SSTV via Skype, VoIP or similar?

Forum for discussion of SSTV topics. Slow Scan television (SSTV) is a picture transmission method used mainly by amateur radio operators, to transmit and receive static pictures via radio in monochrome or colour.

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SSTV via Skype, VoIP or similar?

Postby Steve Anderson » Sat Jun 26, 2021 8:24 pm

Without an Amateur Radio license here I cannot transmit, and I believe SSTV isn't allowed here anyway...uncertain on that.

So after a call to the UK via Skype I thought it might be worth a try...why not? Or any other method that would allow SSTV signals (VoIP?), suggestions welcome. However, compression/companding may corrupt the signal. I know it's not the same as 'proper radio', but what else choice is there?

The obvious way is to simply e-mail .wav files, but it's not 'live' and can sit quite happily in your in-box until the next time you check it. In fact, within limits this forum could be used in the same manner...

I use Skype a lot to call the UK but even so I never use anywhere near the time I'm allowed each month...nearly seven hours...I might use just one hour each month...

I'd been interested in sending someone a SSTV signal where they record it then send it back to me via a telephone circuit. No cost to them with the six hours or so per month I have available...it's cheap enough to 'top-up' the hours if more are needed...

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Re: SSTV via Skype, VoIP or similar?

Postby Dave Moll » Sun Jun 27, 2021 5:40 pm

Does the recipient also need a Skype account?
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Re: SSTV via Skype, VoIP or similar?

Postby Steve Anderson » Sun Jun 27, 2021 7:04 pm

Dave Moll wrote:Does the recipient also need a Skype account?

No if using Skype-to-Phone, and just like ordinary phone calls there's no charge for the recipient. Skype-to-Phone is where I use my laptop at this end, the signals travel over the 'net, then locally to the recipient it's changed into a good old analogue phone call.

Skype-ing between two PCs is totally free (even internationally) with no usage limitations. Conferencing calls work too. Many work-related conference calls are conducted via Skype with sometimes a dozen participants. There is also a video version, also free if PC-to-PC.

If contemplating using Skype check their site first, the arrangement I have has been in place for 5-6 years now, things may have changed.

https://www.skype.com

Note: With Skype-to-Phone you have to specify the country you wish to call, in my case it's just the UK, any UK number including mobiles. Others countries can be added but of course fees increase...

My Skype-to-Phone arrangement is UK-only, 6.6 hours/month (400 minutes) for GBP5.00/month, a fiver. A normal international call Thailand-UK will cost that for around 15 minutes. If you don't use all the Skype time up, bad luck, you lose it.

I have no idea what happens if you try and go over your time limit, I've never got anywhere near it.

P.S. Don't forget time-zone differences, people tend to get upset if woken up at 3AM by a phone call!

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Re: SSTV via Skype, VoIP or similar?

Postby Klaas Robers » Sun Jun 27, 2021 8:11 pm

In the past I did some experiments with NBTV signals, to store them as an MP3-file. This did not work good enough. MP3 is developped to store human speech and music in a way that we do'nt HEAR the distortion. But the introduced distortion was very well visible in the analogue video.

I never did experiments with the SSTV frequency modulated subcarrier. As well I don't know how the vocoder of skype behaves with such a signal. I can imagine that the fast changes in frequency cannot be encoded and/or reproduced. The only way to experience it, is to do it.
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Re: SSTV via Skype, VoIP or similar?

Postby Steve Anderson » Mon Jun 28, 2021 11:41 am

Klaas Robers wrote:...The only way to experience it, is to do it.

Yes, true. As I mentioned above there's two ways to do it, PC-to-PC (easy and free), or PC-to phone. PC-to phone will require a telephone hybrid/balance unit of some description. Not impossible to build yourself but will have no approval if you want to interface other equipment to a physical phone line, so not recommended.

Skype PC-to-PC just uses the 'net and goes nowhere near a 'proper' phone line.

I recall your experiment with MP3 and NBTV, the result doesn't surprise me. However NBTV is usually two signals, video and audio, so with the crosstalk and compression it's what I would have expected. SSTV is usually one signal, how that would fare with MP3 compression I don't know.

Steve A.

There may be other providers of a similar service to Skype, but I don't know of any...
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Re: SSTV via Skype, VoIP or similar?

Postby Lowtone » Mon Jun 28, 2021 2:09 pm

Just use skype video ? :wink:
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Re: SSTV via Skype, VoIP or similar?

Postby Lowtone » Mon Jun 28, 2021 2:10 pm

I experimented NBTV on skype about ten years ago, it works, but the signal is degraded.
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Re: SSTV via Skype, VoIP or similar?

Postby Steve Anderson » Mon Jun 28, 2021 4:18 pm

Lowtone wrote:I experimented NBTV on skype about ten years ago, it works, but the signal is degraded.

Well, perhaps the Skype PC-to-PC audio only version is configured to emulate/replace a phone system, i.e. 300-3,000Hz or thereabouts. In my experience using Skype in that mode over the past few years it's generally better sounding than that, but not what I would call 'Hi-Fi'. As a very rough guess 'maybe' 150-5,000Hz, but still not good enough for baseband NBTV...particularly at the LF end.

