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GB3LE Mark one 70 centimetre repeater, Provisional Specification |
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(This material is copyright of the Leicestershire Repeater Group)
UHF FM Repeater Project
The current project of the group is a 70cm repeater using modern design practice with a
better than average specification. The licence application has been made to the R.S.G.B.
and the call sign GB3LE has been allocated.
The repeater is due to come into service in phase 2 of the UHF Repeater Plan, commencing APRIL 1977. The repeater is however in an advanced state of construction and it is hoped that all tests will have been completed well before this time.
The original channel allocation for this repeater was RB10, but the group made representation to the R.W.G. of the RSGB, on the grounds that this channel was the third harmonic of the local RAYNET frequency of 144.950 MHz. The current channel allocation for GB3LE is RB4 i.e. Rx-434.70 MHz. TX-433.10 MHz.
GB3LE Operation
The operation of the repeater is deliberately kept as simple as possible, primarily to
promote activity, and also because the group feels that over sophistication prior to
operational evaluation is unnecessary. We will of course carefully evaluate the performance
and operation of the repeater, and make any changes that we feel are necessary.
Basically GB3LE receives signals on 434.7 MHz and relays them on 433.1 MHz. To obtain access, transmit on 434.70 MHz and send a tone at 1750 Hz + 50 Hz for 400 milliseconds with a minimum deviation of + 2KHz. If you have accessed successfully the repeater will send its call sign. Relayed speech is suppressed during the call sign period. Once accessed it is unnecessary to send the tone at the start of every over.
There is no "K" or 'roger bleep' fitted on GB3LE so please leave a short gap between overs. There is no short term limit to transmission time so you won't be timed out, but you are requested to keep overs to less than 2 minutes. If the repeater is in operation for a prolonged period, it will identify itself approximately every 10 minutes. Once the repeater receiver mute closes, its transmitter carrier will stay on for approximately 8 seconds. If no other station opens the mute during this period, the repeater transmitter will switch off after the F2 ident.
Remember, there may be mobile or other stations waiting to use the repeater, so please keep your overs to 2 minutes or less, and don't forget to leave a pause.
GB3LE SUMMARY TECHNICAL SPECIFICATION
| Receiver | |
|---|---|
| Frequency | 434.70 MHz |
| Bandwidth | 3db for + 15KHz |
| Sensitivity | 0.5 µV for 20db noise quieting |
| Mute | opens 0. 3 µV Closes 0.1 µV |
| Blocking | Starts at 20 mV in 50 Ohm at +1.6 MHz |
| Intermediate Frequency | 1st IF... 10.7 MHz, 2nd IF... 455 kHz |
| Spurious Response (Including image) | -75db |
| AF Response | -6db/octave from 300 Hz |
| Access Tone | 1750 Hz + 50 Hz |
| Access Time | 300 mS + l00 mS |
| Frequency Stability | Not exceeding + 2KHz of nominal between -10° C and +50° C |
| Transmitter | |
| Frequency | 433.10 MHz + 1kHz |
| Output Power | Adjustable up to 20 watts |
| Spurious Outputs | less than 2.5 µWatts each |
| Noise at Receiver Frequency | not greater than 0.5 x 10 -6 Watts |
| Modulation Deviation | + 5KHz peak (F3) |
| Ident Deviation | + 1kHz (F2) Tone at 800 Hz |
| Frequency Stability | Not exceeding + 2KHz of nominal between -10° C and +50° C |
| Antenna | |
| IMPEDANCE | 50 Ohm |
| TYPE | 6 db Collinear |
| Height | Base of mast at proposed site 680 ft. ASL. |
| Location | Proposed site is in ZM24J at Markfield Near Leicester. |
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