Using SDR Sharp with Fldigi (or trying to) with an RTL-SDR

[sacentre]

Hi, I'm completely new to SDR and decoding but I hope someone suggest something I haven't tried yet to fix this problem. I posted this on the Nbems forum but have received no replies so far. Meanwhile I thought I'd ask if anyone here can assist.

(I'm expecting some antenna components to arrive and while waiting, I've been surfing around on the AirSpy server Network. There are so many signals and modes available that I wonder if I really need to bother with an SDR device at all. However, that's another story).

My problem
I'm trying to get SDR Sharp to "talk" to Fldigi (or Fldigi to "listen" to SDR Sharp) via the free VB audio cable driver when trying to decode for example, a simple RTTY 45/170 signal (the only mode I've so far learned to identify from the sound). There's no waterfall on Fldigi and only gibberish on the output screen. At this point, I don't know if it's SDR Sharp or Fldigi that's the problem or something with the way I have my PC setup or a combination of all three. I couldn't see anything in the Fldigi manual that covers using the app with an SDR.

I've been at this for several days now and reading stuff on various forums from others who seem to have similar problems but I haven't found a solution yet. A clean re-install of SDR# and the VB driver as well as Fldigi didn't improve things. I also tried the alternative VAC_Lite audio cable because someone posted that this had fixed the same problem but it made no difference. Obviously, I'm missing something and knowing me, it'll probably turn out to be something completely stupid that I forgot to do. I just haven't found out what yet. Any advice about this would be appreciated.

Generic RTL-SDR dongle
OS Windows Pro x64 (19042.844)
SDR# v1.0.0.1810
VB Cable Pack43, VACLite465
Fldigi v4.1.18

Thanks for reading.

 

[spongella]

It's been a while since I used FLdigi but it sounds like you need to go to the Configuration page and click on Sound Card and fill in the proper input/output settings. You also have to set the output setting on the SDR# menu to the proper one also. I use VB cable too to make the SDR communicate with SDR#. It may take some trial and error to get it right though.

I can tell you from experience that most (but not all) RTTY comms on HF are encrypted. Best to listen to RTTY on the ham bands where there's no encryption. There's one German meteorology station on 10.101 mHz that continually xmits RTTY that's not encrypted.

Seeing gibberish on the screen is normal even when no signal is being received. I like FlDigi for WEFAX (Weatherfax) and prefer MMTTY (freeware) for RTTY.

Hope this helps.

 

[ka3jjz]

What are you trying to decode using FLDigi? This app is primarily set up for the HF bands, and many RTL-SDR variants won't work as it won't go below 25 Mhz. And of course, there's the antenna - but there's a separate forum for that.....

As mentioned in another thread, there's plenty of HF digital that isn't encrypted. Most RTTY that sounds like RTTY is actually a STANAG mode; while you can catch them running test tapes in the clear, you have to have a certain amount of luck to get them

Mike

 

[sacentre]

Hi spongella, ka3jjz

Thanks for the replies. I'm pretty sure I have the VB cable and sound card Input/Output settings filled in correctly. I'm not sure about the " output setting on the SDR# menu " though. I don't know what that is. Duh! Can you point me to it?

As for what I'm trying to decode - I'm just trying to get the system working on a test RTTY 45/170 recording so I can at least see it decoding. After that, it'll be mainly HF I'll be looking at. My RTL-SDR dongle says 100Khz - 1.7Ghz on the box so I assume that's ok. I bought a cheapo generic on but am waiting for the RTL-SDR Blog V3 dongle for comparison.

I'll give MMTTY a try. Is it easy to set up with SDR assuming the VB driver and sound card settings are correct?

 

[KE5MC]

One stumbling block for me after several months of not using my working SDR, VAC and DSD+ Fastlane was the sample rate in my VAC setup. Somehow the rate was lower than it should be and distortion of the audio signal kept DSD from working well. DSD would be your Fldigi. Other suggestion are good too. From antenna to speaker it is a serial process, anything not correct along the way will halt/stop/corrupt getting expected objective.
Good Luck!

 

[sacentre]

One stumbling block for me after several months of not using my working SDR, VAC and DSD+ Fastlane was the sample rate in my VAC setup. Somehow the rate was lower than it should be and distortion of the audio signal kept DSD from working well. DSD would be your Fldigi. Other suggestion are good too. From antenna to speaker it is a serial process, anything not correct along the way will halt/stop/corrupt getting expected objective.
Good Luck!

Thanks for the input. I note you are using the VAC driver. Is the sample rate something I need to worry about with the VB audio cable I'm using? However, I'm not even seeing anything on the WF on Fldigi. The gibberish I mentioned in my OP is there no matter whether there's an input signal or not. I'm assuming it's just responding to noise in the system.

