[hpsdr] thor

[Steven Doyle]

Hi Alex,

We are considering rectifying striaght off the mains, but the prototype has 
a transformer, noise issues asside the main reason being the voltage at the 
FET drain can typically reach 3-4 times the supply voltage which exceeds the 
break down voltage of most of the popular power FETS. We are using a 120VDC 
supply in the prototype.

I wasn't aware of any legal issues with rectifing stright off the mains. I 
will investigate this.

73s

Steve
G1YLB


----- Original Message ----- 
From: "Phil Harman" <phil at pharman.org>
To: "Murray Lang" <murray.lang at westnet.com.au>
Cc: <hpsdr at openhpsdr.org>
Sent: Friday, August 21, 2009 3:13 AM
Subject: Re: [hpsdr] thor


> ***** 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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