[Lowfer] Question

[Bill Ashlock]

Hi Dave,

Thanks for the advice. When one gets so used to 1W beaconing it's easy to 
neglect some of the 'givens' at high power.

> > the current and Rr are calculated. The resonant capacitor voltage
> >comes to less than 1000v so there's nothing exotic required to build > 
> >this.

>True, nothing exotic, but watch the current rating on the cap-you may >need 
>a series-parallel arrangement to keep the current per cap down to >an 
>acceptable figure --  eg. 4700pF 500 volt polystyrenes (despite an 
> >excellent measured Q value) typically fail at any more than about 1.5 
> >amps continuous.(at 180 kHz)  A practical continuous rating for them 
> >appears to be 1 amp. Other cap values and types of dielectric will no 
> >doubt have a range of ratings but the continuous current rating for >the 
>required frequency has to be determined experimentally for most >types.

Good point. At the moment I'm running about 4A on the .02uf dipped mica cap 
on the test loop (hard to believe this is only 1w!) and I can sense
a small heating effect. I'd be using approx 800pf on the 500ft wide loop 
(~1mh) and the current would be about 7A. (Not exactly woods- burning 
current in case HM is on board <G>) Fortunately, the actual loop, no matter 
what the size, can be simulated with a small coil, and these variables can 
be worked out in a warm bench environment. Now I'm thinking about the danger 
of the radiation from this coil. Yikes! No problem keeping those late-night 
snacks warm <G>.

BTW, I contacted one of the major manufactures of mica capacitors as to the 
RF losses of the 2000pf, 500v caps that I use a lot of. They actually ran a 
test on 10 caps in their engineering lab for me at 185k and at the 
approximate current I run, so that they could give me a 'good' value.

Bill


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