The All-band HF Amateur Radio Transceiver: Just waiting to be modified
Rod KM6SN has updated his manual for the KD8CEC firmware for the µBITx that is pretty popular because it requires no hardware mods.
The updates to the manual:
1. incorporate feedback received on the manual, with some new
operating tips
2. enhance the Memory Manager section a bit
3. improve readability.
As before, please send any feedback to the email address shown in the manual. A new manual for KD8CEC firmware rev 1.07 is forthcoming, as is a manual on the Memory Manager.
Nik VK4PLN has now supplied a Schematic for his Raduino replacement board (for an Arduino Nano fed either with I2C or parallel pins).
These boards can be ordered directly by writing to Nik.
The TDA2822 audio amplifier chip (now infamous because of the self-combusting WX versions) now comes installed in a socket for easy replacement from HF Signals (the µBITx manufacturer).
There are still regular reports of spectacular end points for the WX chips on the list. Most are finding that TDA replacements work reliably with no need for a regulator to feed them with a lower voltage. To be safe and secure, however, you can easily feed them with 5-9v via a regulator.
In related news, some constructors are substituting the readily available NTE7155 chip which is 100% pin compatible with the TDA2822.
HF Signals seems to be catching up with their huge backlog of µBITx orders. The latest posts from members of the BITX20 List shows that orders up to 17 March are being shipped at present. This suggests that the manufacturer is just a month behind on shipments now, compared to two months behind in March. This will be good news for constructors eagerly awaiting their kits. Note that shipping time is additional (around a week for DHL shipping worldwide and 2-5 weeks for IndiaPost depending on destination).
Michael VE1LEB has been scratch-building a uBITx. This is the first time he has built a crystal filter. The photo below shows the response curve of the 12MHz SSB filter output by his PHSNA:
To select the crystals, Michael used the K8IQY crystal test fixture and chose the closest ones to 12MHz from a bag of 50 inexpensive computer crystals.
He is not sure whether his PHSNA is accurately calibrated or how much error there is in the frequency readings. However, the -20dBm passband is less than 2.5khz. He received a new bag of 100 crystals, and was wondering if he should take the time to
Rod KS6SM commented,
“In the ubitx, the crystal filter is driven/terminated in a 200 ohm impedance. It is likely your PHSNA is 50 ohms. The passband ripple you are seeing can be severely influenced by driving/terminating impedances.
“Are you measuring the filter with the transformers at each end, or are you going direct to the crystal connections?
“It is normal for the passband to be below 12 MHz. On my ubitx, the BFO is at 11,997,117 Hz, so that will give you a sense of how far below 12 MHz the passband is.”
It turned out that Michael was measuring the filter ‘naked’, without the transformers. He measured it again but through the transformers, and the result is much “softer”:
Satish VU2SNK said, “In both the curves without and with transformer your filters loss appears to be around -7 db. In my opinion this is bit too high -3db is just right up to -5db is acceptable according to the experts, what type of capacitors are used in this filter? The multi layer ceramic capacitors
are really of low loss. If you use the modern SMD ones in my opinion that will reduce the loss in the filter.”
Allison KB1GMX also suggested, “One warning when measuring narrow filter use a very slow sweep. At narrow resolutions if the sweep is too fast the curve will not match the actual. It is as much detector response time as its filter delays. When too fast the it will appear tilted, and when you slow down you will see more accurate result.
The filter insertion loss in the 4 to 7 db range sounds correct. Though I might be better if higher Q capacitors are used we are not talking a 3DB difference. Also dId you calibrate out the transformers first? That can add a DB of loss sometimes more.”
In responding to the suggestions from Allison and Satish, Michael said, “I’m using chinesium SMD 1206 capacitors.
“I realize now that I had not accounted for loss in my cables, and perhaps I’m not appreciating fully the implications of my test equipment. I’m a dopey artist, not an engineer! When shorted, the cables out-of and into the PHSNA present a 3.5 dBm loss. Each transformer adds 1.9 dBm loss, so double that and add the loss in the cables will represent a total loss of 7.3 dBm. When I bias the PHSNA for the 7.3 dBm loss and attach the filter (including the transformers on each end), I get this result, which puts me well inside the 4-7 dBm loss that you mention.”
There has been a bit of discussion on the BITX20 Groups IO list about Baofeng mics, mods required to work with the µBITx, and what to do about a mic jack. This article tries to sum up thoughts on using the Baofeng mic.
Basics
The Baofeng Speaker/Mic can be obtained very cheaply, either direct from China (e.g. on Aliexpress.com or Banggood.com, or eBay.com) or via third parties in your country. Be warned that almost none of these will be a genuine Baofeng mic. There are many different varieties of “knock-off”, and they are of very varying quality. However, most are adequate for µBITx use.
The wiring in the microphone is not standardised (i.e the colour of the wires varies). In some cases the wiring simply doesn’t work. In this instance, you should throw away the Speaker-Mic as the wiring is non-repairable. Buy several to safeguard against the odd one that has wiring issues.
The microphone element is so-so, you can replace the one in the Speaker/Mic with the element that comes with the kit as required. You may also need to drill out the tiny hole to be a bit bigger to make a reasonable air passage to the element. The speaker is not high quality and will not give much volume. When using the speaker-mic in the µBITx, most of us don’t use the speaker at all.
Standard wiring will work on the BITx40, and the LED in the Speaker/Mic will even light up. It won’t on the µBITx, because the PTT line works differently. This is connected to +5v from an arduino line (messing up the bias on the microphone).
Disassemble the mic, and rewire (using a multimeter to test connections) so that the PTT switch is wired separately from the microphone element. You can use a common ground return for the mic, speaker and PTT. See the original circuit diagram for the speaker/mic here.
