The SB-8X was the last of the SB series radios, introduced in 1981. As you can see from the photo this is a much newer, more sophisticated radio than previous SB series models. The SB-8X is a 6, 15, and 40 meter SSB/CW transceiver with 10W ouput. It is perhaps the only Mizuho transceiver with a digital display, albeit with only 1kHz resolution. The digital display can double as a digital clock and the rig has both a sleep timer and an alarm clock function. Those two large buttons in the front are for setting the clock. The SB-8X is basically an analog design with a digital frequency counter. The rig was designed for mobile use, with thumbwheels to attach a mobile bracket included with the radio.
The rig is a typical Mizuho VXO design. Each click of the main tuning knob is 20kHz, with the VXO control allowing an excursion of + or - 15kHz (30kHz total) from the center frequency. In addition there is a fine tuning control concentric with the VXO control. At the flip of a switch this becomes RIT. As is typical with Mizuho gear there are no bells and whistles. The only other feature is a noise blanker. There are separate connectors for both an external speaker (mini jack) and headphones (1/4" phono jack).
The receiver performance seems to be typical of a later analog design. The 2.4kHz filter is fine for SSB. There is no narrower CW filter and there is no allowance for one. The specs claim the rig covers 7.0-7.1MHz on 40m but the rig actually will tune 800kHz per band. As you approach the top of the American 40m band at 7.300 receiver sensitivity declines somewhat. Output power stays at 10W or very close to it throughout the band.
The mic. is the same as provided on the earlier SB-2X with a round four pin connector typical of rigs of that era. The form factor of the radio is unusual: very slim and short, typical of a 2m mobile rig of that era, but very, very long. Power consumption for 10W out is just 2.5A.
7.00-7.30MHz, 21.00-21.45MHz, 50.00-50.80MHz
Mode: A3J (SSB), A1
Frequency Control: VXO
Frequency Stability: ±100Hz per 30 minutes from 60 minutes after power on at 23°C. ±500Hz during first 60 minutes.
Power requirements: 13.8VDC
Power consumption: max. 2.5A transmit, 340mA receive
Size: 165mm(W) x 62mm(H) x 312mm(D)
RF Output Power: 10W (PEP)
Spurious Radiation: 7/21MHz: less than -40dB, 50MHz: less than -60dB
Carrier Suppression: more than 40dB
Unwanted Sideband Suppression: more than 40dB
Receiving System: single conversion
Intermediate Frequency: 9.055MHz
Sensitivity: less than 0.5µV for 15dB S/N
Selectivity: 2.4kHz at -6dB, 4.8kHz at -60dB
Microphone impedance: 600 ohms
Audio Output: 1W at 8 ohms
Block diagram (PDF format)
-Last updated 10 July 2006