In the early 90's, some X-band GaAsFET preamps appeared on the surplus market.  Primarily sourced by Avantek and manufactured in the the 1986-1987 time frame, these were reportedly used in short-range X-band tactical RADAR on jet fighters.

For some reason, these units were obsoleted and pulled from service and those held as spares were released as surplus.  While likely a misfortune to the taxpayer in general (the reported cost of these units was in the $3k-$4.5k range each) this were a boon to those interested in experimentation on the 10 GHz amateur radio band.

Note:  Preamps of this model were acquired and made available by another Utah ham in the early 1990's and a number of them were sold to members of the San Bernardino Microwave Society (SBMS) and reportedly referred to as the "Utah Preamp."  Since this source has dried up (all of them were sold) they are probably not readily available.
 

The X-band GaAsFET preamp - suitable for 10 GHz amateur radio use.
Click on image for a larger version.

These units are variously labeled, but one variation is as follows:

FETAMP - XM213303

97942-585R600H05

The NSN (National Stock Number) would appear to be:  1270-01-153-8700WF

While few "official" specifications are available for these amplifiers, some general information was obtained form the manufacturer.

• The minimum and maximum gain at the test frequency is 30 db and 33 db, respectively.
• The amplifier's gain and nosie figure specifications are stated over a frequency range of 650 MHz.
• There is a "low gain" setting that is reduces the gain of the amplifier by 15 db when active.  This attenuation is switched in post-amplifier.
• There is a built-in noise generator used for testing the integrity of the amplifier.  This noise generator is rated at an ENR of 14.0 db.
• The intercept point is rated at +20 dbm minimum, but the test data shows units typically testing at +24 dbm.

• The actual rated noise figure.  All noise figure test measurements are relative to "NFB" - an unlisted specification.
• The frequency range is coded in relative terms and is never specified directly.

Pinout information:

• 1:  +15 volt supply
• 2:  Return, case ground
• 3:  -15 volt supply
• 4:  n/c
• 5:  Static gating, RS-485 control (goes to pin 2 of a 26LS32 line receiver, complement of pin 7)
• 6:  Terminal output (seems to connect to pin 7 through a 13 ohm resistor)
• 7:  Static gating, RS-485 control (goes to pin 1 of a 26LS32 line receiver, complement of pin 5)
• 8:  n/c
• 9:  +5 volt supply (for 26LS32 line receiver)
• 10:  n/c
• 11:  n/c
• 12:  Gain control (pin 6 of a 26LS32 line receiver)
• 13:  B.I.T. (noise test) enable (goes to pin 14 of a 26LS32 line receiver)
• 14:  n/c
• 15:  n/c

For normal operation (e.g. high gain mode, noise test disabled) pins 5 and 12 are tied to ground (pin 2.)

It has also been observed that the amplifier appears to work properly with just a single positive supply connected at pin 1 in the range of 12-15 volts.  The additional supplies appear to be required only if additional features (such as the gain control, noise test) are needed.

Typical Voltage/current consumption:

• +15 volt supply:  215 mA
• +5 volt supply:  55 mA
• -15 volt supply:  15 mA

• High speed gating:  On to Off - typically 25 nanoseconds
• High speed gating:  Off to On (to within 0.5 db of final gain) - typically 65 nanoseconds.

Misc. Notes:

• The input connector is WR-90 waveguide.  There is an isolator on the input of the amplifier that is not easily removed without damaging the preamp.
• The output connector is SMA.  It is not known if there is an isolator on the amplifier's output.
• The power/control connector is a standard 15 pin D-type.
• The amplifier itself is backfilled with dry nitrogen and is laser-welded shut.

This page last updated 20050205