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Friday, January 22, 2010

Watch the Band Edges!

The following is a portion of a post in the January 01, 2010, column "It Seems to Us" by David Sumner, K1ZZ, the ARRL CEO, which appeared in the January 2010 issue of QST. It bears repeating here as many of us get involved in the heat of the chase for the DX and forget that just clicking on a spot may place us outside our band or sub-band privileges. Also, the comments about how close an SSB signal can get and still be within the band is something we all need to keep aware of, lest we stray out of the band.

It's a good idea to post your allowed operating frequencies in a conspicuous place near your operating position so you will be constantly reminded and be able to check whenever you think you "may" be out-of-band.

========== Excerpt of "It Seems to Us" ==========

Watch the Band Edges!

Following the relocation of most broadcasting stations from the 7100-7200 kHz band there has been a significant increase in DX activity by US amateurs on 40 meter phone. Judging from what we're hearing and what others are reporting from around the country, a reminder about band edges is in order.

When in SSB mode, most transceivers display the frequency of the suppressed carrier. This can be a bit confusing, because ideally your station isn't emitting any energy at all on that frequency. All of your transmitter power is going into the voice passband that extends roughly from 300 to 3000 Hz on one side or the other of that frequency.

The bottom edge of the US phone band for Amateur Extra and Advanced licensees is 7125 kHz. Without getting into hair-splitting debates about how wide your SSB signal might be compared to others, if you're operating on lower sideband (LSB) with a carrier frequency below 7128 kHz you're out of the band because some of your transmitter power is below 7125 kHz. For General licensees the band edge is 7175 kHz, so the lowest carrier frequency a General can use on LSB is 7178 kHz. At the top edge, as long as you're on LSB the situation is different; if you're confident that your opposite sideband and carrier suppression are up to snuff you can snuggle up to the band edge of 7300 kHz.

Two other bands where "falling off the edge" is too common an occurrence are 20 and 17 meters, and here -- because upper sideband (USB) is the norm on these bands -- the problem occurs at the top end. Carrier frequencies above 14,347 kHz and 18,165 kHz respectively are verboten. On these bands the lower band edge is not generally a problem because on USB, the carrier and lower sideband are suppressed.

As station licensees and control operators we are responsible for the proper operation of our stations. If a DX Cluster spot lures us out of the US phone band that's our fault, not the spotter's. If a DX station is on 18,160 kHz and is listening "5 to 10 up" it's our fault, not his, if we go up more than 5. And as long as we're talking about 17 meters -- a great band, by the way -- US amateurs must remember that RTTY and data modes are not allowed above 18,110 kHz, even if a RTTY DX pileup extends above that frequency. And remember, too, that if you're generating a RTTY or data signal by injecting audio into an SSB transmitter your actual operating frequency is different from what's shown on your display. How much different? Only you and your software know for sure!

========== "Reprinted with the permission of the ARRL. Copyright ARRL." ==========

You can view the entire "It Seems to Us" column by clicking HERE.