Megaimpulse NPG-20/3500 User manual

NANOSECOND PULSE GENERATOR
NPG-20/3500
and
NPG-20/3500N
USER MANUAL
© 2021 Megaimpulse Ltd.
v.1.0

Copyright © 2021 MEGAIMPULSE Ltd. All Rights Reserved.
MEGAIMPULSE LTD. PROVIDES THIS MANUAL "AS IS" WITHOUT WARRANTY OF ANY KIND,
EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTIES OR
CONDITIONS OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
SHALL MEGAIMPULSE LTD., ITS DIRECTORS, OFFICERS, EMPLOYEES OR AGENTS BE LIABLE FOR
ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES (INCLUDING DAMAGES
FOR LOSS OF PROFITS, LOSS OF BUSINESS, LOSS OF USE OR DATA, INTERRUPTION OF BUSINESS
AND THE LIKE), EVEN IF MEGAIMPULSE LTD. HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
DAMAGES ARISING FROM ANY DEFECT OR ERROR IN THIS MANUAL OR PRODUCT.
SPECIFICATIONS AND INFORMATION CONTAINED IN THIS MANUAL ARE FURNISHED FOR
INFORMATION ONLY, AND ARE SUBJECT TO CHANGE AT ANY TIME WITHOUT NOTICE, AND
SHOULD NOT BE CONSTRUED AS A COMMITMENT BY MEGAIMPULSE LTD. MEGAIMPULSE LTD.
ASSUMES NO RESPONSIBILITY OR LIABILITY FOR ANY ERRORS OR INACCURACIES THAT MAY
APPEAR IN THIS MANUAL, INCLUDING THE PRODUCTS AND SOFTWARE DESCRIBED IN IT.
Products and corporate names appearing in this manual may or may not be registered trademarks or copyrights of
their respective companies, and are used only for identification or explanation and to the owners' benefit, without
intent to infringe.
Megaimpulse Ltd. contact information
Address: 28 Polytechnicheskaya str., St. Petersburg, 194064 Russia
www: http://www.megaimpulse.com
e-mail: [e-mail]
fax: [phone]

CONTENTS
Safety manual ............................................................................................... 2
Package content ............................................................................................ 3
General view of NPG-20/3500 nanosecond pulse generator ............................ 3
Description ................................................................................................... 4
Technical specification ................................................................................. 5
Front and rear panels view ............................................................................. 6
Putting the generator into operation .............................................................. 7
Triggering of the generator ........................................................................... 9
Overheat mode .............................................................................................. 10
Output pulse monitoring ................................................................................ 11
Fuse replacement .......................................................................................... 12
Warranty ....................................................................................................... 13
NPG
-
20/3500
and
NPG
-
20/3500N
User
manual
1

SAFETY MANUAL
Electrical safety
 NPG-20/3500 (NPG-20/3500N) generator is high voltage equipment.
Please be very careful and operate by qualified personnel only.
 There is a risk of electric shock, strong electromagnetic interference,
damage the generator or other electronic equipment in case of improper
use.
 Do not turn on the generator without proper grounding. We recommend
using a grounding cable connected to the terminal on the rear panel of the
generator or a three-terminal power supply outlet with proper ground
contact.
 It is strongly prohibited to switch on the generator without an output
coaxial cable attached. There is a risk of electrical arcing on the open
coaxial connector and damage to the output circuit of the generator. Please
use our special high voltage coaxial connector and cable only. Standard
UHF, N-type, or 7/3-type connectors are not suitable.
 When adding or removing the generator to or from the system, ensure that
the power supply ON/OFF switch is switched off and the power supply
cable is unplugged before the output cable is connected or disconnected.
 Please connect or disconnect any equipment, toggle generator from internal
to external triggering mode or vice versa while the generator is in high
voltage OFF state only by HV ON/HV OFF switch.
Operation safety
 Please read this manual before installing and using the generator.
 Before using the product, make sure that all cables are applicable and not
damaged. High voltage connectors should be clean and dry, free from dust,
dirt, and any obstacles.
 To avoid a short circuit, keep metal parts like clips, screws, and staples
away from the generator.
 The generator is designed to work in normal laboratory conditions. Avoid
dust, humidity, and temperature extremes. Do not place the generator in any
place where it may become wet.
 Place the generator on a stable surface.
 If you encounter any technical problem with the generator, please contact
Megaimpulse Ltd. Do not try to repair the generator by yourself.
MEGAIMPULSE LTD. 2

