Amplifier Systems

Yes. Multiple Tomco amplifiers, generally of the same type and model number, can be combined in parallel to give higher power systems. Tomco offers suitable hybrid and radial power combiners.












This will happen at very low duty cycle and/or low power. Assuming you are getting an output signal as expected then the amplfiier is operating normally but the threshold for turning on the RF Power LED is not being reached. This can be ignored.












This is strongly advised. Mains surges can damage the amplifier power supplies.














Yes. Tomco CW amplifiers include gating to optimise noise performance. A GATE (+5V to enable), or PTT (0V to enable) signal, must be applied for the amplifier to operate.

If you are only operating in CW mode and don't require noise blanking, the simplest way to apply the required signal is to fit a 50Ohm termination to the PTT input, or link GND to PTT (pin 21 to pin 16) on the parallel interface. This holds PTT low continuously.

A suitable 50Ohm termination:

GATE and PTT can be applied either via the BNC connectors on the rear panel or via the parallel interface. Apply GATE or PTT, not both!








No. This is factory set to ensure adequate protection of the amplifier.












That depends on whether you are using a pulsed or CW amplifier.

In standard pulsed systems the amplifier will shutdown and will automatically restart once the load mismatch is within the specified limits (generally VSWR < 3:1).
In standard CW systems, automatic level control (ALC) is implemented. When the load mismatch limit is exceeded the gain of the amplifier automatically adjusts to protect the amplifier. The output power will decrease but the amplifier will not shutdown. Once the mismatch is addressed, the amplifier will automatically operate at full rated output power again.

Note that amplifier modules (as opposed to amplifier systems) do not have mismatch protection. If you exceed the load mismatch of an amplifier module you will probably cause damage to the output transistor. We advise using external mismatch protection with amplifier modules.














Remote monitoring and control is via a parallel interface. In standard air-cooled systems the parallel interface is via one 25-pin D connector (connector 1 in "Interface document"). In water cooled, and some customized air-cooled system, it is via two 25-pin D connectors (connectors 1 and 2 in "Interface Document").

The pinout for the parallel interface can be found here: Interface Document

Tomco systems do not include a serial interface as standard, however, the parallel interface can be readily converted to RS232/RS485/Ethernet and USB using an off-the-shelf datalogger.






In standard amps, local status monitoring is via LEDs on the front panel indicating:

  • DC Power
  • RF Power
  • Enable
  • Selected (only relevant for multi-chassis systems)
  • Over temperature
  • Mismatch (not present for amplifiers designed to handle infinite mismatch)
  • Over duty (pulsed amps only)
  • Shutdown

An RF sample port is also available on the rear panel

Optional extras include Vreflected and Vforward sample ports or digital displays

Customized local monitoring configurations are available on request










Tomco RF amplifiers are protected against damage due to the following conditions:

  • Over-temperature
  • Over-drive
  • Excessive duty-cycle (pulsed systems only)
  • Excessive pulse width (pulsed systems only)
  • Excessive load SWR
  • Our of band inputs

Water cooled amplifiers have the following additional protection:

  • Low water flow
  • Water leakage (via condensation and humidity detection)

All protection is self-resetting. The amplifier will continue operation once parameters are within normal limits without user intervention.

Note:  SWR protection is not included in Tomco’s amplifier modules




In many pulsed amplifiers it is necessary to switch between pulsed and CW mode (either manually or via a control interface) in order to permit CW operation. This is not necessary with Tomco's standard amplifiers. The switching is performed automatically. If the RF input level is sufficiently low, the duty-cycle limiter is disabled and full CW operation is possible. When the RF input level is raised above the threshold (typically about 10% of the full drive level), the duty-cycle limiter becomes active and the specified limits for pulsed operation are asserted.

In other words, to produce a CW output in a pulsed amplifier, reduce the RF input level to about 10% of full rated drive level) and hold the gate input high. For example, a Tomco standard amplifier that is rated for 1kW pulsed will be able to produce around 100W of CW by decreasing the drive level to approx. -10dBm. This CW operation is intended for short burst CW operation only (typically up to 1 minute).

Note that if higher power, or longer term CW operation is required, we offer custom pulsed systems which include CW switching to facilitate this.
















Tomco standard amplifiers are supplied with a User's handbook, factory test results, mains power cord and earth cable. RF cables are the responsibility of the user unless otherwise agreed.






