At 06:08 AM 2/19/05, you wrote:
>I apologize ahead of time if this posting doesn't meet your
>criteria. I am with a law enforcement agency and we have recently
>killed our tactical repeater
What is your current tactical repeater?
I'll bet it can be fixed for not a lot of money.
What killed it?
>and are trying to build a temporary one from two HT1000 portable radios.
>I am in search of some expertise on whether this can be
>done successfully and if so how to do it.
In a word, it won't work.
Trying to use two back-to-back handhelds as a tactical
repeater is like trying to empty a swimming pool with a
measuring cup. It's underpowered and was never made
for the job.
One, the handhelds are not shielded from each other, and
the transmitting radio's signal will drown out the signal that
the receiving radio is trying to hear. Imagine yourself standing
next to a stage trying to listen to a whisper across a room
while a rock band is warming up.
Second, the repeater transmitter needs to be built for
full-time transmitting. Try this: take a fully charged battery
and clip it onto the MT-1000. Put a few rubber bands around
the PTT button so it stays on. Wait 4-5 minutes. I'll bet
that the radio is noticeably warm in your hand. Unkey, and
swap batteries to a fresh one. Again lock the PTT button
down and wait 4-5 minutes. Unkey, and swap batteries to
a third fresh one. Again lock the PTT button down and wait
4-5 minutes. Can you hold onto the radio?
And realize that the guts of the radio are much hotter than
the outside of the case - it takes time for the heat to travel
outside.
This is why you need a made-for-the-job tactical repeater.
If you are in an incident where a squad is coordinating an
operation you don't want an overheated radio dying on you.
Remember that the repeater is talking at full power whenever
anyone is transmitting on the input frequency. A back and
forth conversation can easily keep the transmitter up for 10
minutes. Locally the ham radio repeaters are in constant
transmission for several hours during prime commute hours.
Most of them are based on retired commercial repeaters or
paging base stations... both are built to run for 7x24 operation.
The better ones are built so that they don't have to rely on
fans for cooling (fans can wear out and die).
>We are on 100Mhz VHF and are
>trying to decide how to best hook them up. I have the
>factory cables for cross connect and was thinking about
>using a VOX switch to key up the second portable.
There are better ways.
How did you plan on powering the portables?
>I was also thinking about purchasing
>a small duplexer from Tessco to keep a single antenna.
Most small duplexers are designed to notch just the repeater's own
transmitter out of the repeater's own receiver (and vice versa).
Anything else walks right in and can swamp the receiver.
So if you are out on an operation with any other organization that
uses the same range of frequencies (and maybe more than that,
see below*) you will have your repeater lose sensitivity when they
key down - even if they are not on your channel and you can't hear
them.
A duplexer is a good idea but you want one that includes a pass
function in front of the receiver.
* We had a 450mhz repeater get desensed by a 931mhz paging
transmitter. While the paging TX was up our repeater was totally
deaf. Likewise the local 156mhz fire channel had a problem with
a 152mhz paging transmitter. Both were cured with a pass cavity.
Picture an operation with several agencies working together....
Police, fire, sheriff, maybe a federal agency or two...
The last thing you need is to have the tactical squad
communications take a hit when an ambulance driver calls
back to his base station to co-ordinate a replacement due
to shift change.
You need a radio made for repeat duty with decent front
end filtering.
>Another option is to use a pre-made device from Transcrypt
>www.transcrypt.com called the Transpeater that claims to do
>the same thing but at a price of $650 US.
And any port that hears a signal keys up all the other ports.
You need near-continuous duty rated radios for that. And a
radio that won't hear itself or another radio in the same vehicle.
>Please advise
>
>Denny
Bite the bullet and do it right. Get a real repeater (made for
repeat duty) and put it behind a real duplexer (pass and
notch functions).
Mike
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