"New" resonant circuit.

I don't think it's new. There's no such thing as a free lunch... do a power consumption analysis. ...Jim Thompson

Den torsdag den 21. januar 2016 kl. 18.17.49 UTC+1 skrev George Herold:

I don't see anything new, that's a common way to do NMR probes

-Lasse

Yeah well since the Q is usually set by the coil resistance, twice the current is going to mean twice the loss and 1/2 the Q... If the Q was limited by something else.. say the cap maybe it would help?

George H.

Yeah we do something like that, but with a series resonant circuit and parallel coupling cap.

in----+-------LLLLL----CCCC---GND | | C Resonant C --coupling C | GND

But the coupling cap is big compared to the resonant cap.

George H.

That is impressively trivial. NMR RF coils are most always tuned, and gradiant coils hardly ever.

Given some Q, why stop at 2:1 current boost?

On a sunny day (Thu, 21 Jan 2016 09:17:36 -0800 (PST)) it happened George Herold wrote in :

You can 'multiply currents' by using a simple transformer.

In fact the CCL is just that, impedance matching.

I believe the two are equivalent, the caps just have to have different values to get the same match and tuning, so sometimes one or the other is preferable

one advantage of the series is that the matching doesn't affect the tuning

-Lasse

Definitely not new.

I think I've built 3 or 4 probes with that circuit back when high-end was 100 MHz.

Modern probes get more complicated - 2, 3, 4, occasionally five simultaneous channels with >40 db isolation between channels, balanced circuitry feeding the coil (better B1 field homogeneity and good field match between channels). BOMs for the electronic bits can run into the

Den torsdag den 21. januar 2016 kl. 19.17.33 UTC+1 skrev John Larkin:

Generator.html

t before.

almost

you wouldn't, you'd match to 50R because you usually have a 50R PA and use the same probe for receiving

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SYMBOL cap 176 112 R0 WINDOW 0 21 10 Left 2 SYMATTR InstName C1 SYMATTR Value 120p SYMBOL cap 128 80 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C2 SYMATTR Value 19p SYMBOL voltage -224 112 R0 WINDOW 0 36 58 Left 2 WINDOW 3 -239 53 Left 2 WINDOW 123 -1 123 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value SINE(0 1 13.45e6) SYMATTR Value2 AC 1 SYMBOL res -128 80 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1 SYMATTR Value 50 TEXT -226 268 Left 2 !.tran 1m

-LAsse

The edn article was a little thin... but the link for the company selling high power amps had more meat.

Hmm do you mean you can add another cap somewhere and get more current?

The talking around equation 15 indicates that it's really an impedance transformer. And that the resonance frequency is cut in half... that's not very good for NMR.

(once I get more than one C and one L, I get confused and turn to my EE friends for help :^)

George H.

Hi Jan, Well the article claims this is a impedance transformer.. so OK. I don't think there is any impedance matching (to 50 ohms) in this case, If that's what you meant by impedance matching.

George H.

Hi Lasse, yeah I agree they are similar. I know for the one I drew, we have to tune the coil a bit off resonance to get the coupling set... minimize the reflection. I've only got a hand wavy understanding of that though. (Of resonance the coil/cap looks inductive (on one side) and that with the coupling cap makes it look like 50 ohms. (at one frequency)) I guess I should do the math one day.

George H.

You can also do the "Colpitts" config (series two caps across the L) and drive the tap. Go for 100:1 maybe.

The RF boys habitually match impedances. There's not much new here.

Seems to me this is a way to get around not having the proper amplifier. Which is OK. Am I wrong?

That said, Hey Jan, any use for this with the Chinese Induction Heating modules? As "Tim the tool man" said, "more power!"

Mikek

Hi Grizz, (I trust I can be a bit familiar.) Were both caps part of the resonance circuit? Or was one for coupling/ impedance matching?

"scratch, scratch"... what do you mean by channels? Is there just one coil with multiple "taps" driving it?

Say if it's not a problem can you tell us where you work? (And are you/they looking for a middle aged physicist?)

George H.

The capacitor in parallel with the coil is considered tuning. The series cap is matching. Interaction is strong with that particular circuit.

One coil tuned to several different frequencies. Sometimes two orthogonal coils (1H on a low inductance loop to reduce E field and consequent sample heating and sensitivity to sample conductivity). Typical nuclei for the bio people would be 14N, 15N, 2H, 13C and 31P. Materials science types don't care much about carbon but they'll ask for the rest of the periodic table.

I just looked you up on LI and sent a connect invite.

Chemical NMR systems often work at two frequencies using the same RF coil, one freq for the research and one proton or duterium lock channel, as a frequency reference. That needs a dual matching network.

chapter 3

-Lasse

Might be new to the writer but it's just a tapped capacitor step down tuned tank to anyone else.