Thanks so much, Bill. I'm still going to play with the
scope tonight, but I'd be willing to bet the input is
to a mono mic input. I had to reach back in the dark
with a flashlight and a mirror and probably did it
wrong. I'll pull the computer out tonight and check
it. Some day computers will be designed to be useful
with a front panel instead of pretty with everything
on the rear.
I, and I'm sure others, appreciate your knowledge and
patience getting us up to speed.
Eric
KE6US
www.ke6us.com
--- Bill Tracey <kd5tfd@...> wrote:
Ahh the small board -- good question as to why is it
so dang small -- I
think one of Tony's original goals for the gizmo was
more of a
demonstration vehicle than an experimenter vehicle.
I for one wish it had
more working room, but I will say the experience has
vastly improved my
soldering and rework in small places.
The central hump you're seeing around 7.056 is
normal. The gunk you're
seeing around this is a consequence of the software
architecture. What is
happening is that the hardware takes the swath of RF
centered and 7.056 and
downconverts it such that 7.056 is essentially at
DC. Also down there
near DC is noise and 60 hz (and its harmonics) hum.
When one tries to tune
down near 7.056, the local software oscillator will
be down in the 100's of
hz's. The output of this will be Software LO +/- 60
Hz (and
harmonics). Things will always be a bit messy
near the center frequency
-- quieter less hummy sound cards can help, but I
don't believe there's any
practical way to get rid of all the gunk in the
middle.
If you want to check out the hardware sans computer,
and have a signal
generator and a scope you can put in a -30 dbm
signal at 7.050 or so into
the antenna. Look at the audio output on the I and
Q channels -- it should
be about 6 khz (7.056 - 7.060) and on the order of
about 0.8 Vpp or so
(don't take my nums as precision numbers, they are
all from memory). The
thing to look at is if both the I and Q channels are
comparable in
magnitude -- if one is half the other something is
not quite right in the
hardware. You can also take a look at the phase
relationship -- it should
be about 90 degrees between teh two channels. While
you've got the scope
out check the clocking signals to the FST3126. If
you've got a generator
and no scope, you might be able to compare the two
channels with a good RMS
voltmeter.
One last thing to check -- make sure you're using a
sound card with a
stereo input. Using a mono mic in input would
give the symptom of not
being able to null the image.
Hope this helps.
Regards,
Bill (kd5tfd)
------------------------ Yahoo! Groups Sponsor
--------------------~-->
Get fast access to your favorite Yahoo! Groups. Make
Yahoo! your home page
--------------------------------------------------------------------~->
Yahoo! Groups Links
softrock40-unsubscribe@...
__________________________________
Yahoo! Mail - PC Magazine Editors' Choice 2005
