SDR# - Visible signal but no output?

I'm hoping someone can help me? Firstly, I'm completely new to this - I'm trying to put together a (cheap) SDR set-up in order to track a high-altitude balloon for my entry into the Global Space Balloon Challenge (https://www.balloonchallenge.org/).

So far I have:

- SDR Sharp and Fldigi installed
- Pi-In-The-Sky tracker mounted to a Raspberry Pi and outputting a signal
- A NooElec dongle I bought on amazon

I'm following this UKHAS guide [UKHAS Wiki] and trying to get my data to output from SDR Sharp and into fldigi via a Virtual Audio Cable (apologies for all the links, I don't know how 'universal' any of these names will be).

I've got to the point where I can see what I think is the output from the tracker in SDR Sharp (a spike that appears when I power up the GPS tracker and a red/yellow stream on the waterfall chart) - should I also be able to hear something (there is no noise, just silence?)

Also, is there any way to test whether the virtual audio cable is working correctly? The results window in fldigi just fills with gibberish that appears to be the program translating noise, I'm not sure how to test whether this is the case though?

Any assistance on this would be appreciated, please let me know if more information from me would be useful.

Thanks,

Adam

A screenshot of your SDR# screen (with the spectrum display zoomed in on your signal) would be a good start. And I'd ditch VAC and use VB-Cable instead.

First thing I might suspect would be if you're using the defaults for SDR# and you haven't adjusted much of anything then perhaps checking on the RF gain aspects would come in handy. If you're tuning in a signal from a GPS transmitter or whatever that RPi is doing and that signal is "powerful" in the sense that it's right there on the bench with you and not several miles up in the sky then you could be looking at a potential overload issue distorting it so badly that what's being passed through SDR# over that virtual audio cable to Fldigi is just mucked up, it's tough to say.

The suggestion above about providing a screenshot (or several) of what you've got even if it's not working correctly still provides a wealth of info for troubleshooting. And I also agree with the suggestion to use VB-Cable - it's much easier to get working in a functional state than using Virtual Audio Cable, and it's cheaper to boot (donationware so if you do find it useful then make sure to donate a few bucks if you can).

To answer part of the OP question: No, you should not hear anything if the audio from SDR# is going through a virtual cable to FLDIGI. If you want to verify reception, then route the audio to your computer's normal audio output temporarily so you can listen to the signal.

Thanks all for your replied and apologies for the delay in responding.

I've taken some screenshots, there doesn't appear to be a way for me to include them in the thread (perhaps because I'm new) so I've included them in the links below:

My SDR# install before I power up my RPi tracker:

Screenshot 1

When I power up the tracker, the spike on the left in this screenshot appears (I have assumed that this is the signal from the tracker itself?)

Screenshot 2

This is what the spike on the left looks like when I zoom in on it:

Screenshot 3

I installed VB-Cable and have it configured as so:

Screenshot 4

I set up my fl-digi according to the instructions on the Pi-in-the-Sky website but don't appear to be getting any sensible output from it (gibberish in the output window and no data in the waterfall chart area).

Screenshot 5

In terms of my set-up, both the aerial and the tracker are both on the bench and so right next to each other. I'm using the cheap extendable aerial that came with the USB dongle but I had the same problem when I used my Watson WSM-270 70cm 3/4 wave antenna (albeit with a different, cheaper SDR dongle).

Thanks again for your help so far with this, really hoping that you can point me in the right direction!

Adam

Well,

- you're not using USB mode like the instructions call for

- you're using a huge 180 kHz bandwidth filter for a narrow signal

- you might as well enable Correct IQ to eliminate the DC spike in the spectrum display

- you're filtering the output audio, which is probably distorting the signal

- your FFT size is too small to see the signal's spectral details

- you don't appear to actually be tuned to the signal - it's at 434.625, but you're tuned to 434.65; or maybe you just haven't set the dongle's PPM correction value yet/properly

slicerwizard said:

Well,

- you're not using USB mode like the instructions call for

- you're using a huge 180 kHz bandwidth filter for a narrow signal

- you might as well enable Correct IQ to eliminate the DC spike in the spectrum display

- you're filtering the output audio, which is probably distorting the signal

- your FFT size is too small to see the signal's spectral details

- you don't appear to actually be tuned to the signal - it's at 434.625, but you're tuned to 434.65; or maybe you just haven't set the dongle's PPM correction value yet/properly

Click to expand...

Many thanks for the response! Reading your post and revisiting the problem with fresh eyes revealed a couple of small mistakes. Having messed around with it a bit more I now have a decoded signal in my fl-digi.

There still seems to be a bit of noise in the decoding, I will try it again with a 'proper' antenna and a pre-amp for the dongle and hopefully get a more consistent signal.

As for the signal I was tuned to, this was simply the 'spike' that appeared when I turned on my tracker. It seems to jump around a little more than I expected (for some reason it seems to jump once the GPS signal locks but stays pretty stable after that). I'll have to read up on PPM correction values and see if that solves my problem.

In the meantime, thanks again!

Adam

AdamDynamic said:

for some reason it seems to jump once the GPS signal locks but stays pretty stable after that

Click to expand...

The transmitter may be using a 1PPS signal from the GPS hardware as a frequency reference.