Hello Chris,
My answers in line
At 08:10 PM 10/6/2005, you wrote:
Hi Guys,
I am working on getting this little receiver up and running but noticed a
few things I wanted to ask of those more experienced.
I connected my generator and set it to 7.040 Mhz at -60 dBm then went to the
General tab and clicked on Calibration. I set the frequency in the field to
the generator frequency and clicked on start and it gave me a Frequency
Calibration Complete message.
Hmm -- not sure the freq calibration will have any effect with the soft rock as that is used to calibrate the DDS reference osc, and there ain't one in a SoftRock setup. The way to get the freq calibrated for a SoftRock is to set the center frequency on the SoftRock page in setup.
I did the same thing for amplitude, so now
the peak on the spectrum display is at -60 dBm. However the displayed
reading for the RX meter at the top right says -83.2 dBm. As I tune around
and the peak disappears the reading changes. What causes the discrepancy
between the signal meter reading and the spectrum peak's value- is the
reading an average between the signal and the noise floor?
It is not the diff between the sig and the noise floor, I think it's the average power across the bandpass selected or something like that. Try putting your known signal inside a 500 khz passband and see how the meter correlates with the panadpater display.
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I worked more with the Image Reject feature under DSP and I can only null it
by about 10 dB. It is sitting at about -65 dBm right now. The best null
comes with the Phase all the way to 400 at far right and the Gain all the
way to -500 at far left. The controls are at the end of their setting so I
need more range and I don't get the twitchy response that Bill mentioned. I
went back to the General tab and clicked on calibrate Image Null (above
values) and got an message that says "Error calculating image null. Please
try again."
I do not think the automatic calibrate on the image null will work with the Soft Rock, I've always done it by hand.
Does this mean that the receiver is bad or is there something in the
software I need to change?
This sounds like a hardware issue - one should not need to go to the extremes to null the image. I don't think I've ever seen a properly working SoftRock that needed to go the extremes to null the image signal.
First thing to check is that you're using a stereo input, some laptops only have a mic input and it is typically mono. Second thing to try is reversing the left and right inputs to the sound card. Third thing to look at is the hardware itself. If you have a scope try feeding a -30 dbm or so 7.050 MHz signal to the Soft Rock antenna input and look at the I and Q outputs on the scope. They should be a 4-6 khz signal and about 0.8 Vp-p. They should also be of similar amplitude -- within about 20-30% of each other. The phase relationship should be about 90 degrees between them.
If the IQ sigs are not of similar amplitude, check the soldering on the FST3125 bus switch, and check that you see clock inputs on all the control lines. 99% or soft rock hardware problems seem to be the connection of the signals on the FST chip.
If that does not get it going, come on back and we'll debug some more.
Cheers,
Bill (kd5tfd)
