Decoding SCA with HDSDR and SDR#

[@alcampbell]

KD6CFE was here. SCA= Subsidiary Communications Authorization. Of course I had to look it up. LOL. Good job Jay for experimenting with the SDR boards and clarifying a lot of stuff for us.

[@tubeDude48]

*SCA* = Subsidiary Communications Authority. At 2:55, it also transmitted PRN Physicians Radio Network!

[@beauthompson5338]

how did you get source in sdrsharp to other sound card?

[@n1vca]

Thanks for the hint on piping the IF data from HDSDR into SDR# to take a closer look - very simple and brilliant idea!

[@dewdude]

It's FM baseband.

[@n1vca]

Right its behind the demodulator

[@misterguts]

Thanks for this, Jay! It was great geeking out with you.. Ever since I learned what SCA was, I've wanted to listen in..

[@jvanb231]

Works for me, thanks! Anyone else here because of Fran's SCA receiver?

[@tubeDude48]

With an SCA decoder attached to the detector of an FM receiver, you can receive SCA channels!

[@df9999999999]

Nice! I was able to do this with two instances of HDSDR and Virtual Audio Cable. You actually CAN see the subcarriers on the first instance of HDSDR, in the audio waterfall at the bottom, if you expand out the bandwidth to 100KHz. You can’t listen to them, however. On the second instance of HDSDR,the main channel is AM modulated at zero KHz. The stereo pilot is at 19KHz, just an unmodulated carrier, audible as a tone in CW mode. The L-R stereo is DSB AM modulated with a suppressed carrier, ending 15KHz either side of 38 KHz. You can listen on either upper or lower sideband mode. Vocals that have no stereo separation are attenuated in this signal, kind of like a karaoke filter. In my area, some stereo stations broadcast only on lower side and is SSB mode (experimental) which eliminates interference the upper side band would cause to RDS and the FM SCA subcarriers farther up. Surprisingly, the local NPR outlet still broadcasts CRIS radio reading service for the blind at 67KHz! Muzak, PRN, stock ticker data, and agricultural stations are all gone in the Chicago market. RDS has a narrow-band subcarrier at 57KHz, but I found it to be inaudible and almost invisible on the waterfall display. I got interested in SCA radii in the early 70s about when I discovered phone phreaking and blue boxes. I built a decoder from a Signetics 565 PLL chip that worked surprisingly well. Thanks for the video. Great idea.

[@unklewink]

I don't seem to have the (other) soundcard input option on my SDR Sharp device selection dropdown. (?)

[@almeisam]

Me either.

[@robertr64]

Can this be done with SDRConsole or other programs besides sdrsharp? Or better still, do it from 1 program rather than piping HDSDR into something?

[@NetCast3]

I've listened to WETA 90.9 my whole life; never knew they had an SCA signal. Small world! Wonder why the noise floor appears lower around baseband than in the higher frequencies?

[@markanderson8066]

welcome, Jay, to ham radio! fyi I use my sdr WITH my Kenwood ts590sg to see the spectrum. great combo! 73, WB2SMK

[@balaramaraju4135]

Is NooElec NESDR Mini 2 SDR capable of transmiting signals??

[@ryantoomey611]

Is there a way to decode AM stereo C-QUAM transmissions with down-converter?

[@dewdude]

Theres a program that will do it.

[@unklewink]

SDR Sharp wants IQ input from the sound card. When I run it with HDSDR, using this setup, I get some kind of slow oscillation effect and no signal decoding. What am I doing wrong?

[@daveb5041]

So why can't you pick that up in SDR# alone? I have an SDRPlay (best receive only SDR in my opinion) and hear WETA and have seen those signals but just thought they were digital. Still can't figure out why you couldn't just see those in SDR# or SDRUno (really cool "HAM radio unit" looking interface with buttons like a real radio instead of menus makes for very fast tuning around ).

[@dewdude]

The thing to remember about FM MPX (which includes stereo and SCA carriers) is that all the sub carriers are multiplexed with the main audio. So essentially the main program (analog audio) is mixed with all the pre-generated RF subcarriers at their frequency relative to baseband, and they are all modulated at once. In theory, you can recover an SCA without full demodulation; but only if the main program audio is silent. The modulation index of commercial FM is very large, so the minute the main audio program starts coming up, it quickly begins to deviate over where the SCA. So do to a proper SCA decode (or even MPX), you have to demodulate the entire FM signal to it's baseband (analog mono audio at 1-15khz and then your subcarriers further up). Only then will you be able to recover the SCA carriers without deviation issues. The dual SDR# method was the only one I found that worked at that time. I've since gotten an SDR play and found I still need SDR# and HDSDR; one to give me an unfiltered FM baseband and the other to demodulate the NFM carrier within the SCA. SDRUno doesn't give unfiltered output at all. In order to do it with a single copy of a program, there would need to be a plugin that would demodulate the baseband and simultaneously demodulate the SCA. None such plugin exists that I've found.

