30 meter noise


AA8QQJMauch@...
 

Hi All,
I put another fw loop in the attic today. This time made from coax. Still
getting what I thot was power line noise. Turns out the noise is from the
video card in the station PC. If I let the Green Machine timer shut down the
video to the monitor, the noise disappears. If I disconnect the VGA cable at
the PC, the noise goes away. Only problem is, once the video is gone, I
can't work PSK. This seems to happen on 30 meters, and on 6 if I turn the
quad toward the shack.

Speaking of a fw coax loop, has anybody ever tried making a full wave
shielded loop (like they make for RX) that you can TX on?

Any ideas? Any one?

73,
Jay - AA8QQ


AA8QQJMauch@...
 

Steve,
I tried a lower res mode, but it only reduced the noise slightly. Think a
higher res might help? What's the Sys Tray thing you mentioned?

Jay - AA8QQ


Steve W3HF
 

Hi All,
I put another fw loop in the attic today. This time made from coax.
Still getting what I thot was power line noise. Turns out the noise
is from the video card in the station PC. If I let the Green Machine
timer shut down the video to the monitor, the noise disappears. If I
disconnect the VGA cable at the PC, the noise goes away. Only problem
is, once the video is gone, I can't work PSK. This seems to happen on
30 meters, and on 6 if I turn the quad toward the shack.

Speaking of a fw coax loop, has anybody ever tried making a full wave
shielded loop (like they make for RX) that you can TX on?

Any ideas? Any one?

73,
Jay - AA8QQ
Jay -

Try running a different video mode, i.e., a different resolution.

On my machine here, I use 1280x1024 most of the time, but have to
switch to something else when I work 15m, as the hash is in the
PSK band.

You can use a System Tray utility to switch the mode on the fly,
without a reboot. Takes me about 20 seconds. (I do it while I switch
the antenna and tuner.)

Steve
W3HF


Steve W3HF
 

Steve,
I tried a lower res mode, but it only reduced the noise slightly.
Think a higher res might help? What's the Sys Tray thing you
mentioned?

Jay - AA8QQ
Any change in mode should help. Assuming the noise you see is
similar to mine, it's some multiple of either the line rate. So it's a
combination of your (vertical) resolution and your refresh rate.

Let's see, if you have a refresh rate of 72 Hz (that's 72 video frames
per second) and a video mode that has 1024 lines, that's 72x1024
lines per second, or 73.728 kHz. Depending on the design of your
video card, there are probably harmonics out the wazoo.

But if you were to switch to an 800 line mode, the line rate is 57.6
kHz. And if you went to a 1280 line mode, it would be 92.160 kHz.
The trick is to find one that's clean at the frequency you want to use.

The system tray utility is something that may or may not be needed
depending on your version of Windows. Earlier versions (some
Win95, for example) required you to reboot whenever you switched
modes. There was a utility that came with the Windows Power Toys
set called QuickRes that let you pop up a utility that did the switch on
the fly. Once that came out, many video board manufacturers added
it to their own utilities, so it may not be needed for you.

Steve


Steve W3HF
 

Oops, typed too fast.

similar to mine, it's some multiple of either the line rate. So it's a
Delete the "either." I changed thoughts in mid-sentence and didn't
correct it.