1. Standby Mode
When the repeater is not in
use, it routinely sends CW idents every five minutes. Every fifth beacon
is longer than the rest, in that it includes the location of the
repeater. Beacons are transmitted without CTCSS.
Prior
to sending a beacon, the software checks the receiver squelch. If the
squelch is open, the beacon is sent at a tone frequency of 2100Hz.
Otherwise, the beacon frequency is 1750Hz. If the repeater has shut down
due to a timeout, and the signal which caused the timeout is still
present when a beacon is due, the beacon is sent at a tone frequency of
800Hz.
2.Access Procedure
The repeater requires that a caller gives some
indication that his signal is valid, in order to discriminate it
against any interfering signals which may be present. Two methods are
acceptable for this:
A. CTCSS
If your
transmission is accompanied by a CTCSS tone at 110.9Hz, the software
will grant immediate talkthrough. This is the preferred method of
accessing the repeater, and is the only way to access whilst a
standby-mode beacon is being sent.
B. 1750Hz
tone access
After keying your
microphone, your radio should transmit a tone at 1750Hz +/- 5Hz.
This tone must last for at least 200 milliseconds (one-fifth
of a second).
After your tone has
ended, the repeater looks for a continuation of your
transmission for a further 200mS. Once these criteria have been met,
the repeater will open and allow talkthrough.
It
is worth re-stating the point that the repeater will only open-up
after your 1750Hz tone has ceased, not before. If your automatic
toneburst is unduly long, you should make allowances to wait for it
to end before starting to speak, otherwise no-one will hear you.
The
requirement for a carrier after the toneburst has ended is a
mechanism to thwart "Blippers", who press the tone button
on their rigs to activate a repeater.
Once
the repeater has granted talkthrough, further 1750Hz tones serve
only to annoy others. The software is not interested in access tones
once it is in talkthrough.
N.B. Neither
GB3GD nor GB3IM have any requirement for audio to be present in
order to gain access.
3. Talkthrough
Once access is granted, the ensuing transmission
must last for at least 3 seconds if the repeater is to remain open
when that transmission ends.
If you drop
carrier within 3 seconds of access, the repeater will "hang"
for 1.5 seconds and then shutdown quietly.
If
your transmission lasts for 3 seconds or more, the process of timing
your "over" begins. The software counts down from 180
seconds (three minutes) towards zero.
When
your transmission ends, the software begins another timer. In this
case, it waits for one second of silence and then transmits an
"End-of-over" (EOO) signal. This signal can be any one of a
"Pip", "T" or "B".
- If CTCSS was present on the last received
transmission, the EOO is a "T", to indicate that a
Tone was received.
- If no CTCSS was detected, the EOO is a
"Pip".
- If the radio is running on a backup supply, the
EOO unconditionally changes to a "B" (for battery).
After a further 3 seconds of silence, a further
"Pip" is sent.
The transmitter is
then turned off after a further 3 seconds.
4. Signal validation
The repeater software includes "Noise
Elimination" routines which are designed to give protection
against intermittent signals. Often these very broken signals are due
to noise, or other forms of interference, and need to be
ignored.
The software begins timing a 3
second interval when the squelch first opens. During this period the
software keeps track of how long the squelch has been opened against
how long it has been closed. At the end of the 3 seconds, the software
checks to see whether the squelch has been open for a total time of at
least 1.6 seconds. If this is the case, the signal is given the
benefit of the doubt, and is treated as valid. If not, the signal is
treated as thought it was never there.
You
will hear this feature in use quite often on 'GD, when assorted noises
keep cracking the squelch, but the software simply ignores them.
This
feature (concept due to G4TUZ) has proved to be extremely effective in
preventing a "cracking" squelch from holding the repeater
open.
Unfortunately it is impossible to
discriminate between a badly broken "legitimate" signal and
a badly broken interfering one. For this reason, mobiles with badly
broken signals can often suffer the indignity of the repeater shutting
down on them. Although that is unfortunate, the repeater will only
ignore a transmission with a presence of less than 50%. Such a
transmission would be unreadable anyway.
To
avoid having the repeater drop out on your transmission, I suggest
that you employ CTCSS, since the repeater will then open up
immediately your signal returns.
5. Timeout
If your transmission lasts for too long you will run
into the repeater's timeout behaviour.
The software monitors the duration of each
transmission, counting down towards zero seconds. As the count passes
through 20 seconds, the software primes itself to issue a reprimand to
the offending user. As this point it will transmit a discreet
"S" at 800Hz to indicate that the warning threshold has been
passed.
If the user drops carrier prior to the count
reaching zero, the first EOO signal becomes a "5" (five
dots), to tell the offender that he nearly timed-out.
If the transmission continues beyond the count
reaching zero, the repeater will close the audio path, send the
"End-of-work" signal (VA) and then close down.
Assuming that the repeater remains closed-down,
there is no way for others to tell when the timed-out station has
ended his transmission. To assist in this, when his transmission does
finally end, the repeater will transmit a "C" (Input Clear)
and then shut down again.
6. Timeout Re-access
It is possible to re-open the repeater following a
timeout.
Provided that your signal is stronger at the
repeater site than the one which timed-out, you can transmit
"over-the-top" and the repeater will re-open. Of course your
transmission must carry the appropriate access tone(s) as described
above.
When a station is re-accessed in this way, he will
get a full 180 seconds of talk time. However, when his transmission
finally comes to an end, the repeater will send a "0" (five
dashes) as a telling-off that he had timed-out and been re-accessed.
7. Getting the 'Pip'
What does the 'pip' actually signify? Well, it is
simply this:
Once the software has sent a 'Pip', you know that
any ensuing transmission will be allowed 180 seconds of talkthrough
before timeout.
If you "Tail-End" someone else's
transmission without allowing a 'pip' to be sent, you will inherit the
time which remained at the end of the previous transmission. In other
words the counter will not reset to 180 seconds for your
"over".
The 'Pip' or End-Of-Over signal is taken as the
first signal which the repeater sends after an incoming transmission
has ended. Regardless whether it is a 'Pip', a "T", a
"B", a "5" or a "0", the same message is
carried - the timer will be reset after this signal.
Many people have been heard to say "I'll just
get a 'pip'" when the end-of-over signal was one of those just
mentioned. There's no need. The "5", or the "0" or
whatever, WAS the 'Pip', and there's no need to wait for another.
The second 'Pip' is merely a time marker. It serves
no other purpose other than to indicate the passage of 3 seconds. It
does find application when allowing time for another station to
break-in, when others can simply wait for the second 'pip' and then
carry on.
8. CTCSS
The repeater does not transmit CTCSS continuously
whilst it is on-air.
Whenever the repeater is relaying a signal, CTCSS
will be encoded. At the end of that transmission, the CTCSS tone is
turned off immediately after the first End-Of-Over Signal (if you
listen carefully, you will hear a faint click when that happens).
If a signal appears during the interval between the
'Pip' and shutdown, CTCSS will be re-enabled.
CTCSS is not transmitted with standby mode beacons
unless the repeater is accessed during that beacon.
In most cases, CTCSS is invariably dropped prior to
the transmitter being turned off. This allows radios with "Tone
Squelch" to mute quietly when the repeater shuts down, avoiding
the "Crunch" of a squelch tail.