M at 7.000.5 or .6 ?

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Today, I got a responce from ARRL. Basically, assuming a bandwidth of 500 hz on CW, if your rig is farely recent and has a tcxo (temperature compensated crystal oscillator), setting the dial to 7.000.5 you should still be 250 hz inside the band or 7.000.25.

For someone running 1.5 gallon (or more!), it's hard to say exactly where they'd end up. I am still inclined to use the old rule of thumb, concearning older equipment. 2 to 2.5 khz from the edge !

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ok, I misjudged by 10hz according to this info from ARRL labs;

If your bandwidth is 500Hz, operating on 7.00025 doesn't give any room
for dial or TCXO error. Dial error is at best +/- one count, or 10Hz.
The TCXO adds 3.5 Hz error.

Thus, I come up with 7.00026 as the closest you can come to the edge.
If you operate this close you should actually measure your frequency,
and not assume your equipment is fully within specifications.

Zack Lau W1VT

ARRL Senior Lab Engineer