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PostPosted: Sun Aug 14, 2016 1:00 am 
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Cool! Have you checked how much difference it makes if you change the synchronization by 1, 2, 3 samples? I'm curious how precise it needs to be, and also if sub-sample precision would be needed.


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PostPosted: Sun Aug 14, 2016 1:06 am 

Joined: Thu Aug 06, 2015 4:01 am
Posts: 27
Location: Iraklion
It's rather coarse. I don't think it will make such a difference. It will work at 33-34-35 samples with best audio at 34.

I don't think you need to bother using subsample precision, if you oversample 3x and it is piece of cake you may try it but I think people are already in enough trouble trying to make this work.

Proper adjustments would require a USB-SDR which I failed to carry today on the test spot :(

Then, I could play a Bessel and try to clear the null, or check a sine on 57 KHz for clarity. I have to admit that my exciters are POS in terms of frequency stability. Having DDS with GPS reference would be a breeze.


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PostPosted: Sun Aug 14, 2016 1:23 am 

Joined: Thu Aug 06, 2015 4:01 am
Posts: 27
Location: Iraklion
And a final (tip? thought? warning?) on the subject. If the target area is extremely hot on long-distance (reflected over 3 km away) multipath anyway, don't expect miracles. Surely SFN, SSB Stereo and the multipath clipper could push you quite a bit forward, but no, it won't get you CD-quality audio.
The target is to stop your audience from reaching the "change station" buttons of their car. If you can avoid that without investing $$$$$, then you should be extremely happy with Stereo tool's SFN, as I already am.

the RS on video is http://www.radio972.gr


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PostPosted: Tue Nov 22, 2016 8:16 am 

Joined: Thu Mar 19, 2015 12:24 am
Posts: 76
Hi All,

Just checking in on this thread and to post an update on our Synchronous transmission project.

We finally got all the gear in place and StereoTool running on the primary playout node which also pushes program via STL to our remote site.

That's all working fine and I have separated the MPX outputs for the primary site and the remote site.

Today we split the MPX outputs into primary and secondary sites (secondary via STL).

I spent about 4 hours at the crossover point (approx 8klms from the remote site) trying to configure delay and samples in the SFN configuration area. After trying multiple configurations in both settings, I was not able to obtain a decent listening experience. It sounded awful, mono and choppy, signals cancelling out each other, regardless of what I tried.

I noticed the "invert" button which I clicked and it immediately made a big difference at the remote end - the audio was very good, much clearer and something I could further fine tune.

I was not sure how this setting affected the primary site, so I didn't leave it enabled, however after travelling back to the primary site reception area I enabled it and I could hear no difference on-air.

After reading through the doco, I could not find anything that talked specifically about the invert function.

My question is... what does the invert button do ?

I assume it reverses the primary site to become the site NOT relayed (ie: the remote site becomes delayed).

Can someone clarify so I can take another look tomorrow.

BTW running 8.12, very good in terms of CPU usage and quality for TruBass - much clearer than previous and it sounds very tidy on-air.

Many thanks


BeDazzler.


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PostPosted: Tue Nov 22, 2016 11:25 am 
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Invert means that we invert the waveform, thus shifting the phase by 180 degrees. Basically similar to swapping the cables. The way things are currently hooked up in your system, one of the transmitters is running in anti-phase.


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PostPosted: Tue Nov 22, 2016 7:05 pm 

Joined: Thu Mar 19, 2015 12:24 am
Posts: 76
Hi Hans,

Thanks for that.

The feed from our primary site is composite (MPX).

It's interesting that inverting the audio makes such a big difference.

Today I will head back to the area and have another try at getting it to work.

Should I use the extra delay feature or just the sampling feature ?

I have been using both in testing yesterday.

Many thanks

BeDazzler.


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PostPosted: Tue Nov 22, 2016 9:32 pm 
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What do you mean by sampling feature?


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PostPosted: Tue Nov 22, 2016 10:08 pm 

Joined: Thu Mar 19, 2015 12:24 am
Posts: 76
Hi Hans,

In the SFN configuration under delay the feature is "samples".

I assume this controls the number of samples behind the delayed MPX output has.

Which do I use ?? Do I use both or is it a matter of testing and finding the right combination ?


BeDazzler.


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PostPosted: Wed Nov 23, 2016 7:51 pm 

Joined: Thu Mar 19, 2015 12:24 am
Posts: 76
Hi There,

Just a quick update on this as I have received a few messages asking how it all went.

We got 8.12 with SFN working across our primary and secondary sites yesterday.

It did take some patience, driving around and adjustment of both the extra delay and sampling features in SFN.

I marked the cross-over point by driving to the location where reception was at it's worst, then adjusted ST via remote control until the signal was clearer. This involved using the invert function along with setting extra delay to 0.055s, then adjusting the samples to around 12 or 13.

Just as Bojcha says in an earlier message, it's no perfect, but compared to what we had before it is pretty good. I can now drive from primary transmission site all the way to the secondary site listening to the same frequency. It still has 1 area of challenging reception, but it's better than signals stomping all over each other in 10 different places, so it works well.

Unfortunately we now have an issue where there is a clicking noise audible on-air (FM only) so I have raised a separate thread in bugs after reading about this issue in a previous release.

Otherwise, very good and a big difference on-air.

BeDazzler.


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PostPosted: Wed Jan 04, 2017 4:11 pm 

Joined: Sat Nov 20, 2010 6:27 pm
Posts: 7
Hello,

A perfect overlap with 2 transmitters on the same frequency is only possible if the two PLL circuits are locked to each other. This is impossible to do over a distance - however what could be done is to sync both transmitters to the same master clock. This is something i want to do in the near future, and as a spoiler, it will probably involve a third transmitter operating on one of the shortwave amateur bands.


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