missing parts

Ashhar Farhan
 

a number of new builders are mystified about the parts missing around the modulator and the bfo. here is the story :

when the bitx40 first started shipping, we had an analog vfo tuner with a varactor. this proved to be drifty. we soon introduced the raduino board - an arduino controlled si5351 board for general purpose rig control. this feeds into the vfo circuitry. we kept the original pcb design so that our past and future builders dont have different boards, we just skip some parts to prevent the vfo from oscillating and inject the si5351 signal into the vfo's base. there are still purists out there who insist on using the analog vfo. they can add those caps on their own.

the balanced modulator/demodulator originally used a pair of 1n4148 diodes balanced with a 100 ohms preset. this too proved a tough thing to set for those who didnt have a scope. we changed that, thanks to mvs sarma's recommendation, to bat54s diode pair l. the bat54s is a matched pair in smd format that doesnt need balancing. this is why you see a number of components missing around the det/modulator.

have fun, poke around and see if anything else needs explanations.

73, f.

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