[hpsdr] thor

[Graham / KE9H]

Steve:

I think that in the context of European Electrical Safety rules,
which are the most stringent globally, that it is possible
to do off line switching, but when you do that, all parts of
the electrical system connected to the off line switcher power
supply become subject to the voltage breakdown isolation and
isolation tracking distances for the primary or line side of the power
supply.  From memory, this means that all parts of the circuit need
to observe some two centimeters isolation clearance to ground
and to any operator connected conductive surfaces, etc.

So, technically, you can do it.  And Phil's washing machine
probably complies.  But since I personally would find it
challenging to build a RF PA where all connections to the power
supply, including the power supply ground, had to be isolated
from the real/safetyRF ground by some 2 cm tracking distance, I would
personally use a power transformer and restrict the safety
compliance issues to the primary side of the transformer.

The rules apply to commercially manufactured and sold items.
I have no idea how the regulations apply to home built
equipment.

--- Graham / KE9H

==

Steven Doyle wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> 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.
>>>
>>>


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