bias tees

Have you played with conical-wound broadband inductors? There are some amazing examples. E.g.

Clifford Heath

Capacitor and two pieces of wire?

To first order

Yes, we'll probably use them in production. The bias tees are for testing parts first.

It looks like the Piconics patents ran out, so other people are making conicals. Prices have dropped roughly 4:1.

These are cool, ferrite filled like the conicals but higher current.

I don't understand how they can have "Flat bandwidth with high impedance to 6 GHz" but an SRF of 235MHz. Surely if they turn capacitive above

Clifford Heath.

Huh, will you post pics? I did a bias Tee in our laser head, I've only tested it to ~ 200 MHz.... (no HF source) I'm very sure it does not go to 6 GHz. (but that would be a cool frequency to get to!) (Rb hyper-fine transitions and all.)

George H.

That was $4.00? Dang.

GH

Piconics was the first conical inductor company. Gowanda also sells them. A VX had some too, last I checked. Conicals are fragile and Production always hates them.

One has to be careful in interpreting current rating across vendors. John's Tee says 0.5 A, but no conditions accompany it. The CCI BCL-652JL is 6.5 u

emperature delta is measured. It seems like a thermocouple would draw heat away from the thing it was measuring. For a small thing, maybe that matters .

$34 looks like.

Dang ain't nobody going hongry in the bias tee business!

They have impedance:frequency curves.

Sure they get capacitive at very high frequencies; all inductors do that. But the impedance is still high.

Capacitors are still useful above their SRF too. A 47 uF ceramic cap is going to have a pretty low SRF!

$29. He paid an extra $4 for fast shipping.

The connector ground pads on the pcb look de-soldered? Don't I want my pcb grounded right at the in/outputs? (that's what I always do.)

George H.

One could measure its resistance, or thermal image it.

No, $30 each. The extra $4 was for overnight delivery.

A long time ago, we tried them for the DFB lasers in our fiberoptic transceivers. Worked very good, but at $35 a pop impossible for production. Thanks goddess, that Piconics patent has exspired now.

I once told the MCL sales guy that they might sell one for each ERA-8 if the price was right. He was all ears. :-)

One of my colleagues put some RF ferrite into a mortar, added some epoxy and formed a conical core himself. That looked ugly but performed quite well. Cost a lot more than Piconics and was unfit for production. But educating. :-)

For upto 10 GHz, 100nF 0402 is OK as the capacitor, esp. if you only want nice optical eyes.

The choke is harder; it can be made from really cheap parts but it takes a day at the VNA, some creative soldering and the inductor / ferrite / resistor kit.

This here is a PicoSecondPulseLabs 5828-108 amplifier. 15 GHz / 22ps tr.

and the notes I made when I opened it some years ago is to the right. (and even further right some of Gerhard's adventures)

Data sheet of the amplifier: <

Input is to the left, output right and on the underside there is a CCS made from LM3xx. There is also some ferrite rubber glued to the upper lid to dampen the box modes.

They use a monolayer capacitor that is about as wide as the microstrip. The ustrip has just a narrow cut and the other side of the monolayer cap is contacted with a piece of wide Cu foil. Parallel to the monolayer C there are 2 additional 0402 caps, soldered on top.

On the output side, there is a series RC to gnd after the first coil to dampen some resonance. Don't use too much inductance to push down the lower frequency limit. It stores energy and if you short Vcc that may kill the amplifier chip / DUT.

cheers, Gerhard

We use the sideways caps for fast stuff, like 0306 instead of 0603. Much better at speed.

What did that cost?

Fog on hills. Looks a bit like San Francisco.

Here's an ancient ebay PSPL bias tee:

The pcb layout was obviously for edge-launch SMAs, but maybe they got the flange parts cheap.

Am 05.02.19 um 05:00 schrieb John Larkin:

I have some of them here, but never really used.

Also interesting are XY capacitors with contacts also in the middle of the long side. Available vom Johanson and some others. They are designed with via placement to VCC and GND plane in mind. The flux from the vias cancels.

Don't remember. Bought them on ebay from some guy in Switzerland.

THAT kind of fog in SF would be scaring. Maybe when St.Andreas wakes up. That's a hi temperature field in Iceland. They skimp on warning signs. But when there is one, you better respect it. If you walk there, you might break into a hole with hot sulfuric slime around your knees.

Oh, and it stinks. Mother Earth, the Queen of farts.

regards, Gerhard