Paul:
Thanks for asking. I know it is confusing. It is why I resisted adding
the wider scope for so long. People often do not realize the
consequences of their requests and this is one of them. It is NOT a bug.
The signals as they arrive from the radio are below, at, and above the
local oscillator frequency:
BBBBBBBBBBBBBBBBBBXAAAAAAAAIAAAAAAAAA
B is below, X is at, and A is above the local oscillator. We have a
special point above. It is called I.
I is OUR last IF. We put it there because in a lot of sound cards, you
can see junk at X because of DC, hum, ground loops, 1/f noise, etc.
Our last IF is at 11025 Hz for historical reasons. It probably could be
lower with the D44, etc.
When we demodulate, we spin this spectrum to the LEFT and do it
circularly so after we are done it looks like this:
BBBBBBBBBXAAAAAAAAIAAAAAAAAABBBBBBBBB
I is just below, at, or just above 0 frequency after we do the
"spinning". We apply the upper sideband, lower sideband or real
bandpass filter here depending on the mode.
We wrap it around the left, but we MUST take those that fall off the
left and push them down on the top on the right. There is no escape
from this mathematical fact. There is nothing we can do about it. It
is the reality of our system. I suppose we should put in a mode that
has the "green box" for the filter in the right hand side of the SPEC
screen and then does full width asymmetric display. We will need to do
this to enable N watch receivers on the passband anyway for click tuning
anyway.
Bob
Paul Shaffer wrote:
I need some advice for the panadapter as I learn to setup sdr-1000
for 96k sampling.
If I tune to a sw broadcast, for example Radio Netherlands at 9.845MHz,
then tune the radio up, the signal moves off to the left and you can see it
on the panadapter out to the 20k mark, but when I tune down, the signal
vanishes at the right by about the 15k mark. Do I need to do something
to correct this? Is this normal? If it's a bug I'll file it, but I have no idea.
Another problem is that I see signals on the right side of the panadapter
around the 15k line, but when I click tune them (or just tune them),
they are gone. Using the 1.6.0 verion but saw this in the previous.
Thanks for any suggestions.
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AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats,
NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman
Laziness is the number one inspiration for ingenuity. Guilty as charged!
