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RF amplifier (200 MHz to 1GHz), JFET biasing design question

Discussion in 'Radio and Communications' started by Clint Mclean, Sep 25, 2016.

  1. Clint Mclean

    Clint Mclean New Member

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    Thanks for the information Ron.


    This reference just refers to resonant frequencies:

    Lin, JC (1989) Electromagnetic interaction with biological systems. Plenum Press, New York.

    It's the Cazzamalli experiments where the transmitted signal is modulated with biological EEG electrical activity.

    This link describes the experiments in more detail and also further experiments that repeated Cazzamalli's:

    https://sm4csi.home.xs4all.nl/nwo/MindControl/radio_waves&Life.htm

    These are described in the section “Some Early Reports” and “Effects on Humans”. A resonant frequency, between 380 to 500 MHz and unique to each individual, is also mentioned.

    It's said that Cazzamalli never mentioned the power of his transmitter. In the experiments duplicating his work they mention an oscillator of only milliwatts, although they don't specifically state whether they duplicated his experiment of receiving the modulated RF.


    The antenna I use is just one of those basic 20cm to 1.5m telescopic antennas. It seems to give better results at 20 cm, probably because at a longer length it receives more RF from other sources and when moving towards it that energy is blocked, reducing the reading, where with the shorter length antenna it increases the reading.


    With the amplifiers I'm going to use filters to try and determine the frequency that's being emitted or re radiated from myself. I'm also thinking of using a very directional antenna such as a yagi or a satellite dish design to reduce the effect of other RF sources.
     
    • Informative Informative x 1
  2. RadioRon

    RadioRon Well-Known Member

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    I did some reading of the Lin book, but realized pretty early on that biological affects of RF is not my area of expertise and I would have to put in a great deal of effort to catch up, so I decided to stop. The subject of biological affects of RF/uwaves has been a huge area of study by others in the last two decades due to the avalanche of personal wireless devices being introduced since 1980. For that reason alone, I think your references, that is, Lin and Cazzamalli and the references in the web site you linked to are all too old in my opinion and I must wonder where is the more recent work, preferably published in scholarly scientific or engineering journals. I encourage you to do your own experiments, but keep an open mind to the possibility that you have a lot to learn about electromagnetic fields and experimental methods in this subject. I would be happy to give advice on instrumentation and your experimental setup.
     
  3. Mosaic

    Mosaic Well-Known Member

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    RF is my current challenge. Been reading up on it, watching webinars, acquiring test gear incl. VNA, DSA, NF analyzer, 3Ghz real time scope with 4 Ghz probes, Sig Gens, microwattmeter, assorted mixers, couplers, attenuators, matched YIGs, all kinds of RF transistors, Bipolars, GaAs, Phemt, as well as RF mmics and some Rogers Duroid PCBs and 0.8mm FR4 for 'lower' freq fun
    Most of my gear is acquired used (auctions) and then I repair it if required or else it would be out of my reach. Also most of the gear only goes to about 3Ghz. Best deal so far was an Agilent E4432B DSG 250Khz to 3Ghz with many options including an OXCO and dual arb gen, $600 with a fault in the RF output board. Took me 2 days but was able to 'fix' it with a 20K resistor as the bias for the burst PIN diode modulator had gotten 'lost' somewhere resulting in a 0% duty cycle on the RF sig.
    Next best deal was a Tek SG504 leveled SG calibration plugin for $150. Someone had hot air reworked the cavity oscillator amp and 'sucked' a bias smt cap into a large solder glob. Fixing that fixed the unit, no parts required.

    Worst headache was obtaining good 4Ghz probes for the TDS694C, Calibrated 3Ghz scope ($2K cost). Finally got 3 good probes ( averaging about $170) after two returns but 'lost' the 4th ($150) trying to 'fix' an intermittent tip. Very fragile micro circuitry in the tip (P6217).

