EMRFD Message Archive 6786

Message Date From Subject
6786 2011-11-07 17:17:18 wa9cgz Negative Resistance Preamplifier
John Sutton developed a circuit for a Active ELF antenna for Magnetic
Fields while working for NASA. Has anyone tried to reproduce this
project or is this a pipe dream?
I found the schematic with values for operation at 24khz and may
give it a try if it's real. Take a look at John Sutton with Google.


Joe wa9cgz
6787 2011-11-07 18:13:50 Chris Trask Re: Negative Resistance Preamplifier
>
> John Sutton developed a circuit for a Active ELF antenna for Magnetic
> Fields while working for NASA. Has anyone tried to reproduce this
> project or is this a pipe dream?
> I found the schematic with values for operation at 24khz and may
> give it a try if it's real. Take a look at John Sutton with Google.
>

US Patent #5,296,866, also:

Sutton, John F. and G. Craig Spaniol
A Broadband Active Antenna for ELF Magnetic Fields
Physics Essays
Vol 6, #1, March 1993

Chris
6806 2011-11-08 18:29:05 ehydra Re: Negative Resistance Preamplifier
Hi Chris -

Once I read this patent but thought it is a useless one. You even
mention it on your website (I think of otherwise good references).

What do you think about this circuit?

Anyone tested it?

regards -
Henry


Chris Trask schrieb:
>> John Sutton developed a circuit for a Active ELF antenna for Magnetic
>> Fields while working for NASA. Has anyone tried to reproduce this
>> project or is this a pipe dream?
>> I found the schematic with values for operation at 24khz and may
>> give it a try if it's real. Take a look at John Sutton with Google.
>>
>
> US Patent #5,296,866, also:
>
> Sutton, John F. and G. Craig Spaniol
> A Broadband Active Antenna for ELF Magnetic Fields
> Physics Essays
> Vol 6, #1, March 1993

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6817 2011-11-11 13:56:05 Chris Trask Re: Negative Resistance Preamplifier
>
> >
> > > John Sutton developed a circuit for a Active ELF antenna
> > > for Magnetic Fields while working for NASA. Has anyone
> > > tried to reproduce this project or is this a pipe dream?
> > > I found the schematic with values for operation at 24khz
> > > and may give it a try if it's real. Take a look at John
> > > Sutton with Google.
> > >
> >
> > US Patent #5,296,866, also:
> >
> > Sutton, John F. and G. Craig Spaniol
> > A Broadband Active Antenna for ELF Magnetic Fields
> > Physics Essays
> > Vol 6, #1, March 1993
>
>
> Once I read this patent but thought it is a useless one. You
> even mention it on your website (I think of otherwise good
> references).
>
> What do you think about this circuit?
>

There's a number of such active antennas, usually oriented towards underwater applications. Having the positive feedback determined by the turns ratio on the antenna (rod) is an elegant solution.

I'm looking at two approaches for loop antenna resistance negation. One uses a pair of tunnel diodes, which is fairly simple to implement but their negative resistance is too high to be used right at the antenna. The other uses a pair of bipolar transistors and fits nicely in my loop varactor tuner, but biasing and coupling is a bit messy.

The varactor approach will probably end up as a somewhat interesting all-diode preselector/preamplifier. The tunnel diodes should have less of a tendency to "latch up" as other Q-multipliers tend to do. I'm lacking a suitable 50- or 100-ohm potentiometer for the gain control at the moment, otherwise I'd have it up and running already. I need to make a junk yard run today or tomorrow and raid their potentiometer bins.

The bipolar transistor approach will easily provide the lower negative resistance, but it requires collector currents of 25mA and to keep the NF down and keep the high frequency cutoff up you need to use a medium power UHF or better transistor like the 2N5109, NE46134, or BQF19. The circuit requires three or four low-impedance wideband transformers, and those can be a pain.


Chris Trask
N7ZWY / WDX3HLB
Senior Member IEEE
http://www.home.earthlink.net/~christrask/
6821 2011-11-13 22:09:37 ehydra Re: Negative Resistance Preamplifier
Thank you for your comment, Chris.

- Henry


Chris Trask schrieb:
> There's a number of such active antennas, usually oriented towards underwater applications. Having the positive feedback determined by the turns ratio on the antenna (rod) is an elegant solution.
>
> I'm looking at two approaches for loop antenna resistance negation. One uses a pair of tunnel diodes, which is fairly simple to implement but their negative resistance is too high to be used right at the antenna. The other uses a pair of bipolar transistors and fits nicely in my loop varactor tuner, but biasing and coupling is a bit messy.
>
> The varactor approach will probably end up as a somewhat interesting all-diode preselector/preamplifier. The tunnel diodes should have less of a tendency to "latch up" as other Q-multipliers tend to do. I'm lacking a suitable 50- or 100-ohm potentiometer for the gain control at the moment, otherwise I'd have it up and running already. I need to make a junk yard run today or tomorrow and raid their potentiometer bins.
>
> The bipolar transistor approach will easily provide the lower negative resistance, but it requires collector currents of 25mA and to keep the NF down and keep the high frequency cutoff up you need to use a medium power UHF or better transistor like the 2N5109, NE46134, or BQF19. The circuit requires three or four low-impedance wideband transformers, and those can be a pain.
>
>
> Chris Trask

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