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From: ornitz@kodak.kodak.com (Barry Ornitz)
Subject: Re: Passive Repeater?
Organization: Eastman Kodak Company, Eastman Chemical Company Research Labs
Date: Fri, 5 Jun 92 17:32:21 GMT

In article <telecom12.448.9@eecs.nwu.edu> srm@dimacs.rutgers.edu
(Scott R. Myers) writes:

> I have read briefly in a recent {Mobile Magazine} and also saw in the
> store window a camera store that sells Cellular a device called a
> passive repeater.  It looks like a standard through the glass mount
> antenna with some type of 3x3x3in box with coax connectors on two
> sides.

I am not familiar with this device, but we use something quite similar
with our plant trunking radio system.  We have a number of metal
buildings at this plant site that have poor radio coverage with our
trunking system. To alleviate the problems, we have installed "passive
repeaters" on many of them.  These are nothing more than two antennas
connected toegether; one antenna is on the inside of the building and
the other is on the outside.  The antenna on the inside picks up a
small amount of a user's handheld signal and re-radiates it using the
outside antenna.  During reception, the inside antenna re-radiates the
signal picked up by the outside antenna.  The two antennas do not have
to be mounted near each other; they can be connected together via any
conveneient length of transmission line (coaxial cable usually).  Thus
a basement antenna can connect to one on the roof.

As one can imagine, the performance of such a system will be poor.
There will be considerable loss in the system, especially if a
significant run of transmission line is used.  However the effective
path loss from handheld to the base station will usually be far less
than that without the passive repeater.  In the case of several of our
containment buildings, the passive repeater allows radio communication
that would have been impossible without it.

A pickup antenna within the car located near the handheld connected to
an outside antenna just might decrease path loss enough to permit
cellular communications in fringe locations.  Whether a "passive
repeater" will help or not depends highly on how many problems you
currently have with your system.

> BTW the wrapping on the one I saw displayed said something like "Works
> through proven Microwave technology."  Sounds like marketing hype 

It sure does!


Barry L. Ornitz  ornitz@kodak.com

From: John De Armond
Subject: Re: weak signal to pagers ( was: pagers )
Date: 3 Mar 89 20:47:47 GMT
Organization: Sales Technologies Inc., Atlanta, GA

In article <telecom-v09i0076m05@vector.UUCP> Mike Morris <morris@jade.jpl.
nasa.gov> writes:
>
>Edited to reduce bandwidth...
>
>>I am using a Motorola Display pager and was
>>wondering is there was any way of amplifying the signal that comes into
>>the pager.  ...my office is located in the basement
>>and every so often I receive a page
>>down there.  

>The above solution, however "traps" the pager into one spot.  There are
>a couple more solutions that will allow you to leave the pager on your belt,
>but are more expensive.    One trick I used was to roof mount a directional
>antenna pointed to the paging transmitter, run good quality coaxial
>cable (_not_ the cheap stuff Radio Shlock sells for CB) down into the
>building, mount an amplifier tuned to 158.7 in a phone closet, and run
>more coax to the area in question.  There a small ground plane antenna
>(omnidirectional) was hung from the ceiling (upside down - coax on top).
>This worked _real well_.  the amplifier was custom made for the job, but
>cost < $75 using all new parts.  Running the coax was the hardest part.
>
>BTW, most of the "FM" amplifiers have circuitry that limits the frequencies
>amplified to the 88 to 108mhz range - way to low for your application.
>
>If none of this makes any sense, print this out and show it to a technically
>oriented ham radio operator.  You mailing address suggests that you are
>at MIT, there is a ham club there.


One each, ham operator at your service :-)  The above solution works but 
can lead to intereference from other amplified signals and is possibly
illegal because it could be considered an unlicensed transmitter.

The good news is an amplifier is not necessary.  I use a similiar setup in
my basement office in order to hear the local VHF ham repeater.  I have
a small yagi antenna on the roof connected to a ground plane antenna in 
my basement (mounted just like above).  I carry my handi-talkie in my
hip pocket while in the office.  Works like a champ.  the best part for me
is that it is 2-way - I can transmit into this system too.

You should be able to get all you need from a ham radio store.  If there's
not one in your area, Email me and I'll give you a couple of 800 numbers.
You will want to buy about a 9 element yagi for 2 meters (cushcraft is a
good brand), some RG-214 coaxial cable, and a 5/8 wave magnetic mount
mobile antenna for 2 meters. (Larson or Antenna Specialists is fine).  This
setup should cost you perhaps 125 bux or so depending on the length of
coax you need.  Simply mount the yagi on the roof pointed at the paging
transmitter and the 5/8 wave magmount on a convenient file cabinet.  
Hook the 2 together with the coax and away you go.  Unless you are in
a real fringe area (not indicated by your statement that it sometimes
works in the basement), this should work 100% with the pager on your
belt.  Will work for everybody else on the same paging system too.

The above assumes your paging frequency is near the 144-148 mhz ham band
(frequency is normally on the nameplate)  If your pager is in the UHF
band (45x mhz) then you will need to buy the same type antennas but for
the amateur 440 band.  Amateur equipment is generally cheaper than 
commercial gear of the same type.

And Hey! While you're at the ham store, get a license manual and consider
getting a license.  You'll have a blast.

73 john




 
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