Operational differences: Tomco pulsed amplifiers will limit the duty-cycle and maximum pulse width to specified maximum levels. If these limits are exceeded the amplifier will shutdown and auto-restart once they are within normal limits. Tomco CW amps will operate at up to 100% duty cycle with no limiting. Mismatch protection in pulsed amplifiers is shutdown (and auto-restart) if the VSWR limit is exceeded. CW amplifiers incorporate ALC protection (gain is automatically reduced if VSWR limits are exceeded so that the amplifer continues operating but at reduced power)

Performance differences: Pulsed amplifiers include many features such as high-speed noise gating, which reduces the output noise level to almost zero in-between pulses.  In Tomco's standard amplifiers these features are present in both pulsed and CW systems. Tomco CW systems can operate in true pulsed mode at duty cycles up to 100%. Pulse droop, rise and fall times, phase shift through the pulse, overshoot and other pulsed specifications are fully met in both our pulsed and CW amplifiers. In general, CW amplifiers from other manufacturers do not include these features. There are no major performance differences between our pulsed and CW amplifiers.

Cost differences: A good quality pulsed amplifier that is rated for, say, 1kW pulsed power at 20% duty-cycle, will contain just as many power transistors as a 1kW CW amplifier. However, the power supply and cooling requirements for the pulsed amplifier are much less, since it is rated for only 200W average power. The 1kW pulsed amplfiier will be lower cost and physically smaller than the 1kW CW version.










Amplifier Modules

An amplifier system includes all required power supplies, cooling and all protection systems, including mismatch protection. It is supplied in a 19" equipment chassis and is a stand alone, fully operational system. An amplifier module is an amplifier board only mounted in an enclosure. User must supply DC power, cooling if required and mismatch protection

Definitions and Terms

PEP stands for Peak Envelope Power. It is equal to the product of the RMS voltage and RMS current when the signal is at its maximum level.
The concept of PEP is useful in situations where the amplitude of an RF signal varies rapidly with time. In mathematical terms, the product of RMS voltage and RMS current is called the “average power”. Unfortunately this is easily confused with the average power of a varying signal level measured over a period of time.
For example, imagine an amplifier that is outputting a constant CW level of 100W. The average output power is obviously 100W, and the PEP is also 100W. Now imagine the same amplifier running at the same input signal level, except that the input signal is switched on and off rapidly such that it is on for only 10% of the time. In other words, it is pulsed at 10% duty-cycle. The average output power is now 10W, but the PEP is still 100W.

This example suggests that the difference between average power and PEP is somewhat dependent on time scales, and in that sense the distinction is slightly arbitrary. In terms of RF power amplifiers, the distinction basically relates to the capacity of the amplifier’s cooling system, so the timescales involved are of the same order as the thermal time constants of the RF power transistors and heatsinks. These time constants very enormously from one amplifier to another, but typically the transition from a “pulsed” specification to a “CW” specification occurs at pulse widths between a few tens to a few hundreds of milliseconds.
For example, an amplifier that only needs to run at 100W for one millisecond every ten milliseconds would be a pulsed amplifier rated for 100W PEP, 10W average. But an amplifier that must run at 100 watts continuously for one day every ten days would not be called a “pulsed” amplifier, and would need to be specified for “100W CW”, not “100W PEP, 10W average”.

Gain flatness is a measure of how the gain of the amplifier changes with frequency. To ensure that the figure doesn’t include any false “improvements” due to gain compression, the gain flatness is measured at low signal levels – usually at one-tenth of the rated output power. For a broadband high-power amplifier, a gain flatness figure of +/-2dB is generally considered good. It is important not to confuse gain flatness with rated output power; a Tomco amplifier that is rated for 1kW output will be capable of producing at least 1kW across its full frequency range. However, the RF input level required to produce that 1kW output will vary with frequency

The RF output of a power amplifier always includes some internally-generated harmonics of the RF input signal. The harmonics are measured with the amplifier running at its specified P1dB level. They are expressed as “dBc” figures: for example, a third harmonic of -20dBc at 1MHz means that if you apply a pure 1MHz sinewave to the input of the amplifier, the output will include the amplified 1MHz signal plus a 3MHz signal that is 20dB (100 times) smaller

Gate delay is measured from the rising edge of the applied gate pulse, to the point where RF just begins to appear at the amplifier output. The measurement is made using continuous RF applied to the amplifier’s RF input. It is typically less than 1 microsecond for Tomco pulsed amplifiers

Pulse rise and fall times are measured between the 10% and 90% output voltage levels. The measurement is made using a “pre-gated” RF input signal so that the gate risetime and gate delay are not included in the figures

This is the output power from the amplifier when an input level of 0dBm is applied (0dBm is the standard maximum input level for Tomco amplifiers)

This is the minimum RF output power level at which the amplifier’s gain will have dropped by 1dB compared to its gain at one-tenth output power. It is a measure of the amplifier’s linearity at high power levels. The P1dB specification for Tomco amplifiers is a guaranteed minimum across the freuqency band.

This is the minimum RF output power that the amplifier will produce, when the full specified input level is applied to it. The full specified input level for Tomco amplifiers is usually 0dBm (1 milliwatt). The rated power specification for Tomco amplifiers is a guaranteed minimum.

RF Measurements