Re: wireless technology

[JAMES COTTON]

WMU is running one pair of Karlnet units at 902-928Mhz in a base 
station/satellite configuration.  The spare has been used once as a satellite 
for service restoration when a well drilling crew drilled thru a CATV/Fiber duct 
bank.  The units have been in operation approximately 1 1/2 years.

WMU's units have the first generation NCR wavelan card that was resold by DEC.

The distance involved is approximately 1/2 mile.

One end has an 18 element yagi antenna fed with 100' of RG-8X coax with crimp on 
'N' connectors.  The yagi antenna has been replaced once due to weather related 
degredation.  The second unit was coated with clear krylon to aid in weather 
proofing which appears to have been effective.  It should be noted that at 
900Mhz the krylon is probably somewhat rf conductive but I didn't have the 
equipment to check it.  Anyway it works.  The unit dumps .25 watt into the cable 
which has (if I remember correctly... 9db of attenuation at 1000Mhz for 1000').  
I didn't worry about the standing wave ratio by the time the RF got to the 
antenna.

The six foot yagi antenna has enough surface for wind loading that it took three 
attempts to find a robust enough method to secure it in place.

The yagi is horizontally polarized since both sites are within a mile of a 100+ 
watt 900Mhz paging terminal that is vertically polarized and line of sight.

The central site has a horizontally polarized gain onmidirectional antenna 
(turnstile/cloverleaf design).  Picture a three foot long, one foot diameter 
tube mounted on 20' of pipe.  It is fed by 50' of RG-8X.

Both sites are well grounded and have Polyphaser brand lightning protectors 
installed.  All connectors are wrapped with self sealing silcone tape and a 
layer of electrical tape for waterproofing.

The users have been happy with the speed/throughput of the device.  The flashrom 
option provides a set of idiot lights on the front of the unit that indicate the 
receive signal quality and level of traffic being forwarded. 

Jim Cotton, N8QOH            |  jim.cotton@wmich.edu
Western Michigan University  |  Phone: (616) 387-6421    
Network Systems Group        |  Fax: (616) 387-5473

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