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Stereo/Mono question Max Pro III Can someone help pleeeese?

 
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Stereo/Mono question Max Pro III Can someone help pleeeese?
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rickv152
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Post Stereo/Mono question Max Pro III Can someone help pleeeese? Reply with quote
we recently acquired this transmitter w/SE4 DSP stereo generator (coder). at first there was no 19khz pilot detectable on any radio; we had to set audio inputlevel input on Max Pro to max to get stereo indication on receivers. However no audio is still being sent in stereo. For testing, we can sent only left or right audio to SE4, but all stereo receivers still receive audio on both channels.

We tried another stereo generator into Max Pro with same results; no stereo audio is decoded in any stereo receiver; almost like the ssb 38khz is not present; being filtered out.

Is there some setting/jumper on Max Pro that blocks the stereo? how can this happen? please give me a clue... Display on Max Pro does not give option of stereo/mono settings. thanks in advance. Richardo.
Mon Jul 04, 2005 9:42 pm View user's profile Send private message
pcs
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Post Reply with quote
Disable preemphasis in max pro I

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Mon Jul 04, 2005 10:11 pm View user's profile Send private message Visit poster's website
rickv152
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Post Reply with quote
on the Max pro:
1) physical jumper for pre-emphasis is not connected;
2) via display, pre-emphasis may have been set to 75 uS. Is this what you mean to disable? thanks in advance.
Ricardo
Mon Jul 04, 2005 10:19 pm View user's profile Send private message
rickv152
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Post It worked!! Reply with quote
setting pre-emphasis "off" from panel worked; now it's stereo with no pre-emphasis; so how to make it stereo and have 75 uS pre emphasis is my next question. regards,
Tue Jul 05, 2005 4:44 am View user's profile Send private message
Rio
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Post Re: It worked!! Reply with quote
rickv152 wrote:
so how to make it stereo and have 75 uS pre emphasis is my next question. regards,

As far as I know human ear can hear between 20 to 20.000 (20k) hertz, and pre-emphasis (PE) work by emphasizing higher frequency of that range (let say it would boost sounds which has freq. above 15 khz). It is necesarry in FM transmission to separate noise (which also has high frequency) with the real sound modulation which using high frequency for eg. hi octave song, screaming sound etc.
The problem came if care not taken when using PE with stereo encoders (SE).
Some SE use freq. 19 Khz as pilot tone which mean it use this freq. as signal to separate Left and Right sounds. Thus, if we activate PE right after output signal from SE (which called as Composite Signal) it will also emphasizing those pilot tone. And this situation will make the receiver a bit confuse to recognize it as pilot signal or a part of sound signal. By losing this pilot tone, then the receiver treat it as mono reception.

You can still using PE though by activate it on SE if your SE has this feature, or right before the signal came into the SE (in modulator, mixer, sound processor, compressor/limiter etc.)

Just my 2 cents, pls correct me if I'm wrong since I also newbies in LPFM fields, and I think my english is quite bad
Wed May 03, 2006 11:06 am View user's profile Send private message
cliffyk
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Post Reply with quote
Pre-emphasis is applied to the each audio channel independently, after the 15 kHz low-pass filtering, and prior to stereo encoding.

It is ususally (in our class of broadcasting) applied by the stereo encoder, in your case the SE4 will do this, and according to the manual (you did RTFM, didn't you?) it is configurable for either the 50 uS or 75 uS time constant), since you are in the US is was probably delivered at the 75 uS setting.

Pre-emphasis is used to boost higher audio frequencies prior to encoding (or transmission for monaural broadcasting) as stated by another poster.

Since higher frequencies are nearly always at lesser levels than low frequency content this can be accomplished without affecting deviation to any great extent, and it has the distinct benefit that when de-emphasis is applied at the receiver to reduce the high frequency content back to its original level any HF (audio) noise added during the transmission process is also reduced. The original Dolby noise reduction process worked exactly like this--Ray Dolby didn't really invent a thing...

The PE setting in the exciter is available should you be transmitting a mono signal directly input to the exciter. If you have PE switched in on the exciter and supply it with a stereo encoded signal then the exciter PE will boost the 19 kHz pilot to a very great extent, and the 23-53 kHz
L-R signal to stratospheric levels causing your RF signal to be grossly overmodulated--I am surprised you were able to receive anything other than a visit from the FCC.

-cliff-

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Wed May 03, 2006 12:53 pm View user's profile Send private message Visit poster's website
rickv152
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Post Reply with quote
I'm sorry; I was not even aware that this post was still here. let alone this BBS was back up and running consistently. I wish to say "THANK YOU" for everyone's helpful information.
As far as Pre-Emphasis (PE) and Stereo is concerned I am quite aware with how they work; used to teach their theory at university. My basic problem was configuring this transmitter to make it work with our external stereo generator of different quality compared to PCS.
We were able to bypass the SE board and run the stereo PE "mix" into the exciter directly.
We also were able to get the PCS150 power to 140-150 watts: barely!, by bringing the power supply's voltage to it's MAX, and tuning the PA. Getting 40% ERP from our antenna gave us only 60 watts out which was within FCC min ERP for Low Pwr.
One other problem IF ANYONE OUT THERE KNOWS HOW TO FIX THIS PROBLEM? is: any power setting above 90 watts output from this transmitter would LOCK up the display on the front and cause the transmitter's setting to oscillate till it was shut down and restarted at the new setting: display gave an error display. PCS has recommended placing additional caps on display board but won't tell us "Where" to put them on the display board.
However, this PCS 150 is not FCC certified, so we use it as backup only; now using a Nicom 250 watter to a single bay circular antenna which gives us close to 100 watts ERP. Low Power stations will be gone over with a fine toothed comb in the "near future" by the FCC and shut down if they do not comply with ALL rules respecting equipment.
One further note: a LPFM can run twice the 100 watts ERP legally using circular polarized antenna; i.e.- 100 watts vertical; 100 watts horiz = 200 watts from transmitter which makes for "REAL" improved coverage.
Email me and I can send link on this issue.
Over and out,
Thu May 04, 2006 3:35 pm View user's profile Send private message
cliffyk
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Post Reply with quote
Mea culpa as well, I hadn't paid any attention to the original posting date...

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Fri May 05, 2006 12:51 am View user's profile Send private message Visit poster's website
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