Aaron,
Verify that you do not have the "skewed pot" issue pictured in the following message:
/g/BITX20/message/73189

If that is the problem, then most likely you will have to replace one of the finals.? IRF510s are relatively cheap and readily available.

After the visual inspection, I would validate that the Bias regulator is delivering 5volts when the PTT is pressed and that there is a gate bias on each of the IRF510 output transistors.? All of this should be done into a good 50ohm dummy load rated for at least 10 watts.? The 20watt QRP-Labs dummy load is a good low-cost dummy load for up to 20 watts at only $8.50 plus shipping


The last test would be to readjust the bias on the finals to verify operation.? REMEMBER that the pots are REVERSED.? Minimum bias (current) is fully CLOCKWISE? You turn them counterclockwise to increase the current, being VERY careful not to exceed 150ma for each device.? Here is the HF Signals bias settings page:


If you can adjust the bias, then most likely the finals are OK.? The next most vulnerable device in the chain is then Q90.? This transistor has been know to be blown by nearby high power transmitters.? There is a recommended back to back diodes (1n4148 as an example) from the switched antenna lead on K1 pin 12 for the receive section to ground.? This will not affect receive sensitivity, yet protect when a high power transmitter keys up when in receive or powered down.

The above are just suggestions.? You should review the schematic and do the measurements to validate before making the mods.

Good luck hunting down the issues.
73
Evan
AC9TU

I received my uBitx a week and a half ago after DHL inexplicably held onto it for two weeks *after* I’d paid the import dues.?

Today I found the time to ‘build’ it. Half an hour’s work.

I’ve tuned the BFO but I can’t find any documents for configuring it otherwise.?

The rejection of noise on receive is unbelievable! Compared to my ft-818 on the same antenna (a 40/20 fan dipole @ 5m) it is *so* quiet.

However using that comparison I’ve noticed that the frequency is off 1500kHz compared to the Yaesu. That might explain my failure to make a QSO. How can I correct this? I only seem to have two menu options, one of which requires a 10000kHz signal the other tunes the BFO which I did using the page at HF Signals.?

Help?

开云体育

Yeah I had it in CW mode when I was testing it with the wattmeter. I do see the TX come on the screen when I push the PTT on the mic. I also hear the relay clicking when I push the PTT button. I do have a nicer mic, I don't know if it has a preamp or not built-in but I want to make sure that the rig works before I do any mods to it.?
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'72

Aaron,
First, don’t get discouraged.
Have you tried putting the uBITX in CW mode and pushing the PTT button on the microphone with the watt meter connected? Start out on the 80 or 40 meter bands first. Does the TX light come on? Can you heard a relay click?
Have you tried another microphone yet? I replaced mine with a CB microphone having a built-in preamplifier. It made a tremendous difference in power output for the phone mode.
I’ll let other folks chime in with more technical troubleshooting advice now.
Stephen

That looks awesome, makes me want a 3D printer!
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'72

I have been wondering why I have not made a single QSO on my uBITX V6. I just assumed that it was bad band conditions, poor antenna, low power a number of things. I never really tried hard to get QSO's I just tried a little bit every now and then. This afternoon I hooked up a watt meter to it and sadly found out that it isn't transmitting at all. I checked the wattmeter on other rigs and it worked just fine. I put it back on the uBITX and nothing. So does this mean that I need to replace my finals before I get my first QSO on it??
I can't think of anything else, I hope that you guys have some ideas.?
--
'72

Since my radio always sits in the same spot I made a hold-down and because the stand makes the speaker angle away I also made an ugly sound deflector.




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Lee - N9LO? "I Void Warranties"

?

I got bored staying home due to Covid-19 so I used Tinkercad to draw up these accessories.? The carrying handle doubles as a stand.? The knob inserts bulge up.? I attached the .stl files if you would like to print your own in your favorite color.





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Lee - N9LO? "I Void Warranties"

?

I've got some questions on my ever-evolving uBITX, specifically associated with some additional elements I've added to both the TX and RX audio lines.? (No schematics available at the moment, but will post later/if needed.)

RX audio:

I homebrewed a narrow CW audio filter using a TL974 op amp, powered with +5V from my regulator.? The CW filter is centered at ~700 Hz, with ~200 Hz bandwidth, and uses 3 sections of the TL974.? The 4th section of the TL974 is used as a line-out buffer for a separate line-out that goes to a rear-panel mounted RCA jack.? The input to the filter is connected to the VOL-H tap on the schematic, i.e. prior to the volume control.? The output of the filter is connected to a toggle switch to allow bypassing the filter; the output of the switch is tied both to (a) the top of the volume pot, as well as (b) the input to the line-out buffer.? So the line-out is NOT controlled by the volume control.

Issues/Questions:

(1) The filter passband appears to be about right.? I do notice, however, that as I tune a signal into the center of the passband, as it gets stronger I get some additional audible artifacts, almost a buzzing sound.? It appears to correlate to loudness... if I turn down the volume, it will go away, but then the overall volume of the signal is greatly reduced.? I will note that this is using the headphone output, which IS controlled by the volume pot.? Any thoughts on what could be causing this?? I will also note that signals will tend to move in and out of this artifact region, and when they do so, their volume changes (which is annoying).

(2) I use the ND6T RF AGC from kit-projects.? Where should I be taking the audio signal from to control the (RF) AGC?? Normally, it's from the top of the volume pot.? I actually soldered a wire from the volume side of R70 to the AGC.? But that means that my AGC can potentially be controlled by audio signals that are inside the IF passband of the crystal filter, but are outside the AF passband of the CW filter when it's in use.? Should I have the AGC input come from after the audio filter?

TX audio:

I also have a line-in signal on the back panel.? I've built a circuit with a TL972 op amp that I uses for two purposes:? (1) one section is used as a mic preamp (see ref A below), and (2) the second section is used as a simple active mixer to mix the mic input and the line input.? The output of the mixer is connected (via capacitor) to the MIC input on the uBITX V5 schematic.? These new circuits are all powered off full-time +5V from the regulator (not the TX DC line that powers the Q6 mic preamp).

Issues/Questions:

(3) I noticed that, even without pressing the PTT, if I speak into the mic, I hear the mic audio in my headphones.? I'm assuming this is because they are "always on".? However, I also assumed that, since the TX power to Q6 is disabled if the PTT is not depressed, that transmit audio would not get through.? Is this a bad assumption? Is this a normal effect of this circuit, or is it possible that I have too much mic gain now, that manages to push itself through Q6 even when TX is off?

Thanks for any input you can provide!

Rob KC4UPR

Ref A: http://rason.org/Projects/hbmic/hbmic.htm

The best way to prevent noise is to use a linear regulator as you only have to flatten out the 60 hz line noise and prevent rf from the radio getting back into it.

As far as the raduino goes, it uses the 7805, a linear regulator and is by nature quiet.? If you are concerned about heat add a heat sink.? You might consider a couple diodes in series rather than a resistor.?

Other regulators in the radio include the arduino, as well there is another 7805 to control the bias of the drive MOSFETs.

all the best
Dave