Yaesu FT-901DM Maintenance Service Manual page 5

A BRIEF HISTORY OF THE FT-901 SERIES
The FT-901 transceiver first appeared in the USA early in 1978 and immediately established a position
of pre-eminence among "top-of-the-line" transceivers on the market. The FT-901 series has brought a
number of never-before-possible technical features to the amateur community, along with traditional
Yaesu quality design and purity of emissions.
The receiver section, in particular, has impressive credentials. A dual-filter variable IF bandwidth control
allows continuous variation of the IF passband, from 2.4 kHz down to 300 Hz. Also included is a
rejection tuning control, for nulling out of any interfering signal within the remaining IF passband. For CW,
and audio peak filter (APF) provides a significant reduction in background noise, in addition to razor-
sharp selectivity. The receiver dynamic range — typically well in excess of 85 dB in CW bandwidth — is the
best ever achieved in a production-line amateur solid-state receiver.
The transmit side includes RF negative feedback for purity of emissions. A Curtis 8043 IC keyer is built-in
on the FT-901DM/DE models, providing high reliability and immunity to RF interference. Another
innovation is the 10-second TUNE button, which activates the transmitter for 10 seconds for tuning
purposes, then returns the rig to receive, thus saving the final tubes from excessive key-down time.
The most exciting feature of the FT-901 series is the memory system, which provides for storage and
recall of any frequency for control on transmit, receive, or transceive. This one feature largely eliminates
the need for an external VFO in the traditional sense. That the FV-901DM synthesized scanning external
VFO is hardly traditional bears this point out.
With coverage on all modes (SSB, CW, AM, FSK, and FM) on all bands from 160 through 10 meters, the
FT-901 series is destined to maintain its position of dominance among top transceivers on the market. With
some 2800 components assembled in one box, for a finite price tag, the FT-901 offers more performance
per dollar than any other piece or collection of equipment on the market.