The All-band HF Amateur Radio Transceiver: Just waiting to be modified
Rod KM6SN has put together a comprehensive manual for Ian KD8CEC’s firmware. KD8CEC firmware (version 1.061 current) runs on a standard factory µBITx. No mods are required. There are significant improvements to the user interface and to functionality. An upgrade from Ashhar Farhan VU2ESE factory firmware is recommended to address firmware bugs and add new functionality (memories, CAT control, IF shift, etc.).
Download Rod’s manual here: KD8CEC manual v1.061
John VK2ETA notes that Simon, VK3ELH, pointed out an issue that when inserting an SSM2167 mic compressor circuit between the microphone and the uBitx mic-preamp, it can create feedback when the microphone was placed near the speaker while in RX. This is because the SSM2167 module is always on.
The solution John has applied is to connect the shutdown pin of the SSM2167 (pin 3) to the Raduino T/R digital output (D7) through a 2.7K ohm resistor. This disables the chip while in RX and removed the mic feedback issue.
Pictured above is an indication of where he picked up pin 3 on the SSM2167 on his module. The purple wire is connected to what is the right hand side of resistor R4. The 4.7K resistor on the RHS is for the mic-bias and the 51K resistor on the top-left is for bringing the compression ratio towards 4.
John feeds the Vcc pin on the board from the regulated 5V of his Raduino. Measured consumption at 2mA is a very small extra load on the Raduino regulator.
There is a DC blocking cap on the input and output circuits of the board already, so no external blocking capacitors are needed. However, a bias resistor does need to be added for the microphone.
The 2.7K resistor is not mounted on the module, so is not shown in the picture.
Also not shown on the picture are an axial choke of 100uH between the “in” connection and the Mic, plus a 1nF capacitor between the “in” connection and ground to block RF feedback when Txing on higher frequencies. For John, RF feedback was noticeable from 15m through 10m. Others may not have this issue.
John also has a 10K adjustable potentiometer between the “out” connection on the module and the original Mic input to the uBitx. His is turned to about 80% through its range.
John mounted his board on header pins so he can remove it as required. He extended the header pin on the “out” side (bottom LHS on picture) past the board to provide an extra connection for the shutdown wire.
John finds the compression and noise gate work quite well on the module. When he is silent the background noise does not trigger any movement of the power needle, but it goes up as soon as he speaks into the Mic. Also despite showing quite an increase in average power, he hasn’t had any negative comments on his audio. I was told that it was noticeable, but not unpleasant, “good for DX”. And this was with a change in the standard resistor value for compression to give around 4: 1 compression.
John, VK2ETA, has implemented a range of changes in Ian KD8CEC’s software targeted at portable operations (the software can be downloaded here in the files section of the BITX20 IO Group).
The scope of these modifications is described below:
Options for various features – These can be turned on or off. Key objective is to be able to customise the rig based on your needs and unfortunately on the restricted memory size of the Nano. So not all features can be selected at once. Choices, choices…
ATU control – A servo-based L-Network ATU. The communication between the Raduino and the ATU Arduino is via I2C. There is a separate sketch for the ATU Arduino (Nano or Pro-mini). ATU operating mode can be set to OFF, Manual as in on-demand, or auto-RX meaning that it pre-tunes based on historical data on a change of band and after first change of dial frequency (for a quick scan of the bands). It uses the EEPROM data of the closest stored frequency for pre-tune or tune on-demand to accelerate the tuning process.
Handsfree microphone/headphone – Using an Android style 3 rings (TTRS) handsfree earpieces/mic combination, with 1 or 3 buttons (Play/Pause, +, -), the PTT is controlled by Play/Pause as toggle, and I use long presses on + and – as respectively pre-tune and smart-tune of the ATU. Short + or – presses could be used for frequency up and down. Requires a very simple hardware mod to free-up A6 (see below).
S-meter measure and display – using analogue input A7 from an 2N7002 based AGC or a MAX9814 circuit or any other for that matter.
Software based AGC range extender – to augment (as in double or triple) the dynamic range of an audio AGC. This uses the slope of the 1st If filter at 45Mhz to attenuate the Rx signal when the audio AGC reaches its limit. Adds over 50dB of dynamic range.
Forward power and SWR measure and display – Currently assumes that the ATU is providing that info over I2C. Otherwise could be adapted with a pair of analogue inputs for measure. See the excellent NT6D design on the wiki.
Options for displaying the S-Meter, SWR and forward power – in either easy to see “fat” bars with no number, or “skinny” bars with more text and numbers.
Enable a “Memory mode” – selectable by menu, which cycles through all the populated memories (channels). Dial lock also locks the change of channels.
Made some rarely used or once-off functions as options – to recover program memory after initial tuning and allow for more options to be selected.
Fixed some issues with the IF-shift option – Ian has resolved these in his new V1.06 and later releases. Two issues were present: IF-shift in USB would change the receive frequency and it was applied to TX as well. Now applies to Rx only.
Hardware modifications required to use VK2ETA software mod
The only required hardware mod is to connect the CW key input to the PTT. Since in Ian’s software we select the mode by menu, there is no need to have a separate analogue input tied-up for the CW key. This frees-up analogue input 6 for use by other functions like the handsfree option above.
Still to come
John plans to apply Ian’s improvements in v1.06, especially the CW transmit frequency option and if possible the WSPR beacon mode (as a further add-in option).
How to use VK2ETA software
Download the zip files, and unzip these in your Arduino sketches folder. Edit the ubitx_20 options sections, using #define for enabled and #undef for disabled.
Perform a CTRL-R to compile and check how much memory is used. If you go over the limit, a warning is issued. Providing you have enough memory to run the software, upload the sketch to the Arduino.