PACKAGE CONTENT
Please check the package for the following items:
 NPG-20/3500 (positive polarity) or NPG-20/3500 (negative polarity)
nanosecond pulse generator (hereinafter "generator")
 Power supply cable
 High voltage output coaxial cable
 User manual
Fig.1. General view of NPG-20/3500 nanosecond pulse generator.
NPG-20/3500 and NPG-20/3500N User manual 3

DESCRIPTION
NPG-20/3500 (NPG-20/3500N) generates high voltage unipolar nanosecond range
pulses. The pulse width is fixed, while the amplitude and repetition rate can be
adjusted by the front panel knobs. The typical output pulse waveform is shown in
Fig.2.
Fig.2. Typical output pulse waveform of NPG-20/3500 on matched 50 Ohm
load. Amplitude knob is in max position.
The generator is designed for operation with 50 Ohm impedance load only,
for example properly made antenna. In spite of the generator has protection
from overheating and damage by the reflected pulses energy in case of unmatched
load, RG213 or RG214 cables are not suitable for the long-time operation with
high impedance load at high frequency.
 Please choose for the discharge applications 75 Ohm impedance models of
nanosecond pulse generators, for example, NPG-18/100k or NPG-18/3500.
MEGAIMPULSE LTD. 4

TECHNICAL SPECIFICATION
Output pulse amplitude (typical) Regulated 10 kV ... 20 kV on matched
50 Ohm load
Output impedance / output cable 50 Ohm / RG213 or RG214
Pulse polarity positive (NPG-20/3500)
negative (NPG-20/3500N)
Pulse rise time
(fast part of output pulse) < 4 ns
Pulse width (FWHM) 10 ns
Min/max pulse energy 10 mJ / 40 mJ
Peak pulse power up to 8 MW
Repetition rate from 1 Hz up to 3.5 kHz
Single pulse mode yes, in external triggering mode
Triggering internal or external
External triggering BNC input connector; +2.5V ... +15V
amplitude, 50 μs ... 200 μs pulse width
Internal generator delay 1 μs
Jitter RMS (typical) 1 ns
Output pulse monitoring BNC connector, 2.5V@50Ω/5V@1MΩ
Generator power supply AC 110-230V / 50-60 Hz
Size 248 х 90 х 250 mm3
Weight 4 kg
Ordering:
NPG-20/3500 – generator with positive output pulse polarity
NPG-20/3500N – generator with negative output pulse polarity
NPG-20/3500 and NPG-20/3500N User manual 5

FRONT VIEW
7 8 9
2 4 5 6 10
REAR VIEW
1 3 11 12
1 - power supply ON/OFF switch
2 - output coaxial connector
3 - power supply connector and fuse holder
4 - HV ON/HV OFF - high voltage on/off switch
5 –EXT/INT - external/internal triggering switch
6 - BNC SYNC IN connector
7 - OVERHEAT LED
8 - AMPLITUDE regulation knob
9 - FREQUENCY regulation knob
10 - BNC SYNC OUT connector
11 - fans
12 - ground terminal
MEGAIMPULSE LTD. 6

