The All-band HF Amateur Radio Transceiver: Just waiting to be modified
David N8DAH who is using the well regarded SOTAbeams LaserBeam Dual variable kit. He didn’t like the limited mounting options or the point-to-point wiring of the filter kit so he designed a board for his own projects and let the list loose on the remainder (which all went quickly).
Ian KD8CEC has released version 1.072 firmware. This includes support for both 20×4 and the standard 16×2 LCD screens (using i2c). It enables constructors to include or remove bits of code, and it allows the integration of an US$8 RTL-SDR to work on all HF bands to give full DSP, waterfall display, etc.
For more details see his website at www.hamskey.com
Download the manual (ug1072_087) for the KD8CEC v1.072, which has been updated by Rod KM6SN and his peer reviewers.
Gordon W2TTT asked on the BITX20 Group list, “Does anyone have some links to the display/ Raduino extension cable parts? I want to remote the display from the main board.”
If you want to separate your display from the main board, you should separate the display from the rest of the raduino and plug the “arduino nano” bit into the connector on the main board. The reason for this is that you don’t want long leads spraying RF around from the oscillator outputs from the si5351a. This is a sure recipe for birdies in your RX.
Use Dupont connectors (Male to Female) to do this. Most will find either 10cm or 20cm connectors are suitable.
Jack W8TEE comments “Jumper wires (aka Dupont wires) are great for breadboarding and experimenting, but my experience is that some of them don’t make a solid connection after recycling (connect/disconnect) a few times. We were getting a lot of noise on a TFT display line and finally tracked it to a faulty Dupont. The Chinese imports seem especially susceptible. If you experience noise or hashing on a display or in the audio, this would be one of the first places I’d look.”
Jose CO2JA says “Put an L attenuator on the driver output and turn off the finals. Use a saturated NPN switch driven from the +TX to key the transverter”.
Allison KB1GMX says “The ubitx sans driver and finals will put out roughly the right power for most modern transverters without the problem of too much power. The receiver is a good match as well.”
Geoff, G8BMI is cross-fertilising ideas across hobbies…
He has been assembling a uBITX, and found that the volume control has a 5mm shaft rather than the usual 1/4 inch. This means that none of his spare knobs fit. We’ve all been there. Most of us threw the supplied pot into the junk box and moved on with another standard potentiometer.
However, a waking inspiration suggested a very short length of 1/4 inch OD copper pipe, as used in model steam engines, could be used to ‘sleeve down’ a 1/4 inch bore knob. And it does!.
Geoff turned down the copper tube in the lathe, using a file just to ease the fit [It could be mounted in a power drill chuck to get the same result]. It only needs a skim. His tubing was 0.210 inches bore, which is just over 5 mm (5.18)
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.”
