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... SAT tests ...

With education having become an industry, many of the tests are there to enhance the establishment's reputation - either by rejecting people who would later fail and complain, or by getting people that will do well. They don't mind missing the high risk "awkward" candidate.

When at CCL we occasionally discussed the recruitment process over a beer. We usually ended up concluding that we weren't sure we would have hired some of the extremely capable people at CCL. We suspect that personal recommendation played a part in the recruitment of those people.

Oh yes, very true.

My daughter's work experience and first job demonstrated that to her. Some of the misapprehensions she came across were worrying and some heartbreaking.

Books? What are they? Something you see in museums and old people's houses?

I (and others) are reading more than ever, but fewer books than ever.

At that age, I would hope so!

But it isn't true for post-toddlers. I would hope it was true for teens, and am pleasantly surprised when it is true for pre-teens.

Yup.

When hiring, interesting practical experience and technical prizes always made me look hard at a CV.

Sounds about right. But any cost-effectiveness calcs should include all the costs of their "trial period".

Thanks. I'll play with that. Maybe I can do the low frequency stuff with opamps and use the transformer thing at higher frequencies. Maybe switch between the versions in two bands.

RC Polyphase aka "Gingell" networks can be made very wideband at audio to low RF frequencies, are op-amp friendly and avoid wound components.

piglet

I did an audio (3 Hz to 3 kHz) phase sequence filter. (I think 10 R/C stages) It's been years but I think there were ~1 to 2 degree phase wiggles between the quadrature channels. (that was a spice thing with some variation in parameters put in by hand.) RF would be harder I'd guess.

I just finished reading Byline by Ernest Hemingway, A collection of magazine articles starting in the 20's, through the Spanish civil war, WWII and after. I'm wouldn't say you should go an buy copy, but interesting, I got it for free.

George H.

As usual, Williams&Taylor has answers.

That one is 300-3K Hz accurate to 0.2 degrees. There are tables for various order filters, and I could do 1000:1 to 2 deg with 8 opamps, or two switchable 50:1 shifters with 6 amps each, good to 1 degree.

If I go to maybe 20 MHz, I'd need fast amps and the amps might start to matter, so I might have to tweak the last stage or two to preserve the phase shift.

Agreed, getting the tapped inductors would be a pain. The inductor-capacitor tee network is interesting.

I was going to do a simple single-frequency shifter, one R and one C, but a wideband allpass doesn't look bad.

Huh, (sorry I'm late to the discussion) How the bleep does that work? What should I search under to find some other reference/ article?

george H.

Thanks.. I don't have Williams and Taylor... do they do some analysis?

So the phase one each side is winding up but the difference stays at

George H.

That book is a must-have. It has some good theory and practical design tables. I also like Don Lancaster's "Active Filter Cookbook" for quick simple stuff. Amazon has used paperbacks for $83. Must be a collector's item.

I also use TI's FilterPro program to do quick filter designs; it can find standard values that work, which is a real pain to do yourself. It does allpass, but not very well.

Right. It's impossible to do a real wideband absolute 90 degree shifter, namely a Hilbert box. It's like an ideal lowpass filter, non-causal.

Some fifty-odd years ago I built a SSB exciter where the RF phase shift was achieved with two loosely coupled tuned circuits, one slightly above the nominal frequency and the other slightly below the single nominal frequency.

For an operational amplifier all-pass node, there is a description in AOE (page 415 on 3rd ed).

Thanks I know the all pass. I made this quadrature oscillator by chaining two all-passes, (one high pass and the other low pass... or however you describe the two configurations.) It was good to maybe 1 degree or so... the AGC is what screws it up.

George H.

A variable delay line? That's wide band, but only good for one frequency at a time... which I think all the above ones are too... at least the phase sequence type things. I posted the step response of my phase sequence filter here once... it's a strange beast. Here

It 'exists' on a number of time scales.

The two pathseach generate both sidebands, but one of the sidebands is in phase, the other is out of phase. Add them and one sideband cancels.

Clifford Heath.

To buy, yes, but trivial to wind: my test subject was just seven turns quadrifilar wound on a small toroid and connected the right way. Quickest toroid I've ever wound.

Clifford Heath.

Did you use four different wire colors? The version in Williams uses one center-tapped inductor and one cap per allpass stage, but in two different chains.

Toroids need to be designed, wound, terminated, and mounted. A pick-and-place can shoot down an opamp and a cap and three resistors in about 5 seconds.

In a wideband shifter, don't the inductor values have to change?

I had two colors of enamelled wire the same size. I buzzed them out and twisted the centers together.

Yes, it's not a solution for you.

Yes, but I only needed one stage.