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Model 300T2G8

If no generator is connected and the CW mode is selected, the unit will operate in the CW mode and the amplifier
will amplify the RF input signal, i.e. the unit will operate as a unit without pulsing.

In the pulse mode it is expected that the user

will

connect a pulse generator to the pulse input. If a generator is

connected and the PULSE mode is selected, the unit will operate in the pulse mode; it will amplify the rf only
when the pulse input is set to high level, into the pulse input’s approximately 50 ohms input impedance. This
impedance to signal ground has been selected to reduce reflections. For best response, the user should make the
connection to the generator using a 50 ohm coaxial cable.

NOTE: If the user does not have a pulse generator connected to the pulse input, there will be no rf output (when

the pulse mode is selected).

3.10 TWTA GENERAL CONSIDERATIONS

This section is intended to offer some guidelines regarding operation, storage and use of Amplifier Research
TWTAs.

Storage:

TWTAs, as with other electronic equipment, are best stored in a benign environment at reasonably

constant temperature. Service life is not improved by periodic operation.

Availability:

For critical missions, and after long periods of storage, it is recommended that TWTA operation be

checked sufficiently in advance of the mission to permit repair if required. Though service life is not improved by
periodic operation, users experiencing amplifier trip due to body over current may benefit by periodically
operating a unit with high voltage and grid on, but no rf drive. Such operation for about one hour on a weekly
basis should effectively reduce nuisance tripping. Since the cathode structure has finite life, extended periods of
non-functional operation of TWTAs is not recommended. An alternate approach, if periodic trip off has been
observed, is to operate the unit without rf input for 1-2 hours before planned functional operation, resetting the
unit after occasional trip off.

Cooling during Operate Mode:

AR TWTAs have their air outlets and inlets on the rear panels. It is important

to prevent the heated air, which is expelled from the TWTA’s air outlets, from being recycled into the air inlets.
Applications should have a clearance behind the TWTA of at least two feet for single bench top units and at least
three feet for the higher power units, or the heated air should be ducted away.

Operation in Standby Mode:

Standby mode for TWTAs readies the unit for operation. In this mode the

filaments are on but the high voltage is off. TWTAs should not be left in this Standby mode for extended periods.
Where practical, operational procedures should limit the time on Standby mode to less than approximately one
hour. (See

Explanation of….,

below)

Operate Turn on:

When selecting the Operate mode, when high voltage is first turned on, there may be some

internal TWT arcing which can cause protective circuits to deselect the Operate mode, thereby returning the unit
to the Standby mode. There may be a report of body over-current fault. In either case, if there is no other
contraindication, the Operate mode may be selected again. This procedure may be repeated, if needed up to 25
times, until the Operate mode is actually set. If this condition persists, contact Amplifier Research Service for
additional assistance. (See

Explanation of…,

below).

Noise Power Density (NPD):

TWTAs produce rf noise over their operating frequency range, as specified by the

Noise Power Density (NPD). This noise is significantly higher than the noise produced by typical solid state
amplifiers, and is inherent in present TWTAs. The noise may surprise users new to TWTAs when it accumulates
and results in a significant indication in a broadband measurement device – such as a power meter or field probe.

Rev A