HR1 emergency transmitter

This 12 volt transistorised 500 kc/s transmitter was run off the power supply of the Redifon receiver so there was not much drain on the power supply.

General Instructions on Operation of Emergency 500/487.5Khz Transmitter

The equipment is situated at the Receiving Station, Auckland Radio, in the Emergency Radio rack.

Power is obtained from the Redfern Power Supply at 13V, 3.7 Amps.

Supply Input, Remote and Key controls are situated at the rear of the equipment.

To Operate:

The left hand switch marked 500/487.5 selects the desired frequency as well as switching the supply to the equipment.

The remote switch operates the changeover relay RL1 which connects the aerial to the output and applies voltage to the RF and MOD sections.

Operating the Key applies voltage to the RF and MOD oscillators and the transmitter is in operation.

The right hand switch allows the battery supply to be read and checked, and also gives a reading of RF Power out. This reading of RF power enables the operator to ascertain that power is being fed to the output and that the transmitter is operational.

A list of normal voltage readings has been tabulated and these readings are also shown on the circuit diagram.

Maintenance Instructions for Emergency 500/487.5Khz Transmitter, Type HR1


Check both frequencies observing that the Power Out is above the Min RF indication on the meter.

Ensure that the signal is clear and not distorted.

Check the Battery Supply meter reading, (13V).

Normally, once a week the Receiving Station tests with Wellington Radio on 500Khz for signal strength, audibility, etc. Check with the Receiving Station to see if the test has been carried out and use their results as a indication of the transmitter’s performance.

6 Monthly:

Observe the signal on an oscilloscope to ensure that the modulation is not distorted and correctly set, (approx. 30-40%).

Check, using the power meter, that the power out is 14 watts or greater at 30-40% mod.

Check all connectors and leads for tightnesss and conductivity.

List of Typical Readings for
500/487.5 Khz Standby Transmitter

Transistor V Collector V Base V Emitter Remarks
BC107 3.9V 1.2V 0.6V R.F. Oscillator, D.C. Scale, –
ve earth
2SC445 11.2V 4.9V 4.3V R.F. Stage, D.C. Scale, – ve
2N3569 11.6V 4.3V 5.2V R.F. Stage. D.C. Scale, – ve
2N3766 11.8V 2.5V* 2.5V* R.F. Driver, Vc measured D.C.
– ve earth
        *Vb & Ve measured A.C. VTVM. –
ve earth
2SC513 11.8V 1.3V R.F. Final Vc’s measured D.C.
– ve earth
Two of. 11.8V 1.3V Vb measured at C.T. of
Transformer across 5.6ohm w.r.t. earth. – ve
BC107 0.25V 0.5V* 0.5V* A.F. Mod Oscillator, Vc
measured ON Load D.C. – ve earth
        * Vb & Ve measured OFF Load
D.C. – ve earth
BC107 11.5V 2.5V 3.0V Mod Amplifier, D.C.Scale – ve
40314 12.0V 0.78V 1.34V Mod Driver, D.C.Scale – ve
40250 11.7V 0.15V* 0.45V Mod Final, Vc’s & Ve measured
D.C. – ve earth
        * Vb measured at C.T. of
transformer between 560ohm & 10ohm. w.r.t. +ve earth
        Note:  All readings above
are taken on Load unless otherwise stated.
Supply Voltage: 
On Load = 12.75V
Off Load = 13.0V
Current Drain:  
 On Remote, Key Up, (Changeover Relay Operative), = 270ma.
On Remote, Key Down, On Load, = 3.7 Amps  (500 & 487.5 KHz).
H.T. to R.F.
Section: Off Load = 12.4V
H.T. to R.F.
Oscillator: On Load = 12.4V
H.T. to Modulator
Section: On Load = 12.5V.
The Transistors
are N.P.N. and the equipment is negative earthed.

The Main Fuse rating is 5 Amp.