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Re: Terry's New Plane Wave Antenna



Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Terry and Dmitry,

I've been following this thread with much interest.  Some observation perhaps:

1. Eddy currents dont seem to be a problem (or at least a proven problem).
2. The field distortion from a streamer seems like it could affect the calibration (it could increase the effective capacitance between the top load and the antenna) unless the streamer was directed away from the antenna on the opposite side. 3. If a breakout point was added to direct the streamers, then the breakout voltage would be reduced and top load voltage measurements would not reflect the true top load voltage without a breakout point. 4. For the calibration to be valid, the field distribution needs to be the same as for the conditions that are to be measured. Seems like calibrating at NST voltages with 60 Hz would work just fine if streamers and corona did not happen to distort the e-field from what exist at 60 Hz. Not sure about this so please comment.

Question:

What does the low frequency cutoff (10-15Hz) affect?? If this is a problem, then adding a wide BW amp at the antenna would allow one to source terminate in 50 ohms and the input impedance of the scope would not be a problem. Response would go down to much closer to "DC" (depends on the loading affect the amp has on the antenna.

I tend to worry about transmission lines that have little to no termination at both ends cause reflections can linger a long time and affect subsequent measurements (even if rise time is greater than the "bounce" time).

Gerry R

Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,

At 11:24 AM 12/25/2005, you wrote:


> The etched pattern is to fight eddy currents.  However, since the
> frequencies are pretty low, you could probably use a solid plane just > fine.

eddy currents from what - from primary mag field, secondary one,
toroid displacement current? :-)
btw - in what way can eddy currents affect the voltage on C2?

"Any" eddy currents. However, you are right in that there may not be any anyway. In general, flat conductors tend to reflect radio waves, but in our case, they may be better than the etched pattern. I would not worry about just leaving the surface a solid flat plate. The etched pattern may serve no use other than "looking" cool ;-)



> The 16nF is not critical at all.  for the size, that value works out
> well though.

i think that 16nF value is very critical - it (together with 1M input
resistance of the scope) defines lower cutoff frequency. of course if
you use antenna in only non-sparking conditions this makes no problem
to you, but what if you want to see the transients, associated with
the sparks formation?

If you want to see things lower than 16Hz, then us even a bigger cap! But in general, it does not mater if it is say 10nF or 50nF...


> The present etch pattern and back plane structure does have advantages > at > very high frequencies, but that may not be an issue at all for most > work.

can you be more specific on this one - what exactly advantages are you
talkin about, except eddy (?) currents? resonances with self
inductance of the flat copper plate? i think this is not a problem
comparing with just bare wire antena (without C2).

I did not want the thing to self resonant thus the pattern. However, that probably was never a problem anyway at less than 500MHz ;-)) I guess we can just forget about the pattern for our stuff since it does not help anything...

how can you see anything, if you eventually short C2 with 1M of scope
input resistance?

1,000,000 ohms is not a "short" ;-))

how can you see anything, if C2 is about 487805 times bigger than C3?

If the input voltage is 250kV, the voltage to the scope is about 0.5 volts. The scope goes down to 0.001V/div so no problem seeing the signal! The input signal has a very good S/N ratio (signal to noise) so the waveforms look fine.

definitely not only at the leader head, but instead all area of the
"jacket" of charge - all this charge is screening the head and in the
end causes the leader to stop.

http://hot-streamer.com/temp/Leader-model.gif

One would have to be carful if the streamers were significant!

Cheers,

        Terry