µBITX v3 Thoughts

I like the µBITX a lot.  I should say that I like the concept of the µBITX a lot.  It is a great concept to produce a decent super-het using fundamental building blocks and provides a great learning experience to those who take the time to examine the schematic.  It's been fun modifying the radio. The receiver is actually pretty good.

The only downside is that the transmit power output is wildly variable based on the band.  I have come to accept this as a function of the compromises made for a low price point.  I did spend some time experimenting with exchanging the TX pre-amp transistors with more substantial 2N2222s but found that the upgrade was not really worth the effort.  This may be due to possibly bad/fake transistors (watch what you buy on eBay)...

Its too bad that everything is on one board (again to keep costs down).  If the receiver and transmitter exciter were on one board with the final TX amp and low pass filters on another, I could have easily used a different power amplifier (like the great QRP Labs 10w linear amp).

I learned a lot playing around with this radio.  I may still take a hack saw to the board and chop off the amplifier...

µBITX v3 Audio Pop Fix

One of the items on my to-do list with my version 3 µBITX is to reduce the pop when starting transmitting and then again when going back to receive.  Thanks to a ubitx.net page describing a fix to the audio pop issue, my radio can transition from TX to RX without a loud, obnoxious POP.  It turns out that this modification was implemented in the next version of the µBITX (V4).  It basically mutes the audio when the transmit logic line goes high but still allows CW sidetone.

What I like about this solution is that it uses a header mounted on the main board and then a perf board has the updated circuit.  I had a few 8-pin headers so I used two pins to make the anchor to ground which I think will make it more mechanically secure.  I did not have the 1µF capacitor so I used two .47µF in parallel.

I drilled the holes by hand which was surprisingly easy.  The challenging (and aggravating) part was building the circuit paths on the perf board with bits of wire and globs of solder.  But, after a few deep breaths and some muttering, it worked out.

Now all I hear on the transmitter transitions is a couple of relay clicks -- nice and quiet.

Plug in the Si5351

Noise on WSPR waterfall display

I felt that running the Si5351 from the breadboard might be the cause of some noise I was seeing on the WSPR waterfall display.  Maybe the 10 cm jumper wires were radiating clock pulses.  And the breadboard connections were not reliable; signals would drop out and a little wire wiggling would cause them to pop back in.

Si5351 plugged into µBITX

I soldered 0.1uF caps and ground wires onto the Adafruit board (as described at ubitx.net) and pushed the ends into the µBITX connector.  The connection is much more secure now.
But the noise is still on the WSPR waterfall display.
My next theory is that the Teensy LC is radiating some digital noise.  I applied the Snooze library to put the µC to sleep and see if that makes a difference.  So far, I still see the noise.

Noise or not, I am receiving signals and have enabled the transmitter for WSPR.

Teensy LC wired up for transceiver support

Addendum:  After investigating a bit more, I discovered that the microphone input level was set way too high in the Windows sound settings.  After setting an appropriate level (around 25), everything is operating nominally.

Bye Bye LCD

So lately I have some extra time around the house.  Others are going stir crazy sequestering in their homes but I think they just need a hobby.  Amateur radio and fooling around with electronics are great ways to keep happily occupied for hours.

Years ago, I acquired some cool LED matrix displays at a hamfest.  I had no idea what to do with them but I thought they looked neat and I knew that at some point I'd incorporate them in a radio project.  Well, the time is now!

The SLO-2016 displays have 4 characters per display. It uses a parallel interface with 7-bit data, 2-bit address, and a display write pin.  This allows for multiple displays to have their data and address lines wired together and use the write enable line to chose the display.  I have 3 displays which means I would need 12 pins from the microcontroller unless we come up with a different solution.
Using two 8-bit serial shift registers (74hc595) tied together, we can use the SPI interface to send 16 bits that include 7 data bits, 2 address bits, and 3 display select bits.  One digital output pin of the µC is used as a SPI slave select and another is used to send a pulse to latch the register values.  The 3 display selection bits are wired to inputs of NAND gates (74hc00) with the other inputs wired to the latch pulse line.  The outputs of the NAND gates are used as the display write enable lines.