John has uploaded both the Raduino as well as the Arduino sketch for the ATU and SWR measurement. They can be found in the folder “Variations on Ian Lee’s Software (by VK2ETA) + ATU sketch”.
John KK5VH has been working on understanding the audio pop problem for a while. He doesn’t have a fix yet, but he has identified that:
John has been simulating the circuit via LTspice with some results.
He increased C64 to 517µF by paralleling a 470 µF cap across it and changed C52 from 47µF to 0.1 µF. That made a timing difference that cured the turn on pop but left a gigantic pop on turning off the rig or moving from TX back to RX.
After all of this playing around he still don’t have a good hardware answer to the problem!
However, John suggests that if the Arduino Nano controlled K3, this could solve the problem using timing delays. A simple sequence would in moving from RX to TX, first turn on K3 (disconnecting the audio chain) then switch on K1 into TX mode. When finished with TX mode, hold K3 on for a number of milliseconds to all the RX circuits to stabilize before switching back to RX on K1. Hopefully, this would solve the problem. John welcomes comments!
The trifilar wound transformers in the from the uBitX schematic have polarisation as indicated above. The transformers use a 6 pin IC base legend, with the pin numbering as indicated above.
Nigel G4ZAL asked what people saw in KD8CEC’s UBITx Manager for their calibrations.
Nikos, SV1IYF, sent Nigel his settings, and they may be useful for others who want to recalibrate roughly to get going:
Rob, AG5OV, discovered the uBITX around Christmas and promised myself that when he got his Extra licence, he would setup his first HF shack. The uBITX removed the financial barrier and two weeks after he discovered the uBITX he passed his Extra exam (50 of 50!).
Rob’s adventure was in full-swing. He was aware of the anecdote of not to QRP for your first rig, but some frustration and failures did not dissuade him easily. He decided against building his own antenna for the first go round, as the uBITX was already going to be somewhat of a variable. After all, the fewer variables, the better!
He went with an EFHW from MyAntennas, which seems pretty well regarded. He learned about configurations, gotchas of EF’s, radiation patterns and about slingshotting fishing weights over tree limbs.
While waiting for his uBITX to ship he read every single post on the BITX20 list. If there was a part number, he went and read up on it. If there was something he needed for his µBITx, he ordered it. (He now has a stash of TDA2822’s, sockets, IRF510’s, RD16HFF1’s and BN’s sitting around). He bought a new soldering iron, bought a handful of newly discovered SMD practice boards and then read some more.
His uBITX eventually arrived and proved to have the dreaded WX version of the TDA2822 chip. He was not discouraged for he had a stash of step-downs from eBay.
He rushed putting his uBITX together with a build that aesthetically belongs in class of what not to look like. He printed a mic enclosure and a double paddle (and he has been practicing his CW regularly). The rig was brought to life. There were VOICES on his radio! He tried some SSB CQs, but his output looked very low… something to follow-up on.
Next he built an audio interface (using an EasyDigi design, but without the kit) and tried some FT8 because he had two young helpers who needed to see results… The young helpers make activist investors look like puppy dogs! They don’t want to hear their Dad endlessly calling CQ, they need action!
Rob had his first uBITX QSO on FT8 last week and with his helpers they have looked at the map everyday. They worked Mexico and down to Colombia shortly after. Last night they managed a first FT8 QSO across the pond to Slovenia and Hungary on the junkyard uBITX.
Rob wrote out his story not for himself, but because all this happened when the uBITX became available and it changed a “someday”activity into a “Hmm, I can do this right now” activity. It ignited a grand adventure for himself and a couple of young men.
Next up, Rob plans to use his µBITx on CW and SSB. He has already met a local HF’er via FT8, who’s going to be his testbed for SSB and he’s been practicing for his first QRS CW QSO.
Rob extends a big “Thank you” to Ashhar Farhan VU2ESE for making the little hackable “platform of discovery” and he also extends a big “Thank you” to the community of constructors on the BITX20 List for imparting the “Yeah, I can do this” motivation.
Jim Reagan asks, “Can anyone give me the manufacturer of the LCD display? Or the exact size?”
Jerry, KE7ER responding noting that “Adafruit says they nominally measure 24x69mm, mine measures 24x71mm https://www.adafruit.com/product/181″
“The 16×2 LCD (or 1602) is a generic display and there are clones of clones of clones for this display. Who built it first has long since been lost to the mists of time, as has pretty much everything from the 1980’s. But hobbyists have taken to it because it’s cheap, and speaks via 5v logic just like the equally ancient tech of their Arduino boards. So they still get cranked out, by manufacturers too embarrassed to put a name on them. The going price on eBay is down around $1.60.”
The LCD that comes with many uBitx is the JHD 162: https://www.sunrom.com/get/526000
The dimensions shown on page 16 are 24.1 x 72.2 mm.
Those pre-preparing a front panel while awaiting the arrival of their µBITx are advised to make a hole smaller than these dimensions, just in case the dimensions don’t match. There is quite a bit of variation in 1602 display dimensions.
Nik VK4PLN has been doing further work on upgrading the linear amp to Mitsubishi finals in his µBITx. He says,
“So looking good so far. I am getting these output values: (RV1 adjusted(75%) for 20W on 80/40)
80m : 20W
40m : 20W
20m : 18W
15m : 17W
10m : 14W
“No feedback, but I have yet to test a QSO on 20/15/10m…
The configuration is:
RD16HHF1 finals,
The finals run cool at 20+w with 330pf Mica cap. Nik is still considering changing out the driver and pre-driver transistors.
