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 Post subject: A few questions
PostPosted: Wed Mar 24, 2010 1:03 am 

Joined: Wed Mar 24, 2010 12:45 am
Posts: 35
Hi, firstly I just want to say that StereoTool is an awesome program! We run a local radio station here in NZ and are trialling it

I have some questions though:

1) If we use MPX out on StereoTool, what would be the line out pins to use from the soundcard?

2) We are looking at an ATV transmitter and receiver for transmission of our audio stream instead of "fm transmitter -> fm receiver -> fm transmitter", to minimize the problems we have with our current system (1st transmitter needs some maintenance), we will use the video feed with AD - DA converters to gain full power of the ATV equipment, we won't be using stereo with it, but if we did would the translation here be affecting the stereo pilot signal in any bad way?

3) I have read and asked people about this, they say that broadcasting in stereo requires more transmitter power and lose transmission range. Is this just for stereo mode only? does it affect the mono portion of the signal as well?

Thanks
Russell


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 Post subject: Re: A few questions
PostPosted: Wed Mar 24, 2010 1:44 am 
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Joined: Tue Mar 17, 2009 2:56 pm
Posts: 4151
Hi Russel,

1) MPX Out will be your Left or Right LineOut from soundcard. You need really good soundcard with possibility of 192kHz samplerate. You can read in other forum sections that the best choice is ESI Juli@ and Marian Trace Alpha.

2) if i understand you correctly, you are asking is it possible to send mpx thru your system. Yes, But...
Sending MPX signal is always been hard task, always is recommended to use cable to connect MPX output to Transmitter's MPX input to get best possible quality.

3) RF Signal is transmitted same no metter is it stereo or mono, but for ordinary listener mono transmitted signal will be better then stereo at same transmitter power because more noise is audible generated by lower received signal on receiver.


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 Post subject: Re: A few questions
PostPosted: Wed Mar 24, 2010 10:20 am 

Joined: Wed Mar 24, 2010 12:45 am
Posts: 35
Hi Bojcha, thanks for the response

1) Can I use a converter plug (3.5mm mono to mono RCA) for this? presumably so
2) Thats a shame, our main transmitter is located ~150 meters up the road, guess we can always try it out :S
3) So does that mean the the mono signal will still have the same distance whether the transmitter is in mono or stereo mode?

Thanks Russell


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 Post subject: Re: A few questions
PostPosted: Sat Mar 27, 2010 1:32 am 
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Joined: Mon Mar 17, 2008 1:40 am
Posts: 11185
Welcome Russell,

1. Use either the left or right channel, or both if the volume for a single channel is too low or you're getting distortion. (If you broadcast a test signal on just one channel, distortion will show as crackle on loud sounds on the other channel).

2. I don't know anything about the device you're using and its capabilities. Basically, you'll need something that can transport frequencies up to 53 kHz (stereo, no RDS) or 60 kHz (with RDS). If possible with as little change (phase shifts, high frequency rolloff) as possible - although (to some extent) phase and frequency response differences can be fixed using Stereo Tool's "FM Calibration" settings.

If possible, an easier solution might be to transport the stereo signal to your transmitter and run Stereo Tool there. That avoids frequency response and phase shift problems. You could even choose to perform the compression on one end (to avoid amplifying noise if you have a noisy connection), and run a limiter (and possibly noise gate) and create the MPX signal at the transmitter.

3. The signal itself is not stronger or weaker. But listeners will be likely to get a stereo hiss, which is of course not present in the mono signal. If the receiver switches to mono, that hiss should be gone. Also, the FM pilot (which is by default at 9% of the maximum output volume) leaves 9% (about 1 dB) less room for the actual audio, so if the reception is bad there will be slightly more noise. The stereo signal itself also takes up some space, which is also lost in case of mono reception. Still, these effects should be relatively small - if the reception is so bad that this becomes an issue people probably won't listen to it anyway.


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 Post subject: Re: A few questions
PostPosted: Sun Mar 28, 2010 5:27 am 

Joined: Wed Mar 24, 2010 12:45 am
Posts: 35
Thanks guys.