PUTTING THE GENERATOR INTO OPERATION
 Please follow strictly the described steps. It helps to prevent damage the
generator, other equipment, and personnel injury.
Step 1.
Unpack the generator and check the presence into the package of the following
items:
- NPG-20/3500 (NPG-20/3500N) generator;
- power supply cable;
- output 50 Ohm coaxial cable.
Step 2.
Set up the generator. Ground it obligatory by connecting ground cable to terminal
on the rear panel (12) and/or use three-terminal power supply outlet with
grounding contact.
Step 3.
Check the output coaxial female connector on the front panel of the generator (2)
and co-pair male connector on the cable. Both connectors should be clean and dry,
free from dust, dirt, and any obstacles. Clean the connectors with alcohol and/or
cotton bud if necessary, put a drop of silicone oil onto the Teflon insulating parts.
Attach the cable connector to the generator front panel connector (2). The tight and
firm contact of the connectors is very important for the normal operation of the
generator. Even a small air gap between the connectors may result in arcing,
destroying the generator and the cable.
To obtain good and tight contact the following procedure is recommended:
1. Align both connectors.
2. Hold the generator by one hand to prevent moving and press the cable
connector by another hand toward the generator connector.
3. Screw the cable connector nut by hand, usually one or two turns. Do not
rotate the cable connector body.
4. Press the cable connector toward the generator connector again.
5. Once more screw the cable connector nut one or two turns.
6. Repeat steps 4 and 5 up to tight contact. Finally screw the cable connector
nut firmly by hand.
It is recommended to check whether the tight contact obtained or not after the first
test operation of the generator. Unscrew the cable connector; there should be no
ozone or burnt smell from the cable connector, even a little, or any burnt traces.
Please do not connect and disconnect the high voltage connectors many times to
prevent the contacts from wearing.
NPG-20/3500 and NPG-20/3500N User manual 7

Step 4.
Connect the other side of the coaxial cable directly to the load by soldering, or
through an additional suitable HV HF connector. In case of using the wires
between the coaxial cable and the load, please make them as short as possible.
 More than 5 cm additional wires between the load and coaxial cable result
in excessive stray inductance in series with the load.
 The length of the output coaxial cable is about 3 meters. The shorter cable
may result in permanent damage the generator in case of load breaks and
operation on a short or open load.
Step 5.
Toggle HV ON/HV OFF switch (4) to HV OFF state.
Toggle EXT/INT switch (5) to INT state.
Place both "AMPLITUDE" (8) and "FREQUENCY" (9) knobs to the most
counterclockwise position, which corresponds to minimum amplitude and
frequency.
Connect power supply cable to the power outlet.
Switch on the generator by the power switch (1) on the rear panel. The internal
fans (11) of the generator should start to rotate.
Step 6.
Switch on the high voltage by HV ON/HV OFF switch (4). The output high
voltage pulses should be generated. The internal red lamp in HV ON/HV OFF
switch (4) lights on and indicates the triggering of the generator. Increase the
amplitude and frequency by corresponding knobs as necessary. The output pulses
frequency in internal triggering mode is about proportional to the rotation angle of
FREQUENCY regulation knob (9). The output pulses amplitude increases
proportionally to the rotation angle of AMPLITUDE regulation knob (8).
Step 7.
Always stop the operation of the generator by HV ON/HV OFF switch (4), after
that you can switch off the generator by power switch (1). After long time of
operation at high output pulse amplitude and frequency please allow fans to rotate
several minutes in idle mode for cooling.
NPG-18/3500(N) nanosecond pulse generator user manual 7 MEGAIMPULSE LTD. 8

TRIGGERING OF THE GENERATOR
The generator can operate in three different triggering modes:
Internal triggering
Internal triggering mode is set by switching EXT/INT toggle switch (5) to INT
position. No additional triggering generator is required for operation in this mode.
The output pulses repetition rate can be adjusted by FREQUENCY regulation
knob (9) on the front panel of the generator.
External triggering
External triggering mode is set by switching EXT/INT toggle switch (5) to EXT
position. The external triggering pulse should be applied to BNC SYNC IN
connector (6) by coaxial cable. Recommended triggering pulse width is 100 µs, the
acceptable pulse width is from 50 µs to 200 µs. Triggering pulse amplitude should
be from 2.5V to 15V, which allows triggering the generator by TTL, CMOS, or
3.3V LVTTL/LVCMOS level signals. The delay between triggering pulse front
and output pulse (internal generator delay) is about 1 µs, typical jitter (RMS) is
about 1 ns. The internal red lamp in HV ON/HV OFF switch (4) lights on and
indicates the generator triggering.
 The maximum allowable pulse repetition rate in this mode is limited by
FREQUENCY regulation knob (9) on the front panel of the generator.
Therefore, internal generator frequency sets the upper limit for external triggering
pulses frequency. Please rotate FREQUENCY regulation knob (9) to the most
clockwise position to allow the maximum external triggering pulses frequency.
The generator can operate also in single pulse mode.
Burst mode
The burst operation mode can be simply organized by using an external triggering
pulse generator. Set EXT/INT toggle switch (5) to EXT position and apply
external ENABLE pulse to BNC SYNC IN connector (6). The output pulse
repetition rate is set by FREQUENCY regulation knob (9) on the front panel of the
generator, and burst length is determined by the duration of ENABLE pulse. For
example, 10 ms duration external ENABLE pulse applied to BNC SYNC IN
connector (6), and 1 kHz set frequency result in 10 output pulses burst.
NPG-20/3500 and NPG-20/3500N User manual 9

