Good to hear you got it working again. ?Pretty cool! Not many people can get an RF burn from 5 Watts. ?You might have some other ham look over how you have that antenna set up. ?(OK, I now see Raj has offered to do just that, very nice of him.) ?Or draw a diagram up showing all the wires and labeling all the parts. ?And tie the Bitx40 ground to earth ground, perhaps the ground pin of an electrical outlet. ?(We used to look for a cold water pipe, but they are all plastic now.) ? ?

Jerry, KE7ER

Hey, Jerry, ?never felt like it was getting enough audio power to the final amplifier. That's why I was still chasing the white rabbit. I just wanted to share with you and the others that I replaced the PA again, the diodes with 1N4148's, and the microphone. The PA was burned out. I went with the other diodes because of almost same forward voltage drop as the SMD part. At this point it was louder and higher wattage into the dummy load. And it still wasn't drawing much current, like 240mA, we've already established my meter isn't fast enough to show peak current. And it still sounded like I was talking into a fan, so I swapped the mic out too. It sounds better now.

I have been careful not to screw around with it because it wasn't working right early on. But after my last post I kinda felt like it's broken now, go ahead and try something. So I followed Toms solution, fixed the PA, changed the mic out with one of the same size. And now I think it's fixed better than the last time I thought it was fixed. And I am not going to tell ya about the whole trace I lifted between the PA center pin and corner of the closest toroid ?and had to jumper the connection on the back side of the board. Remember, I considered it broken.?

Hey, something new for ya. I got an RF burn on my lip from the mic. This didn't happen with the old one. Any ideas? My antenna is grounded with a coax choke balun at the feed point.. When I enclose it I can connect it to the bus bar.

I am really sick and tired of this thing. I got too invested, and couldn't stop. I need a vacation!

Hi all,

My Bitx40 arrived couple days ago and now I've got some time to play around. Decided to start with Raduino first, wired the tuning pot, and put the scope probe on brown and red wires (VFO out). I see a square wave of about 3.3 Vpp, but frequency is only 1.055 MHz when display shows 7.0000 LSB. When I go up to 7.5000 LSB, I see the output of 950 kHz. This obviously is not correct. Raduino shows version 1.01 on power up. Does anyone have any explanation for this behaviour? I'll try to reload the sketch, but first have to sort out the compile error messages due to new version of the etherkit library ... aarghh. I'll continue tomorrow ...

73

Having bought an early version without the Raduino I tried the FLL by IK3OIL. I made a small board fitting under the VFO section which contains a varicap (giving about 15khz swing from 9 to 5 volts) and a buffer amplifier. This works ok. The FLL waits for 30 seconds before locking at which point a LED goes off and the system locks. However after a few minutes the LED lights and lock is lost and I have to power off to get it going again. There is a reference in the documentation about this which I don't understand. The PWM duty cycle has been exceeded.?

Anybody got any ideas?

Also is it possible to buy the Raduino board separately?

Great project.....

Thanks

David G3RYP

Farhan's in here somewhere saying that the board's designed for 13.8V nominal with a max of 15.

/g/BITX20/message/18201?p=Created,,,20,1,0,0::Relevance,,voltage,20,2,0,4105151

You can run one of the lithium variants as long as you don't fully charge them. ?Since lithium cobalt (typical 'LiPo' cells) hold much of their energy at higher voltage, you'll lose capacity. ?If you want to run lithium, run LiFePO4 - it has a flat discharge curve, carries most of its energy at around 3.2V per cell, and you'll have about 90% capacity/run time if you run it between 10 and 14V in a 4S string.

73

Andy

Thank you very much for your help!

I made a list of the resistors in the three blocks of the circuit, and using the schematic tested and wrote down the resistance from the component on either side of the resistor.? I was able to find a cold solder joint in R45, which was fixed with a little bit of heat.? I went back and checked the Q voltages and things look much better with Q1-3 and Q4-6 all giving similar results.? The audio sounds good and seems stable.? I am very happy with the receiver so I call the receiver fixed.

There is no change in the transmit problem, unfortunately.? I don't believe I ever transmitted with this radio earlier, so I don't know for sure if it worked originally.

The relay clicks, and I hear a hum while transmitting, but no output showing on the swr/power meter.

First off, out of curiosity, are you swapping out that dual diode for any particular reason? ?There's one confirmed case of that part causing low power output, if that's what you are chasing. ?But dozens of different reasons power output might be low. ?You generally want to figure out a problem before randomly replacing parts.

Sounds like you blew the IRF510. ?Can't imagine how changing out those diodes would do that. ?Maybe you went and touched something else too? ?If you can remember what that was, that could be a clue here. ? Monitor current into the rig, main power and PA 12v too. ?I think it should be on the order of 100ma for receive, maybe 300ma? on transmit with no audio into the mike. ?If it's much more, see what's getting hot. ?Glad I'm not in the same room. ?Hope you're wearing safety glasses. ?Did you ever get a 50 ohm 5 watt dummy load of some sort? ?You really need one. ?Hope you haven't yet gotten around to reversing the +/- leads from your power supply, that could fry most of the rig.

Those 1n60's will likely work well enough. ?1n4148's might be a safer bet, since they have been getting used in Bitx's for over a decade. ?The 100 ohm pot is used to balance out the residual carrier if the diodes aren't quite matched. ?I wouldn't bother with that till everything is working, if then.?

Need an ace in the hole? ?Buy another Bitx40. ?You'd be in for $118, still cheaper than any alternative. ?And have a whole bunch of spare parts. ?You've gotten way more than $59 worth of education out of it already.

I must say, you are at least persistent.

Jerry, KE7ER

Randy -Great video resource! ?The BitX has come a long ways since I bought mine from Doug Hendricks four years ago. I saw you had other videos, so I know how I'm going to spend my Friday night right after I build my Marker Generator kit that I just got in the mail from QRPGuys.com.?

73, Guy N7BIR

Hi

Links are in the video's comment section.

Please let know of other resources.

73

Randy, K7AGE

To:?G4NQX post# 21853

I measured the forward voltage drop of the smd dual diode and got 336mV in circuit, then 1n4148 on a strip and got 864mV, finally a 1n60 with 350mV. Which one of these through hole diodes is the better replacement choice? I am thinking about the original design with a trim pot and smd 1n4148's. What was the value of the trimmer? And how to adjust it? Or is it better to string two through hole diodes between the empty smd pads for D15 and D16 and the big hole for the center pin of the trim pot, observing polarity as marked on the board?

After chasing the white rabbit this far down the hole, I have become cautious and hesitant. It sounds like we're almost there on this.

USB output is lower because the Raduino flips from LSB to USB by moving the VFO from 5mhz to 19mhz, either of which when mixed with the incoming 7mhz result in a 12mhz product that can pass the IF filter. ? 5+7=12mhz ? 19-7=12mhz. ? Various parts, especially the diode ring mixer, may have less response at 19mhz than 5mhz. ?A better way to flip from LSB to USB is to move the BFO. ?Currently that is crytal controlled, and involves hacking L5 and C103. ?Using a second Si5351 channel to generate the BFO would allow the Raduino to control the BFO frequency. ?Moving the BFO up a few khz from 11.9985mhz to 12.0015mhz would flip the Bitx40 from LSB to USB, the VFO remaining at 5mhz. ?For now, perhaps you can just increase the drive level at R137 when transmitting on USB with the VFO at 19mhz. ?Yes, I'd bet it also affects RX. ?Though not all that noticeable, as the receiver has an incredible dynamic range. ?

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