I do not believe Tim's experience is either normal or universal. On the
other hand, if you are adversely impacted by very wide 1/f noise of the
soundcard, turn spur reduction off. This will keep that noise from
being visible. It is still there, just hidden. Possibly it is not
clear to you what that green stripe means on the panadapter. That is
where the brick wall filter is applied. If you see the "hump on the
left" get to within (oh say) 1 Khz of that green bar, then you have a
problem. The response of that filter is down oh, about 140 dB or so
outside its main lobe where that stuff is on the left. (whats a small
thing like 140 dB down from -110 dBm going to do to you anyway?). I
suggest that we could improve the the feel of this slightly by swapping
to the other side of zero and moving the "small hump" to the right when
we are LSB modes. This would be a cosmetic and psychological
improvement ONLY unless you have a problem with your system (ground
loops, etc.).
THIS is why I insisted on the limitation to the panadapter window size
because there was always going to be a few who had ground loop problems
and in the early days we did not have these good sound cards at our
disposal. That said, it is clear that even the good ones can have a
problem. I just didn't want to deal with the questions ;-). As a
group, we all have learned a lot and no one has learned more about all
of this than me: thank you for letting me have this learning experience.
Bob
Jiri Sanda wrote:
I do not understand ?
If the transmitted noise get so much worse when "spur. reduction" is on
why is it there at all ? What positive it does ?
73 !
Jiri
OK1RI
On Mon, 5 Dec 2005, Eric Wachsmann - FlexRadio wrote:
Jeff nailed this one on the head. The jumping around is because when
spur reduction is turned on, the radio hardware is only tuned every
~3.051kHz. We do the fine tuning using a software oscillator. Also
worthy of note is that we use an 11kHz IF. So what you are seeing is
the junk around DC on the left side of the spectrum.
Eric Wachsmann
FlexRadio Systems
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Tim Ellison
Sent: Friday, December 02, 2005 11:23 PM
To: flexRadio@flex-radio.biz
Subject: [Flexradio] Interesting behavior when connected to a dummy load
I was testing tonight into a dummy load and noticed some very peculiar
behavior.
When connected to the dummy load on 14.179 MHz (USB) I see the noise
floor (signal) in the panadapter as a flat line from -10K to +10K Hz at
about -145 dBm. That looks good to me
Now I change frequency to 14.178 MHz and I see the signal rise to -130
dBm between -10K and -9.5K Hz. It is flat at -145dBm across the rest of
the spectrum. Looks like more noise on the low end. Not so good.
If I change the frequency the to 14.177 MHz I see the signal rise to
-113 dBm between -10K and -9.5K Hz. It is flat at -145dBm across the
rest of the spectrum This shows a *lot* more noise.
Here come the strange part.
I change the frequency to 14.176 MHz and the signal looks just like the
signal on 14.179. Flat across the entire spectrum at -145 dBm.
By changing the frequency down one kHz to 14.175, I see the signal that
looks like 14.178 MHz. A small rise to -130 dBm at the low end again.
If I decrement the frequency down an additional kHz to 14.174, I see the
signal that looks like 14.177 MHz. A large rise to -113 dBm at the low
end again.
This pattern repeats itself through out the entire 20 meter band. The
rise in the noise floor is a little less in magnitude at the very bottom
of 20 meters (14.050), but by the time I get to 14.150 the rise in the
noise floor is back to approximately -110 dBm.
I checked other bands and it exhibits this behavior on ALL bands.
Always a three kHz stepping to repeat the pattern.
Anyone have a clue what might cause this behavior? I'm using the Delta
44 with the breakout box eliminator.
-Tim
---
<mailto:[EMAIL PROTECTED]> Tim Ellison
<http://www.itsco.com/> Integrated Technical Services
Apex, NC USA
919.674.0044 Ext. 25 / 919.674.0045 (FAX)
919.215.6375 - cell
Skype: kg4rzy
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--
Laziness is the number one inspiration for ingenuity. Guilty as charged!
