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 the AN/APG-68 (see the related
Wikipedia article) fire-control X-Band RADAR on jet
fighters and bombers - namely the F-16C/D fighters and possibly
the B-1B bomber.
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) they were a
boon to those interested in experimentation on the 10 GHz amateur
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
FETAMP - XM213303
additional designation included may be:
On the data sheet, the model number is SA85-2079G and the part
number is 585R600H04
The NSN (National Stock Number) would appear to be:
Note: If you "Google" the above NSN you can
divine additional information about the application of this
While few "official" specifications are available for these
amplifiers, some general information was obtained form the
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.
What is not shown on the data sheet:
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
Having used one of the amplifiers on my homebrew 10 GHz transverter,
I have made several observations:
As noted below, they will run fine on a single 12 volt,
The saturation power output is on the order of +13dBm
Reports from others who have used these LNAs indicate that the
noise figure is in the 2-2.5dB area. In my transverter,
using a 17dBi horn, there's an obvious difference in the noise
level between the "hot ground" and the "cold sky."
1: +15 volt supply
2: Return, case ground
3: -15 volt supply
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)
9: +5 volt supply (for 26LS32 line receiver)
12: Gain control (pin 6 of a 26LS32 line
13: B.I.T. (noise test) enable (goes to pin 14
of a 26LS32 line receiver)
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 from the test data:
+15 volt supply: 215 mA
+5 volt supply: 55 mA
-15 volt supply: 15 mA
Additional specifications from the test data:
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.
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
Note: This preamp was second-sourced by at least
one other manufacturer: Information on that unit will be
included if/when it becomes available.