The AM Forum

I have noticed the last few weeks on 80m, down below 3750 or so, some very strange sounding voice signals.  Sounds like SSB, but you can't tune them in intelligibly.  It sounds if the voice signal has been deliberately scrambled.  It's recognisable as a voice , but no matter how you try to tune it in, it always sounds like you are listening on the wrong sideband.

Reception on various receiving antennae here indicates a strong likelihood that it is coming from Europe.

Has anyone else heard this?

BTW tonight close to midnight, there were German speaking SSB signals all over the 3600-3750 kc/s segment of the band.

AM community doing a good job keeping the QSO's spread out.  Band seems to be  recovering from Thursday's flare.

Digital Voice:
http://www.aorusa.com/ard9800.html

We used to use something simular on chicken band years ago.
The were pretty cool. You could program groups, select stations, as well as other pretty nifty things. They worked in Digital or Analog mode.

They also had a GStar type identification system built in. GStar is a General Electric Tone Identification scheme. Each unit has a number, the number is sent out in a packet burst to identify the transmitting station. Most police radio systems use these types of ID systems. There's a bunch of different schemes by each manufacture, Moto, GE, Et cetera.

I believe they were made by SBE but can't remember exactly. Very nice, you could leave the squelch off, increasing your range while still blocking out everyone else. Only those that were part of your group or persons wishing to talk directly to you (provided they were in your group or programmed to allow.) could talk to you. They worked pretty well provided the channel wasn't too noisy.

The difference is you couldn't hear what they were saying or even identify it was voice unless you had the proper decoder and group code.

To someone listening in analog all they would hear was a short high frequency beep, like a whistle, followed by an electronic sounding fart (The GStar type ID), then white noise for as long as the person had the key down. On your end when you key'd up you'd hear a quick brrrrap sound and when it stopped it was OK to start yakkin'.

They worked on any radio and connected between the mic input and the speaker output. For analog mode they also had the digital alert, DTMF Alert, or common CTCSS options.

Wonder if there have been any articles published on this.  Soundl like something that might be interesting to experiment with, but I would prefer to build my own.

I've not seen any Don, however that doesn't mean there aren't any out there.  I have heard it works quite well.  I'd be curious how well it works in AM.  It takes no additional bandwidth, so that's not an issue.  I figure it would sound a lot like FM regardless of the mode.

How do you know Don was listening to ARD9800's ?  Do you have one ?

I've played with them at Dayton but I've never heard one on the air and I suspect that at $550 a pop, few people have either.   


Sam

There are a few stations that operate SSB on 3870 that are using a highly processed (audio) signal that they call voodoo audio. The total signal width sometimes reaches 15kc but you can only tune in about the center 8 kc or so.
It is very difficult to tune in on a boatanchor rx...Google WZ5Q VOODOO AUDIO to get a look at $20k worth of audio gear making a $12 transceiver sound like something else.....

Don,

I heard those SSB signals also.  It doesn't sound digital which should just be white noise like at 3995 kHz.

It sounds like analog scrambled voice, but also sounded like Spanish launguage.  Drug traffic?

That's what I hear.  You can almost recognise, but nothing you do will quite tune it in.  I don't think it is digital.

I remember the old AT&T ship to shore radiotelephones you could monitor in the 2-3 mHz range during the 60's.  It didn't exactly sound like what I'm hearing now, but it was somehow scrambled so you couldn't tune it in.

Not a clue, however my post was an example to what he is hearing, as I've heard the same.  What brand has no bearing on the question.  Could have been any sort of digi voice modem.

So what's the point?

It is digital...  I use an SDR-1000 for a secondary rx, and I can set it to 92khz bandwidth on spectrum mode and it makes no difference.  These signals on my spectrum scope are no wider than a normal SSB emission, about 2.6 khz.  This is not the same as WZ5Q at all.  He is operating real SSB with high fi audio.

I wonder if its AF inversion transmitted using slopbucket.

To compare what you heard, try these frequencies listed here:
http://www.hamradio-dv.org/aor/digital-ssb/digi-call-freq/digi-call-freq.htm

For more info on digital voice, try this:
http://www.hamradio-dv.org/

Wouldn't that just make it appear as the opposite sideband?

Yes Don you're right.  The old inverted speech technique fed in to a SSB transmitter is copied well by listening on the opposite sideband mode that it was transmitted on.

Hello Brian,

KYV's and KLR's description would tend to indicate that the signal is not a digital stream.   Posting nothing but a url to a vendors website for a product that does only one of many forms of digital encoding would tend to indicate that you have heard it and are very sure what it was and may even own one since it would be impossible for a human to discern the encoding method in one of these streams (36 carriers, DQPSK) .  I guess you're saying you don't know what it was that Don heard.
Anyways, to answer your other question, the bandwidth of the AOR system is fairly limited (300 Hz - 2500 Hz) ... a quick web search will yield the details of the system and some sample audo clips that are not particularly impressive..

Sam

the inverted sideband meth was used by Moto...   yes, a product detector was used in the system...       klc

That's a good question.  Years ago my local PD used to use freq inversion before adopting digital to disguise their audio on an FM VHF freq.  I'm just wondering if or some variation of the technique is used.  Wasn't aware that might occur with SSB.

I came across this a few times here....

What I finally determined, is that is was the product of two very strong stations mixing....

The signal I was hearing, and trying to tune in, was on 3.951 (ish)
Once in a while, seemed to be clear....mostly garbled......

After tuning around the band some more, giving up on trying to tune it in....
I came across a strapping signal on 3.885 AM   (W2PFY)....
Then, lower in the band at 3.820 a very strong SSB station....


Hmmmm the difference in frequency between the two  was  65 khz....

well, 3951 (+,-) is 66khz higher than PFY's  signal.............

So, I wonder, is it possible I was hearing a product of the two signals?

Very possible Bruce.  If this was the case, what you are describing is called 3rd order intermodulation distortion (IMD).  The signal at 3951 was one of the 3rd order IMD products.  There would have been another one at 3820 - 65 or 3755 kHz.  This was probably formed in your receiver unless the 2 transmitter sites were very close together.  In that case the distortion originates in one of the transmitters.  This occurs often with commercial and broadcast transmitters.

I'm curious to know what was the receiver in use at the time?

- - - - -

There is no reason to put the simple inverted speech (0 - 3500 Hz becomes 3500 - 0 Hz.) on SSB, easily copied on the receive end.   If the signal were the simple inverted speech we should have been able to copy it.  It was easy to tell that someone was talking though.   But perhaps what we have heard is inverted speech, a more complex technique, broken up into multiple bands, instead of just one band.  Perhaps even with dynamic re-assignment.

'Twas a Kenwoody   ts-450s  Rb.

With an 8.83mhz 1st IF , and 455khz 2nd....

I stand corrected.  That stuff IS phase inverted SSB.  I decoded one easily on my Flex rx on LSB by sliding the entire passband to the upper side of center.  You could also do it in USB and slide the passband to the lower side of center.  The stations I heard seemed to be speaking French, however by the time I figured out what this was, it was getting daylight and most of the stations were gone.