[Amps] HV switch-mode power supply

[Roger]

John Wilson wrote:
> All,
> Here's my take on this, particularly from a VHF contests point of view. 
> We need good HV SMPS because;
>
> 1.  Must be lighter, and hopefully smaller and more efficient than 
> equivalent linear supplies, - lugging heavy PSUs to contest sites is a 
> (back) pain.
>
> 2.  It will cope with poor quality power supplies - we currently have to 
> hire generators for VHF portable contests that are vastly overrated to 
> cope with the huge swing, poor power factor, and distorted current 
> waveform from linear PSU's and still give a reasonably constant voltage.
>
> 3. In the denser parts of Europe, received signals in a VHF contests on 
> a good site can be enormous and so signal quality is very important. The 
> supply therefore needs to be regulated .
> a)  To cope with smaller poorly regulated generators as above,
> b)  To allow the most linear operation of the amplifier to reduce 
> splatter.  Tuning a linear amp and throttling it back to give good 
> linearity needs care even on a decent mains supply. On a mutliband 
> contest site with poor quality power whose voltage is varying with the 
> demands of the other stations, it's a nightmare.
>
> 4. It needs power factor correction.  Again to allow smaller, cheaper, 
> more efficient (hence lower CO2), generators to be used.
>
> 5. It needs low ripple and spurious on its o/p.  Any switching ripple on 
> the high voltage lines will modulate the signal. 100 / 120 Hz ripple on 
> a linear supply is not too serious as it only needs to be say 40 dB 
> below peak speech level i.e 1% and its harmonics will get lost in the 
> intermod / splatter.  However beyond say 10 kHz from carrier, outside 
> the splatter zone, it becomes very serious .  A close by station may 
> well be receiving -20 dBm signals.  His noise level in 3 kHz is likely 
> to be in the -130 to -140 dBm region depending on band thus the ripple 
> needs to be better than about -110 dB down (say <3 mV).  Otherwise local 
> fixed stations will call you and tell you they can hear you at say 75 
> kHz intervals up the band.  I think this is achievable but it will need 
> careful design.  There is also the need to consider induced ripple into 
> other nearby equipment, supplies and cables so well screened enclosures 
> and good mains filtering are important.
>
>   
This reminds me of a W/K 5 that was on six meters during the last peak. 
He did have a very big signal, but man was it broad.  Of course when any 
one mentioned it, he'd go into a tirade about their receivers and poor 
front ends. However the two biggest signals on the band "for me" was a 
station about 5 miles from me running power AND stacked 8L Yagis and 
another about a mile from me. The second one wasn't running a lot of 
power, but at a mile the only station on the band that could outdo him 
was the one at 5 miles. Neither of them had broad signals even though 
they put the s-meter farther over than that 5. I could hear him about 
50-75 KHz up and down the band.

73

Roger (K8RI)