Repeaters
What's Up Doc?
3 days ago by WA1TCCRepeaters
This is a high level review of repeaters and their use.
Repeaters have been around for quite a while but their use
is
becoming increasingly popular especially with the use of
inexpensive HT transceivers.
Repeaters work in two manners – simplex and duplex.
Simplex
uses one frequency and repeats traffic using a delay in
transmission. It is used to boost a weak signal but makes
for
difficult communications due to the delays. Duplex works
by
using a separate input frequency or band and then sends
out
the input on the repeater frequency. Most repeaters are
limited to same band coverage but there are a few that
repeat
from one band to another.
Repeaters are set up in a location that has good coverage
from their antenna for the signal. Many times they are set
up
on commercial antenna masts or water tanks as repeaters
are
frequently used in public service and these locations
provide
a high altitude for the antenna. Since most repeaters are
VHF
and UHF they need line of site for propagation of the
signal
and the higher the tower the better the coverage.
Simplifying the repeater description:
The repeater is a radio transceiver. It is set up for an
incoming frequency which the user sets on their
transmitter.
The repeaters usually use various controls to control
access
to the repeater. The most common is a PL tone which is
published with the repeater information if it is a public
repeater. This is added to the user’s transmitter and is
sent
before a transmission. (See you Transceiver documentation
for
setup instructions) If the repeater reads the signal and
recognizes the tone it then begins to process the signal.
There is a very slight delay then the transmitter on the
repeater is activated and the signal is repeated on the
output
frequency.
This raises the question of how can the repeater receive a
signal and transmit at the same time if it is using the
same
antenna or one on the same mast? Without going into the
complete design of a repeater the answer is filtering.
Even if
the output is going to a second antenna the RF on a close
frequency will interfere with the reception of the
repeater.
Very precise bandwidth filters limit the RF feedback and
allow
the reception on a limited clear bandwidth. This is why
you
get a repeater that is a repeater or have some serious
filters
to build.
So lets talk about coverage.
VHF and UHF is mostly line of sight transmission. Getting
on
a hill is always better then being in a hole. Putting the
repeater antenna high in the air increase the line of
sight
but no matter what the earth is round and that impacts the
signal. The process of an initial signal is from the user
to
the repeater and then from the repeater out to the
receiver.
First step is, if the receiver can receive my signal? I
have
to put out enough signal to get to the repeater and carry
enough signal to be above the background noise – something
that is reduced as we go up in frequency.
The repeater has to be able to read the authorization
command,
in most cases the PL tone, and the tone has to be of the
right
frequency.
The repeater is now listening to the signal. It will
repeat
what it hears. This is where quieting comes in. The signal
must be above the noise level and be readable to the
receiver
in the repeater. All the features of any receiver will be
there and provide as much clarity to the signal but if it
is
not above the noise level the signal out of the repeater
will
not be quieted. This means you will hear broken voice and
low
level of voice as well as background static. To fix the
non
quieting issue, the transmitter has to change the
location,
increase the power, raise the antenna or increase the
forward
gain of the antenna or all of the above. It is a repeater
and
can only put out slightly better than it receives.
What about increasing the repeater power?
Can’t increasing the power help? Yes it will but only as a
coverage fill-in. A power increase will not impact the
coverage area but putting out more power will fill in the
dead
spots in the footprint of the repeater. This does not mean
the
range of the repeater will increase significantly. There
will
be a slight improvement in the coverage pattern for border
line areas but line of sight is still a limiting factor
with
some extra bounce with increased power off of objects.
This
helps fill in dead zones in the pattern. So if the
coverage
pattern of a repeater is plotted and there are dead spots
due
to terrain or buildings an increase in power can help. It
won’t help to get into the next county. Look to linking of
repeaters for that issue. More on linking later.
How do I use a repeater?
Once you are setup and have the repeater programmed
properly
– listen!. And listen some more. Users in the area will
have
their own way of using the repeater. Do not call CQ.
Standard
procedure is to call directly to the station you are
looking
to QSO with or to announce your call sign stating you are
monitoring. There will be other stations monitoring also
and
if they want to talk they will reach out to you.
When keying up to the repeater – wait before talking. Most
have a built in delay and the first part of your
transmission
will be cutoff. Many times this is the call prefix. If you
get
a call in that manner you can repeat the suffix and ask
for
phonetics on the prefix. Phonetics slow the user down so
you
should be able to read their transmission.
Repeaters reset after a few minutes so keep your side of
the
QSO short otherwise you will be dropped. If you have a
lengthy
conversation like an announcement, drop and pick up the
repeater by stopping transmission and restarting. Some
people
say "resetting" but just stopping and starting is usually
more
efficient.
Wait between transmissions in case someone has to use the
repeater for an emergency and needs to break in or in case
someone wants to join your conversation. The bands are
open to
all licensed Amateurs so encourage someone else to jump
into
you discussion.
Know the repeater’s use.
Some repeaters are for short duration calls and others are
available for rag chewing. The local club’s repeater may
be
seldom used so you can enjoy the QSO with a friend but
Florida’s SARS repeaters on 70 CM are for short term QSOs.
Most of all remember it is a shared resource and use
appropriately and join some nets!
Our local area simplex and repeater frequencies:
CITY
FREQUENCY
PL/OFFSET
COMMENTS
Tallahassee
147.030
PL94.8 – +600
Tallahassee ARES district primary repeater
Lee Analog
145.190
PL 123 – -600
Lee Repeater Madison DMR 442.000 447.000 CC white (1) Slot
1
& 2
Lee Analog
145.110
PL 123
Lee Repeater South Side
Any
146.520
Simplex/no PL
National calling channel
Local
146.550
Simplex/no PL
Madison and Suwannee ARES simplex frequency
Local Simplex VHF
Digital Local
Simplex UHF
Digital