[CQ-Contest] Excessive Bandwidth Rule was: Re: Suggestion for Cabrillo -- and the phone skimmer, new idea

Jim Brown k9yc at audiosystemsgroup.com
Mon Apr 13 13:26:01 EDT 2015

On Mon,4/13/2015 6:53 AM, Paul O'Kane wrote:
> However, the rules make no
> attempt to define excessive bandwidth, and I'm not
> aware of any penalties having been imposed for this
> reason alone.  If I'm wrong, I'd be happy to be
> corrected. 

I'm guessing that this is for the same reason that the FCC Rules are 
written more or less the same -- the minimum bandwidth required for the 
means of transmission. That allows for progression of the state of the 
art, and measurements by ARRL Labs show that the current leader for CW 
cleanliness is the Elecraft K3.

This, then, defines the minimum bandwidth required for transmission. 
Second in line seems to be the Kenwood TS590. ICOM's and Yaesu's big 
boats using keying that burns at least twice the bandwidth, and this 
after Yaesu's recent firmware upgrade. Before that it was four times wider.

Further, those numbers assume the user has selected the slowest rise 
time from the rig's menu system. If a faster rise time is selected, 
occupied bandwidth increases.

I've found that I can make measurements with about 75 dB of dynamic 
range and very high frequency resolution with a P3/SVGA connected to a 
K3 as long as I take care to keep that test setup out of overload. This 
test platform isn't nearly good enough to compare the best radios for 
phase noise, which should be much better than 120 dB below the signal, 
but it IS good enough to yield good data down to at least 70 dB below 
the signal with resolution of a few Hz. It's nearly 100X better than my 

This dynamic range can be achieved only with a dummy load and a tap 
feeding the test set, but can be approached with a very strong signal on 
a dead band. I used this setup to test N6TA's FTDX5000 before and after 
he did the firmware upgrade. The improvement is substantial below 40 dB, 
but doesn't do much above that level.

With the measurements I've done, The FTDX5000 and K3 perform quite 
comparably on SSB, and I suspect we will see that with other rigs in 
this class. The trash on SSB and RTTY comes from overdrive in the system 
-- everything from clipping in the audio chain to IMD in the RF chain, 
the use of AGC to set drive to a power amp, and failure to match power 
amps carefully to the antenna. Spectral displays that provide waterfalls 
clearly show splatter produced by SSB signals as horizontal lines on 
splatter peaks.

I think it's long past time for those of us who can accurately observe 
this stuff to be naming names and submitting that info to the contest 

73, Jim K9YC

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