However my guess is that in the majority of cases it's probably adequate for SSTV. As Klaas mentioned, there's only one way to find out...it depends on what processing the signal goes through en-route.

Skype does allow you to record phone calls, though I've never tried it myself, next time I use it I'll give it a try...

Steve A.

How to Record a Call in Skype
During your Skype to Skype call, select...(or a big '+' sign) for more options.
To record your call: On desktop: Click Start recording. ...
A banner will appear in your call letting everyone know you've started recording.
After the call, the recording will be posted to your chat and will be available for 30 days.


...after that copy and save somewhere (if possible) - investigation required as to the format/speed/etc. that is used...

It seems to be saved as an MP3 file, which you can copy from your 'Downloads' folder...it's only for connected devices, PC/cellphone, not for Skype-to-(Landline) Phone...I guess because the recipient on an ordinary landline phone has no way of knowing they're being recorded...however most of us here will be able to think of a way to get around that...no specifics please...yes, it's easy, but keep it to yourself...
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Re: SSTV via Skype, VoIP or similar?

Postby Dave Moll » Mon Jun 28, 2021 6:28 pm

If using Skype-to-phone (which is pretty much the only way I used Skype back in the days when I had an account many years ago and practically no one else did) one is going to be limited by the the bandwidth of the telephone network. As has already been said, this is very limited. I don't know whether this is further downgraded by going international.

The other difficulty I envisage is that to conduct the exercise described, there is the need to be able both to record the signal sent from Skype and to play it back. Whereas I have an answering machine that can perform the first part, I don't know how I could achieve the second - I can't play back a previously-recorded message during a call. The only way I can envisage is to hold the handset of a second 'phone to the speaker of the answering machine, and this would introduce even more distortion.

If there is another UK member who has more sophisticated recording/playback facilities associated with their telephone line, it may be better for them to give it a try.
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Re: SSTV via Skype, VoIP or similar?

Postby Steve Anderson » Mon Jun 28, 2021 7:38 pm

Granted, this would require a sort of phone or internet/PC interface, something I'll consider for a while, but I don't see being complex. Audio in (your microphone), audio out (your headset/speakers). Tap into those circuits at appropriate levels and you should be in business. A facility to mute your mic being useful too...most/all? PCs have mic/headphone I/O...should be quite easy...all you have to do is figure out the TRS/TRRS/TRRRS configuration of the headset I/O jack/connector. In my case the mic and headset are separate 3.5m jacks, but many now are just on one 3.5mm connector...this could well be the biggest headache of the whole exercise...including the reliability of these crappy arrangements...

One TRRS connector being, mic, left earpiece, right earpiece and ground. Not always in that order...a typical consumer mess...

Steve A.

However, if you have an external audio USB I/O device, e.g. my behringer UF0202 device there's no confusion, line in left, line in right, line out left, line out right. Done deal...all on standard RCA/phono connectors, i.e. four of them...I'll lash something up the next time I talk to the UK...however it is primarily designed as an analogue I/O device to record your vinyl collection to digital, and playback...but it should work as I'm thinking...
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Re: SSTV via Skype, VoIP or similar?

Postby Klaas Robers » Wed Jun 30, 2021 6:54 pm

I guess that SSTV over skype and SSTV via MP3 is not that bad. In amateur radio SSTV is done on SSB through IF-crystal filters, two of them, one in the transmitter, the other in the receiver. With strong signals this gave an almost perfect picture.

And about the telephone: in about 1980 I modified a land line telephone such that it featured a DIN connector, compatible to my cassette recorder. I could record the incoming/outgoing call an I could play back a recorded sound as part of a telephone call. Now with smart phones this is less easy. That is called "progress in technology". But if there is a connector for earpieces it should not be too difficult.

Nowadays the land line of my telephone goes not further than my glass fibre modem. There everything is digitized and I don't know if that is better than skype......
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Re: SSTV via Skype, VoIP or similar?

Postby Steve Anderson » Thu Jul 01, 2021 12:49 pm

Klaas Robers wrote:Now with smart phones this is less easy. But if there is a connector for earpieces it should not be too difficult.

That is an option I hadn't thought of. Chop off the ear-buds and microphone bits and wire up as required. I wasn't thinking of using a mobile phone, but it's worth looking into.

Klaas Robers wrote:Nowadays the land line of my telephone goes not further than my glass fibre modem.

Likewise here, all the TV, radio, Internet and up to two 'landline' phone lines all come down one fibre. A single point of failure, but after a few years no problems so far. We used have three copper phone numbers here, (business, fax/ADSL Internet, and private/unlisted) but they were all turned off a few years ago. Our mobiles have replaced them, and no-one uses faxes anymore... when was the last time someone said, "I'll send you a fax"? I haven't heard that said in two decades, maybe more...though a lot of printers still have the ability to send/receive faxes...both my A4 and A3 printers do, though the A1 plotter doesn't...which is probably a good thing!

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