Tag Archives: YIG

Avantek S081-0321 YIG oscillator: not oscillating at all

One of the best sources of microwave signals still are YIG oscillators/YTO. These do require a good amount of power, magnetic coils, etc, but provide stable and rather low noise output, and good modulation capability. Core element is a small YIG sphere, placed in a magnetic field.

However, for the current unit under investigation (from a 18-26 GHz frontend), type S081-0321, 8.0-13.4 GHz, all the magnetic field and effort is wasted – no output detectable at all, not even a faint signal (checked with various equipment). Knocking it with a (small!) hammer, no effect. Varying the coil current – no effect.
Current consumption on the 15 V rail is normal.



Well, with all the basics checked, what to do with such hermetically sealed unit, other than using it to satisfy my curiosity about its internals. Hope to trace the defect to some specific part.

But before we consider more destructive measures, let’s try to re-tune the YIG by slightly adjusting the YIG sphere. This is possibly throught the side opening, which is usually welded shut, but can be drilled up rather easily.


Still no luck, no signal, even after turning the YIG quite a bit.

To look inside, carefully removed the top weld seam on a lathe, and the you can pry the case open.


What you can see is pretty straightforward, despite all the gold wires. There is an input voltage regulator, from +15 V rail, down to 8 volts (measured about 8.15 V), this is then distributed to the 4 active parts via resistors (the bluish elements). Voltage at the resistors is about 4.3 V, so all stages seem to be adequately powered and current flowing as usual. Still no signal. Also probed other parts of the circuit, with a thin wire, under the microscope. No obvious defect. The gold wires and contact point reveal a good amount of adjustment done by placing/removing bond wires as need to adjust bias currents, probably also frequency response, etc.


The coil – rather, the coils. The thick wire is the main tuning coil, which accepts 0.4~0.6 Amps, the small coil around the magnetic center pole is the FM modulation coil. This is for much lower currently but high bandwidth modulation. All is sealed and soaked with epoxy resin. Note the hand made labels which may explain the cost of these units if purchased new… looks like US style handwriting to me.


Well, seems that fixing this is beyond what I can do here with the tools at hand. So will need to look for a spare/used 8-13.4 GHz YIG/YTO somewhere.

HP 8566B Spectrum Analyzer: 2 partial units and some spare parts

This story starts with a set of rather valuable 8566B parts that I received for free a litte while ago:
8566b spare parts

A partial unit, stripped of of most of its RF parts, and missing some boards, and missing the OCXO.
8566b partial unit1

For a long time, I have been looking for another partial unit that can provide the missing boards, the OCXO, and some bits of hardware to complete the instrument. Not worried about the 85662A display units, because I have a perfectly working spare unit around, or could use the unit of the 8568B.
Finally, a unit showed up, also missing some boards and parts, but luckily, not the boards that I needed -except, also no attenuator, and no OCXO here.
8566b partial unit 2
8566b partial unit2

That’s the start, the empty space that is going to hold the RF treasures:
8566b empty space

The YTO assy, missing the YTO, and other bits.
8566b yto loop incomplete

This part, the 5086-7226, to do it fully justice, one would have to talk about it for a few hours. It is a not only gold plated inside and out, but HP used two kinds of solds, of different melting point, to assemble the inner workings in subsequent steps, without melting the already assembled parts….
8566b 5086-7226 YTF

Some more pictures – the YTF driver.
8566b ytf driver front
8566b yig driver back

The 1st and 2nd converter assy, ready for the semi rigid lines to be attached.
8566b 1st and 2nd converter

A high quality input relais and a band pass filter.
8566b input relais and bp filter

Well, unfortunatly, don’t have a spare 8566B/8568B OCXO around, and they go on xbay for no less then USD 50, often, no less then USD 100, that’s ridiculous.
May this unit, which is very low phase noise, very stable, from a HP 3585A analyzer, can be made fit? Ovenaire OSC 73-52.
8566b spare ocxo 0960-0465 ovenaire osc 73-52 10 mhz

After a LOT of fiddly work:
8568b assembly progress

8568b testing

A first signal!! Amazing! Frequency is off by 80/300 MHz – the unit will need a proper alignment, but the PLLs are all locked, which is a great start.
8566b a signal

And, the noise – the effect of harmonic mixing can be clearly seen, so the input stage and mixers seem to be all working!
8566b noise

More to come!

Wiltron 6659A Programmable Sweep Generator: 10 MHz to 26.5 GHz, in a single sweep…

This instrument just needed a few adjustments, still, very interesting to look at.
It is of a very classical design – 4 YIG oscillators (2-8, 8-12, 12-18, 18-26.5 GHz), a coupler, a detector, and all the driver and ALC circuitry to make this work.
There is also a Wiltron-brand downconverter that provides the 10 MHz to 2 GHz output, by conversion of a 4610-6600 MHz input, with a 4600 MHz LO.

The YIGs are all of best quality, Avantek parts.

The coupler, for the ALC loop, a Krytar ultra-broadband part, with a biased detector.

wiltron 6659a

6659a alc detector

wiltron 6659a yig assy

wiltron 6659a front

The generator provides ample power, 10 dBm or more, over most of the bands; about +6 dBm, at above 18 GHz – and, around 23 GHz, there is a dip in the power curve (see scope screen, showing the ALC/power signal vs. horizontal sweep). Checked the bias (was set at a constant +11 V) – changing it, and going up to +15 V, no change. Also checked the power directly at the YIG output – still, the dip. So it seems, nothing we can do about it, but for most practical purposes, about 0 dBm will be plenty, at any frequency.

wiltron 6659a power measurement

After some more alingments, the frequencies and bands are spot-on (no need to re-programm the linearizer EPROMs – all YIGs are still tracking perfectly fine), some some cleaning, using 50% isopropyl alcohol – done.

The only thing left to be done – a back-up of the 2716 EPROMs that still hold the firmware, after about 30 years.