Logic: GB 3 SU

Logic: GB 3 SU: The TAITs

The Tait twin mobiles were designed to mobiles, however due to excellent RF design, they were also designed to be paired together, as a repeater, which We have mounted in a 19" rack module.
We have made modifications, like fitting an a APF, and the fitting of a massive heatsink on the transmitter, this is helped by not running full power from the transmitter unit, as the aerial brings up the Effective radiated Power..
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, which was a Storno purpose built repeater, which was time served. This was introduced in November 1995 as GB3EA, its failure was caused by it's Power unit.
The Storno repeater was replaced by a Yaesu Repeater a FTR5410B, around 1999, under the SMC branded name, that repeater was a brand new commercial unit, The callsign was changed to GB3SU when we moved to the
British Gas site in St Marys Road, Southampton in 2006, and was run until July 11th 2020. That unit with its G3RKL mark 1 logic is now moth-balled just in case. The Yaesu Unit never failed during its working life.
It was replaced by Private funding by two members due to its old age.

During the course of time we were able to have a VHF repeater, when the half channels with 12 ½ kc working was introduced.
With a threat of an unavailable RF power Brick, should a PA failure occur, ( it never did ) 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, We tried to introduce this while We were at British Gas, however it suffered from behavioural
problems when it was the "on air repeater" several times while We tried to tame its internal logic. The biggest annoyance being deleting through audio when it was transmitting its CWID, for this We have worked
out a "work-around", it is an internal problem built-in by TAIT, that as such We cant fix. Before this "work-around" was pondered upon another board ( APF ) has been fitted which controls access.
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 simple patch lead connecting the pair together.
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 logic as such can cost several hundred pounds, or did ,when they
were purchased, and then interfaced somehow.

User information
GB3 SU consists of four main parts: An external Power Unit which also powers GB7IV and charges the back-up battery, Receiver, APF, Transmitter, and Shut down.
The Power Unit is a 16Amp Linear Power Supply t using 4 of 2N 3055 pass transistors, with a simple battery charging module. This is a purpose designed 4U rack mounted unit.
The transmitter and receiver are a pair of Tait TM 8110 25Watt UHF mobiles, What we consider to be "logic" is the external APF board, and part of the both the receiver and transmitter circuitry.
Shut down is a relay on the PTT line. A "key" is used to shut o it off and on.
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 and characteristics.
The "Logic" is the part of the repeater system which enables you to access, it encodes the CTCSS, inserts the pip: if the transmission is long enough, and when another timer dictates generates the Morse code Identity: the "CWID".
What the repeater does
On Your call to the the repeater input, with your 71.9Hz, the APF starts several timers,:
i) Your transmission is far too short,.... the repeater will ignore you, and not even open. ( just like the Yaesu ) This is to discourage Kerr-chunkers, / PTT blippers.
ii) Your transmission is a bit longer, it will give a blank carrier and drop, No pip is sent.
iii) Your transmission is the correct length, ...it then sends a pip, which you are unlikely to hear as you are the transmitting station! ,... This is because your transceiver, has to switch from Transmit into
Receive, which takes time, and it can't do this faster then the repeater sends the Pip! Generally the cheap radios are more slow then the quality Yaesu, Icom & Kenwood brands. Listeners will of course hear your call, and the pip!
iv) the "over timer" ( Hog timer ) is started, this is 5 minutes, then you Time out.
v) transmitter timer, this is 3 hours!

Is simple and straightforward. It's timer sets it off, at the given interval. It will do this whatever is going on, the CWID generator is unaware of what else is / not going on.
Due to a design fault which We can't overcome, when it sends the CWID, which is set to be as fast as possible, your audio will be replaced by the CWID! Also: it is not possible to turn off the
CTCSS during CWID, However we believe our "workaround" means the CWID will not be an annoying in operation.

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" or using other childish terminology, please ignore such people!
* The repeater cannot tell you how strong your signal is!
* No "CWID on demand" facility.
* The CWID is at the same volume level during contacts ( who's audio it will replace ) or when the repeater is idle.
* The Logic sends: " GB3SU B ", The QTH detail has been deleted it only 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 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, contacts / QSO's and the CWID, thus you will not be disturbed by any other signal on the frequency.
Its good at home too, as the family is not driven mad by wide band inane squawks, that originate around 433.910MHz!
Also the advantage of your receiver being CTCSS controlled, the Logic in the repeaters Logic cuts the CTCSS tone off before shutting the transmitter off.. you don't get a squelch tail!
Some cheap rigs dont do this!, Example : 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 Transceiver is only Squelch controlled, you hear everything on channel, including QRM, 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.

Andy G4MYS Repeater Keeper