Hi Scott,

Actually, I'm using the 10Ghz M/A Com gunnplexer from shfmicro (the company
that you told me about in a personal email which was a reply to a question
on the piclist months ago). Thanks for telling me about them, it's a great
company!

I did some back of the envelope calculations using the datasheet for the
gunnplexer and this suggests that you should be able to get a 1:1 signal to
noise ratio in a typical audio bandwidth (a few kHz) with the 10mW source
and the small (about 5 inch wide) horn when pointed at an object of 1m^2
radar cross section at 50 feet away. In my circuit, the audio amplifier
produces about the same amount of noise as the gunnplexer, and I am barely
able to detect with my ear echos from cars as far away as 100 feet. At 50
feet the echo can be easily heard. I think that an audio filter helps, but
I am puzzled as to why you didn't get similar performance.

About the electrons vs. ions, I wonder what the RCS of an Hg ion is at
10GHz? I have actually seen the figure for a free electron, and it's pretty
darn small :-), although if you have trillions of them(or even more!), it
does add up!

I saw an article from a car magazine where they tested various police radar
countermeasures. They said that some of them contained several fluorescent
tubes with wire wrapped around them (like you said) and they had no effect.
This is probably a case of something that would work if you made it very
carefully and energized the tube properly but has little chance of working
if you just throw it together in a plastic case.

Sean


At 07:11 AM 2/23/02 -0600, you wrote:
>Mine only worked for 5-10 feet, with a milliwatt gunnplexer and a
>'low-noise' audio amp (LF353 is 15nV/Hz^-2 IIRC). Maybe if I had a 100mW
>diode, an big horn with a lens(rather than a six inch one) and a filter to
>limit the audio bandwidth to a KHz I could get similar performance? I tried
>one from an alarm from a ham-fest. You can also find old radar detectors
>with even weaker outputs, that can be improved by removing those 'idler'
>screws designed to prevent the local osc from radiating.
>
> > For the most part, I understand how this works. However, one thing puzzles
> > me: when I point it at a fluorescent light, I hear a VERY loud 60Hz hum
> > (might actually be 120Hz, it is hard to tell because most of what we
> > usually attribute to 60Hz is really full wave rectified 60Hz which is
> > actually 120Hz).
>
>Probably 120 Hz
>
> >So, my only guess is that the radar is
> > seeing an echo from all the mercury (?) ions being jostled around inside
> > the light at 60 or 120Hz. I'm not surprised that I would be able to detect
> > such an echo, only surprised that it is SO strong, it is much stronger,
>for
> > example, than the echo from my power supply fan.
> >
> > Any ideas?
>
>Probably not the Hg ions, but the electrons themselves. Simply, the plasma
>switches between conductor and non-conductor 120 Hz. It is not merely 60 Hz
>capacitive or inductively coupled noise, but that could be a component if
>your circuit is not capacitively and inductively shielded.
>
>Plasma is very interesting. It has several types of resonant frequencies,
>and
>is affected by the earths magnetic field. I heard cases where spiral wires
>are wrapped aroundfluorescent tubes, making them into a kind of TWT
>(microwave traveling wave
>tube) that can even amplify and reflect radar, jamming it. You know those
>license plates with the fluorescent tubes wrapped around them? I hear they
>have a high-frequency ballast, so police radars are jammed by the noise they
>create. Just what I've read, FWIW.
>
>Scott
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