Yea, they have been simulcasting paging, including tone and voice here in this country for MANY years. UHS Oscillators and offsets of 1 to about 8Hz causes any nulling that will happen in overlap areas to "move" around in the overlap area. It is very important that ALL audio be as perfectly in phase as possible we used to use Allen Aviation (I think) delay lines. the problem is if you have multiple receivers. Then you have to thoes togeather with delay lines going to a single site for re distribution. Good luck! AC0Y
--- In [email protected], "Al Wolfe" <[EMAIL PROTECTED]> wrote: > Back in the 1970's several of the European broadcasters experimented > with simulcasting with multiple transmitters on the same frequency. It seems > to me that they settled on 50 htz for an offset (carrier frequency > difference) between adjacent transmitters. This is low enough to not be a > problem with PL tones and high enough to mask the beat note issue in the > overlapping "mush" zones. Not sure how they maintained their frequency > stabiliy back then. > > Al, K9SI > > > > Date: Wed, 04 May 2005 08:53:07 -0400 > > From: Kevin Custer <[EMAIL PROTECTED]> > > Subject: Re: voting receivers with simulcast transmitters > > > > Joe, > > > > Did you mean "offset" when you said stability? I'd agree that 1/2, to a > > few Hertz would be annoying. In testing here, and as shown in practice, > > simple systems sound better if run at about 10 - 20 Hz offset. This > > makes the beating more tolerable without being able to be reproduced > > (very well) by the listening speaker. This is also why it is nice to > > have high pass filtering in the listening receivers. Radios with PL > > filters do nicely, something like the Com-Spec TS-64's PL filter works > > well. Unfortunately, many made for ham rigs don't have adequate (if > > any) high-pass filtering even if the radio has PL decode. Simulcast > > Systems are one area that benefit from Total HPF of a PL filter, where > > Notch Filtering would do no good for the Simulcast beats in the very low > > frequency range; <60 Hz. > > > > Of course, at 10 Hz offset, a few Hz. of instability at each transmitter > > could result in something very annoying; as the two drifting > > transmitters could come within a few Hz. of one another or worse yet, > > zero beat. > > > > I remember one particular instance many years ago where we did testing > > of two transmitters that were close together and run at 67 Hz offset. > > You could decode this PL tone when you heard both transmitter sites, but > > they didn't have HSO's and drifted enough that PL decoding was not > > reliable. > > > > Kevin Custer > > > > mch wrote: > > > >>To work well, you will need more than 'a few Hz' stability. Even 1/2 Hz > >>is very noticable and annoying. > >> > >>Joe M. > >> > >>Thomas Oliver wrote: > >> > >> > >>>You will need the three transmitters to have uhso (high stab oscilators) > >>>to > >>>keep them within a few hz of each other, you will have to delay the audio > >>>so all three transmitters transmit the audio at the same time. I do not > >>>know what effect the multipath from buildings will have on the recieved > >>>signal. I think it is worth a shot. > >>> > >>>tom n8ies > >>> > > Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
