[Test-Equipment] Olders HP Spectrum Analyzers - The YIG?

[J. Forster]

In the photos, if you are referring to the blue hockey puck looking thing with
the two visible N connectors in the lower RH corner, that's almost certainly a
ferrite isolator. There should be another port located a further 120 degrees
around the perimeter with a termination likely screwed on to it.

Isolators are used like check valves. They allow RF power to flow in one
direction but not in the reverse direction. Likely this is part of the first
mixer circuit. Such isolators of that vintage have an operating frequency range
of about an octave or less. From a rough guess of it's size, I'd say perhaps 1.5
to 3 or 2 to 4 GHz, but it's only a guess. The insertion loss is typically 1 or
2 db and the isolation in the reverse direction is typically 20 to 35 db.

FWIW,
-John

wolfbob wrote:

> YIG is Yittrium-iron-garnat, a low loss ferrite that is resonate like in a
> tuned circuit at micrwave frequencies determind by a static magnetic field.
> They are used as a preselector as they can be sychronously tuned with the
> BWO. They look a lot like a circulator which is also ferrite device used to
> provide a match to one port no matter what you hang on the other port.
>
> WBob
> .----- Original Message -----
> From: "John Miles" <jmiles at pop.net>
> To: "Greg Mijal" <bluebirdtele at earthlink.net>;
> <test-equipment at mailman.qth.net>
> Sent: Saturday, January 29, 2005 3:51 PM
> Subject: RE: [Test-Equipment] Olders HP Spectrum Analyzers - The YIG?
>
> > Nope; that's a circulator; I forget what its purpose in the instrument is.
> >
> > The BWO is the large, black, highly-magnetized rectangular prism-shaped
> > object with the Watkins-Johnson label.  This is basically a
> > travelling-wave
> > tube that's optimized for voltage-controlled oscillator service.
> >
> > -- john KE5FX
> >
> > -----Original Message-----
> > From: test-equipment-bounces at mailman.qth.net
> > [mailto:test-equipment-bounces at mailman.qth.net]On Behalf Of Greg Mijal
> > Sent: Saturday, January 29, 2005 3:46 PM
> > To: test-equipment at mailman.qth.net
> > Subject: [Test-Equipment] Olders HP Spectrum Analyzers - The YIG?
> >
> >
> > Hi:
> >
> > I recently posted email about the older HP 8551B/851B spectrum analyzers.
> > The response was informative and helpful.  The consensus is that this is a
> > very robust machine.  I have decided to take a try at getting one of the
> > units going after I run a "drying out" process to the units.
> > Here's my question.  Someone mentioned that the YIG conversion was good
> > for
> > the machine and I think I found what he was talking about.  Would you
> > please
> > have a look at the pictures and confirm that that is what he was speaking
> > about. It is lower right in the photos. HV tubes removed for safe keeping.
> > http://home.earthlink.net/~bluebirdtele/yy.jpg
> > http://home.earthlink.net/~bluebirdtele/yx.jpg
> > Your thoughts are appreciated. Or should I say I am hanging on every word?
> >
> > Greg