OVERHEAT MODE
NPG-20/3500 (NPG-20/3500N) generator has 50 Ohm impedance coaxial output
connector and 50 Ohm impedance output cable. If the generator operates on an
unmatched load with an impedance not exactly equal to 50 Ohm, then part of the
pulse energy inevitably reflects from the load, returns back to the generator, and
dissipates in it. The generator can withstand operation with unmatched load, but it
may be overheated in case of long-time operation in such a regime.
OVERHEAT LED (7) lights on in this case and the generator stops the operation.
Please turn off high voltage by HV ON/HV OFF switch (4) and allow fans to cool
the generator for several minutes. OVERHEAT LED (7) lights off after the
cooling and the generator is ready for operation again.
Unfortunately, the matching with the load usually is not exact. To estimate the
portion of the energy reflected from the load please check the amplitude of the
secondary and following pulses by an oscilloscope with a high voltage probe
connected to the load. You should use 500 MHz or more bandwidth oscilloscope
and >20 kV pulse voltage probe, for example, Tektronix TDS 3052C and
Tektronix P6015A probe.
OVERHEAT LED (7) blinks for a short time when you switch on or switch off the
generator by power switch (1) on the rear panel. This is normal and indicates that
the generator control and protection system is in working condition.
MEGAIMPULSE LTD. 10

OUTPUT PULSE MONITORING
The generator has BNC connector for the output SYNC OUT pulse (10). The
SYNC OUT pulse amplitude is 2.5 V on 50 Ohm load and 5 V on high impedance
load, the pulse width is about 1 μs. The typical oscillograms of the external
triggering pulse (Channel 1) and SYNC OUT pulse (Channel 2) are shown in
Fig.3.
The high voltage few nanoseconds rise time output pulses are the source of strong
interference. Therefore, one can see the noise on the oscillograms at the moment of
the output pulse generation. The measured in Fig.3 delay between external
triggering pulse and the output pulse is 1.03 μs. The front of SYNC OUT pulse
precedes the output high voltage pulse for about 0.8 μs.
Fig.3. The measurement of internal generator delay. Typical oscillograms of the
external triggering pulse (Channel 1) and SYNC OUT pulse (Channel 2) of the
generator. The internal delay from the front of the triggering pulse to the high
voltage output pulse is about 1 µs.
NPG-20/3500 and NPG-20/3500N User manual 11

FUSE REPLACEMENT
 The type of the fuse is 4A/250V slow switching, cylindrical glass 5mm x 20mm.
The fuse holder is located in the three-terminal power supply connector. Please use
a flat screwdriver or another suitable tool to remove the fuse holder (see Fig.4.).
Fig.4. Removing of the fuse holder by a flat screwdriver.
There are two fuses in the fuse holder including one spare (see Fig.5).
Fig.5. Two fuses in fuse holder including one spare (upper in
the figure).
MEGAIMPULSE LTD. 12

WARRANTY
Please see your sales agreement to determine the warranty period and warranty
condition. The generator has warranty seals on the front and rear panels (see
Fig.6.)
 Removing of the warranty seals terminates the warranty.
Fig.6. Warranty seals on the front and real panels.
NPG-20/3500 and NPG-20/3500N User manual 13