MMDVM

So, I am interested in building a MMDVM (Multimode Digital Voice Modem) for hooking into DSTAR. So, I spent 8 hours working on a PI-Hat similar to the ZumSpot Pi Zero. Since ZumSpot seems to be dead, I decided to build my own. I finally have the schematic done, board placed and routed. Now, to get them built.

FWIW, I love the ST Micro STM32 MCUs. I use them in our professional work, through I am using a less powerful one on this design.

Here are photos of top and bottom:

 

MMDVM HS top

 

MMDVM HS bottom

uBITX finished

Last night I finished putting the uBITX together and testing it out. I did a 30 Meter CW contact (straight key) and listened up and down the bands. Nice little radio.

Here it is in completed form. The case was printed by Dave Schmidt, who has done these case for a number of BIT40X and uBITX folk.

 

IMG 2399

Now, what to do with the uBITX?

The uBITX comes with a 2 line display and an Arduino CPU. (not shown). I am designing a 5″ display, Cortex-A8 (minimum) CPU with the Si5351A Synthesizer chip, and will be writing the FW for it. Also, will be designing a circuit to tap off the IF and provide a band scope/waterfall on the 5″ display. In addition, will be designing an audio circuit so that the radio can be plugged into a computer to run digital modes. (Maybe include a decoder in the FW?). Maybe just put a bluetooth module and write a control protocol, and build an iOS app/macOS App to run the radio. Now, this sounds ambitious, and it is, but I really want to build the radio they way I want to. I will probably add a remote facility to control it via a network, or better the web (OpenWebRX?). I am hoping to be similar to the display in the second picture. If it turns out well, it could become a side business.  The display will look somewhat like this:

Screen Shot on 2018 02 18 at 15 08 47

The uBitx is on the way

I got notified the other day that my uBitx is shipping from India. I cannot wait to try this radio. Meanwhile, I have been working on a better display system. I plan on re-doing the Raduino in my own way. New main display board using a 2.8” display, and maybe a more powerful Arduino, or even switching to a different CPU (cortex-m0?). I am working out the circuit as we speak (as well as working on stuff I do for work, so the new front panel console will be done in my own time). I have even considered putting in a 4”-5” LCD and adding a landscape to the receiver. Anyways, now a days it is great to be a home brewer and the toolset to make your own stuff, while expensive, is powerful.

New SDRPlay RSP-2Pro

Well, I have received a SDRPlay RSP-2Pro and I love it. Such a beautiful SDR. The folks at SDRPlay really did a nice job on this thing. I run SDRUno with it on a (ick) Windows 10 installation in BootCamp on my MacBook Pro and it is a nice combo. (Hey SDRPlay, you should have me port SDRUno to macOS!). What I like about the RSP-2pro is the metal case, and that it has 3 antenna inputs. a Hi-Z, a standard SMA antenna connection, and a bias-t SMA antenna connection (to power those LNAs, etc). The thing really shines, and compared to the RSP-1, the difference is amazing. Another SDR for the shack!

 

The QRPLabs QCX 5W CW transceiver.

I ordered back in October of 2017, a QRPLabs QCX 30 meter transceiver. As most of you know, I am a QRPer (in addition to an SDR enthusiast), so this was a great opportunity to build a single band, 5W QRP rig that has amazing features like a CW Beacon, WSPR beacon, a CW keyed and a really nice receiver. In addition, all the settings do not require external equipment to tune up the radio. In addition, the radio offers built int east equipment to test other things. Quite a handy little package.

 

Anyways, I was thrilled to build it. It took about 10 hours, total, due to the winding of a transformer and 4 toroids, but it was fun to build.

Go over to QRPLabs and look at the QCX transceiver for yourself.

Here is the completed rig:

IMG 2312

More hacking/mod’ng the BITX40

I did some mods to my BITX40. I added a 10 turn 10K pot for the tuning, to get better granularity, and I added UpperSideband (USB), so i could use it to work digital modes.

The 10K pot was straight forward, but the USB mode introduced clicking when tuning across the band. So, I added a 1000uF Electrolytic and a 100nF cap, in parallel, across the digital VFO’s power regulator. I also added a 56ohm resistor between rig power and the digital VFO power. Clicking was still there. I discovered I had linked with version 2.0.3 of the SI5351 library, and saw a note on the BITX40 Facebook group, that one should link with version 2.0.1. I did that, uploaded the sketch and viola! The clicking was gone. In fact, adding the filtering got rid of a number of other things I was hearing when I tuned. Pretty cool.

So my next mods will be to put a 8 pin microphone connector in, add in a mode switch to get the rig into calibration. Also, adding a voltage divider to put the current input voltage on the display and last but not least, a S meter circuit, to use the bottom left row of the display as an S-meter.

The BITX40 is a lot of fun. And modifying it so I can do JT65 and such will be a blast.

Cheers,

KD1IT