Hi David,
I found it possible to compare down to the mHz region for the 1kHz
tones, but of course it requires good propagation, hanging around for
the continuous carrier periods of RWM and a disproportionate level of
patience!
A GPSDO is certainly the way to go for a quick, reliable and highly
accurate frequency reference - and it's a godsend if you have test gear
with a reference input. In fact a pal of mine has recently bought a
TS950 transceiver which already has an input for a 10MHz reference -
sadly my IC756Pro2 doesn't have that but at least I can check it accurately.
You'll probably find, like me, that once you have cracked the issue of
frequency accuracy you'll start fretting about amplitude accuracy when
you test and align things!
All the best,
David, G4IRQ
PS. When locating the GPS aerial, if possible try and get a clear view
from W, through South and around to East. That arc is where you'll see
the most satellites; from NW through North to NE has poor coverage.
On 13/10/2011 06:18, David J Taylor wrote:
The problem with all of these comparative techniques is that you are
always dealing with relative error vs finite error. However the
result is usually well in excess of that needed for ham ops.
Yes, something like 100 Hz at 100MHz is good enough for my current
needs, but it's nice to be ahead of the game!
Another trick is to load one memory with a 1kHz RWM offset in USB and
another with a 1kHz offset in LSB so as to generate a tone for each
sideband. You then feed the AF into SpectrumLab and repeatedly toggle
between the two memories whilst adjusting the LO.
If you adjust the LO so that the difference between the LSB and USB
audio tone is at a minimum, that will give you the most accurate
setting. Any errors in the sound card will cancel out because you are
comparing the /difference /between the two 1kHz signals, any
remaining errors will be down to variables within the radio.
Hope that helps,
73 de David, G4IRQ
An excellent suggestion, David. At one point, I could get both the 10
MHz and 15 MHz RWM signals, and switching between those showed less
than a 1 Hz difference in the 1 KHz tone. Barely visible on the
Spectrum Lab display (covering about 1200 HZ total on a 1600 pixel
wide display).
Having said all that, I've now ordered a low-cost GPSDO as it seems
that many of these off-air standards may not last too much longer!
73,
David GM8ARV
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