A key question that those with a Baofeng Speaker/Mic, is whether you should retain the 3.5mm and 2.5mm plug, or cut it off.
John KG5WJQ observes that they sell a combined jack on Alibaba and the price is fine. The problem is that it is a PCB mount jack so that can result in some difficulties with mounting the jack in a case.
Craig KM4YEC uses panel mount mono jacks, one 3.5″ and one 2.5″, sourced from Radio Shack in store stock (but they could probably be ordered online). He says, “If you turn these back to back, and butt them against each other, with the ears turned out, it is a perfect fit for spacing.”
Craig uses only the PTT, and the Mic element in the enclosure. He enlarges the hole in front of the element, removes the speaker, and makes sure the only two circuits are PTT and Mic. He went as far as removing all the SMD components and unnecessary trace runs using exacto knife cuts.
Glenn VK3PE fitted standard 3.5 and 2.5mm jacks at the rear of his uBITX build. NOTE the 3.5mm jack needs to be insulated from the chassis to work as the PTT is connected to what is normally ‘ground’ on a stereo socket. Glenn used some plastic washers to insulate it.
The challenge with this approach is that the spacing between the two jacks needs to be reasonably precise.
There is nothing to stop you from cutting off the plug and wiring it directly into the circuit. This is a cheap option (no plug and socket required), but is a bit inconvenient when it comes to moving the rig, as the microphone is permanently attached.
The other option is to remove the plug altogether and use different connectors. Many constructors like to use a standard 4 pin mic jack or similar style 8 pin jack used by the big three Japanese amateur rig manufacturers as illustrated below:
Mike ZL1AXG uses Kenwood wiring on a standard 8 pin mic connector as shown below.
Dave K8WPE felt his Baofeng speaker mike was of such poor quality that he went ahead and bought an almost identical microphone from Btech. This is a QHM22, a much better product, for US$23.00. The speaker is top notch and reports of his voice quality are also very good. So the Btech mike might be a better choice.
Ian KD8CEC is working on a new release of his CEC firmware for the uBITx that will be more modular in approach (picking up on John VK2ETA’s mods to Ian’s firmware), interface with a range of displays (I2C versions of the 1602 and 2004 displays as well as the display that comes with the Raduino). More importantly, however, this new version will enable the µBITx front-end of the receiver to be connected to an RTL-SDR USB device. The RTL-SDR device will draw on the HF receive sensitivity of the µBITx along with the front end bandpass filter and first IF roofing filter and associated IF stage amplifier (normally at 12MHz) to produce a quality SDR receiver (for just a few $s invested in the RTL-SDR tuner).
This version is available to download (1.071 Beta) from Ian’s website now.
Jim Sheldon – W0EB has released W0EB/W2CTX I2C software Version 4.00R for I2C enabled uBITX Raduino cards and the W0EB/W2CTX/N5IB RadI2CIno cards.
This software will NOT run on a stock standard Raduino card unless it has been modified to operate with an I2C display This version is for an I2C enabled 2 X 16 LCD display. (The 4 line x 20 character version will be released later).
Some sleuthing by group members suggests that not all I2C backpacks for 1602 and 2004 LCD displays are the same.
if your library call for an I2C display doesn’t work this may be why.
John VK2ETA has some pretty good ideas. A few days ago he worked on an AGC system using the first IF stage (at 45MHz) to control gain at the front end of the system. He has now got some pretty good results using a limited amount of memory in the firmware to flatten out the power curve on transmit. At this stage it only works in voice and digital modes (LSB and USB). Because CW is achieved by unbalancing the first mixer after the IF filter, this approach will not work on CW.
By shifting the IF frequency on the filter, John is able to produce a fixed attenuation that keeps the output power within the required limits.
The process is two fold:
John has used 5W and 10W as targets for the Low and High values.
His results (remembering he has modified the final stage with RD16s and a number of other changes have been made to his transceiver):
His ATU uses a 2nd Arduino. He has used a spare digital output to send a 1500Hz tone, low-pass filtered, to the microphone input for calibration purposes. The audio filtering plus the 2nd IF filter take care of the audio harmonics and the signal is clean. This could be done in the Raduino if digital lines are freed up, such as by using an I2C display.
The tone also provides a tune up facility in low power.
He can transmit in digital modes in low power mode without having to adjust the drive every time he changes bands. Perfect!
John will update the code in the file section so that others can incorporate this new feature into their firmware if they desire.
John acknowledges Jerry KE7ER’s idea of using fixed tables to perform the High/Low calibration function.
John has uploaded an update of the KD8CEC based software (V1.04 based) for Raduino and ATU Arduino.
Key changes in Version 20180411:
– Made the menu system dynamic so that items can be inserted at compile time or can be context-dependant at run time.
– Added output power attenuation for 80 to 10M using first IF shift.
– Added new menu item “Power Level”: low/high/max for SSB modes.
– Made CW menu items display dependant on having CW modes selected.
– Reduced the level at which the software AGC comes in. Adjusted the correction of S-Meter when software AGC comes into play.
– Changed tone generation for ATU tuning sequence from CW to using SSB with the 2nd Arduino generated tone.
– Change tune sequence to
a)Select the “Low” power setting before performing a tune and
b)Change tune frequency to tune on carrier (offset by audio tone frequency).
Assumes the following hardware change (only if using an ATU): a digital output on the ATU Arduino is used to generate a tone. An audio filter identical to the Raduino CW audio tone filter is used and it’s output is connected to the mic input of the SSM2167 module. If digital outputs are freed-up on the Raduino, for example by using an I2C display, the same can be implemented with only the Raduino.
This allows a low power tune function.