[UK-CONTEST] Slightly OT....

[G3RAU at aol.com]

I wish more people understood linear design as well as  Adrian  obviously 
does, but unfortunately there still seem to be a lot of people who  don't 
understand their licence conditions regarding power output and all the  thinking that 
goes into the design of big linears.
To deliver 400 watts into a UHF antenna up a high mast with inevitable  
feeder loss could need a kilowatt or more of RF pumping in to it.
Allowing a 40-50% efficient linear you now need more than 2KW of DC  power.  
The PSU needs to be tough enough not to sag (drop voltage) when on  full load, 
as this just helps to reduce linearity and encourage splatter.  So a 3KW 
xformer is perfectly sensible. Of course there are  transformers with a continuous 
rating of 3 Kw for ever and ever in the tropics,  or ones rated for 
intermittent amateur use at room temperature which will  probably be half the size & 
weight. The old ones are often much  cheaper but bulky & heavy, whereas  the 
domestic grade frequently  give up and die when faced with a 48 hours contest.  I 
know  which I would use in a home brew.
 
You can't really take the Mickey out of somebody's transformer until it is  
so big you need to stand on a chair to alter the voltage taps.........
 
Happy home brewing
Derek G3RAU