I probed a Bitx40 during transmit using a Rigol DS1052 and a 10x probe. ?Probe has a 6" wire to an alligator clip for grounding. ?The loop formed by that ground wire and the probe body is enough to pick up around 20mv of random noise when probing a busy board like this. ?Good enough for casual probing, but you get a much cleaner scope trace when shorting the ground ring at the probe tip to a ground very near the signal you are probing. ?Maybe build a special cover for the probe tip with two spring loaded wires or pins sticking out that allows you to easily probe across a 1206 resistor or cap, where one side of that 1206 is at AC or DC ground. ?I made my measurements quickly, using AC coupling and the convenient 6" ground lead on the probe.?

I got tired of saying AHHHHHHH after about 30 seconds, so spent the following 30 seconds adding a line to the Arduino sketch (anywhere) in the setup() function:

? ? tone(A0, 750);

The Raduino is then emitting a 5v square wave at 750hz on the A0 pin. ?(I prefer listening to 750 hz all day over 1khz.) ?That's the black wire on one end of the 8 pin connector, the other end of that same connector has 3 wires over to the tuning pot. ?I ran the black wire to a 1k resistor and a 20 ohm resistor in series to ground. ?From the top of the 20 ohm resistor to ground (the bottom of the 20 ohm resistor is ground) I now have a 100mv 750hz square wave, which I ran into the microphone input. ?Gives me a consistent signal to measure and make comparisons. ?(That square wave is nowhere clean enough to put CW on the air.) ? Pot R136 is set to mid-range. ?Bias voltage into the IRF510 is set to 100ma as described in the WireUp instructions on HFSigs (though bias is not critical critical, anything within 20ma is fine). ?Most of the probing can be done with the PA 12v disconnected from the rig except when probing around the IRF510.

Haven't yet tried it, but here's an RF probe that those without a scope could use to make similar measurements:

? ??

The cap at the probe tip blocks any DC component of the signal present, so the resistance of the meter will tend to pull any AC component down until it is centered on ground. ?Once that AC waveform is pulled down to where the bottom tips are going below ground, the diode conducts and keeps the AC waveform from going any lower. ?So the top of the diode has an AC waveform sitting between zero volts and whatever the top of that AC waveform is. ?The resistor and cap to ground form a low pass filter so the meter sees an average voltage for that AC waveform. ?The 4.7meg resistor and the 10meg internal resistance of the meter form a resistive divider to divide that average voltage by 1.414, giving a direct reading RMS voltage (assumes we're looking at a sine wave) instead of a peak voltage. ?I'd like to reduce the 4.7meg resistor to less than 1meg (200k?) so this gives consistent peak (not rms) readings with meters having anything between 1meg and 10meg of internal resistance. ?But at 200k there will be several microamps through the diode, and as current goes up the diode becomes less sensitive to small voltages. ?Perhaps use an inductor instead of the 4.7meg resistor? ?Perhaps we all use a Raduino ADC pin as a voltmeter (can be our battery monitor otherwise) so we have a consistent internal resistance on the meter? ?Add a 2n3904 amp for use when looking at low level signals? ?A 1n34 or 1n60 diode is roughly linear down to 200mv, good for repeatable (but not linear) readings down to just a few mv if the diode current is kept low, a shottky is not quite so sensitive but much easier to obtain and less sensitive to temperature. ?The probe on the N5ESE webpage is similar except that it assumes the capacitance inside the meter is part of the low pass filter, which most people writing up RF probe descriptions seem to not be aware of. ?

With all that said, here's my rough and quick AC coupled scope measurements using the 10x probe. ?R136 is set half way, power supply at 12.0v, 50 ohm dummy load. ?Unplug PA 12v except when measuring right at the IRF510 to avoid heating it up. ?My rig can give about 5W to the antenna, not much more. ?That diode RF probe is reading pk voltages, not pk-pk, so will see roughly half these values, even less if the internal meter resistance brings it down to an rms value.

Generate 700hz 5v square wave from A0 on Raduino with this in setup():   "tone(A0, 750);"
mic:  5v*20/1020 = 100mv pk-pk at 700hz    (Drive 5v square wave into 1k + 20 ohms to ground)
c107 200mv pk-pk square, but linearly droops 80mv toward center each half cycle
c63  150mv pk-pk, mostly near ground with 200us long periods of  overshoot/undershoot 
c61  350mv pk-pk, very choppy, mostly 12mhz
c53  150mv pk-pk, 12mhz sine wave
c51  400mv pk-pk, 12mhz, choppy due to loading from mixer
c43  350mv pk-pk, choppy 7mhz
c41  800mv pk-pk, 7mhz sine wave
c132 400mv pk-pk, 7mhz from here on out
c141 1v pk-pk	(R136 at halfway position)
c152 5v pk-pk  (down to a dirty looking 4v pk-pk when 12v to PA turned on due to miller effect)
into LPF  50v pk-pk 
from LPF  40v pk-pk 

Q10 emitter of BFO   4v pk-pk
Q11 base of BFO      300mv pk-pk
Q11 emitter of BFO   800mv pk-pk

The problem I was looking for appears to have been an intermittent solder short under C107. Saw zero ohms to ground at C107, and far side of diodes was nowhere near zero ohms. Assumed a short between windings on T4 and was about to pull it off and rewind it. But found that heating up C107 with a soldering iron cleared the problem. So removed C107, cleaned the pads, and put it back in place.

Jerry, KE7ER

Thanks Jerry, I figured it was a the problem.? I will try to get the original back on, or count the windings on it and match the L4 coil to it.

Jason

Ordered my bitx40 and waiting for it to ship to the US. I've been reading the forum here and I'm getting kinda concerned if my rig will work OK out of the box. Did I just buy a possible big a boo? Kinda difficult to tell if the issues folks are having are from the get go or after some experimentation.

Really excited to get this rig, but don't want to have to fiddle too much to just get it working. Thoughts?

73

Tim KM4WII

L1 is part of the 7mhz bandpass filter, used during both transmit and receive, though trouble here will be more noticeable during transmit. ? L1 has the same number of turns as L2, L3. ?Reuse the old core if it is not broken. ?L4 is totally different, meant to be used in the 12mhz analog VFO if you don't want to use the Raduino.?

Thanks Armin. That worked.

Mine is drawing 0.18A at 13.8V when in RX and 1.2A at 13.8V when in TX.

Remove the power from the PA amplifier and check the current again.

You do not need to have the PA powered when in RX.
--
Ion

VA3NOI

My BITX40V3 was putting out between 7-10 watts at 13.8V input power.? Everything was working fine, and I took my kit to my radio club meeting to show others last week.? Yesterday I turned it on for the first time since then, and had no power output.? I looked at L1 which had a broken lead on arrival when I got the board.? It had broke loose again.? The kit came with a spare toroid, I removed the old L1, and installed the spare one in the kit.? I know get 2 watts output at 13.8V.? How many wraps is L1 supposed to have, and could this be my issue, or is there something else going wrong.? I looked in the files section, for the document that used to be in there with several mods and troubleshooting tips, but can't find it anymore.?

Any help?

Jason

N3YUG

开云体育

I made that suggestion, and asked you think about how to make it work before shooting it down. And I am glad you did!

I looked in the subscription tab and found the member integration button, and found two options. Dropbox, and Google Drive. If you can put an up front message for new members, and a reminder for the not new members to to attach files from your own storage account. And move this group files to a BITX Dropbox or something, that would be great. The only sticky bit I see is broken links in the future after people delete files, or close the account.

So, is that how it would work? I haven't setup the integration, so I don't know how it works yet. But I soon will.

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