It has the center spike problem. I have tried everything to get rid of it and nothing works.
I have also put the software on 2 desktops and they are doing the same thing, I am lost with what to do about it?
Maybe close the internal sound card and get a USB one?
The problem is usually current flowing on the screen of the audio
cable. Investigate by disconnecting everything from your Softrock
including the audio cable.
1) Connect the audio cable.
There should be no difference.
2) Connect the USB cable.
You may see a difference now. There could be two reasons.
You may have a magnetic field that induces a current in the
ground loop you have formed with the two cables. Try to make
a tight bunch of the cables to minimize the area for magnetic
pick-up.
There could be a voltage difference between soundcard ground
and USB ground. Try to connect them to each other at the computer
with a fairly thick wire (2 mm or so.) Make the wire as short
as possible.
Another alternative is to connect a fairly thick wire in parallel
with the screen of the audio cable. Run it in a tight bunch with
the other cables.
Ultimately there should be no difference when the USB is connected.
3) Connect the cable to the power supply. The supply must be running,
but the +12V disconnected so you only connect to the ground in the
Softrock.
There should be no difference. If you see any difference you have
formed another ground loop.
There are several ways to eliminate this. You can try to route
the DC supply cable via the computer and connect its ground to
USB ground or soundcard ground on the computer. Then run it in the
bunch together with the other cables.
You may connect a 1k resistor between the minus side of your psu
and computer ground. (Nothing else connected, but psu running.)
Measure the voltage across the resistor. It should be very small.
Also measure the DC resistance between psu ground and computer
ground (Nothing else connected, but psu running.) Resistance should
be very high.
4) Connect the +12V to the Softrock. You should see some wideband noise
and some extra noise at the center ( 1/f noise) but not very much.
5) Connect the screen of your antenna cable to the Softrock while leaving
the center conductor un-connected. This should not make any difference
with respect to step 4. In the most probable case that you find that it
makes a difference, connect 0.1 uF between RF gnd and analog GND in
the Softrock:
(The relevant part starts about two and a half minute into the video.)
With the capacitor in place you should no longer see any difference when
connecting the antenna screen to RF ground on the Softrock.
If the capacitor does not help, route the antenna cable via the computer
and connect its screen to computer ground.
6) Your computer is not at ground potential with respect to your antenna.
It is necessary to put a choke or a low capacitance transformer to
prevent currents on the antenna cable from reaching the antenna.
The choke/transformer should be outside your house if possible.
and the screen of the antenna cable should be grounded near the antenna.
The problems of sending conducted interference on antenna cables and related
things are illustrated in these 4 (long) videos:
Good luck:-)
73
Leif
