[Elecraft] regarding the green wire

[Fred Jensen]

On 9/5/2011 11:30 AM, Mark Bayern wrote:
>>> "whose output transformer is very small with few windings ...
>
> But that is not a transformer-less SMPS. It does have a transformer.

No magic here.  Aircraft AC power used to be 400 Hz, and may still be. 
It was[is] pretty simple.  At 400 Hz, you need a lot less iron in 
alternators, motors, and transformers so they weigh a lot less.  The 
concept has been around a long time.  The turbine generators we used on 
airborne missions in the mid-60's were 400 Hz, both for weight and 
because turbines run at high RPM.  Two troops could easily carry a 10 
KVA turbine generator at a jog.  Its diesel 50-60 Hz equivalent was 
mounted on a trailer and weighed about 1,500 lbs.  The 400 Hz power 
supplies for the KWM-2A's, replacing the 516-F's, weighed about 3-4 lbs, 
including case.

Nothing magic about 400 Hz either, that's just what was "engineering-ly 
convenient" in airplanes since it was generated by rotating machinery. 
Use an electronic switch at 25 KHz to create a square wave and you can 
use a transformer wound on a ferrite core ... even lighter ... but still 
a transformer.

Good for us that power distribution stayed around 25-60 Hz.  25 KHz 
would have radiated all over the place, and does from an SMPS -- right 
into your receiver.  SAQ in Grimeton, Sweden was on 17.2 KHz and did 
pretty well on the transatlantic circuit. :-)  If I ever make it to 
Scandinavia, that alternator is on my "must see" list.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2011 Cal QSO Party 1-2 Oct 2011
- www.cqp.org