21 / 100
Review
February 2016
21
readable. It has a wide viewing angle and
the visibility holds well under bright lighting
conditions unlike some other displays.
The upper part of the display shows the
frequency, status indicators and icons, with
both frequencies shown in split operation
or with a clarifier offset. The S-meter is a
bargraph and on transmit shows one of six
selectable items including power output,
SWR, ALC and compression level. The lower
part of the display shows a spectrum scan.
The microphone plugs into the front panel
and uses an 8-pin RJ45 (Ethernet) connector.
Yaesu’s traditional MH-31 hand microphone
is supplied with the radio. 3.5mm jack
sockets on the front panel connect to a CW
keying paddle and headphones. Computer
keying or a straight key can additionally be
connected to one pin of the data mini-DIN
connector on the rear panel.
Rear panel
There are two antenna sockets on the rear
panel, an SO239 for HF/6m and a type-N for
2m/70cm. Type-N is only fitted to UK and
EU supplied models. There are two mini-DIN
multiway connectors. One is for connecting
an external linear amplifier or an ATU and
provides coded band data. The other is for
interfacing FSK and audio AFSK lines for
RTTY and data mode connections. A 9-pin D
connector provides an RS232 computer link
for CAT control or alternatively it provides
an interface to an external GPS unit for
location data on C4FM. A USB connection
is also provided for CAT control, firmware
upgrading and also for passing audio signals
and transmission control to and from the
computer. A suitable USB driver is available
from the Yaesu website. The optional FH-2
keypad accessory may be connected to a
jack on the rear panel. This can be used as a
more convenient method of transmitting pre-
recorded contest messages on SSB or CW.
This dual-purpose jack also provides an ALC
feedback connection from an external linear
amplifier, but not for both uses at the same
time.
The usual Yaesu style instruction manual
is provided, very comprehensive and
running to 150 pages but there are no circuit
diagrams included. I noticed, however,
some minor errors. Additional manuals are
available on the Yaesu website covering
CAT operation, firmware upgrading and the
relevant firmware files.
Radio design and architecture
The receiver in the FT-991 is an up-
conversion triple superhet with a first IF of
69.45MHz, a second IF of 9MHz and a third
IF of 24kHz feeding the DSP unit where
all signal processing and filtering functions
are performed. On FM and C4FM modes
the receiver is a double superhet where the
second IF is 450kHz and a conventional
demodulator is used. Two separate front
end signal paths are used. On HF to 6m a
quad first mixer is used preceded by two
switchable preamplifiers providing 10dB or
20dB gain or 0dB when switched out (IPO).
A 12dB attenuator is also selectable. 2m and
70cm use separate filters and amplifiers to a
common VHF/UHF first mixer. The amplifiers
on these bands are in-circuit at all times and
cannot be switched out. Two roofing filters
are fitted at the first IF; a 15kHz bandwidth
unit on AM, FM and C4FM modes and a
3kHz bandwidth unit on all other modes.
Manual selection is not provided.
On transmit, a common amplifier is used
to provide 50W on both 2m and 70cm and
a separate amplifier chain provides 100W
on HF and 6m. A 0.5ppm TCXO reference
oscillator is fitted to ensure high stability.
The radio is solidly constructed in typical
Yaesu style with the usual substantial diecast
frame and integral heatsink. A fan is recessed
in the rear panel and operates when the
temperature rises, the speed increasing with
temperature but even at higher speeds is still
very quiet. A 65mm speaker fits in the case
top.
Receive and transmit features
The usual receiver functions are all provided,
a very comprehensive set. The main tuning
knob is a good size at 45mm in diameter
and tunes in 10Hz steps on all modes except
FM/C4FM with 200 steps (2kHz) per knob
FT-991 rear panel.
FT-991 underneath top cover showing HF PA (top) and VHF and UHF PA (bottom).
Peter Hart, G3SJX
peter@g3sjx.freeserve.co.uk