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Registered Member #518
Joined: Tue Feb 13 2007, 05:20AM
Location: New York
Posts: 168
I don't have a 100kV DC power supply, if anyone has it can they test out my idea for me...
The idea is simple... two metal cones separated by an inductor... you charge the bottom cone (the top once charges with it) and then discharge the bottom one through a spark gap...
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
You could make something similar using a UHF TV antenna, an ignition coil and a couple of feet of coax. Charge up the coax with the ignition coil, then discharge it into the antenna feedpoint using a little spark gap in series with the centre conductor.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
It's a very early - pre-Marconi - spark gap wireless transmitter (left) and receiver (right).
In the transmitter, two cones in series with inductors are excited by the passage of a spark across the gap between them. I would imagine the efficiency - the ratio of input energy to radiated energy - was very low.
The big issues with high power UWB pulse transmission are impedance matching, pulse rise-time, and transmission line and radiator flashover.
In spark gap type UWB devices, the output pulses of, for example only, a Marx impulse generator are shortened by means of a pulse forming line (very often co-axial), by magnetic compression, and 'shortening' gaps, and often a combination of these methods. Matching a PFN to a suitable UWB antenna is non-trivial, and often involves having to accept high losses. For example, a bow-tie antenna (not dissimilar to your cones) may require shorting the antenna ends to Earth by means of a high power resistor network to get anything approaching a decent match without flashover, and thereby shunting more energy to Earthy than is actually radiated!
Registered Member #518
Joined: Tue Feb 13 2007, 05:20AM
Location: New York
Posts: 168
Using my method, you don't need a pulse forming network... it works like a TEA laser.... you charge top and bottom cones... when you discharge the bottom through a spark gap, the top one remains charged and there is a sudden voltage difference between them, which should put out a lot of RF energy.... advanced versions can use SF6 gas to suppress arcing.. it someone can test out this approach i would appreciate it... thanks.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The problem with your circuit is the inductance of the "Gnd" path. It would work better if you did it like Lodge, with a spark gap between the cones. Creating a voltage difference slowly, and then discharging it suddenly, works just fine. You charge the cones to opposite DC voltages and then discharge them to each other.
No pulse forming network is necessary. The discharge of the spark gap kicks the antenna into resonance, and it functions as its own pulse forming network, perfectly matched to itself by definition. :)
Sandia Labs actually built a device like this to test EMP hardening of military equipment. Firing was a two-stage process. The cones were charged to opposite voltages by a bipolar Marx generator, and then discharged to each other through a pressurised gas gap in the middle.
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New HERF idea...
