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[Ham-80211] What is it? (probably off-topic)

Ron Olexa golexa at charter.net
Mon Feb 14 18:17:23 UTC 2005


I think this may be an "in car repeater".  I remember testing such a device 
back in the mid 80's when I was CTO of one of the big cellular 
carriers.  It was built by Decibel Products (now part of Allen Telecom) and 
was designed as a way to improve the coverage of a portable cellphone when 
used in a car.  It appeared to be a simple amplifier pair with appropriate 
filters.  The unit connected to an outside antenna to overcome signal 
attenuation of the vehicle.  The unit was about 7"x2"x3" if I remember 
correctly.  It was a black anodized aluminum extruded box.  It had an short 
(3 inch) rubber duck style antenna on it.

The unit worked as 2 independent broadband amps with filters to shape the 
transmit and receive bandpass, and duplexers to combine the TX/RX signals 
on the same antennas.

I found that it didn't provide significant benefit when used in a well 
designed cellular system, and since cell companies were constantly adding 
new sites for capacity, the service to portables rapidly improved as well.

Your device sounds like a similar product designed for use with 900 MHz 
trunked radio systems.  Probably designed to do the same thing: help an HT 
get better coverage when used in a vehicle.  Since Trunked systems relied 
on single transmitters located on high elevation (like Amateur repeaters) a 
product like this might have actually provided improved coverage to the 
HT.  Maybe this is the evolution of DB Product's failed cellular in car 
repeater.





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