Setting Up an Emergency Repeater

(originally written for the Link, 12/1999)

During some conversations with other hams this summer, I speculated that it
would be interesting to simulate a repeater by using some mobile rigs.
Dave, W4SAR, the Orange County EC, took this suggestion to heart and made
it part of the Orange County ARES SET this fall.  So, when we opened our
sealed instructions, Dan, KR4UB, and I found that we were supposed to
assume that the 442.150 repeater was out of service and we were supposed
to try to duplicate its function.  Ironically, the repeater had failed that
morning, so it wasn't quite as artificial an exercise as had been planned.

Both Dan and I have Standard C5900 tri-band rigs in our car. And believe it
or not, we both had our manuals with us so setting things up went quite
smoothly.  What we were planning to do was much like the way the DFMA has
been using the 147.225 repeater during the last few months.  That is, we
were going to use one mobile rig as the receiver (like the Red Mountain
receiver has been used) and the other rig as the transmitter (like the
Hillsborough site on the Hill has been used.)  Just like the link between
Red Mountain and Hillsborough, we were going to link between our two mobile
rigs.  This was simple enough since the rigs have cross-band capabilities.

Since I run my mobile rig from a large battery in the trunk (separate from
the car's battery), it seemed logical that I would assume the power-hungry
transmitter task, transmitting at high power on the 70cm band while
listening to Dan's 2 meter link signal.  Dan would be the receiver,
listening for users of our "repeater" on the 70cm band and sending that
signal to me at low power on our 2 meter link.  We entered these frequencies
as shown in the diagram below.  Since the repeater we were emulating is a
70cm repeater, our link frequency was a 2 meter simplex frequency.  On the
Standards mobile rigs, we entered the two meter simplex link frequencies
into the left sides of these dual radio rigs and the our 70cm link
frequencies into the right sides.

receiving on 447.150                         transmitting on 442.150
.     .     .                       .             .     .           . 
  .   .   .                               .        .   .       .
    . . .                                       .   . .   .       
      o                       L I N K                o 
      | . . . . . . . . > 146.580 simplex. . . . . > |
      |                                              |
      |  -------                                     |  -------
    .---/___|___\------,                           .---/___|___\-----;
    \     KR4UB        \                           \     KU4GC       \  
    =-(*)-----------(*)-:                          =-(*)----------(*)-:          
                                          

We set this all up in about 15 minutes.   One question was how far apart did
we have to be to avoid interfering with each other.   We used about 1/4 mile
and that seemed to work fine.  We were actually located on the access road to
the 147.225 repeater, so we were operating from a fairly high elevation.

Now we were ready for the smoke test.  Each of us put our mobile rigs into
cross-band mode and, seeing no smoke, waited for traffic.

Well, although everything worked fine, we were not overwhelmed.  Our first
call was from WA4AHR, Dewey, in down-town Hillsborough.  W4SAR, Dave,
checked in while driving towards Chapel Hill.  K4MNB, Ken, checked in from
his qth near Efland.  We received a couple of calls from the Orange County
Emergency Management/911 Center on New Hope Church Road (where the VE
sessions are held).  So, our coverage was good, but not outstanding.  We
could not hear hams participating in the SET from Chapel Hill.  It's rather
hard to match the coverage provided by an antenna 1000 feet up on a tower.
Being so close to the DFMA Hillsborough tower with all of its paging traffic
may also have been a mistake since it may have de-sensed Dan's receiver.

However, for something set up in less than half an hour, we were able to
emulate a regular repeater that, except for the fact that we had to ID
manually, worked just like the regular repeater.

This is definitely a technique to keep in mind.  With some advance
preparation, using some real antennas, one can put together an effective
emergency repeater service.  If club members with towers or other
extraordinary antenna situations can all be set up in advance, then one could
replace a failed or ailing repeater quite effectively in a matter of minutes
using a couple of mobile rigs with cross-band capabilities.                 

Dee, KU4GC