[BC] WLS dead cxr prob. this a.m. at ~6:50
Paul Christensen
pchristensen
Sat Jul 1 09:25:52 CDT 2006
> That's the beauty of the GSC3000. When the signal strength on the STL
> goes below a certain threshold, a macro is triggered to dial the back-up
> codec and then put it on the air automatically before the STL fades.
That's an indispensable technology to have in these instances as well as
microwave paths affected by rain fades (e.g., 23 GHz switching to 950 MHz or
telco backups). I suppose the only thing the GSC3000 could not protect
against is a total failure of the unit, and hence the loss of the BER-based
switching control. Mike, maybe you can clarify on that point. This type of
sampling and path switching may be best located external and independently
to the very equipment it's sampling for that reason.
Prior to the availability of a software solution or even BER detection, we
had to design the path-fade hysteresis algorithm by hardware. In once
instance, the only triggering source available was a DC voltage that
appeared on a 23 GHz gunnplexer. In a nutshell more or less, here's how the
scheme worked...
- Sample the gunnplexer at the antenna through series R and lightning
abatement;
- Route the sample down a spare conductor of the gunnplexer control cable;
- At the mod/demod equipment below, install a simple A/D converter based on
a 10-segment LED bar. The gunnplexer dynamic range was approx 0-10VDC and
produced 0 to 10 LED bars, depending on signal;
- Control switching sample at LED segments 3 and 9 (corresponds to
gunnplexer V of 3V and 9 V, respectively);
- When the path fades to 3 segments, circuit automatically switches to 950
MHz or telco;
- When the event is nearly complete, circuit automatically switches back to
main STL when 9 LED segments is achieved BUT must remain at 9 segments for a
continuous time of 2 to 5 minutes (this protects against rapid, ragged-edge
switching as the signal goes above and below a predetermined level).
So, to take this hardware mess and do it all with software based on what
really counts (BER), is a real salvation today.
Paul
====================================
Paul Christensen, CPBE, CBNT
LAW OFFICE OF PAUL B. CHRISTENSEN, P.A.
3749 Southern Hills, Jacksonville, Florida 32225
Office: (904) 379-7802 Facsimile: (904) 212-0050
pchristensen at ieee.org
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