Technical Talk - Sportsman's Paradise Amateur Radio Club K4WAK
Sportsman's Paradise Amateur Radio Club
Why Ham Radio?
Why Ham Radio?
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This page is to help with some of the basics on repeaters in our area. it is just a basic
rundown on the more common modes and features
communications on the typical repeater
used in amateur radio. For more detailed information on the items listed, just click on the
With UHF and VHF radios, the range of your signal only goes so far... If your using a handheld,
your range could be just over 10 miles on
flat terrain. Enter the repeater. A repeater will take
your signal and as the name suggest, 'repeat' it. Where your signal only went 10 miles before,
it could go 60 or more
miles with a typical repeater in the flat land of Florida. Most repeaters are
located on commercial towers or tall buildings with antennas often
at 200 - 400 feet high. The
repeater will have an antenna much higher, offering a very impressive coverage area, or
Not only are these repeaters on towers, but they are often running a power output
of 15 to 100 watts.
Considering your typical handheld has
a maximum power output of about 5
watts, you end up with a fantasic coverage area with it when used with a repeater. The
coverage of any
given repeater varies from one to another. Differences in height, quality of
materials used, and repeater output power all have major bearing on
the performance of a repeater.
Reference the diagram (to the right) of the two cars and antenna tower. Imagine those cars are
about 100 miles apart. Given that distance and
the little hill between them, any signal of one station
is very unlikely to get to the other station using VHF or UHF. But with the repeater on top
signal from one is
easily picked up by the repeater and retransmitted for the other to hear.
Almost every transeiver has a squelch control. Squelch is used to 'quieten' recieved noise. With the
squelch all the way 'open', you will hear
static and noise typical on our planet. Squelch can be
thought of like a 'gate' or 'levy'. Noise is always there, and we now have a gate to keep the
(squelch control). We adjust the squelch control as one would the height of a flood gate on a dam.
The higher the noise/water level,
the higer we adjust that gate to stop the flow of noise/water. If
you open that gate/squelch all the way, all that noise/water flows in.
(PL or CTCSS = 'Private Line' or 'Continuous Tone Coded Squelch System')
Tone allows us another way of squelching out noise and unwanted signals. Most modern amateur
radios are equiped with 38 or more sub-audible
tones for transmitting while your talking in order to
'open up' a repeater. While
tones are considered to be 'Sub Audible', it's often heard if you
A tone value, which usually varies from 88 to 250, is used much like a key on a door.
Without the right key, that door remains
locked. In our case, if the correct tone isn't being transmitted
(encoded), the repeater rejects the signal. This works great for times when a signal
on the same frequency manges to come in range of our local repeater. That signal isn't
intended for our area and could be
considered interference. Fortunately, it is customary for repeaters
that share the same frequency to use very differnt tones. Tones also keep other
interference such as
lighting storms, dirty power supplies, and florecent lighting from causing the repeater to retransmit the
noise. If a repeater
is programed for a PL tone of 100, then you need to program your radio to send that
same PL tone in order to take advantage of it's use. Many
repeaters will not only decode your PL tone,
but they may also send out a PL tone as well. This doesn't have to be the same PL tone value but it
usually is. Having a repeater that sends out a PL tone with repeated signals is really neat as it allows us
to program our radios to reject all signals
except when that signal has a PL tone too. Basically, your
sending a tone to unlock the repeater, and the repeater is sending a tone to unlock
your radio. The tone
to be recieved is called Tone Squelch or Decode. When tone squelch is enabled on your radio, the squelch
knob has no real
function or use as all signals are being rejected unless they include the proper tone.
While it is required to have a PL tone Encode programed for
repeaters, it is not required to have the
tone squelch to recieve it. You can leave the tone squelch off and still recieve the signal if desired.
There are other methods to do the same job as PL tones, such as
DCS - Digitally Coded Squelch, and
DPL - Digital Private Line for example. These
operate with the same concept, only digitally instead of the
Common Repeater Modes:
FM, or frequency modulation, is the most common method of transmission for repeaters in amateur radio.
For the sake of keeping things
simple, we will keep the
explanation to a minimum. FM is the same mode
used by your favorite FM music radio station. It is also commonly
refered to as 'analog'.
C4FM - Yaesu System Fusion
This is a fast growing digital mode. In fact, all three amateur radio repeaters in Wakulla County use this
mode (our repeaters work on both
analog FM and the digital C4FM/Fusion. It is a FDMA mode (Frequency
Domaine Multiple Acess). This mode includes a error correction mode that
is supurb at ensuring a clean
signal. PL tones are not used for digital modes. However DCS can be in some cases
P-25, or Project 25, is a digital mode designed primarily for public service (Law Enforcement, Fire, EMS, etc).
It operates in similar form to the
C4FM above, only P-25 is TDMA - Time Division Multiple Access. This
isn't very popular in amateur radio for our area, but it does exist. And
Yaesu C4FM, P-25
works on FM as
However, there is a P-25 phase 1 and P-25 phase 2. Phase 2 radios are backwards
phase 1 but phase one will not fully communicate with phase 2 equipment.
Like the P-25 above, DMR - Digital Mobile Radio is TDMA - Time Division Multiple Access. DMR was
in Europe but has been implemented
all over the world. A DMR repeater is present in
It is not uncommon to talk with other amateurs in distant cities as
via the internet. With the correct 'code plug', one can connect at
will to a specific
DMR repeater in a
or country to chat or listen. As with P-25, DMR has been
upgraded a few
times over the years
and the earliest
equipment may not
have full functionality or
incorporates an effective error
D-Star was one of the first digital modes to be offered commercially for amateur radio. This mode is based
MSK - Minimum Shift Keying
method. Designed by a amateur radio group in Japan, the concept is
marketed by Icom International. This mode has been adopted
by many for use in emergency
radio groups in Alabama have coordinated with each other to develop a robust
network. As with
DMR, D-Star repeaters are often connected to the internet for repeater
NXDN was designed by Icom (IDAS) and Kenwood (NEXEDGE) in a joint venture. It incorporates FSK
Shift Keying) as well as FDMA
Multiple Access). Clean audio and impressive
is due to error correction. NXDN was also designed with Public
Service in mind but
also entered into the amateur
This is a very short list and explanation of what choices one has with local repeaters. Unfortunately, one
isn't compatable with another.
While two different modes may use similar methods such as
FDMA, several other things
are much different like the codecs.
Nor is it common to find two or
capabilities on a single transiever (we
hope to see this change one day). In short, if you plan on
digital mode capable rig,
choose wisely. With three
individual repeaters runing the Yaesu System
C4FM in Wakulla, it's a no brainer if you plan
on spending most of
your time in the area. That
even though the local repeaters are YSF/C4FM, we typically use simple FM 99% of the time, so
picking up a
radio that does not have digital capabilities if still a great choice.
But if you have
few friends using DMR in Tampa or Chicago, the DMR with the right code plugs
you better. Or
you can get both types!
are other modes and features available in addition to these.
Not all require
One of the best decisions you can
make would be to
up with a local
club to see what modes and
methods are popular or prefered in your area, as well as have
to see them
first hand. While it is required to pass an exam to talk on any
amateur radio devise,
you won't be required to pass any engineering test to
qualify for using a digital mode.
ut knowing about
different types in your particular area can help make better decisons. FM
is still the
mode on VHF/UHF and
be for some time. And during an emergency or recovery, FM
is the best
communications in most of Florida.
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