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)
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