[hpsdr] thor

[alex]

no i mean run the amp on 340 volts from mains but modulate the duty 
cycle of the rf into the pa (so with only 1 semiconductor (+ diodes) for 
the whole pa/psu)

> ***** High Performance Software Defined Radio Discussion List *****
>
> Hi Alex,
>
> That is exactly what is planned. Basically you build a switching PSU
> running at say 200kHz.  You use the your modulation envelope signal to PWM
> the PSU and that gives you a DC voltage that varies in sympathy with the
> modulation.
>
> At bit like the AM modulators we built years ago. There is one significant
> difference.If you think of the envelope of an SSB two tone test signal
> then as the envelope passes through zero volts the signal rapidly changes
> direction. You need a wide enough  LPF to pass this signal but still able
> to attenuate the (200kHz say) switching frequency.
>
> This is one of these techniques that 'works beautifully on the white
> board' :-).
>
> Not sure about Murray's comment on rectifying the mains directly. Our
> washing machine does this and does not have a mains transformer to be seen
> - and produces the most QRN of any device I've ever come across!
>
> 73's Phil...VK6APH
>
>
>
>   
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> alex wrote:
>>     
>>> ***** High Performance Software Defined Radio Discussion List *****
>>>
>>> why bother having a separate modulated psu, why not run the pa off
>>> rectified mains and modulate the duty cycle.
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>>>       
>> Hi Alex,
>>
>> I don't know about the US, but in Australia I think it is illegal to
>> rectify the mains directly. There must be a transformer first.
>>
>> Murray VK6HL
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>>     
>
>
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