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Bruker BFX-5 RF amplifier

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TheMerovingian

Mon Oct 12 2009, 01:06PM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

Harry wrote ...

What about making your own NMR rig with it? I've seen very simple circuits designed for the home constructor.

Or you could use it as a linear for SSB

Yeah, i will power it with a tri-phase 5T cryomagnet :D

Seriously I will store it till i find someone interested, but only for a reasonable price, i don't want to regret selling it for less than 100$

In italy the law is regularly broken without being conscious of what people are doing

Proud Mary

Mon Oct 12 2009, 02:27PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

TheMerovingian wrote ...

Harry wrote ...

What about making your own NMR rig with it? I've seen very simple circuits designed for the home constructor.

Or you could use it as a linear for SSB

Yeah, i will power it with a tri-phase 5T cryomagnet :D

I tried to find a Google reference to the home made Earth's Field NMR, but wasn't able to find it. I can however remember its essential features.

A field coil connected to a VFO-amp is wound round a glass cell containing the sample

Also wound round the cell are a second winding referred to 50Hz.

And a third winding connected to an oscilloscope.

When the VFO is tuned through the resonance point appropriate to the earth's magnetic field, there is an indication on the oscilloscope, as the 50Hz magnetic field sweeps the protons back and forth through resonance.

I recall that the Larmor frequencies used inf Earth's Field NMR are in the low audio range, a few kHz for hydrogen nucleii.

Nowadays, I should have thought no home was really complete without at least basic NMR. For example, I imagine it could be used for estimating the residual water content during routine baking and degassing operations of high vacuum apparatus.

There are coil construction details and circuit diagrams of an EFNMR apparatus developed for Antarctic use here:

TheMerovingian

Mon Oct 12 2009, 02:56PM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

Being the earth magnetic field very weak the signal will be weak as well and it will be difficult to detect the signal of the sample. Maybe a bood bunch of neodymium magnets will work but with horrible homogeneity, placing the sample in the middle of them and the doing a CW NMR with a function generator and the amp. The better is to use s frequency sweep generator sincronized with the storage o-scope and recording a small spectra (placing dioxane like internal reference for chemical shift). It would be possible to record H1 spectra for VERY concentrated or pure liquid samples at some 10-20MHz (0.25-0.5T in the neo magnets) but with significative broadening due to the inhomogeneity, maybe adding some current-controlled shim-coils would reduce the problem

Proud Mary

Mon Oct 12 2009, 04:31PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

TheMerovingian wrote ...

Being the earth magnetic field very weak the signal will be weak as well and it will be difficult to detect the signal of the sample.

The EFNMR used by the New Zealand Antarctic Survey in the link in my post above uses OP200 as preamp, and I have a tube or two of them - and, I noticed, just about all the other components they use.

I am not an NMR-nik, by I understood that the advantage of using the earth's field - weak thought it may well be - is its great homogeneity, allowing large samples to be used.

Anyway, this is really another topic than this thread's, but there's an awful lot of things you could do with your amplifier, so I'd keep it!

TheMerovingian

Tue Oct 13 2009, 09:13AM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

Today i will test it with the oscope, function generator and dummy load

Steve Conner

Tue Oct 13 2009, 09:36AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Well, as you can see from the paper, the magnetic fields in EFNMR are so weak that the nuclear resonance frequencies are a lot lower. The paper quotes 2.4kHz, so you don't need an RF amp any more!

I was maybe too pessimistic earlier. If you built a tiny DIY transmitter with an output of a few milliwatts, you could maybe use this amplifier to boost it to 5 watts.

Proud Mary

Tue Oct 13 2009, 12:16PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Steve McConner wrote ...

Well, as you can see from the paper, the magnetic fields in EFNMR are so weak that the nuclear resonance frequencies are a lot lower. The paper quotes 2.4kHz, so you don't need an RF amp any more!

I was maybe too pessimistic earlier. If you built a tiny DIY transmitter with an output of a few milliwatts, you could maybe use this amplifier to boost it to 5 watts.

With the right earth and antenna, and good propagation conditions, you can reach out thousands of kilometres with just five watts of HF.

I once communicated directly from Svalbard right over the North Pole to Axel Heiberg Land in the Canadian Arctic using only a Racal Syncal on Low Power SSB - 1 W - (The batteries were so cold that High Power - 5W - created unworkable distortion)

You've got all the makings of a really nice little sender to which you only need add an oscillator-buffer on the input side and an C-L-C match on the output to be in business. And at 5W you can use ordinary receiving type VC's for your pi-match, so costly parts are not required.

TheMerovingian

Tue Oct 13 2009, 01:36PM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

THis amplifier must have some minimum bandwitch or i don't know how to operate it correctly. Cannot obtain a reasonable signal or output power (in 50ohm load) at 1MHz. I tried all inputs and basically none worked. The HP/AM AC input gave me a distorted waveform similar to a rectified sinewave (asimmetric though), the other two inputs gave me nothing and where shorting my input waveform, the RCP3 input gave me some forward power but with horrible waveform....

too bad i don't have a 20Mhz signal generator to test this thing

If i cannot test/operate it my only choice is to sel it without warranty (basically at 1/10 of its value)

Proud Mary

Tue Oct 13 2009, 03:24PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

TheMerovingian wrote ...

THis amplifier must have some minimum bandwitch. Cannot obtain a reasonable signal or output power (in 50ohm load) at 1MHz. I tried all inputs and basically none worked. The HP/AM AC input gave me a distorted waveform similar to a rectified sinewave (asimmetric though), the other two inputs gave me nothing and where shorting my input waveform, the RCP3 input gave me some forward power but with horrible waveform....

too bad i don't have a 50Mhz signal generator to test this thing

You don't say what your signal source is, and the RF voltage you are putting into the inputs.

One thing is clear, as your unit has no gain controls, it is clearly intended for use with a variable attenuator placed between the signal source and the signal inputs to the amp.

Here's what I'd suggest: choose one of the inputs that produces a distorted output waveform, and then attenuate the input signal until (hopefully) the distortion disappears.

TheMerovingian

Tue Oct 13 2009, 03:26PM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

The RF source is a sinewave at 1MHz, with voltage between 0.1V and 5V

I don't understand correctly how to use the inputs; need i to supply both the carrier and the modulating signal?

I tried to do what you mention, but simply the output waveform loses amplitude (it further loses amplitude if i change the frequency to lower levels)

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