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Jim

i would do some probing with a continuity checker (like your DVM) to see what is what with your construction.? if rig goes into transmit when plugging in your microphone, somehow it is making a connection to ground.? the matter at hand is there needs to a common connection between the mic audio return, and the unswitched end for PTT -- to allow suitable current flow for each function.? if you can tell which microphone connection is attached to the 'braid' this may solve your issue.? or try reversing PTT and ground in the wiring.?

now if somehow in your microphone wiring both PTT and common are simultaneously connected - then you would have a short in your microphone wiring.?

73 Curt

The spec's say that the Eventek switcher has "ripple and noise" of "0.5% V P-P", so 0.005*12 = 60mv P-P at 12v out.
The MFJ4230MV has "ripple and noise < 100mv", that may be rms, definitely worse than the Eventek.
The Tekpower says "CV < 1mv rms", so more than an order of magnitude better than the other two.

The MFJ4230MV has the worst spec of the bunch, but works fine with my Swan 100MX.
Depends on the frequency components of that noise, better not radiate stuff above 1mhz.
Assumes the high gain audio amps in the receiver reject supply voltage noise.
About the best you can do is try it and see.
I've never tried the MFJ4230MV on my uBitx.

If using plastic boxes or the like, you can line the case and shield in important areas with copper foil available quite cheap on ebay:




73 Steve

I hope that fine case maker in India comes up with a slope front case for the JackAl add-on with options for 5" or 7" display.? I currently have a plastic case uBitx and it works fine.
--
Lee - N9LO? "I Void Warranties"

?

Well when we build a radio into a metal box, then attach several wires to it, that can compromise the shielding. And cut a large opening for a display its not as shielded.

I have a slight preference for a metal case, but its effectiveness can be exaggerated.? it is a bit more effective as gathering conductors together.

When EM fields outside the box are similar to what's inside, there isn't a strong case for shielding. and even in a metal box, I remember a few rigs that require more distance away from a linear power supply.

Your choice may depend upon available packaging materials and your ability to work them. Some folk are using nice 3d printed or other plastic cases can weigh in. Nor am I trying to reduce business for a fine ubitx case maker in India.

73 enjoy your build and radiations.

Curt

The Tekpower TP3005T looks like an excellent bench supply.
A linear power supply using a tapped transformer, so likely cleaner than most switchers,
still reasonably efficient.
Though at $80, kind of spendy for somebody who spent considerably less on their Bitx40.

Here's a cheaper one, this one is a switcher so is probably (but not necessarily if they did it right) noisier:
? ??

Lots and lots of cheap switching power supplies that only have one knob to set the output voltage.
Here's a nice 30 Amp switching power supply for use with a 100 Watt transceiver:?
? ??
So for the same price as the Tekpower, you can have 6 times the current out.
You can set the output voltage to anything between 4 and 16 Volts.
The meter can monitor either voltage out, or output current.
Seems to be about as RF quiet as any linear power supply.
But does NOT allow you to set the maximum current like the Tekpower,?
it's always ready and waiting?to give your project 30 Amps.

The Tekpower has that extra knob, allows you to set the maximum current.
If you are first checking out a uBitx on receive, you could set the maximum current to perhaps 300ma.
So the Tekpower will deliver 12v to the uBitx (or whatever voltage you set) up to 300ma,
If the uBitx has a short somewhere, the Tekpower then reduces its output voltage until the current is 300ma,
perhaps down to a voltage of nearly zero if that's what it takes.? No burned traces, no smoke.

To check out a zener diode, just put it across the output terminals of the Tekpower and set the max current to 10ma.
(I'm assuming that you can accurately set the current low enough.? May not be the case.)

The way you set the max current is to put a short across the output terminals,
then twiddle the knob for the desired current.

Weird that there are not more supplies that provide this extra knob to set the maximum current,
the additional electronics required is minimal.

There is another form of current limiting that you might want to be aware of:? Foldback current limiting.
If your project exceeds the maximum set current, the power supply shuts down entirely until reset.
Pretty much like a circuit breaker.
This is not as common (or useful) in a bench supply as the simple current limiting of the Tekpower supply.
?
If you want cheap, I suggest going to a second hand store and buy
a 12v desktop "brick" style supply good for 3 to 5 Amps.
If it's too noisy during receive (compare it to running from a 12v battery)
buy another and use the noisy one for other projects.
But these bricks will not have adjustable max output current like the Tekpower.

Jerry, KE7ER

Hi,

Shielding also protects the receiver circuits from external "crud". So much for the QRP argument. *All of my radios live in steel or aluminum, even the one with pretty plastic panels on the outside. Those are for cosmetics only. Plastic can shield against water:) Stay indoors and it won't get wet.

73,

Bill KU8H

--
bark less - wag more

This was my scope capture with the CW key pressed.

?

John, K5GT

Barry, Evan,

Thanks... It is good to know that microphonics an happen to a working board.? Now I can chase other things that may be part of the distorted audio and low sensitivity!? ...Then on to tackle the TX problems.
TNX - Woody? KZ4AK

Hi all,

So far hadn't touched my uBitX v3 for a while. This week I started building the AGC-kit I had ordered a while ago and added another 3.5mm audio connector to make a separate connection for a paddle.

Have not used CW as of yet, first have to practice? bit more ;) So far my operation have been limited to the higher bands (20+) and FT8.

Now that I was playing around and recently also obtained a GP5-SSB I was able to listen to my signal using a dummy load. Listening I discovered that when the key or paddle is not pressed you hear a faint tone (keypress is much louder) Is this because I am so close to my uBitX and is it the zero beat of the 700Hz? that I am hearing?

John
K5GT

Some have built in metal boxes, some use plastic boxes, and some put metal shielding inside the plastic boxes.? Is it a ,should do, must do, or doesn't really matter at these low power levels.?? Can you also explain why you made your choice?? Thinking about options for for my JackAl add-on new radio build.
--
Lee - N9LO? "I Void Warranties"

?

Looking at the output of my uBITX on 160m on a spectrum analyser, you don't want to go there!
However, a simple external low pass filter makes all the difference.
Attached is the circuit of a LPF that I built, along with before and after analyser screen shots of the output of my uBITX.

73 de Barry, G4BUD

Supplies made for amateur radio are usually quiet. You don't need instruments - if you hear the supply in your transceiver it's too noisy.

I have two 30 amp linear supplies, but my precocious desktop space goes to a Samlex SEC123 switching supply. I use a fused distribution box from a Sotabeam kit.

If you are interested in QRP, building kits and different voltages you might consider a bench power supply. I use a Tekpower TP3005T Variable Linear DC Power Supply, 0-30V @ 0-5A which provides current limiting as well as voltage regulation.

Looking on the components side of the Bitx 40 board right side about 1/2 way, I see a 2 prong connector labeled TUNING. My instruction sheet from HF Signals shows nothing, no connections. anyone have any idea if this is connected and where to?

If you bought one and decided not to use it, I'd like to fine one.?

?

Thanks
John K5MO

my rad had a bad usb port on it. turns out i had to nudge a small tang of metal inside the connector on the nano. if your cable goes vall the way in the disregard this post.
Dave n4lkn