new active antenna with bootstrapping of the SFET to minimize the input capacitance

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With active antennas, the input capacitance of the SFET forms a voltage  
divider with the capacitance of the passive antenna part.

One can minimize the input capacitance of the SFET and maximize the  
input impedance with the help of a bip. trans. And boostrapping of the  
drain.

www.leobaumann.de/newsgroups/Boot.jpg

The input capacitance and input impedance of the SFET are included in  
the calculation of the optimal length of the passive antenna part. With  
the input capacities achieved in this way in the femto range,  
geometrically particularly small passive radiators result.

The electronics shown here have a noise of 1.73 nV / sqrt (Hz). At the  
desired 20 dB S / N, with a bandwidth of 2.7 kHz, the antenna input  
sensitivity is 0.9 uV.

[Thanks to Rolf Bombach for the idea of bootstrapping]

regards - Leo :)

Re: new active antenna with bootstrapping of the SFET to minimize the input capacitance
wrote:

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At v(out)? Change R9 to 1 meg and it will be even less!

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A 50 ohm source driving a jfet follower makes for poor power transfer.
People tune antenna front ends to get better s/n, although atmospheric
noise usually swamps everything else.

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--  

John Larkin      Highland Technology, Inc

The best designs are necessarily accidental.


  

Re: new active antenna with bootstrapping of the SFET to minimize the input capacitance
Am 27.12.2020 um 17:16 schrieb snipped-for-privacy@highlandsniptechnology.com:
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You are kidding.

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I guess You don't know the theory of active antenna. Active antenne will  
be designed by noise-matching ...

Theory of active Antenna:
www.leobaumann.de/Theorie_aktiver_Antennen.pdf

... sorry, I have no translation of it ...

:)


Re: new active antenna with bootstrapping of the SFET to minimize the input capacitance
wrote:

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Not at all. The bigger R9, the lower the output noise. It even reduces
the atmospheric noise.

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--  

John Larkin      Highland Technology, Inc

The best designs are necessarily accidental.


  

Re: new active antenna with bootstrapping of the SFET to minimize the input capacitance
Am 27.12.2020 um 18:33 schrieb snipped-for-privacy@highlandsniptechnology.com:
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R939%.8 Ohm is the correct additional resistor for power-matching to the  
50 Ohm-receiver-input or coax-cable.

Re: new active antenna with bootstrapping of the SFET to minimize the input capacitance
wrote:

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It throws away half the signal. If the coax is end terminated, why
source terminate too?



--  

John Larkin      Highland Technology, Inc

The best designs are necessarily accidental.


  

Re: new active antenna with bootstrapping of the SFET to minimize the input capacitance
Am 27.12.2020 um 21:32 schrieb snipped-for-privacy@highlandsniptechnology.com:
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Maybe the coax-cable is long, so it is necessary.

regards

Re: new active antenna with bootstrapping of the SFET to minimize the input capacitance
wrote:

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Makes no sense. There will be no reflection from an end termination,
no matter how long the cable.

At the source end, an end-terminated coax looks like a 50 ohm
resistor.



--  

John Larkin      Highland Technology, Inc

The best designs are necessarily accidental.


  

Re: new active antenna with bootstrapping of the SFET to minimize the input capacitance
Am 27.12.2020 um 21:56 schrieb snipped-for-privacy@highlandsniptechnology.com:
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If You don't match to the coax-cable at the source, the crazy  
source-impedanz will be transformed to the end of the cable and then You  
have a totally wrong match at the end.

:)

Re: new active antenna with bootstrapping of the SFET to minimize the input capacitance
wrote:

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That statement is itself "totally wrong".

Spice it and see.



--  

John Larkin      Highland Technology, Inc

The best designs are necessarily accidental.


  

Re: new active antenna with bootstrapping of the SFET to minimize the input capacitance
Am 27.12.2020 um 23:29 schrieb snipped-for-privacy@highlandsniptechnology.com:
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good bye John Larkin - I recommend a university to you


Re: new active antenna with bootstrapping of the SFET to minimize the input capacitance
On 12/27/20 5:37 PM, Leo Baumann wrote:
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So you don't think a properly-terminated transmission line looks like a  
Z0 resistor on the input end?  What _does_ it look like, then, in your view?

