Correction:
The QCX CW Transceiver does not have CAT control.
The QSX SSB/CW/PSK31/... Transceiver will.

The KB1OIQ hacks for the uBitx pointed to by my first link
? ??/g/BITX20/topic/17349156
look ideal for the vision impaired.
Hadn't looked into that before, impressive!

Jerry, KE7ER

Kb1oiq on April 14 describes mods he made for a visually impaired ham. Look up his message here for info.

Curt

Don't have a QCX, so can't compare the two except to say the QCX does not do SSB.
The QSX should come out someday, and will do CW and SSB, and a bunch more.
Downside is that the firmware of the QCX/QSX is closed source.
Though both have a CAT interface, should be possible to use that to make it usable
for the visually impaired.? And if not, Hans may be inclined to make it usable
once he has some time.

The Bitx40 can be clean, except for this spur:? /g/BITX20/message/62326
Reports vary on whether that spur is within legal limits, but it is fairly close,
so better than the v3,v4 uBitx in that regard.
Spur can be cured with a high side vfo by going to Allard's v2 firmware and mods:
? ??


The Bitx40, like the uBitx, could use AGC and a pop fix, as per the kits that Kees?
had out in the past (but no longer has).? Worth copying that stuff into any Bitx40/uBitx.?
Could also use protection for Q13 if a nearby transmitter or electrical storm might blow it.
Somewhere in this thread, Kees talks about those kits, and where he hid all the?
design notes up in our groups.io files section:
? ??/g/BITX20/topic/nd6t_agc_implementation_for/18098324
Or look for "AGC" and "pop fix" over on ubitx.net

The best thing about the Bitx40 for this application is that it is simple and open source.
So somebody competent in programming an Arduino could make it friendly to a blind person.
Or do away with the Arduino entirely and drive it from a RasberryPi,? has the computing power
and memory available to do most anything you want.?
With an easy path to the uBitx if more bands are ever wanted.

You might take a look at some of the previous work reported in this forum:
??/g/BITX20/topic/17349156
??/g/BITX20/topic/4181753
??/g/BITX20/topic/4192181

Jerry, KE7ER?

??

I am looking at options for a 40M qrp radio for a mostly blind ham. He would like to have SSB and CW if possible. Ease of use is paramount.?

He has looked at the qcx40. How does the bitx40 compare?

?I will be putting together whatever we come up with.?

Mike
AI4NS

Should not be any need to remove L8 and C160 when going around the LPF.
I'd just put that 3W 51 ohm resistor across C160, nothing on the antenna connector,, see how quickly it gets hot

You should be adjusting the quiescent drain current through the IRF510 for 100ma or so (with PTT pressed so it is trying to transmit).
Did you succeed at this?? No RF need be generated when doing this adjustment, so no need to speak into the mike.
When you get that 100ma quiescent current, the drain of the IRF510 should be at your supply voltage (typically 12 volts dc)
and the gate will be around 4v.? Be careful when making this adjustment, the bias pot is backwards, so fully counter-clockwise is max current
which will be several amps of drain current, and the IRF510 will smoke unless you have a fuse in the power supply line of 2 amps or so.

The instructions to set the bias current are at? ?
under "Alignment of the Bitx40".

Did R136 get twiddled, and left too far clockwise (also backwards, so fully clockwise is zero watts out).

If you can adjust for 100ma of IRF510 drain current, then the IRF510 is probably fine.
Problem is somewhere between the mike and the IRF510 gate, too small of a signal is getting through.
Could be a broken/shorted/cold-soldered wire on one of those torroids?


Here's a bunch of other suggestions, not in any particular order:

Verify your DC power supply is holding up at 12v when you key try to transmit.

Verify your dummy load is correctly connected to the antenna/ground connector into the Bitx40.
The BNC connectors that come with these kits are sometimes not quite machined to spec,
and the center pin of the BNC plug may not be making contact.? Cables can also fail.

Do the mods that Allard suggests (v1 or v2) to implement CW mode.?
If you get sufficient power out in CW mode, that means the trouble is between the mike and the dual diode modulator.

If CW power out is also low, could be trouble in the transmit LPF.? Remove L8 and C160 from the circuit,
couple what was the top of C160 out to your 50 ohm dummy load.
There will be lots of harmonics now, but should see adequate power if the trouble was in the LPF.

Perhaps your power meter is haywire.??
Build a low power dummy load of 3 or 4 watts so it heats up?quickly, perhaps using Mouser 283-51-RC.
Get a feel for how fast it heats up when transmitting CW for a few seconds,
then try to get the same effect by wiring that same 50 ohm resistor to a variable power supply?or a string of batteries.??
For example, watts = volts * volts / 50ohms,? so sqrt(10Watts*50ohms) = 22.4 volts DC?
should also heat up that same 50 ohm resistor at a 10 Watt rate.

Q13 and R141 run hotter than they should.? If you fed your Bitx40 more than 12v, they could have smoked.
Also, atmospheric static or a local QRO station with it's antenna near your Bitx40 antenna can blow Q13.
Check the DC emitter-to-ground voltage at Q13 and Q14 when transmitting with no audio, Randy says about 3.5 and 0.5 volts respectively:
? ? /g/BITX20/files/K7AGE/BITX40%20Voltage%20Measurments.pdf?
Search "Q13 R141" in this bitx20 forum web page for more info.

