[Repeater-Builder] basic repeater 101 article

Tue, 23 Aug 2005 10:14:08 -0700

looks to me like paul just wrote the article. little fluffing and folding and its good to go.
but,,,
thats only my opinion ...i could be wrong..
mdm
probably need some sexy pictures to augment it...

Paul Kelley <[EMAIL PROTECTED]> wrote:
I haven't seen any replies to this yet so I'll take a stab
at explaining the basics. (Hey guys, this sort of thing is
a FAQ, obviously... maybe we need a good basic "Repeater
Building 101" article for RBTIP? If there is one, I
haven't found it. I am aware of the "What's a Repeater"
article but that seems to be aimed more at repeater USERS
and is a bit too basic for the novice builder, IMHO. Just
curious / asking....)

Scott, I gather you are thinking of using both radios... one
as a receiver and one as a transmitter. That will work,
but with those radios I think another option is to use just
one of them. Take out the receiver and transmitter, mount
them in two separate metal boxes (for shielding).
Preferably all wires coming out of each box would by via
feedthrough capacitors to filter any stray RF (except the
coax of course). I will leave it at that since I have not
built a repeater from those rigs myself.

You will probably want to add a tone decoder to the
receiver. I know I'll open a can of worms with this, but I
pretty much subscribe to the belief that most, if not all
repeaters these days should use tone access... not just
carrier squelch. There's just soooooo much RF out
there.... in and out of band.

You will need a repeater controller. This could be very
basic, providing ID, timeout timer, and of course keying
the transmitter whenever the receiver goes active. Or it
could have many other features like fancy courtesy beeps,
voice ID, DTMF control of repeater functions, etc. etc. I
would suggest you check out the repeater controller
suppliers listed on this page to see what they have to
offer. That may give you a better idea what you want...

http://www.repeater-builder.com/rbtip/supplyindex.html

The controller, at its most basic level, takes audio and
carrier / tone detect from the receiver and supplies audio
and PTT to the transmitter as needed.

If you want to run on a single antenna (repeater transmits
and receives on the same antenna) you will need a duplexer.
This is an expensive component. Its function is to block
the transmitter carrier from entering the receiver and
either damaging it or overloading it so that it can't hear
what it is supposed to be hearing... and also to keep noise
generated by the transmitter (which spreads out around the
carrier and some of it will fall on the repeater receive
frequency) from degrading receive performance.

If you have enough space you can run on two antennas without
a duplexer. Since I haven't built a 222 repeater this is a
guess, but I'll take a stab in the dark and say perhaps 50
feet of vertical separation between antennas or 200 feet
horizontal separation. Perhaps someone with 222 experience
will offer to correct me on this. Vertical separation is
more effective because most repeater / base station
antennas are designed to radiate best toward the horizon
and have nulls in the up / down directions. Vertically
spaced antennas are mounted in each other's null, thus
increasing isolation between them... whereas horizontally
spaced antennas are in each other's maximum radiation lobe.
One difficulty with two antennas is trying to match receive
and transmit coverage... especially if one antenna is
mounted above the tower and one is side mounted.

Antennas can be chosen to suit your requirements (where do
you have to mount them and what coverage do you need?) but
there are a few things to watch out for. It is desirable
to use an antenna that is rugged enough to survive
conditions at your repeater site. Wind and ice factors
vary with location, tower height, height of hill /
mountain, etc. Also be aware that some "ham grade"
antennas may be noisy in duplex service (single antenna
repeater).

All interconnecting cables on the repeater should be good
quality double shielded cable. I like RG-214 but RG-400 is
suitable for short runs to interconnect receiver,
transmitter, duplexer, etc. The feedline run to the
antenna(s) can be RG-214 if it is very short, otherwise
hardline.

It is important (especially for the single antenna repeater)
that all connections and hardware in and around the antenna
/ tower be tight and not able to move... also free of rust.
Loose parts or rusty hardware can cause noise that your
duplexer will not be able to keep out of the receiver.

Where do you plan to put the repeater? If at a managed site
with other repeaters / communications, there may be
specific technical requirements you have to meet in order
to be allowed at the site. Some of them may require
additional equipment not mentioned here (for example an
isolator).

What did I forget to mention? Of course there are many fine
points I didn't attempt to cover here.

Paul, N1BUG


On Sunday 21 August 2005 02:46 am, n7any_1 wrote:
> I'm new to building repeaters, I have had a cobra 200
> since they came out and used it as mobil rig, I have
> aquired a midland 13-509 and would like to build a 222
> mhz repeater out of them. Since I know almost nothing of
> the details of building a repeater any information would
> be welcome. I am especially interested in a description
> of the main parts of a simple repeater ie. radios
> controllers, antennas, duplexers, whatever I will need to
> put this together. I am also interested any experiences
> others have had building a repeater from these rigs?
> Thanks
> Scott Frazier
> N7ANY






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MDM Radio Ltd -    
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