 

[KE5MC]

I was using a FLEX3000 at the time I needed a virtual audio cable so I went with the pay to use version. No help with VB, but what I have read the startup configuration is usually good to use. Other likely will have a better answer. Waterfall is usually a good indicator of FLdigi getting a signal. It does require some setup to get away from black screen. Audio levels, waterfall gain and contrast after you point FLdigi to the correct named audio channel input for this application. As commented gibberish is typical. It can take much hand waving and gashing of teeth, but once it starts working its like pushing over a stack of dominos. Hours to setup and over in seconds.

 

[ka3jjz]

Once you get the kinks out, take a look at this article from our wiki - all of these are readable with the right software....

Testing Your New Setup - The RadioReference Wiki

wiki.radioreference.com

And of course you will need an antenna - go here, and let folks know your situation (can you put something outside? How much room do you have? etc.)

Receive Antennas (below 30MHz)

For all topics related to receive antennas used on HF, MW, LW, etc. For transmit antennas use the Amateur Radio Antennas forum.

forums.radioreference.com

Mike

 

[sacentre]

Hi Mike
Thanks for the reply and the link. I'm on a steep learning curve where antennas are concerned and given my restricted living environment am beginning to think my chances of getting a half way decent solution, well nigh impossible. What makes things more challenging is the lack of any RF ground point.

The only thing I can think of is to stick a long plastic pole out of a window at about 30 degrees from vertical with some sort of antenna on the end of it.

The first thing I'll be trying is a Chinese knock off SA0RDT mini whip since these can be had for $10/- or so. I can even make the pole telescopic using different dias of tubing. I estimate it can easily be about 3 meters fully extended. This would take it above the roof at least.

I have no idea if the results will be total crap as a lot of folks have described results with this type of antenna. Still, it's not costing much to try (financial outlay with SDR is zero to negligible compared to hardware receivers). If results are poor, I might try an MLA30 loop - again on the end of the plastic pole which can easily be rotated.

Thanks again. I'm very grateful to you and others who have kindly offered help and suggestions.
Trevor

 

[KE5MC]

Trevor,
For now if only focused on receive then requirements for a workable antenna are greatly reduced. Stick with voice communications until you have a working setup and some experience with what you can hear and how well. Then move to digital as you know what your setup can do on voice and can focus on digital which adds a significant level of setup. Once figured out I'm sure you will look back and say that's not so hard.
Good Luck!
Mike

 

[sacentre]

Thanks, Mike. Sound like good advice.

I have a lot of other questions but will post them to the group as they come up.
Trevor

 

[sacentre]

Hi Mike
In case it's of interest, I seem to have made a modicum of progress on the decoding issue. To what extent remains to be seen. I realise I'm skipping around quite a bit but I'm trying different things while waiting to set up an antenna. The aim is to discover what part of the chain is preventing the decoder from hearing the audio output.

This morning I downloaded Black Cat WEFAX software. On launch, the Input Device field by default showed "Cable Output (VB-Audio Virtual ...." and when I played a WEFAX sample file from the Artemis database, it immediately began to decode a WEFAX picture.

My take away from this is that at least one decoding program is able to "hear" the VB-Audio cable which may mean that Fldigi or MMTTY are simply configured incorrectly. My next step it to see if I can decode a real WEFAX signal from one of the AirSpy servers.
Thanks for reading
Trevor

 

[spongella]

Yep. All in the configuration. WEFAX is lots of fun, there are more stations out there than RTTY and they run around the clock. You'll do better with an outdoor antenna though.

A great program I've used a lot is MultiPSK which supports many modes. It is free but a one time reasonable registration fee (I paid $40 several years ago) will give you full access to all the digital modes it supports. Good luck with your SDR station. This article is a good introduction: http://www.tele-audiovision.com/TELE-audiovision-1501/eng/feature-dongle.pdf

 

[KE5MC]

I can't say that I have ever had a decoding program select the correct audio input. Time to buy a lottery ticket.

WEFAX is showing you the typical name the operating system assigns to a virtual audio cable. I use SDRuno, but expect SDR# to operate the same. In SDRuno I would find the place to direct the audio out and select "VB-Audio...". Then in the decode program I would configure audio input to use "VB-Audio...". I now have my audio "piped" from one application to another. In SDR# disable any of the audio processing features as they work well for our hearing, but not for digital decoding.

I had to go back to the email notification as its a little different than your current post. Typical to loose audio to the speaker, but somewhere in the operating system control panel is a check box to enable monitoring. I think once you get the decoding program(s) setup the waterfall and other indicators will become your ears and hearing the recovered audio not so important. You will learn the sounds of different coding protocols, but some are so similar you can see the difference easier than hear it. It's possible monitoring can be enable at the decode program level, but not sure on that.

For me on my MicroSoft PC I find configuring the audio the most tedious and confusing. There is the old school 'control panel' which to me is straight forward then Win10 has this other layer of 'setup'. I swear they don't play well together and sometimes I think they 'mess with me' just for the fun of it.

