|Subject:||Re: LF: SAQ 17.2 kHz|
|From:||Dick Rollema <[email protected]>|
|Date:||Mon, 22 May 2006 14:39:08 +0200|
To All from PA0SE|
The control circuitry for an alternator transmitter takes into account that the drive motor needs to receive more power during key down than during key up condition. The key not only drives the magnetic amplifier that passes or shuts off RF, but also an auxiliary circuit that throttles back power to the motor when the key is up. There is a grand rheostat to trim the key-up speed to match the key-down speed. However, I expect this is a fairly delicate balancing act; and, I don't believe the motor control system can respond quite as quickly to a state change as the magnetic amplifier does.
Here is a circuit diagram of the SAQ station. To get it through the reflector I had to compress it heavily. But you can recognise the magnetic amplifier at the right. When the key is down a dc current saturates the core and the aerial circuit is closed. In two of the phases feeding the notor transformer like objects can be seen. at the left. In reality these are chokes with a secondary winding carrying dc current saturating the core when the key is down.
The rheostat John mentions is in the rotor circuit of the motor and can be seen above the motor.
73, Dick, PA0SE
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