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PostPosted: Sun Jul 24, 2016 1:08 am 

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

I have a challenging problem where we have 2x FM transmission sites in different locations, broadcasting the same program on the same frequency (ie: synchronous).

The audio is shipped from location A to location B via STL and that all works fine, the audio does not appear to have any noticeable delay - ie: I can turn off location B and still hear signal from location A, albeit weak, but when I turn back on the FM transmitter at location B the audio matches. The STL receive at location B audio also matches with off-air signal from location A, so I am convinced there is very little delay, certainly none that I can notice.

The challenge is, when travelling between location A and location B, the overlapping signal is just awful, ranging from mono to patchy garbage, sometimes complete cancellation, before returning to normal once location B's signal is stronger and can dominate over the signal of location A.

My question here is, can I fine-tune StereoTool to reduce the challenge of overlapping signal for listeners when they are travelling between the transmitters ?

Yes I am aware of SFN but I am not sure how to use this feature in ST... ie: what timing is a sample equal to, etc ?

Many thanks

BeDazzler.


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PostPosted: Sun Jul 24, 2016 1:52 pm 

Joined: Tue Jan 26, 2016 11:34 pm
Posts: 54
Location: Jugoistočna Srbija
Yes, you can fine-tune the delay with the SFN feature. I think that 1 sample is 1/192 seconds when the sampling rate is 192 kHz. Can you send me a map showing the two FM transmitters and the STLs that feed them, and where are the problem areas located?
See the description in this video. It may be of some help: https://m.youtube.com/watch?v=-oL4REIGb4A


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PostPosted: Sun Jul 24, 2016 8:57 pm 
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Joined: Mon Mar 17, 2008 1:40 am
Posts: 9500
1/192000 second. Except for that, bigc is correct. You should be able to do this... assuming that both transmitters are fed from the same Stereo Tool instance.


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PostPosted: Mon Jul 25, 2016 12:48 pm 
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Joined: Tue Mar 17, 2009 2:56 pm
Posts: 3322
Even if you tune ST all well, it will still be problem. 2 RFs will always 'kill' each other.
There is ways with directional antennas to maximally avoid that but still, it will be bad at points where you have good signal from both.

_________________
control point


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PostPosted: Mon Jul 25, 2016 9:19 pm 
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Yes but you can control *where* they "kill" each other.


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PostPosted: Tue Jul 26, 2016 12:19 pm 

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

Thanks for the replies.

Yes to Hans - both sites will be fed from the same ST instance. I will send the remote site via 2nd MPX output with a delay until I get it right.

Yes to Bochja - I know it will never be perfect at the crossover point, however the remote antenna is directional (pointing away from the primary site) and we have plenty of output power at both sites so I can manipulate until the crossover location is between towns in a less built up area (ie: highway).

I will give this a try.

BeDazzler.


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PostPosted: Tue Jul 26, 2016 12:21 pm 

Joined: Tue Nov 03, 2015 2:28 pm
Posts: 12
Location: Dominican Republic
I think you need the same set-up in location A and B (The same transmitter and STL) and a SFN exciter with GPS Input.


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PostPosted: Tue Jul 26, 2016 2:29 pm 
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I think you need to delay the 1st site :)

O, and most people try to get the best possible sound *on* the highway because many people listen in their cars. But I suppose you know your listeners better than I do :)


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PostPosted: Wed Jul 27, 2016 11:17 am 

Joined: Thu Mar 19, 2015 12:24 am
Posts: 76
Thanks Hans, yes I will be delaying the primary site.

There is a small blackspot... about 2klms in length where the road goes between 2 large rocks and that is where I plan to move the crossover point to. Reception there is rubbish anyway for about a minute of travel so I will use that opportunity to sync up FM output.

Thanks again for your help.


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PostPosted: Sun Aug 14, 2016 12:56 am 

Joined: Thu Aug 06, 2015 4:01 am
Posts: 27
Location: Iraklion
https://www.youtube.com/watch?v=LoogJ84sANw

This is how the SFN would work in a scenario with two analog links feeding two transmitters. In the video I enable and disable the feature.

The video was made today and has far more better audio than its predecessor.

If you are going to try it, don't go randomly checking. Do your math and ensure that the closest transmitter to the problematic region gets its delay. Mind modulation indicies - volume must be exactly the same on both transmitters and check whether inverting is needed after setting the delay calculated. If you go random on it you won't get really far, but if done right it surely pays off.


Last edited by makrisj on Sun Aug 14, 2016 1:00 am, edited 1 time in total.

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