[@daveb5041]

That makes total sense now. Use HDSDR to get the signals divided out. Use SDR sharp to tune to the subcarrier on narrow band FM on the spectrum and let it demodulate. One program only would just demod and split the signal not demod split and demod again. There is so much you can do with SDR but its not like there is a ultimate users guide. I am still having a hard time decoding things in HF. When I find a signal its hard for me to figure out what exactly it is them apply the proper demodulation. Sigmira has dozens of demods but as far as tuning its not nearly as good as SDRUno so I have to find a signal in uno shut it down open sigmara tune in that freq. then manually keep clicking on each type of modulation (PSKxx etc etc ) and HOPE something read able comes out. There has to be a better way/program.

[@dewdude]

That's kind of it. Technically you're demodulating the FM back to it's baseband component; then further tuning using a second program. You have to remember that an FM broadcast actually has a bandwidth of upwards of 100khz. As far as decoding digi in HF; that's just about the way to do it depending on what modes you want. I never used Sigmira; I always piped the demodulated audio through a virtual sound card directly in to other software to decode. On the flip side of that there may be some modes that are hard to find support for. Picking the right digital mode relies a LOT on being able to identify them by sound as well as what they look like on the spectrum. Since I'm a ham now; I've mostly stuck to playing around with the modes amateurs have at their disposal and don't do much decoding of the military/commercial signals. Modes like PSK you can pick up by sound as well as what it's baud rate is from how it looks. RTTY is a spacing thing..then there are modes that look and sound similar that you kind of have to guess. Often (but not always) on the ham bands you'll find someone using software that supports RSID, which is a standardized method of transmitting the ID of the mode so you don't have to guess. But even then; you have to sometimes guess as to what the person is using.

[@fensterkiller3151]

Thank you so much for this video!

[@AdamEbelgccengineering]

Your link is bad, I cannot access the instructions on how to do this.

[@AdamEbelgccengineering]

@@mikepaige9918 It works way better than than using the HD SDR software. Thank you so much. That MPX Output sure did the trick. I really appreciate this. I want to experiment with SCA-FM subcarriers on my part 15 FM stations, and this will be a great test software to make sure that it works properly. The only SCA-FM subcarrier there is is just a readers service radio station on 67 kHz on 89.5 FM here where I live. I want to build me a basic SCA-FM generator using some VLF NFM nano powered transmitter.

[@aunumero73]

Hi Jay ! What is actually the content of what can be heard on this SCA signal ? Watching your clip, one can only guess a man is talking .. TIA.

[@dewdude]

It's a reading for the blind service. They read newspapers and other stories of interest. They are completely uncensored apparently to.

[@markanderson350]

I have had many SCA receivers and built one using a PLL chip. Subsidiary Communications Authority been around since the 50's

[@markanderson8066]

Mark Anderson hello Mark Anderson. .. from, Mark Anderson!

[@markanderson350]

Small world. Yes I dabbled in electronics service too. I miss the analogue days. You are into all the modern gear.

[@202Electrics]

awsomwe! for a while i wanted to know how rds sounded . now i know. now a way to decode that only signal

[@davidwilson6042]

Why are you not pulling in the filter edge on the lower left window down to 71 KHz and the one at 0 kHz up to 63 kHz. It greatly improves SCA reception to do that.

[@dewdude]

David wilson that would effectively filter the FM signal. You can't do that for SCA. You must pass an unaltered baseband of the entire signal.

[@davidwilson6042]

No-you do not need to pass the unaltered baseband of the entire signal--in fact that is a bad thing in general to do. You can pull in the filters in the MPX display to filter the subcarrier transmission at 63-71 KHz. Pull the right filter edge slope inward to 71 kHz and the left edge (it is at zero in your display and not visible--grab it from top left corner of the MPX display). I have been doing this for years and it greatly improves the s/n for subcarriers. I use HDSDR to feed VBCable to feed SDR#. In fact at the very moment, I am trying to figure out what language is on WMZQ (98.7) 67 kHz subcarrier. I do this also to improve RDS reception feeding RDS Spy.

[@ryantoomey611]

Isn't SCA the text that displays on your radio the name of the station and the song that is playing? Many stations have that.

[@dewdude]

That's RDS. It's a small DSB subcarrier centered around 57khz, you can see it next to the SCA at 67khz in the spectrogram of the FM baseband.

[@unklewink]

If you tune SDR Sharp to (Main channel Freq.) + or - 67khz and set it to the narrow FM mode, you can hear the SCA audio when there is silence on the main channel.

[@gatesmw50]

Jay Moore: There is another SCA subcarrier at 92 kHz also.

[@Coowallsky]

Radio Talking Book. Reading services for the Visually Impaired.

[@assmennfiossa]

One guy in Corpus Christi used to use SCA to sell paging services in the early 2000s

[@KandiKlover]

Kinda lame u gotta use 2. Wish sdrsharp just had a plugin for it.

[@CallForGrandPappy]

Nerd