Hi Eric,
I/Q outputs from U6 should be better than +/- 20% of each other. If one of the control signals to U5 (pins 1, 4, 10 or 13) is missing then the balance would be out by 50%. Please check carefully for opens at all IC pins and for solder bridges between pins.
73,
Tony KB9YIG
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----- Original Message -----
From: "EricJ" <eric_ke6us@...>
To: <softrock40@...>
Sent: Wednesday, September 21, 2005 6:34 PM
Subject: Re: [softrock40] Re: DSP Image Rejection problem and some thoughts
I'll give it a try. I put a scope on I and Q earlier
in the day and discovered more than a small difference
between the two. More like a 50% difference. That
seems excessive, and might suggest something wrong
with U6. Components are all correct value in correct
position.
Thanks, Gene.
Eric
KE6US
www.ke6us.com
--- gene_scot <gmarcus@...> wrote:
Eric,
There may be a small difference in the Softrock40 I
and Q amplitude
that is out of range of the DSP gain/phase
adjustments. I would
suggest opening your computer's Recording Control
window and adjust
the Line Input Balance Control and see if that
allows you null the
image. You will probably have to back to DSP Image
Reject adjustment
to realize a greater than 50 dB null.
I hope this helps.
73,
Gene W3PM GM4YRE
--- In softrock40@..., "Eric"
<eric_ke6us@y...> wrote:
The radio went together fairly easily, though I'm
at
a loss to figure out why an experimenter's radio
is
jammed onto such a small board. This might be OK
for
a production rig, but some room would be nice to
experiment.
That said, the radio works except there is no
image
rejection and the DSP image rejection controls do
nothing. The instructions say, "If the image
cannot
be nulled at least 50 db, then a problem
exists..."
Well, some guidance would have been helpful.
Especially, given my opening criticism.
I am reluctant to tear into this think quite yet
as
there is not a lot of room to work. I originally
thought it may be a transformer mis-wiring on my
part.
Again, we're talking an experimenter's radio on 40
meters where things are relatively less critical
than
other bands, so a little larger toroid with more
room
to make changes would make it a lot easier.
I'm hoping when I fix the image problem that all
that 7.056 +/- 5 khz energy is going to at least
be
diminished. 7.056 is S5. 7.051/7.061 are S3.
Anyway, I have no doubt the problem is my error. I
just want a little direction so that I can
minimize
stress on the board.
Eric
KE6US
www.ke6us.com
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