There is a loop receive antenna. It is the LC circuit with the Q at the order of 100. It has a high resonant peak. The frequency and the amplitude of the peak are sensitive to the component values, temperature, particular parts, etc. I would like to damp the Q down to something like 10, so the parameters would be much more stable and predictable. This can be done by adding a series or a parallel resistor to LC.However the SNR of the antenna drops approx. proportionally to sqrt(Q) due to the thermal noise of the damping resistor. I wonder if it could be possible to implement the noiseless damping. Cooling down the resistor is not an option.One idea is to switch the damping resistor on-off with a high frequency and a low duty ratio. Or to switch or vary the value of the capacitor so the resonance peak will be dithered. It has many side effects, though.Any ideas, suggestions?Vladimir VassilevskyDSP and Mixed Signal Design Consultant

De-tune the antenna?-- Paul Hovnanian -----------------------------------------------------------------------Procrastinators: The leaders for tomorrow.

Noiseless Damping?

Mar 12, 2008 25 Replies

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Vladimir Vassilevsky 18 years ago

Precisely. However I am more interested in the opposite trick: if a small resistor is bootstrapped by a low noise amplifier with the gain close to unity, the input impeadance is multiplied while retaining the voltage noise of the small resistor.

Yes. The simple math shows that it is possible to reduce the noise temperature by about of the order of magnitude.

It works, although there are some pitfalls because of the phase shifts and the stability concerns.

They basically do the same thing plus the C1/C2 transformer feedback coupling. This allows for the additional flexibility, not sure about the stability margin though.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

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JosephKK 18 years ago

My quickest thoughts were using a PIN diode to limit the "Q" or a quiet JFET to reduce "Q" as needed. Both could be dynamically adjustable.

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miso 18 years ago

Wait a minute. Does this mean you can't cut taxes, build up the military and balance the budget at the same time?

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Vladimir Vassilevsky 18 years ago

Of couse you can. Just make debts and print money. What an interesting time! I lived through the disintegration of the USSR, now I experience the demolishion of the USA, I wonder if I will see the demise of China!

VLV

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John Larkin 18 years ago

The US has one of these stock market bubble-meltdowns about every 20 years on average, although modern technology may allow them to get closer together, as in the dot-com bust and the latest mortgage thing; both, as it turns out, being Clinton legacies. The relaxation time constant seems to be about equal to the greed/fear decay time of amateur investors. Some money changes hands, some people get hurt, lots of press gets generated, Congress makes a lot of speeches and a few new laws, and life goes on. The US still has pretty good basics: lots of land and food, a young and vigorous population, a good environment for science and technology and business.

John

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Michael A. Terrell 18 years ago

Then beat the rush and haul your ass to Africa.

aioe.org is home to cowards and terrorists Add this line to your news proxy nfilter.dat file * drop Path:*aioe.org!not-for-mail to drop all aioe.org traffic. http://improve-usenet.org/index.html

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