Inquiring minds want to know. ;)

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: new active antenna with bootstrapping of the SFET to minimize the input capacitance
Am 28.12.2020 um 00:49 schrieb Phil Hobbs:
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I'm looking forward the new Larkin-Chart instead of the Smith-Chart.

Yes, of course, a properly-terminated line looks like a Z0 resistor on  
the input end.

But a non-properly source impedance causes a wrong matching at the end  
of the line, because the non-properly source impedance will be  
transformed to the end of the line.

Every Smith-Chart tells that to You. The other possibility is to  
calculate it:

beta=2*PI/(c/f)
Zout=(Zin*cos(beta*l)+I*ZL*sin(beta*l))/(I*ZIn/ZL*sin(bet*l)+cos(bet*l))

regards

Re: new active antenna with bootstrapping of the SFET to minimize the input capacitance
Leo Baumann wrote:
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Sure, we all know about the impedance-transforming effect of  
transmission lines.  It's due to the phase delays in the reflected waves.

However, if there's no reflection at the far end, there's none at the other.

A good many of us series-terminate line drivers and other output  
devices, because in a point-to-point link that avoids artifacts from  
reflections: it works just the same into an open-circuit load as into a  
properly-matched one, except with twice the signal amplitude (and a good  
deal lower power dissipation in many cases).

Transmitters are the same way, except backwards: you want a good match  
at the antenna end but not at the transmitter, because otherwise you'll  
waste half of your available power.

(Hint: the closed-loop output impedance of an op amp circuit might be 10  
milliohms in some frequency range, but you sure won't get maximum power  
by attaching a 10-milliohm load.)

Cheers

Phil Hobbs

Re: new active antenna with bootstrapping of the SFET to minimize the input capacitance
Am 28.12.2020 um 11:51 schrieb Phil Hobbs:
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The discussion about R9 in the circuit is trivial. To change it to 1  
MOhm like John Larkin said is balderdash. Of course we need matching at  
the input of the coax-cable.

As I see John wants to provokate - I hate this non-science behavior.

Subject was active antenna and reduce input capacitance by bootstrapping.

regards

Re: new active antenna with bootstrapping of the SFET to minimize the input capacitance
Leo Baumann wrote:
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Yup, a real live crazy German.  Welcome!

Cheers

Phil Hobbs

Re: new active antenna with bootstrapping of the SFET to minimize the input capacitance
On Mon, 28 Dec 2020 06:57:19 -0500, Phil Hobbs

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The group benefits from occasional comic relief.

But seriously, only a fraction of the people who fool around with
electronics actually understand the basics.



--  

John Larkin      Highland Technology, Inc

The best designs are necessarily accidental.


  

Re: new active antenna with bootstrapping of the SFET to minimize the input capacitance
wrote:

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Not if the end is terminated. Source termination just wastes half the
signal.

Suppose I built a grounded copper wall that has three bulkhead BNC
connectors, and you are on one side with all the test equipment you
want. On the invisible far side, one has a 50 ohm resistor. One has a
few meters of good hardline coax terminated with a 50 ohm resistor.
One has a light-year of coax with no termination.

What measurements would you do to tell which is which?


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You might change the subject, to what produces the best signal from
the receiver.



--  

John Larkin      Highland Technology, Inc

The best designs are necessarily accidental.


  

Re: new active antenna with bootstrapping of the SFET to minimize the input capacitance
On 28.12.20 18.16, snipped-for-privacy@highlandsniptechnology.com wrote:
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On LF, MF and HF (below 30 MHz), it is far more important
that the amplifier is extremely linear and tolerant to large
signals than absolute best sensitivity.

On a careless amplififer, all the crud on the band creates
far more crud from intermodulations.

--  

-TV


Re: new active antenna with bootstrapping of the SFET to minimize the input capacitance
On Mon, 28 Dec 2020 08:16:38 -0800, snipped-for-privacy@highlandsniptechnology.com
wrote:


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Nobody wants to play? How dull.



--  

John Larkin      Highland Technology, Inc

The best designs are necessarily accidental.


  

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