Note
There was a two-year gap between the end of the SW-717 and the introduction of the SW-7800.
The 7800 is built on three main PC boards plus a small board for the display. The unit’s design includes a broadband, up-converting, double-conversion mixer, and covers from 150 kHz to 30 MHz in 30 overlapping bands. A five-digit LED digital display resolves to 1 kHz. The receiver features switch selection of USB/CW, LSB, or wide or narrow AM.
Other features include fast and slow AGC, a “local/DX” switch (on the rear panel), a telescoping whip antenna, and a front panel output (miniature phone jack) for a tape recorder. This output is unaffected by the volume control.
There is also a built-in speaker, a standard quarter-inch mono headphone jack, an SO-239 antenna connector for a 50Ω antenna, a screw terminal for a hi-Z antenna (normally connected to the on-board whip antenna), and a muting output for use with a transmitter. A rear panel DC power connector is provided for battery operation.
Selectivity is 2.5 kHz for SSB, CW, and AM narrow, and 5.5 kHz for AM wide. The specifications do not refer to the stability of the SW-7800. Since the radio is fully synthesized and uses PLL circuits, one could conclude that the stability should be pretty good. However, a unit in the author’s collection exhibits considerable drift.
Book project technical advisor Gerhard Wagner, DF1DA, made these observations:
"The SW7800 is a remarkable receiver as it is the first (and to my knowledge only) of the Heathkit receivers or transceivers to utilize a state-of-the-art (in 1984) up-conversion scheme. The RF is routed through a broadband band-pass filter and RF attenuation diode (a better solution than the classical reduction of IF or RF gain which deteriorates strong signal capability). It is then up-converted to the 50.455 MHz first IF, which passes through a crystal filter and is then mixed down to the 2nd IF of 455 kHz. The second IF is then passed through a ceramic filter to the detector stages.
The first Mixer is fed by the appropriate VCOs, controlled by the synthesizer. The synthesizer also produces a 50MHz Signal which is then mixed with an analog L/C VFO. So the SW-7800 is not fully synthesized. The VFO is the reason for the drift.
The SW-7800 has 30 overlapping one-megahertz bands, which allow the same band spread from 150 kHz all the way up to 29 MHz.
Due to the up-conversion, the IF mirror reduction is very good and there are no gaps in frequency coverage. The digital frequency display permits precise tuning."
Only a VTVM is required for alignment.
The SW-7800 enjoyed only moderate success. It was seen as expensive and featureless compared to other ready-made shortwave receivers on the market and was eventually pulled as part of Heath’s decision to exit the kit market altogether.
The line cord is not detachable. Only 120 VAC 60 Hz or 12 VDC operation is possible.
References:
Review. QST. Apr 1985, p. 45.
Review (more on). QST. May 1985, p. 47.
Frequency coverage: 150 kHz to 30 MHz in thirty 1 MHz ranges
Frequency readout: 5 digits (LED)
Frequency accuracy: 1 kHz
Frequency control: synthesized (PLL and LC VFO)
Modes: USB/CW, LSB, and AM (wide and narrow)
Sensitivity:
SSB/CW: better than 0.35 µV for 10 db, (S+N)/N
AM: better than 2.5 µV for 10 db, (S+N)/N
Selectivity:
SSB/CW and AM narrow: 2.5 kHz minimum at 6 db
AM wide: 5.5 kHz minimum at 6 db
Selectivity shape factor: 1.5 at 6/50 db
Image rejection: 55 db minimum
Power requirements: 120 VAC, 60 Hz OR 11 to 15 VDC
Photos, general information and specifications from "Heathkit: A Guide to the Amateur Radio Products," by Chuck Penson, WA7ZZE. Used with permission.
