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February 2016
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T
he Gemini 23 is the latest in a
family of medium power solid
state linear amplifiers from
Linear Amp UK [1] that together
cover all bands from HF through
to 1296MHz. Like the lower band
versions, the 1296MHz Gemini 23
RF section was designed in the UK
by Chris Bartram, GW4DGU, who is
a highly respected, professional RF
consultant of many years standing.
Features and functions
The amplifier, manufactured in the UK and
sold by the DX Shop
[2]
, is a “one box,
turnkey amplifier” requiring no other external
components or power supplies. It is fully
self-contained with a built in mains PSU,
and measures 270mm(w) x 120mm (h)
x 300mm (d). It weighs about 10kg and
claims a saturated output power of 210W.
It is designed to meet ETSI EN 301 7831 v
1.21
[3]
and claims all spurii to be <70dBc
at 200W output. For SSB and long periods of
‘key down’ operation such as JT modes, the
output power should be limited to 180W to
avoid distortion. It requires only 8W of drive
to produce full power, so care needs to be
taken with driver rigs such as the TS2000X
to keep the drive within this limit.
Amplifier protection features
The amplifier has several protection circuits
built in, covering overdrive, poor VSWR and
over temperature. The amplifier monitors
input drive level and if the drive limit is
exceeded, it will lock out and switch to
‘straight through’ receive mode and show a
front panel warning light. This can be soft
reset by cycling the standby switch.
If the output VSWR exceeds 2.5:1 the
PTT will be inhibited and the amplifier
will show a front panel warning light. This
lockout can only be reset by turning the
amplifier mains supply off, waiting 5 seconds
and turning it back on again. While this can
be annoying with intermittent VSWR faults if
your amplifier is in a loft or outdoors as may
be the case with EME operation, the fault is
drastic and should force you to pay attention
to it instead of carrying on regardless!
The cooling fans operate at low speed
during receive mode and switch to full
speed when the PTT is enabled. Heatsink
temperature is monitored and if a threshold
temperature is exceeded, the fans remain on
during receive. If a second, higher threshold
(that could potentially harm the device) is
exceeded, an over temperature lockout will
occur and show a front panel warning light.
Unlike the VSWR lockout, the temperature
lockout is self resetting, automatically
Review
Gemini 23
1296MHz
linear amplifier
PHOTO 3:
Rear view of the Gemini 23.
PHOTO 1:
Packaging and box contents.
PHOTO 2:
Front view of the Gemini 23.