[South Florida DX Association] Watch the Band Edges!

[Bill]

Excerpted From An Article "It Seems to Us: Not an Emergency Radio Service?"
http://www.arrl.org/news/features/2010/01/01/11218/?nc=1

By David Sumner, K1ZZ
ARRL Chief Executive Officer
January 01, 2010



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!