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Author Topic: SSTV basics  (Read 8692 times)
K3MQ
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« on: July 14, 2013, 05:46:21 PM »

Today I tried playing around with SSTV with not so great results. Using Multipsk I found tons of good signals on 14.230, but every decoded photo was super grainy. Most were unreadable. I don't understand the poor quality since I had pretty good signal strength. I wasn't expecting National Geographic quality photos, but these were VERY disappointing.

Then I tried downloading and running EasyPal. I could not get this program to display any photo ... excellent signal strength but no decode on 14.230. It would not sync regardless on what I did. I don't understand why Multipsk decodes and EasyPal doesn't. Are there different SSTV formats?
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KD8DVR
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« Reply #1 on: July 14, 2013, 06:02:21 PM »

Easypal and the other program are incompatible.  Easypal is digital sstv.

Get MMSSTV.  This is the best SSTV program out there.  Read and follow the instructions, especially about slant calibration.  The use of "auto slant" is a no-no because it corrects poor pictures that are received, and does nothing to correct a cruddy transmit signal.

Pictures received may not be as sharp as desired.  This is the nature of the HF band.

73
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KB4QAA
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« Reply #2 on: July 14, 2013, 06:49:02 PM »

"Pretty good signal strength".

Signal strength is everything when dealing with video. Even small drops in signal strength result in quite apparent loss of video quality.

 Our eyes are far more sensitive to signal loss than our ears.  While our brains can fill in missing sounds it cannot do the same with video. 
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K7RBW
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« Reply #3 on: July 15, 2013, 07:14:10 AM »

I've experimented with SSTV on 440 MHz FM and gotten grainy pictures (with a strong, full-quieting signal), so I can understand the disappointment. It's not just a function of HF. As others have said, a clean signal is everything for SSTV. That means a clean RF signal to the radio and a clean audio signal through the computer. I had to tweak levels and impedances in the audio lines before I could get a clean picture. But even then, remember it's still very low res (360x240?) so any disturbed pixel will have a big impact on the overall image quality.
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NM3G
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« Reply #4 on: July 15, 2013, 01:20:58 PM »

Easypal frequencies:

Evenings 3713 kHz, 3813 kHz

Daytime 7173 kHz, 14233 kHz

With EasyPal, be sure to watch the signal level (upper left side of the screen, green bar) and ensure your audio level only drives the green bar to roughly 15-30 percent ... if you drive it higher, it will start distorting (SNR starts to drop), and you will drop segments.

If you can't find any activity, drop me a note and we'll work out a schedule.

73
Rick
NM3G
e-mail good on e-ham and qrz



Then I tried downloading and running EasyPal. I could not get this program to display any photo ... excellent signal strength but no decode on 14.230. It would not sync regardless on what I did. I don't understand why Multipsk decodes and EasyPal doesn't. Are there different SSTV formats?
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G4IJE
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« Reply #5 on: July 15, 2013, 01:42:20 PM »

For "classic" analogue SSTV, MMSSTV is the software to use and 14.230 MHz is the frequency to use it on. Have a look at my SSTV "webcam" page here:

http://www.classicsstv.com/rxpics.htm

.. for examples of pictures received with a low antenna (OCF dipole) in a noisy urban environment. Conditions have not been good for me on 20 metres recently ...
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K3MQ
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« Reply #6 on: July 15, 2013, 01:44:54 PM »

Thanks for the info gentlemen.

I downloaded MMSSTV and have it receiving pretty well. I also put Easypal on 14.233 and got a few pixs - really NICE pix!

From what I read digital sstv is pretty touchy about signal dropouts, qrm, propagation, etc., plus high power apparently is recommended. It's also a little more complex to setup successfully.

So I decided to focus on MMSSTV for now. Spent the better part of the afternoon putting together a few pix and some templates so I think I'm ready to go. Transmissions on 14.230 have been almost non-stop today. Does anyone ever use 17 or 30 meters for SSTV? I'd prefer to try out my test xmits where I won't stink up the band if I screw up ...

One other thing - how much power do most ops run in this mode? I take it this is not qrp.

73
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K3MQ
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« Reply #7 on: July 15, 2013, 01:56:27 PM »

I may have answered my own question. I guess sstv is a wide band mode and not allowed on 30 & 10 meters. Nuts.
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K3MQ
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« Reply #8 on: July 15, 2013, 02:32:27 PM »

Success! 1st SSTV qso was with EA1IGB on 20 meters and all went well. Not even bleeding. Thanks to everyone!

73
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G4IJE
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« Reply #9 on: July 16, 2013, 12:19:07 AM »

Success! 1st SSTV qso was with EA1IGB on 20 meters and all went well. Not even bleeding. Thanks to everyone!

73

Congratulations!
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KD8DVR
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« Reply #10 on: July 16, 2013, 07:17:51 PM »

Thanks for the info gentlemen.



One other thing - how much power do most ops run in this mode? I take it this is not qrp.

73

The key (on any DATA) mode is never to allow ANY ALC movement.  On MMSSTV at that point you can run any amount of power you need, without having the needle move.  On modes like psk31, you never should exceed 25 watts.
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G4IJE
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« Reply #11 on: July 19, 2013, 04:13:59 AM »

Not too much QRP but not too many big amplifiers either. Most stations I hear around EU are running 100 watt transceivers at around 60 to 80 watts, just to keep the PA from over-heating. Some rigs handle 100% duty cycle better than others. Personally I wouldn't like running some of the more compact transceivers at 100 watts "key down" for a minute or more, at least not on a hot summer day. If you adjust your sound card audio level to give you slightly less than full output you will likely satisfy the ALC requirements and keep your tones sounding nice and clean.
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STAYVERTICAL
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« Reply #12 on: July 19, 2013, 10:47:16 PM »

SSTV is capable of giving good results, but you need a good signal to noise ration on receive.
That may equate to more signal, less noise or both.
It is analogue and so will decode with varying quality, no matter what.

Easypal is a strictly digital mode, which has error correction capability through users doing a BSR request.
Unfortunately, like all digital modes, unless you cross the threshold of signal to noise ratio, you will be left without a picture.
You may be able to get some portion of the picture by ticking the "Progressive" option under the file menu, and uncheck the RS box.
If you do not get the MSC light on easypal you are not going to get results.
To get the best DX results use a QAM of 4 on easypal with mode B for example.
Many people use the default QAM of 16 and this requires a much higher signal to noise ratio.
There is also a new version of Easypal out with a chat mode.

73
Rob
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