 

[sacentre]

Yep. All in the configuration. WEFAX is lots of fun, there are more stations out there than RTTY and they run around the clock. You'll do better with an outdoor antenna though.

A great program I've used a lot is MultiPSK which supports many modes. It is free but a one time reasonable registration fee (I paid $40 several years ago) will give you full access to all the digital modes it supports. Good luck with your SDR station. This article is a good introduction: http://www.tele-audiovision.com/TELE-audiovision-1501/eng/feature-dongle.pdf

Hi spongella
Thanks for the link - a good introduction. I note that in the section where MultiPSK is mentioned, under the photo it says, "The audio stream from SDR# is fed directly to MultiPSK". By directly, do they mean without the need for a VB cable?

 

[spongella]

Hi spongella
Thanks for the link - a good introduction. I note that in the section where MultiPSK is mentioned, under the photo it says, "The audio stream from SDR# is fed directly to MultiPSK". By directly, do they mean without the need for a VB cable?

No, it is fed via VB cable.

 

[sacentre]

Thanks. Sadly, the very thing I just can't get to work.

 

[KE5MC]

Thanks. Sadly, the very thing I just can't get to work.

Remote instruction/troubleshooting can be difficult, but going to give it a try. I'm using Win10 home edition and no add-on virus applications other than what Win10 provides. Win10 and any underlying support applications are up to date and no interference from 3rd party virus programs.

I using SDRuno, RSPdx and a virtual audio cable which is different from your setup, but the general concepts are the same with differing details. I'm not sure if my copy of Fldigi is current, but is the last I installed several months ago. You will see the version in one of the screen shots. Screen shots will be described and listed A thru G in a somewhat logical order.

Item -A-
At the bottom left is the Virtual Audio Cable installed. At the top under Audio inputs & outputs is what the operating system has done with one audio cable setup in a different item view.
Item -B- and -C-
While they look similar the 1st is the Playback tab and the 2nd is the Recording tab. Conceptually each tab is one end of the digital virtual audio cable. The blue circled vertical bar graph is a relative VU meter moving up/down as the audio level is changes, assuming it is connected and passing audio.
Item -D-
The control panel for my version of virtual audio cable. Very different that the one I looked at for free VB a few years back. The key points is the green circle showing the low and high sample rate (SR). If the sample rate is set low in your VB then the audio is distorted and the decode program will have trouble decoding. The blue circle is another VU meter moving up/down as volume changes showing audio is passing thru the cable. This version of a virtual audio cable is reportedly very high end and used at the profession level. Many of the check boxes and setting I have little idea how to use. The author does have a manual and is very clear about reading and understand it before asking questions.
Item -E-
This is where you get Fldigi to receive input. This is where you get audio from the end of the 'pipe'. I didn't realize it would pass the audio to my speakers as well as decode the audio. Nice feature, but don't expect all decode programs to do that. Typically when you redirect the audio out of your SDR receiver software the speakers go silent without steps to redirect.
Item -F-
The upper half is just the memory panel and a few frequencies stored for easy retrieval. In that picture I am pointing and receiving Pt. Reyes CA, but I believe in the last one captured (-G-) it was N.O. Lusisiana (8502000). For SDRuno I have to go to RX Setting and select the OUT tab and then the drop down arrow to select Line 1 to put the audio into the front of the 'pipe'.
Item -G-
Green circles highlighting version and mode selection along with centering the decode window (red bars) over the audio 'piped' from SDRuno. There are controls to change how the waterfall looks like gain, contrast and color. I don't make any changes. The red circle to the far right is the audio input VU meter. Again I didn't change audio level in Fldigi, but I believe you can. It's been a long time since I used this program and for me, while not all the setting are to my liking I didn't take time to fine tune it. Also the program is not connected to SDRuno so the CAT function of frequency control and modes are not work, but could be. Orange arrow is pointing to the decoded fax weather chart I was receiving at the time. The sync timing is off, because I was doing screen captures and saves which messed with the program keeping up with the received signal sync pulses.

I hope there is enough information to point you in the correct direction and fill in some gaps.
Good Luck!

 

[sacentre]

KE5MC.

I'm sending this quick reply to thank you for the very detailed notes. As soon as I can get to my setup, I'll go through them and let you know how I get on. I too realise how hard remote troubleshooting can be having attempted it plenty of times for friends and relatives with PC and Windows problems, so I very much appreciate the fact that you were willing to sit down and go to all this effort. It must have taken a lot of your time. Anyway, I'll be in touch when I've gone through it all and hope to report a successful outcome. Thanks again!
Trevor

 

[KE5MC]

Trevor,
No worries, time well spent. I find the best way to deepen my knowledge of 'something' is to tell someone else how its done/works or whatever. This effort had me looking closer at how the operating system was using virtual audio cable in the background. Also taking another look at Fldigi from a different perspective and lastly practicing markups on screen captures for the post.
Mike