Check the other voltages Randy gives, see if they more or less? agree with your rig on transmit.?

If power out is still low, time to build a diode RF probe or find a 10MHz (or better) oscilloscope,
see where in the transmit signal chain the signal level is falling off.

So, in answer to your question, there's lots of things to do before blindly replacing the IRF510.
Your trouble could be anywhere between the mike and the power meter inclusive,
and odds are it's not the IRF510.

Jerry, KE7ER

Try this site:


73
Evan
AC9TU

--

…_. _._

Having some trouble with my bitx40 output lately. Using a QRP Guys dummy load, I'm measuring only 3V peak on the output (which translates to 90mW). I went back through the bitx setup instructions and tried adjusting the PA bias. When measuring the PA current draw, the most I got was around 200mA.?

I've tried multiple mics to rule out low audio input problems.?

Is there anything else I should try before replacing the IRF510??

Cheers,
David K4DBZ

The 2x3 connector specified is an IDC connector not a plain pin header. Your suggested method can work but will not be as clean or easy to connect and disconnect as using IDC connectors as Jack is suggesting.

Thanks

开云体育

The transformer is just a minature interstage isolation transformer. ?600:600. ? They are all over ebay.?

--

…_. _._

Hi all,?
I've collecting parts for the upcoming JackAl PCB.?Jack's BOM lists what we need but not where to find the parts.
?I've located most parts. However, I'm having a devil of time finding two parts.?

The two parts are: ?6 Pin, dual row (2x3) IDC male and female connectors. ? ?
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? Audio isolation transformers, 600 ohm, 1:1 ? ?- need correct size for the PCB - lots of different configurations of these out there.

Thanks for any help.

Pete WK8S
pmeier@...
? ? ? ? ? ? ? ? ? ? ?

Here is a 3D printable? .stl file that adapts the audio poteniometer? small shaft to a regular 1/4" shaft.
enjoy.??

Richard VA3NDO

For the price of some electret mic I would try a different one. There are differences. Not always based on price. I generally have to get the mic close to get much out of them. Think of how close you are to a phone mic. From a foot back you won't get much out of them.

Have found that I get approx the same peak on mic as the cw carrier puts out.

If you choose to run higher voltage on the finals would put on bigger heat sinks and fan.

I would agree that the metering gets wonky when transmitting into a mismatched antenna feed line. I made this mistake in believing the power meter with a higher swr. Can still pick up a few ft8 signals when on my dummy load so it isn't as dummy as predicted. My shack has metal siding and roof.

There's a lot more going on here than just replacing R13 with a 1n4007.
We need to send a current through the 1n4007 from a control circuit,
the more current through the 1n4007 the lower its resistance and?
the greater the gain in that IF stage.

If you bridge R13 with a 1n4007, then gain in that IF stage
can never be less than that of a stock radio (not good).
Removing R13 from the board will be the least of your worries.

To get any AGC design to work well, you either have to be
extremely lucky or really know what you are doing.?
Or copy a design that somebody else got working.

If you want AGC, I'd recommend dead-bugging the ND6T scheme here:
??
Use the circuit under the heading "New AGC System", April 16 2018.
That is what Kees shipped out as a kit (he has no more available).
Works on both the Bitx40 and the uBitx.

Kees' version uses jumpers to adjust R6 (in the ND6T schematic)
for values between 330k and 2meg, not just frozen at 1meg.
This allows the AGC hold time to be set to your preference.
Making R6 be 0 ohms would shut down the AGC, so it works like a stock rig.
Kees also added some 0.01uF and 1.0uF bypass caps to the 5v rail.

Allison's 1n4007 would more or less replaces Kees' two 2n7002 FET's.
Details of how to implement Allison's scheme are left as an exercise for the reader.
Good luck! If you want easy, I suggest you use ND6T's scheme.

Jerry, KE7ER

RE:
Allison recommends using a 1n4007 as a pin diode to set the gain in one (or both)
of the bidi IF amps, many of us have a 1n4007 in the junk box:
/g/BITX20/message/45984

Jerry, KE7ER
~~~~~~~~~~~~~~~~~
The link refers to replacing R13 with a 1N400X diode to assist
in leveling the audio and avoiding the booming effect. The "fix"
is simplicity itself even if not totally effective.

This relates to lack of AGC for the UBITX.

A few times listening to a net where some powerhouse station blasts
the audio line is enough to make this a consideration. Seeing the link
above shows that a simple "fix" may be effective but ass to just how
effective it may be is another factor.

My question is whether merely bridging R13 with the 1N400X would
bring about positive results or if adding the diode would be useful
only if R13 is removed? I know the mechanics of removing an SMD
device but bridging the resistor with rhe diode would be much simpler.

Also, it seems obvious that the diode's cathode would be connected
to ground. Is it so obvious that polarity was not mentioned?

Bob — KK5R

--------------------------------------------

Chuck,
Check to see if you have the heat sinks on the finals touching the case. That will blow them. 73 Mike KF6KXG