Logic: GB 3 SU

Logic: GB 3 SU

You will need:,
To be Receiving on 433.200 MHz, with the following set up:
"repeat on"
+1.600Mhz repeater Shift ( you transmit on 434.800MHz with 71.9Hz CTCSS)
CTCSS set to 71.9Hz TX, and turned on,
and depending you: CTCSS 71.9Hz RX: either on or off! As explained further down

A little bit of history..
The groups first repeater was on UHF, as a Yaesu Repeater under the SMC branded name, that repeater was a brand new commercial unit and was introduced in 1995, under the callsign GB3EA.
We were later offered the more appropriate callsign GB3SU ( Southampton UHF, not the university!)
During the course of time we were able to have a VHF repeater, when the half channels with 12 ½ kc working was introduced, the result was a drop in use of the 70cM repeater.
With a threat of an unavailable RF power Brick, should a PA failure occur, and a 1980 designed GB3US Mark 1 logic; and a CTCSS decoder bodged in with a relay to get CTCSS
access running, we took the opportunity of assembling another brand new repeater made from a pair of Tait mobiles, into a 4U tray, while this is now around 8 years old, it has off
course been off air for 5 years due to site loss!
The advantage of the Tait mobile pair is the excellent quality of these radios, and the ease of coupling the Receiver to the Transmitter, via a patch lead connecting the pair.
The radios include circuitry which does useful things similar to repeater "logic", which meant that logic did not have to be brought and or built and then interfaced somehow.

User information
GB3 SU consists of four main parts: Power unit, Receiver, Transmitter, and Shut down.
The power unit is a switch mode type to cope with a wide range of AC supply, it can handle
63 to 300Volts AC or 300Volts DC!
The transmitter and receiver are a pair of Tait TM 8110 25Watt UHF mobiles, What we consider to be "logic" is part of the both the receiver and transmitter circuitry.
Shut down is simply a switch with a key which shuts it off should the need be.
You can see therefore that GB3SU is a fully operational repeater, but a little cut down in fancy features, and this is shown in the way it sounds to us.

Logic purpose
The Logic is the part of the repeater system which enables you to access, encodes the CTCSS, and inserts the Morse code Identity: "CWID".

What is does
On transmitting on the repeater input with your 71.9Hz, the receiver open's,
and the logic does 3 things at the same time:

" strips your CTCSS off, this is done in the receiver.
" inserts its own CTCSS tone of 71.9Hz. done in the transmitter.
" Keys the transmitter its keyed by the receiver!
at the end of your over it the repeater provides one pip, waiting for the pip makes for smooth runnijng of the repeater.


Is simple and straightforward, it only has two states depending on :
Idle mode No CTCSS is sent just its callsign
QSO mode callsign only

Notes for use
" The general rule of thumb is don't time out! ,.. And wait for the pip, 70cm is a gentlemen's band and gentlemen don't think of yelling break please ignore such people!
" The repeater cannot tell you how strong your signal is!
" There is no CWID on demand facility.
" The CWID is at the same volume level during contacts or when the repeater is idle.

The CWID time is every 15 minutes, as required by it's licence, The Logic sends:
" GB3SU B ",
GB3SU is the callsign! ( you should know that !)
the B is the Letter indicating 71.9Hz CTCSS tone .

CTCSS on the receiver the tone is 71.9Hz
As with The co-sited aerial sharing VHF repeater, ( GB3SH,) Use of CTCSS on your receiver is a personal decision, both having it on or off, can have advantages: however due to
increased QRM on 70cm having CTCSS on ( or decode ) may well be preferential....

CTCSS ON your receiver only open's when the repeater is active, with calls or contact's going through it, thus you will not be disturbed by the
CWID every 15 minutes, or any other signal on the frequency.
This means a handheld can be carried without fear of the CWID going off!
Its good at home too, as the family is not driven mad by the CWID or wide band inane squawks, that originate around 433.910MHz!
Also the advantage of your receiver being CTCSS controlled, the Logic in the TX cuts the CTCSS tone off before shutting the transmitter off.. you don't get a squelch tail!
Some rigs dont do this!: Baofeng UV3R+ being an example. IE You get the squelch tail

The best way to operate CTCSS ON receive is to put it in to a memory! Or you may hear nothing on SU20!

CTCSS OFF your receiver's is Squelch controlled, you hear everything on channel, including QRM, the CWIDs et all, a useful way of finding out if there is a lift on,
since you may well hear the other repeater's on channel. Hearing the CWID confirms the repeater is operational .

Other tones :
GB3SU only responds to 71.9Hz, any other tones will result in the logic ignoring you.
There is no Internet connection directly to or from the repeater.
You cannot turn the repeater off either"!

The only other tone which may be heard is a: "bleep bleep bleep bleep" which could go on for hours! It means: Operating on Battery, You may carry on using the repeater as usual.

Remote shut down
Is required by our licence requirements, in case we jam something important like Car Fobbs
this is not controlled by the repeater logic, therefore you cannot shut the repeater off .

Postscript notes:
4U tray U is a measurement of standard 19" racks, used in the radio and computing , intended for mounting many equipment modules. Each module has a
front panel that is 19 inches (482.6mm) wide. The 19-inch dimension includes the edges or ears that protrude on each side which allow the unit to be fastened
to the rack frame with screws. In this regard the U is a unit of measurement of the vertical height of the module it is : 1& ¾ inches or 44.50mm, Per U., the
ARRL reports that 19" U racks were a standard by 1934.

Andy G4MYS Repeater Keeper