> The original application was a
tone and voice paging
> system. You'd have to know what this delay line was
> orignally spec for.
I have two different models. I found the datasheets for both and they were
spec'ed for something like 300-2800 Hz frequency response at something like
+/- 3 dB. There were no specs for distortion or group delay/phase
distortion.
> Nice, but one must start with the initial
> system preformance and align it right. Most
> people don't know how to properly align
> simulcast systems.
I know the prerequisites for both RF and audio performance, including the
potential benefits of staggered frequency offsets, optimization for the
worst overlap area(s) versus simple geographic distance/time delay,
maintaining consistant frequency response and proper AF bandwidth limiting,
minimizing receiver IF distortion/group delay, etc. I'm not saying what I
have on the air right now, without audio delay, is correct...I was just
saying that the transmitters are still on the air GPS-locked, the packages
are all built identically (with well-tuned IF's on the link receivers
listening to the same outbound source transmitter, transmitter AF mods,
etc.) but I haven't dealt with the audio delay issues yet.
> Probably sounds rough in areas with overlap.
It's not great, but it's not terrible. Fortunately the sites are within a
few miles' difference in distance from the origination point so the delay
error is only a few tens of ms. It sounds a bit "watery" in the worst
overlap areas where both signals are relatively weak and compete with each
other by probably only a few dB. In areas where there is a bigger delta in
signal strengths the effect is obviously much less noticible due to capture.
Still sounds better than Nextel anyway :-)
> S-Comm makes a killer digital delay board that's
> really cheap (cost wise) with excellent
> preformance.
The resolution in the delay settings is way too coarse though. The old BBD
devices theoretically could provide the resolution needed, but they have
inherent drawbacks on their own, let alone the time delay stability issues.
Better digital delays are available from Simulcast Solutions and others.
> You could not tell it was a simulcast system,
> other than it was loud in all places and
> sounded great.
Sounds like it worked better than many of the systems that have been
installed within the last few years on 800 MHz around here...
> Then something was not done right. Every one of
> them should sound good, else its back to the
> drawing board.
I think the intentional frequency offets that were done to improve digital
paging worked against them when sending voice pages. What is best for FEC
and minimizing inter-symbol interference for simulcast digital paging isn't
necessarily the most pleasant-sounding when sending voice pages...it may
have been a tradeoff.
--- Jeff
--------------------------------------------
Jeff DePolo WN3A - [EMAIL PROTECTED]
Broadcast and Communications Consultant
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