    As a first project I want to extend the range of my Rigol DSA 815 TG to around 3Ghz., or at least past Wifi Ghz.
    Also I want to understand low noise RF amplifier design and get comfortable with IP3 and 1dB compression vs gain etc.

    The work I have done so far has demonstrated that parasitics quickly trump lumped components unless you're being careful.

    Recently got the AWRDE 11 suite, so...gotta do some tutorials with it and make a few prototypes.
     
  4. dave

    Dave New Member

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  5. RadioRon

    RadioRon Well-Known Member

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    My, but you are hitting it pretty hard. That's quite a list of activities and equipment. I've been using lumped components and "super FR4" (my term for, as an example, Isola FR408) at 6GHz with only minor difficulties. But the lumped components were 0201 size and the dielectric thickness usually on the order of 10 to 15 thou. At these frequencies, I found that resistors typically had significant inductance, but not enough to get in the way as long as you account for it. Besides, we typically don't have resistors in the signal path anyway unless you really want attenuation. I also found it necessary to use very tight tolerance components during tuning, for example Johanson +/- 0.05 pF tolerance caps.
    The one instrument that I rely on for checking the calibration of most of my other stuff is my RF wattmeter. You want to be sure you have a good one since this will be your best reference. I use a surplus Gigatronics unit, but the company I worked for found these sensors from Ladybug Tech to be pretty good. http://www.ladybug-tech.com/LBProductSelector.html

    Used test gear has been getting cheaper in the last few years. For example, the older HP stuff is not too bad now, like an 8753E VNA can be had for relatively cheap.
     
  6. Mosaic

    Mosaic Well-Known Member

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    Well I have the 8753D with test set. I use a Boonton 4210 RF microwattmeter with the 12 Ghz sensor.
    Looking to pickup an Tek S52 TDR 25 pS pulser for use in quantifying scope and probe bandwidth and some TDR work. Seems they can run standalone with a PSU.
     
  7. davenn

    davenn Active Member

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    a lot easier in 1920's he didn't have to contend with a gazillion other RF sources

    I couldn't even imagine how this would work in a normal environment these days. The signal levels of what you are trying to detect would be buried in quagmire of high power transmitters spread across the spectrum

    But that isn't really the problem is it ..... it's the direct arrival of these signals that will swamp the tiny RF signal you are trying to receive


    Dave
     
  8. Clint Mclean

    Clint Mclean New Member

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    Thanks Guys.

    I agree that a faraday cage could be very important for this research.

    So I tried some experiments in a very basic faraday cage that built.

    Using an rtl sdr as a spectrum analyzer and some code that I wrote, I recorded a segment of spectrum from 88 to 108 MHz, the FM radio stations allocation.

    The faraday cage significantly reduces the signal strength of the radio stations. Notice the FM station at 96.7 MHz in the attached images.

    The red graph is outside the faraday cage and the blue within it.

    88_108MHz_comparison.jpg


    However, what I'm trying to determine is what are all those other signals.

    The rtl sdr is plugged into a notebook which I do know generate some RF, I have previously found frequencies around 450 MHz.

    What's all that in those graphs, though? Would a notebook generate such noise throughout the spectrum, could they be harmonics?

    Here's a zoomed in image:

    zoomedin94_100MHz.jpg


    Do you guys think that it's RF noise from the notebook, there seems to be a lot of it for it to be that?

    I'm also going to do some more experiments to determine what RF is being generated by the notebook.
     
  9. RadioRon

    RadioRon Well-Known Member

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    A notebook generates a hugh amount of RF trash spectrum from DC to 2GHz and beyond, with worst stuff below about 800 MHz. There is no doubt that putting the notebook inside the cage to make a measurement of spectrum is a bad idea. Depending on the size of the cage, in fact the cage will make things look worse because the RF radiated from the notebook and cables will bounce off the inside walls and appear to add more noise power than if your cage was anechoic.
     

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