In recent years, more and
more repeaters have appeared that require CTCSS tones, or codes, to access them,
and some of the older repeaters have been modified in this way too. In
fact CTCSS became mandatory in 2004 for new repeaters. This
has both benefits and disadvantages for both sides, so much so that they
seem to balance each other out. By "both sides" we mean the traditional
radio amateur, as opposed to those who want to introduce new technology
- however an anomaly is that repeaters are required to identify
themselves with the archaic Morse Code that dates back to the early
1800's. However, some repeater keepers seem to have had the temerity to
use a speech synthesiser with an extremely offensive American accent!
A CTCSS tone is
a Continuous Tone-Coded Squelch System, something brought over to the
hobby from PMR. Basically what happens is a sub audible tone is
superimposed on your transmission and the repeater recognises this and
opens or re-transmits your signal without the need of the 1750kHz tone.
In practice, you just key the mike and the repeater works without any
further action from you. Some repeaters are yet to be modified, and some
still accept both, but it will all be CTCSS soon, so we need to move on.
The old system meant that you could "whistle up" the repeater without a
tone burst, but also spurious transmissions would activate it as well.
CTCSS does away with that, ensuring that only the correct radio amateur
signals are repeated. That is the supposedly good side of this, but it
means that the majority of radios out there are obsolete, as they don't
have a CTCSS tone facility. No problem, we are technical people, buy an
add-on board and away we go! NO, if only it were so simple.
There are a whole set of tones, see the table below, and every repeater
needs to accurately receive the correct one to work, before 1750kHz was
universal, but now it is infinitely more complex. What would have been
sensible would be to have adopted the same CTCSS tone for all repeaters
in a specific area so you could buy a cheap tone board and easily fit
it, but no, they all need vastly different tones and trying to use an
add-on tone board is impractical.
The upshot is, we feel, a great contributory factor to the demise of 2
metres, the main conduit of conversation, the local repeater, has been
made unavailable to the vast majority who can not justify the expense of
a new radio with the CTCSS feature.
CTCSS was introduced to allow several commercial radio users to
share the same frequency without overhearing the other users
conversations, you could have 2, 3, or 4 companies sharing the same
frequency but each using their own CTCSS tone, so the squelch would
only open for calls intended for them. You can see the advantage of
this in a densely populated area such as The City Of London. On
paper, this looked like a good idea for ham radio, but in practice
it has been disastrous, as even if the repeater is open, without the
tone superimposed on your transmission, it simply will not work.
So CTCSS has to be used, luckily radios are remarkably cheap these days,
with dual band handies 4 or 1Watt out costing under £30 new, and these
incorporate the vital CTCSS tones. Mobiles also have had a dramatic price drop, even Yaesu are down to sub £140 for a full featured 2 Mtr with 50W out
costs around £150 or less, if you can find a dealer these days.
Here is an
example of a Baofeng UV-5R, this does everything and comes at various
prices, the best we found was just under £30.00 including postage and
out high, 1 Watt low, CTCSS tones, VOX, LiIon battery with mains recharger.
This is our
current project for a repeater improver. With the addition of minor
circuitry, it can be modified to randomly access a CTCSS repeater on 2
metres or 70 Cms, play a recorded "message", and close down again.
it will last well over a week with 20 second transmissions every 30
minutes, we are experimenting with a light sensitive diode to switch it
off at night, when it would suffer the highest danger of being found by
outside, near the target repeater, it can be easily concealed, and
collected every week or so for recharging. Make sure you use different
London used the top of a bookcase in the local library every weekend!