开云体育

My BITX40 is #465. It came wrapped in what looks like an ex-candybox. But it was well-packed and survived the journey well.

I had the same problem as you. The initial VFO coverage was ~4870 Khz - 5150 Khz. I removed the 100 pF cap, C95. (C95 was installed, then removed before shipment). That made the VFO cover ~5090-5370 Khz. So I knew I could get about 200 KHz out of it after any small modification.

During removal of C95, C93 was damaged, so I replaced it with a Murata green varicap. Adding back the 100 pF cap, C95 (in the position of C94 since it was easier), I was able to get the VFO to cover a receive of ~7038-7345 KHz. I also installed a 10 turn 10K Vishay pot for tuning. It works well but the Bourn pot is a little better.

The first problem with the rig is the VFO drifts way too much. Most people will use a DDS to overcome this and that is fine. I would suggest trying to replace C91 and C92 in the oscillator with better, layered, npo capacitors. That would go a long way towards fixing the drift. But the real problem is the layout. It is much too small. Even placing one's finger near Q7 will disrupt the oscillator. Perhaps the best solution is a DDS. The BITX, v.3 was much easier. I was able to make a rock-solid VFO on that board. The Eliamady smd version has an external VFO, so that is not a direct problem.

The second problem is with the BFO. It is not quite tuned right with the 22 pF cap (C102). This is a major part of the reason for so much "boominess" reported earlier; the LSB is not quite on the right slope in the passband. My board came with C103 not installed. I put a 20 pF varicap in to test the slope, but it was not quite right. So I removed C102 and replaced it with a 15 pF cap. I also installed a Murata yellow varicap in C105. That did it. Now I am able to tune sharply and eliminate the grubbiness of including part of the upper sideband. The tuning is sharp and the proper adjustment make the voice clear as a bell. There still is a bit of overload, however. Very loud signals will still have a trace of raspiness, probably from mixer overload. CW is clear and digital around 7080 works also. Even strong local CW does not overload the receiver. And now SB does not either.

Important: when replacing parts, MEASURE both the part taken out and the replacement. Know the values. Record your answers so that you will have them for reference.

The receiver is good; It could be better; I know that from the other BITX rigs. Lots of work to do. I have been able to listen clearly to lots of people from Wyoming to South Carolina, and Chicago to New York on a Monday afternoon...I haven't tried the transmitter yet.

CW is easily possible by merely eliminating the balance in the carrier suppression. A switchable capacitor at R106 is the simplest solution. (First, though, you have to work to make the carrier suppression complete. Been there;done that...not on this rig yet. Hi).

john
AD5YE