Transient Protection Devices
EMP and Lightning Protection Devices
Fischer Custom Communications, Inc. has been designing and producing RF coaxial EMP/HPM and lightning protection devices since 1971. Our engineering staff has over 100 man-years of experience in EMP test design and execution as well as designing and producing Mil Std 461 RS 105 systems, Mil Std 188-125 pulsers, antennas, control systems and data acquisition systems. Our in-house pulse generator suite is used to validate performance for a variety of lighting waveforms, double exponential waveforms and Mild Std 188-125 E1 and E2 threats.
Nanosecond Lightning, EMP & Transient Protection
Spikeguard suppressors provide protection from transients originating from switching, lightning, and electromagnetic pulses including high power microwave threats. Spikeguards provide protection for sensitive electronic systems, data communication systems as well as for RF transmitters and receivers at their antenna transmission line terminals.
They exhibit fast response through the UHF region, and are constructed from proven transmission line, gas discharge components, discrete silicon components, and can be subjected to many transients.
Spikeguard transient protection devices (TPD) are organized into five major categories that optimize the protective characteristics.
The FCC-250B series are rated at 10,000 amperes for a duration of 10 microseconds. This series is available in a number of dc breakdown voltages varying from 75 volts to 2000 volts. This series has a pulse breakdown varying from 1000 to 3000 volts for a pulse rise time of 1 kv/nanosecond. The impedance of this series is approximately equivalent to 2.5 picofarads in shunt with the transmission line load. Versions are available for use beyond 3 GHz.
The FCC-350B series is rated at 20,000 peak amperes for a 10 microsecond duration. This series is available in various breakdown voltages varying from 90 to 20,000.
The FCC-250B and FCC-350B series are extremely fast in reacting to transient voltages. For dc trip voltages of 1 KV and higher the overshoot voltages of transients having a ratio of 1 KV/nanosecond is minimal since the trip voltages is achieved in approximately 2 nanoseconds. The impedance of these series is approximately equivalent to 3 picofarads in shunt with the transmission line load
Even though the FCC-250B and FCC-350B series have some overshoot, when used on transmitters up to 100 watts they clamp at 1800 volts or lower for a transient having a risetime gradient of 1 KV/nanosecond, and 1000 volts or lower for a transient having a risetime gradient of 20 kilovolts/microsecond.
In most instances these overshoot voltages will not cause failure of an antenna or transmission line since they will only last for 2 nanoseconds for the 1 KV/nanosecond risetime gradient and 50 nanoseconds for the 20 kilovolt/microsecond gradient
The FCC-450B series Spikeguards provide transient protection for receivers and transmitters up to 100 watts of output power. They are ideal to protect sensitive semiconductor electronic instruments such as spectrum analyzers.
The FCC-450 B family of TPD’s is available with clamping voltages varying from 6 to 300 volts, The 6 to 20 volt units are capable of sustaining 70 amperes of peak current for a triangular pulse having a 4 microsecond pulse width. From 20 volts and up, the units have a decreasing current capability, with the 300 volt unit capable of sustaining 5 amperes of peak current for 15 microseconds.
Since the FCC-450B series can sustain a limited transient pulse, they should be used in combination with a FCC-250B or FCC-350B. The FCC-450B series must be placed as close to the electronic instrument, transmitter or receiver as possible, and the FCC-250B or FCC-350B series unit must be placed as close to the antenna as possible. The FCC-250B or FCC -350B device will intercept the transient first and will limit the overall energy to the low millijoule level, thus not permitting the transient energy to exceed the safe level of the FCC-450B series.
In order to obtain optimum transient protection, the two units must be separated via the coaxial cable by at least 50 feet for a slow transient having a risetime gradient of 20 kilovolts/microsecond; and by 3 feet for a fast transient having a risetime gradient of l megavolt/microsecond.
This hybrid combination provides optimum protection of both transmitters and receivers.
As an example, at transmitter power output levels approach one kilowatt the FCC250B series overshoot performance is nearly equal to that of the FCC-350B series.
The Spikeguard clamp voltage for a one kilowatt transmitter would ideally be about 1100 volts dc, in order to prevent inadvertent firing of the Spikeguard due to transmitter power and antenna VSWR. An 1100 dc volt rated the FCC-250B series will only overshoot to 3000 volts before clamping a 1 KV/nanosecond gradient transient This overshoot will only exist for a period of about one to two nanoseconds. Even for a 100 watt transmitter the condition is not much more severe. A 100 watt transmitter will be rated to clamp at 230 volts dc. A 1 KV/nanosecond gradient transient will cause an overshoot voltage of about 1500 volts. This will only permit the overshoot to exist for a period of approximately two nanoseconds. The energy permitted to exist during either of the two examples would not exceed 200 microjoules, which is insufficient to damage 100-500 watt transmitters.
Transmitter protection is recommended as follows
- For transmitters up to 100 watts output, a hybrid combination of a FCC250B series be placed at or near the antenna, and a FCC-450B series be placed at the transmitter.
- For transmitters of 100 watts or greater a FCC -350B series unit placed near the antenna is recommended.
The FCC-550 series of TPD’s are custom designed to meet specific customer requirements and typically combine the FCC-250B or FCC-350B with the FCC450B series into one package. The FCC-550-5-RJ45 is an example of a very low capacitance TPD that is used to protect electronic instruments and IT systems that are connected via telecom cables having single, two and four pair for 10, 100 and 1000 base T communications. TPD’s for RS 232, RS 422, GPS and other communication and control protocols are available.
The Quarter Wavelength (λ/4) Stub/FCC-250 Series of TPD’s shunts lightning currents to ground. It is an inherently superior method of protecting RF transmitters and receivers. The quarter wavelength stub can dissipate several hundred, twentyfive thousand (25,000) ampere lightning strikes and reduces lightning voltages by 70dB.
The λ/4 stub TPD acts as a short circuit for frequencies operating below the intentional passband and has low RF loss for the transmitted signal. The incident and reflected signals are in phase and the intentional signal does not encounter the short circuit.
The FCC-350A series includes EIA flange suppressors that are ideal for protecting 1 to 10 kilowatt or multi-coupled low power transmitters from the effects of lightning and EMP.
Custom Power Mains TPD’s are designed to meet specific customer requirements.