[CQ-Contest] Out of band

[Tom Rauch]

The rules are specific about out of band emissions, and every radio 
is different in how close to the band edge you can get and be in 
compliance.

97.307(b)  is very clear.
 
The rules do not allow any emissions that are a direct result of the 
modulation (which would include keying on CW) to extend outside 
the band authorized for those emissions. A second catch is we are 
not allowed to cause ANY interference outside the assigned 
frequency range, no matter what the level.

The "stuff" about -40 dB or some other value being legal is 
absolutely incorrect. There is a minimum requirement for 
manufactured equipment, but the more restrictive guideline always 
takes over...so watch out for 97.307b.

If someone can hear your click or buckshot through a flaw in your 
emissions outside your assigned band, you are in violation.

With that in mind, have a look at the typical FT1000MP on CW...or 
almost any rig. Most rigs have unnecessarily hard keying, and have 
clicks extending at least a few hundred Hz up and down. If you 
have a radio problem, you can have garbage for several kHz that is 
easy to hear.

Remember the 3kHz SSB BW is ONLY from a perfect rig. Most 
SSB filters are around -6 dB at 3 kHZ, and around -60 dB at 6 or 
more kHz. That does not consider IMD from the transmitter 
system's amplifiers. 

It's normal, with a low noise floor and strong signals, to hear a SSB 
transmitter 5 or more kHz away on a nearly perfect receiver with 
only a few hundred Hz receiver bandwidth. Technically, such 
emissions (if they fall outside the assigned frequency band) are 
illegal. 

Also, the keying speed limited CW bandwidth we all hear about 
ONLY applies when the CW waveform is shaped to be as soft as 
possible and allow the speed you are sending. 

I looked at some signals rise and fall times recently, and the 
slopes are fast enough to allow 200 WPM CW!  Those boys better 
not get on 7000.5, or they could have problems.

A DX-100 Heathkit would be unsafe 2 kHz from the band edge on 
CW, while a typical FT-1000MP gets shaky at about 500 Hz. 

On the other hand a soft-keyed rig with low phase noise could 
easily operate 7000.1 and not be in violation!

Bottom line is there are no actually cast-in-concrete safe distances 
for band-edge hugging. Just be sure you know your own actual rig 
(not even a same model rig).

It seems design engineers are paying less and less attention to 
transmitted signal purity as they pay more and more attention to 
adding bells and whistles we almost never use. There are actually 
some needlessly nasty radios on the market, and it might be time 
to start raising Cain about them with the manufacturers.





73, Tom W8JI
w8ji at contesting.com


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