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Author Topic: Mobile Light Weight Repeater  (Read 99 times)

Posts: 3

« on: Today at 07:28:32 AM »

Little background: I haven't been as active in HAM as I would have liked for the last few years. I live in a spot where VHF&UHF aren't really used and I would need a larger HF radio to talk to any one else. So my radios have basically been sitting idle. I just have my Tech. would love general but just haven't worked hard enough to get it. Given that info please forgive any thing that Im lacking in.

My Question: I need to come up with a way to carry a VHF/UHF repeater in my back pack / on my snowmobile. My goal is to help our local SAR teams in rescues in the many of valleys. (I live in the high rockies of colorado) My goal is to be able to carry a repeater to the top of a mtn and setup camp during a SAR Mission. Allowing for coms into a valley. For example a lot of people here carry a SPOT beacon. When they have a problem they hit the Help Button, but instead of staying still... they move. By the time the SAR team reaches the location of their beacon, they've moved.. so theres a need to stay in coms during the mission to update them with new grids for a search.

I want to find a way to use my two VX-8DR's to make a repeater. Im pretty sure its just as easy as plugging the two into each other and setting them TX radio to VOX... and the RX radio with a CTCSS tone....? am I wrong? I was planning on carrying a 25' Carbon Fiber Pole to setup with two AT's..

Any thoughts on how i could make this work?

Posts: 15035

« Reply #1 on: Today at 09:09:53 AM »

Repeaters require a lot more work that it might appear on the surface.
The problem is getting the receiver to hear a very weak signal reliably while
a comparatively much stronger transmitter is operating on the same antenna.
Usually what happens in a simple system is that the receiver gets blocked
by the strong signal, even when it isn't on the receive frequency.  Good filters
and shielding are usually required, as well as low spurious responses.

The Santa Barbara (CA) ARES group had a portable repeater they used in
support of SAR that used a pair of HTs:  with the required filters it still took
two guys to load it into the back of a pickup truck.

I have seen some 440 repeaters built using older Motorola mobile radios, because
the transmitter and receiver were separate and both were well shielded.  The
filters are smaller and lighter on 440 as well.  These could, at least, be picked up
with one hand, and might leave enough room in your pack for a jacket and some

Our SAR team tried a "simplex repeater" that someone though was a great idea.
This uses a standard radio by recording the incoming audio, then retransmitting
it when the transmission was finished.  (There are a number of such add-on boxes
available.)  It was cumbersome for the field teams, however, because when you
could hear the other team directly you'd reply at the same time the box was
repeating the original message.  The stations 200 miles away that we were causing
co-channel interference to weren't thrilled, either, as our repeater would cover up
the responses from their field teams.

Probably the simplest solution is to figure out how to use cross-band repeat to
provide the coverage you want.  Battery life (and power dissipation in a hand-held)
are both issues, along with the repeater constantly being keyed up by chatter that
doesn't need to be repeated.  One solution that we used to use in the Forest Service
was to have a manual operator (typically repeaters were on fire lookouts):  a station
that couldn't make contact directly would call the lookout and ask for the repeater to
be turned on.  At the end of the conversation the lookout would switch it off again.
These days we would do the same thing by putting a PL on the repeater.

In the end the SAR team decided that a manual relay team worked better than trying
to rig up some sort of repeater.

Posts: 3

« Reply #2 on: Today at 09:18:52 AM »

I hear what you're saying (Pun Totally Intended!) Smiley Ive been continuing my research. I believe what you're talking about is repeater desensitization? I have found a few references of people keeping ant's more than 15' apart hoz and on different vertical levels. some of that can be minimized? True?

I've looked at some DIY repeaters and it looks like some of the features make them larger than they need to be. Some seam to also have dual ant hook ups when not using a duplexer. How do they get this to work with out problems? If i have to i can make two runs up mtn or use a friend to help in transport. I have about 35-65 lbs of extra payload i can carry, this must include fuel, tent, stove, batteries, radio gear, food, water.... This is why i wanted to use the HT's

Posts: 3

« Reply #3 on: Today at 09:23:41 AM »

Im also already using HighGain's on both my current radios, SRH999'S On them now because I never know what Im going to talk on. If i do this I was thinking of using off the shelf SRH77CA Dual Band +6dB for all the radios.
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