> I have read the comments on the use of an RF transformer to step up the
> output impedance of the PINET simply for the purpose of trying to get away
> with an undersized loading capacitor. This sounds like a bad idea to me, for
> the following reason.
>
> This imposes a requirement to design and build a transformer capable of
> handling 1.5KW over a decade+ of frequency, with low losses. It can be done,
> but just barely and at a high cost. I would appreciate some hard facts from
> someone (preferably an owner of one of these amps) from which I could make my
> own calculations of the potential insertion losses.
Almost all transmatches and "antenna tuners" built for the last 25 + years have
such a transformer; only wired in reverse. No need to re-invent the wheel here.
They work fine as long as power limits are not exceeded. Every transformer
has losses, but I doubt if it is anywhere near 1 db.
I have always questioned the claims in the QRO advertising about harmonic
attenuation attributed to this device, and their inference that this is a quasi-
Pi-L network. It is actually a simple Pi network, and measuring the harmonic
attenuation should bear this out.
The inclusion of this transformer in the QRO products was most likely an
economic decision. Cost savings in variable and fixed capacitors in the
loading section, as well as a gain in chassis space were probably weighed
against the cost of the 4:1 transformer. Also, since this transformer is at D.C.
ground potential, the need for a safety RF choke in the output is eliminated.
(((73)))
Phil, K5PC
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