Just another quick query, when setting the volume control on a mono transmitter for stereo signals, do you turn it up just enough so the stereo light comes on a receiver or just a little bit after that?


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 Post subject: Re: A few questions
PostPosted: Sun Mar 28, 2010 12:33 pm 
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Joined: Tue Mar 17, 2009 2:56 pm
Posts: 4151
no,
You need to send exact 75kHz (100%) of modulation, 6.75kHz of pilot (9%). If in ST Pilot is at 9%.
So, you need some equipment to measure what comes from transmitter.


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 Post subject: Re: A few questions
PostPosted: Sun Mar 28, 2010 11:14 pm 
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Joined: Mon Mar 17, 2008 1:40 am
Posts: 11185
True. The FM pilot tone if - for today's radio's - extremely loud (remember that FM stereo technology was invented in the 1960's!). Most radios will start receiving a stereo signal even at 1/4th of the signal strength. But if you're broadcasting at that level the output volume will be very very low.

A small warning: If you're configuring the broadcast volume, make sure that you don't broadcast too loud (or reduce the transmitter power). Because if you're broadcasting (far) too loud, you might cause disturbances on stations on neighboring frequencies.

Why:
- FM means Frequency Modulation. Basically the frequency changes based on the audio content.
- Say you're broadcasting at 101.2 MHz. Then the range you may use is actually 101.125-101.275 MHz. If you're broadcasting far too loud, you might use a much bigger range, and get into the range of another station at - say - 101.0 MHz (100.925-101.075 MHz).

How to avoid this:
1. Use a good measuring device, to determine the frequency range that you're actually using. Then keep increasing the frequency until it peaks at +/- 75 kHz. There is pretty cheap (around 150 euro) equipment available online that claims to be able to perform this measurement. Or you might contact other stations in your neighborhood to ask how they

2. Alternatively, if you have a hardware limiter that can limit the MPX signal, you might want to use that (in your situation, if you're transmitting the signal through several transmitters which all may cause changes to the signal, this might be a good idea anyway).


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 Post subject: Re: A few questions
PostPosted: Thu Apr 08, 2010 3:50 am 

Joined: Wed Mar 24, 2010 12:45 am
Posts: 35
Hi all, sorry about the late reply

Hans, so if I had a limited mpx signal going into the transmitter, does that make the deviation (volume) control on the transmitter redundant? if so thats good news.

I have a bad feeling I will need to get someone to have a look at this thing with an oscilloscope or deviation meter, neither of which I have or can build :P


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 Post subject: Re: A few questions
PostPosted: Thu Apr 08, 2010 10:53 am 
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Joined: Mon Mar 17, 2008 1:40 am
Posts: 11185
Quote:
Hi all, sorry about the late reply

Hans, so if I had a limited mpx signal going into the transmitter, does that make the deviation (volume) control on the transmitter redundant? if so thats good news.

I have a bad feeling I will need to get someone to have a look at this thing with an oscilloscope or deviation meter, neither of which I have or can build :P
Actually, from your question I'm guessing that your transmitter already has some sort of limiter on board (deviation control? Is that where you can set a maximum deviation of 75 kHz?).

Maybe someone here who knows more about transmitter hardware could shine a light on this...


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 Post subject: Re: A few questions
PostPosted: Tue Jun 01, 2010 1:46 am 

Joined: Wed Mar 24, 2010 12:45 am
Posts: 35
Hi, another late response, been busy @_@

Nice to see a new stereotool version btw, with a gated 3band agc even! Now we won't have to use our (what appears to be) singleband ungated AGC hardware unit (symetrix 422)

We have received the microwave dishes (no, not the food kind :P) for our station, not the TX/RX units yet, those do have analog input/outputs from what I can tell (video RCA, Audio L/R RCA), methinks we might be able to use the video port for the MPX signal, so we'll try

A while ago, we bought a very good "DXable" radio which has tuning steps of 10khz, we are fairly close to 75khz +/- (volume is almost inaudible after 80khz +/-, we are also assuming this method works), its the closest we can get without buying this, but we should get one later on anyway :)

Anyway, tata


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