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Author Topic: 12786 FAX  (Read 1452 times)

Offline Josh

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Re: 12786 FAX
« Reply #15 on: August 18, 2018, 1930 UTC »
A few clean copies today from 12789.9;
https://nofile.io/f/VnCzRTvD2Wx/good.bmp

https://nofile.io/f/zJKP9ag2UEd/good+one+also.bmp

And then the tx just dropped out before the fax was finished;
https://nofile.io/f/aWbxGB5xdhz/dropout+at+1918Z+18AUG18.bmp

The first fax started out well then I noted it needed right justified so I used the decoder's phasing control and after saving the whole fax I noted that the fax was broken, possibly when I adjusted the phase of the image.



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Offline fpeconsultant

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Re: 12786 FAX
« Reply #16 on: August 18, 2018, 2048 UTC »
I can report faxes normal as follows:
New Orleans 2000z 12788khz
Boston 2015z 12748.1khz
Pt. Reyes 2030z 12784.1khz

Honolulu not heard at all on 16133.1khz 2030z.

All 8/18

FPE
Near Chicago, IL USA.  Drake R8, Ten-Tec RX340, JRC NRD545, Watkins Johnson HF-1000, Wellbrook loop at 28', 40m inverted vee.  Please QSL to fpeconsultant@aol.com thanks.

Offline Josh

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Re: 12786 FAX
« Reply #17 on: August 18, 2018, 2101 UTC »
I'm starting to think the decoder or the pc has timing issues, perhaps the decoder doesn't like hpet rather than rtc or similar.

Disabled hpet in bios and os and the issue remains, with multiple decoders.
I wonder if this is related to cpu multiplexing where the individual cpu cores are slowed or sped up according to load? Argh.
« Last Edit: August 18, 2018, 2134 UTC by Josh »
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Offline ChrisSmolinski

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Re: 12786 FAX
« Reply #18 on: August 19, 2018, 1230 UTC »
Decoding issues are typically due to sound card problems, either dropping sampled data (if you get skips/shifts in the fax image) or large sampling rate errors (lots of slant). CPU cores and other things like that aren't a factor. Once the sound has been digitized, nothing needs to be done real time.
Chris Smolinski
Westminster, MD
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Offline Josh

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Re: 12786 FAX
« Reply #19 on: August 19, 2018, 1932 UTC »
Disabled hpet and set system to prioritise foreground rather than background apps and still messed up faxes.

First whole copy of the day;
https://nofile.io/f/2OEhSVKzq9B/1.bmp
Looks fine.

Second faulted about in the middle of the fax as you can see, then the tx dropped completely;
https://nofile.io/f/DjwJxyVTZzB/2.bmp

Mebbe it's the tx site having issues.

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Offline Josh

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Re: 12786 FAX
« Reply #20 on: August 19, 2018, 1951 UTC »
Letting it run on NMF Boston 12750 as New Orleans is ota - the tx that had issues, so far perfect copy barring fade.
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Offline ChrisSmolinski

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Re: 12786 FAX
« Reply #21 on: August 20, 2018, 1354 UTC »
Disabled hpet and set system to prioritise foreground rather than background apps and still messed up faxes.

First whole copy of the day;
https://nofile.io/f/2OEhSVKzq9B/1.bmp
Looks fine.

Second faulted about in the middle of the fax as you can see, then the tx dropped completely;
https://nofile.io/f/DjwJxyVTZzB/2.bmp

Mebbe it's the tx site having issues.

I can't see the images. Maybe try imgur and put the image URL in tags in your message? It's really painless  :)
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 58 ft T2FD / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline Josh

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Re: 12786 FAX
« Reply #22 on: August 20, 2018, 1535 UTC »
But I have to make an acct to use imgur!
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Offline Josh

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Re: 12786 FAX
« Reply #23 on: August 25, 2018, 1945 UTC »
A fax battle! See if you can detect where the fm fax demodulator switched from one cochannel fax to the other in the included image!

https://nofile.io/f/rsKrBT02Ukc/fax+battle.bmp

The battle still rages, dunno if this is due to two separate tx sites being received, two feeds getting smeared together into one, or wtf is going on here.

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Offline Josh

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Re: 12786 FAX
« Reply #24 on: September 05, 2018, 1803 UTC »
Am trying some fax reception with the fractional output resampler locked in SDRuno. Perhaps this will reduce untoward happenstances. First fax was all over the place, after activating resampler lock it's been stable. Should also consider the tcxo takes some time to stabilise as each app controlling the sdr takes control of the sdr, I often switch between HDSDR and SDRuno and each has a different mechanism to handle correcting the master oscillator, both apps provide for automagically setting the reference oscillator to a known standard over the air, I try for the highest wwv signal I can get at the time.

Second fax progressing and it's aligned with the first one, this may be the solution but means fax may only be best received with SDRuno as HDSDR offers no resampler lock.
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Offline Josh

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Re: 12786 FAX
« Reply #25 on: September 06, 2018, 1843 UTC »
On the fractional reticulated sampler platter, don't bother.
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Offline Josh

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Re: 12786 FAX
« Reply #26 on: January 24, 2019, 2347 UTC »
Was trying to see if the haphazard fax reception that has happened to me and others bored enough to decode faxes was due to the sdr or to the pc or what, and used the Icom Pro2 to receive the fax, ruling out the sdr and/or usb connection as only audio was fed to the pc via a transformer isolated cable. I copied a few faxes, enough to feel confident that the sdr/usb connection may have been part of the synch issues, and became certain another aspect was revealed.

See this link for a pic of the results;
http://s000.tinyupload.com/index.php?file_id=32389565419432764128

In the image we see the results from K500 and WCODE both decoding the same input. In the middle of the K500 fax session you see where I changed mode from fm greyscale to fm black and white and much cleaner results are noted. The only time you want greyscale demod is when you are decoding  press fax with black and white pics, or decoding a satellite weather image. The main problem I was trying to resolve is displayed where the fm black and white takes over from the fm greyscale, K500 does not switch modes gracefully, and as you can see synch was lost and restarted elsewhere on the screen.

What this tells us is do not change anything while a desired fax is being decoded or you might cause the decoder to lose synch.

The very weak fax was copied on 17MHz band and was emitted from Pt Reyes California.
« Last Edit: January 24, 2019, 2350 UTC by Josh »
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