Re: Streamer Growth

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

> > > the variation of the echo amplitude with time.  As for resolution, to
> > > get 1 foot resolution you need a bandwidth of around 500 to 600 MHz, and
> > > that's quite another matter......
> >
> > ...to put it another way:
> >
> > Roughly 1 nS/foot
> >
> 
> only if you try and do it in a one shot measurement short pulse.  There are
> a variety of ways to get "superresolution imaging" at < wavelength (or
> 1/bandwidth, roughly the same...), pretty much relying on a series of
> measurements (all tied to power and bandwidth and time... that BT product
> thing..) Yes, there is an issue of coherence length and time for the pulse
> compression, but, there might be a way to back it out.  Think of speckle
> processing on astronomical video to get superresolution.   I'm not saying it
> would be easy, or even practical, but the possibility of RF imaging the "ion
> cloud" around the topload is one that deserves some thought.

	I've read a bit about superresolution lately, but only in connection
with coherent systems and a stable target.  Won't say it's impossible as
I plain don't know, but the target we're trying to measure sure is
neither stable or time stationary.  Furthermore, I suspect there is no
well-defined thing to image on. A "simple" UWB system would probably
come closed to working, but not simple to implement with the kind of
"receiving" equipment (very wide-band scope) that most of us own. 
Generating the transmit pulse is no big deal, but receiving the echoes
sure is.   A few years back I did quite a bit of measuring with an
"impulse radar" put together by some friends of mine.  The transmitter
consisted of a back-biased rectifier diode pulsed into breakdown and
mounted at the feed point of a large (4' square) flared-notch horn. 
Total input power to the diode was a couple of watts average.  The
receiver was another similar horn hooked to the input of a very wide
bandwidth Textronix "digital" scope. Ten thousand dollar transmitter,
all in the purchased horn, but the scope was about 50 k as I remember.
The system was sensitive enough to detect reflections from an Edison
Company power line about a half mile away, particularly when the S/N was
enhanced by averaging the signals from a number of different pulse
receptions.  The bones of that thing are still around, but don't know
where and don't think it could be ressurected.  If it were I think it
would be useful for some of the measurements we're talking about.

Ed