Phil, we're still only half way there on this issue!
An isolator is a device used to force a required impedance on the input
or output circuits of typically, active devices such as GaAsFETS, used
in the early low noise amplifiers. These isolators made them stable by
stopping oscillatory tendencies in or out of band.
Low noise performance was improved despite the insertion loss of the
isolator, around 0.5 dB at microwave frequencies.
Improved RF design techniques and closer PCB tolerances have made the
isolator redundant in most LNA designs, but one still encounters them in
devices such as signal generators, which Joe Ham is likely to connect to
a piece of wet string of zero line length, and wonder why his SWR meter
reads b/s.
Circulators are used on power RF circuits, they have an additional port
equipped with a dummy load capable of handling Joe Ham's reflected
power, which is what Joe Ham was trying (presumably) to infer in his
"SWR quiz", although his terminology got lost.
Ian ZS6BTE
"Phil T. (VA3UX)" wrote:
>
> Uncle! I give-in!
>
> Thanks to all who educated me on the fact that there really is an RF
> device, properly known as an Isolator. Having never worked on anything but
> HF, where isolators apparently aren't common, I admit I'd never heard of
> one. I have seen these "coax isolators" for HF advertised in magazines,
> but I believe they're just ferrite bead baluns - renamed for the new
> application.
>
> Phil
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