The µBITX with a LED matrix display

 
I updated the µBITX code to remove the LCD library and use some code I wrote to display information on the new display.  I updated how the frequency is displayed to squeeze into the 12 characters.

I reconnected the encoder and added push buttons for the menu access and PTT.  That allows me to run the calibration routines.

µBITX Updates

I've had the µBITX on the air for about two weeks straight running WSPR on 20m during the day and 40m over the night.  I have been successful in hearing and reaching around the world with 5 watts.

Sound card and CAT control with a single USB connection

From previously posted pictures, one can see that my cabling is a bit of a rat's nest.  My sound card was a $5 external unit while the CAT control was a separate connection.  I was going to crack open the case of the cheapie sound card to make direct audio connections and use a small hub to have a single USB connection to the PC.  But I stumbled onto a YouTube video from ELEKITSORPARTS that showed a sound card with integrated USB hub to allow CAT control using a single connection to the host computer.  The thing that sold me on it is that it isolates the radio from the computer which is something I would not have been able to accomplish with my hack job.

So I ordered one.  It took a few weeks to get here.  This weekend I wired it up and it seems to be working well with the Raduino.  But I want to replace the Raduino...

The Arduino nano is a fine choice to control a basic radio.  It has plenty of program space, it runs at a decent speed, and it has a bunch of GPIO.  But the RAM is a bit small and it only has a single serial port that is used by for CAT control via USB.  I was looking for options to be able to have multiple serial ports for interfacing various peripherals.

After researching various options, I decided to use the Teensy LC.  It has more of everything in a really small package but it isn't overboard (a Teensy 4 would be fun, but it's a bit much).  It has great support and is almost a drop in replacement for the nano.  I was able to connect the LCD with the same digital pins and wire the Si5351 via I2C.  And I am able to easily compile the µBITX code thanks to the Teensyduino add-on for the Arduino IDE. 

The first attempt at wiring the Teensy to the µBITX

I have used the Si5351 from Adafruit to generate an IF for the SSB6.1 single board radio with good results.  The µBITX uses all three clock outputs to generate the IF and BFO.  I hacked the connections via 10 cm jumpers from a breadboard which isn't ideal but it works for testing.

The only problem I had was what I thought was a failure with communicating with the LCD.  I did not understand the warning that the Teensy bootloader was giving me regarding it dropping out of automatic mode.  The LCD backlight is wired to the USB 5 volt line and without a resistor inline, it caused the Teensy to stop running because it sucked all of the current.  Once I added the resistor, everything ran fine.

Since I did not connect the VFO encoder, the Teensy LC controls the radio via CAT commands.  WSPR-X is able to set the frequency and decode messages...

Teensy LC and Si5351 with the µBITX copying FT-8

µBITX

I picked up a µBITX transceiver from hfsignals.com (aka Micro Bitx) version 3 to play with.  I thought it would make a good radio for digital modes and maybe use it portable.  There are many web sites describing the radio, so I won't duplicate all of that here.
The neat thing is that the RF section is pre-wired yet it allows for easy modifications.  Since it uses an Arduino and the software is freely available, it is a good platform for playing.  There are many posts on ubitx.net that describe how others are modifying (and fixing) the original design.
The included LCD display is adequate and there are some impressive user mods available but I really want to be able to run it headless. Since I already have an Elecraft K3, I decided to implement a subset of their command set (which is similar to the Kenwood TS-480 commands).

A few mods

Things I did to my µBITX:

• Spectral purity updates including relay replacement
• N8DAH AGC mod
• Use 2nd half of audio amp for digital mode RX
• Added a subset of the K3 CAT commands (TS-480 command set) & got computer control working with WSPR-X and fldigi

Next items:

• Audio pop fix
• SOTA Beam digital audio filter
• Single USB interface for sound card and CAT control
• Figure out why power output for 18 MHz and higher is low 
• Design a hardware interface for the radio that allows different user interfaces to be plugged in
• Put it in a case

FT-8

WSPR

Other projects

What time is it?

GPS

I bought a GPS module from adafruit and have been decoding location and time information.  It makes a fun clock when paired with a LED matrix display.  I have to thin down the font to get all the digits to fit...


Halloween fun
Another use for a couple of LED matrix displays...

I call him Morte