The picture shows my Mizuho HF RX connected to the AD9850 DDS box on top.
The DDS is made in an independent box so that it can be used as the 'station' signal generator. This way it serves as external VFO for my GE524 manpack or for any other rig under development.
'Mizuho SG-9' is basically a self contained 'black box', in that it has the following circuitry on-board:
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9MHz SSB xtal filter
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8998.5 KHz xtal oscillator
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DBM which doubles as both modulator & product detector.
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IF amp
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Mic amp
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AF amp
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AGC and
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'S' metering
Mizuho SG-9 boards were manufactured by Mizuho Company of Japan in the '70s. These filter & SSB generator boards were used in many of their other products, such as SB-2M and also in 'Dentron MLX-Mini'
It's an useful building block for the novice and a good test & reference gear for the experienced. Click on 'close-up' for a picture of the SG-9 board used in my receiver.
I have provided an external VFO input to my RX box which also has a built in counter which may be turned off if required. The counter board and the IF,RF, front-end are all well shielded and with all the covers in place, I've not noticed any counter 'digital' interference.
This RX also has a front panel (left) controlled 20dB attenuator.
Strong signal handling of NE602 is not good hence I've incorporated a home brew standard DBM using toroids and four 1N4148 diodes.
I've even experimented with SBL-1 & SRA-1 with excellent results.
Home made DBM's are OK because the commercial SBL-1 & SRA-1 are quite expensive though I picked up mine from a good old junk dealer (Alpha Juliet - for Bangalore HAMS) in Bangalore.
One could, very easily duplicate the 'Mizuho SG-9' IF board using other 'Mixer' devices like NE612, MC1496 etc.
One project of mine in the pipe line is an IF amp using MC1350 which was extensively used in almost all HF projects of ARRL till recently.