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dimensions, which match the rf amplifier. With luck the oscillator will go into the same size box (it did) uid we will have three small matching boxes for the rf head.

I have shown a u* lead (temporary) from fhe diode by-pass japacitor plate, C4 to J3, because this allows a fine check on the rf mixer section. A modulated 43 2, iest oscillator is fed through a coax cable to the input jack and rf tuning and dc voltage out of the diode, with Minibox cover on and off This is important because of oscillator harmonic mixing. This little devil has ruined many an otherwise fine home-brew project, so you'd better be aware of it. It shows up most, on six and two meters, when you start tuning up converters on the bench. That's partly what ali the thousand screen rooms throughout the USA are for! Your mixer is there on the bench* no shielding (yet) and FM, VHF TV, and UHF TV all come boiling in. You re probably using a high gain if, most likely 455 khz. sharp, (doesn't like FM!) and of course, what with many oscillator harmonics and many TV and FM stations, you've had il! Harmonic mixing has been used, and described in the good old RCA 1500 page "Bible" on how to build receivers- The many harmonics simply acl like local oscillators on higher

• BROOMFtELD, COLORADO S0020 303/466-7303 • P, O. BOX 348

• BROOMFtELD, COLORADO S0020 303/466-7303 • P, O. BOX 348

Fig. 7. Coif test set up.

frequencies to produce, at times, a tremendous set of nuisance signals.

Fig, 7 (coil test set-up) shows how to do it in a real painless fashion. Connect your signal generator (the S30 Lafayette job is fine) through an rf cable to L2? solder coil leads to test terminals T1 and F2, connect a "diode plank" ( Fig. 8 you must have one of thosel) ¿1 microam met errand go. I found 35 turns of No- 34 enamel, on about 3/8" diameter coil form to do the trick, with an 8/32 threaded powdered iron slug inserted for tuning. With 100 pf across the coil it tunes from 7.5 to 4.5 mhz reaching the desired 6 mhz with the slug about halfway in. You can have lots of fun checking coils, 0, and slugs this way but, get on with the 432'cr!

Fig. 8. "Diode plank."

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