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High Power Multistation FM VSWR Monitors

boiseengineer

boiseengineer

*What do you use on the output of the combiner to monitor the VSWR?
6 FM stations combined in the lower half of the band.
Around 48 kw in each half of a split-fed CBR antenna.

*Something that is still sold/available!
 
Last I knew, ERI could provide such a monitoring and protective system.

Also could Dielectric, but apparently now they are history for broadcast systems.
 
The problem IS that Dielectric supplied the devices!
Davicom built 'em a long time ago.
Dielectric serviced 'em.
Then Dielectric canceled the project and support on 'em.
 
Check with Bob Tarsio at Broadcast Devices. They also make an intelligent thru-line type RF metering system for various power levels. I think they used to make them under contract for ERI.
 
Eitehr a Wattcher or the high speed Wattcher. Bird is Your (expensive but accurate) Friend. The ERI box also worked well where I had one. If that was from Tarsio, and he now sells it, buy it... I believe it was cheaper than the Wattcher.
 
Eitehr a Wattcher or the high speed Wattcher. Bird is Your (expensive but accurate) Friend.
Click to expand...

The big consideration when monitoring several FMs of different frequencies in the same run(s) of coax is that those FMs will mix in the pickup element of diode-based wattmeter systems. This will not produce the system protection needed. A wattmeter there using a diode pickup needs an r-f filter to limit its input r-f to a single FM station.

Another approach to monitor the output an FM channel combiner is to use r-f directional couplers such as the Dielectric "saddle mount" type to drive r.m.s. power meters -- a custom design, usually.
 
The Davicom (Dielectric) monitor is a true RMS device that computes the VSWR ratio.

The plus of that is the VSWR warning & high VSWR closure settings don't depend on the forward power level.

The minus of that is the VSWR minor & major VSWR closure settings don't depend on the forward power level.
What happens is this. It sees the hundred watts or so that comes from the dozen other FMs on an adjacent tower as VSWR. When there is an "event" such as icing, reducing the TPOs would cause a sudden jump in VSWR. You have to fiddle with the minor and major alarm settings as you reduce power.
 
Sira makes a high power multi station FM power monitor with alarm. Its designed for combiner output monitoring.
we have one operating in Winnipeg in Canada.

Problem is there's no documenation on their website...you have to get it sent to you.
 
About as good as the Coaxial Dynamics web site that informs me "You will need to activate java to view this menu".
Sorry, don't have that on this computer.
 
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