The All-band HF Amateur Radio Transceiver: Just waiting to be modified
Bob N0BHC stumbled across an upload problem with an order of 5 Arduino Nanos this week.
This batch of Nanos used the CH340 USB chip and he was certain the USB driver was correct.
He found there had been a recent change in the Arduino IDE (sometime during March ’18) and to program new “old” Nanos you have to select “ATmega328P (OldBootloader)” from the “Tools – Processor:” Menu. After doing this, sketches uploaded to the Nanos just like before.
Stephen, KD2NDR, has been working on porting the µBitx code to a Teensy.
He has added a few other features with the new expanded memory capability. This includes an I2C 4×20 display, leaving many pins for other uses, and digital beacon modes supporting all JT modes, WSPR and FSQ. Transmission is triggered by a timer interval set through main menu.
The teensy real time clock is updated using a GPS module. Stephen plans to add an option to set the clock manually or via a serial port at a later date. His implementation also allows for dynamic setting of a maidenhead locator (4 or 6 character) based on the GPS data.
Planned features for a future build include an SD Card to store custom messages and logging for digital mode operations. He also plans to provide numeric keypad support sot that text can be entered directly along with setting the frequency. A voltage/ amps monitor for battery operation, and an. swr meter, and more is planned. Stephen promises to make the software available to constructors when he gets more time to test everything in more depth.
In commentary on the measurement of amperage, there were several suggestions for how to do this including the use of cheap “Hall effect” sensors. Probably the best of these came from Arv, K7HKL, who suggests:
” An alternative approach for current monitoring might be available. As part of a workbench system I built a dual-port DC voltmeter using an Arduino NANO.
manually calculate the current from resistance and voltage.
“In a captive system this approach would work because the software would know the resistance value and thus be able to measure differential voltage and from that calculate current flow through that known resistance.
Gian, I7SWX, has shared a mod for replacing the TDA2822 audio amplifier. He intends to apply this circuit after other mods he is experimenting with on his uBITX.
The audio PA is the TDA2003, an amplifier where the bandwidth can be modified. His circuit is designed for 3kHz.
This circuit, with reduced bandwidth, has been tried on an FT920. It is possible that some components values may need to be changed.
It is important to note that Gian has not tried this mod as yet, but others might like to beat him to it!
Bill Schmidt, K9HZ / J68HZ writes, “Thanks to my friend Frans J69DS, freshly built uBITx radios were given to two well deserving young ladies on the island of St. Lucia yesterday.
“They are part of the Youth On The Air (YOTA) movement on J6 and now you can listen for them on their own radios. Getting the radios to them had its challenges but they are very happy to have them! We have more radios to give away too!”
Bill K9HZ has added a tune control to his circuit to even up output power across the bands. This will be featured in his ATU that is expected to b be documented shortly.
With the addition of a transistor driver for an additional relay and one additional potentiometer you can now have a tune button that will tune your rig with lower power output. Pushing a tune button while keying the rig will result in lower power output. Alternatively, you can wire up a DPDT switch for tune with the second throw on the switch wired to PTT.
Making nice labels for the front panel of the µBITx may not be all that intuitive. Many of us use a label writer (e.g. Brother or Dymo device). The best options (depending on your front panel colour) may be to use “black on transparent” or “white on transparent” tapes.
Vic WA4THR was looking for a way to easily label the front panel of his BitX40 and was pointed to the use of an Avery product. It is a transparent plastic with an adhesive backing and you can print using either an inkjet or a laser printer. You then just cut the strips where you designed the label, peel the backing, and place on the panel. Really easy, and the results are pretty good. One sheet can produce a ton of labels, too. The product is Avery 4397.
John WA2FZW uses the same product, but makes one big decal for the entire panel. That way you don’t see the edges of the individual labels. There is a full description of the process used in the documentation for his Magnetic Loop antenna controller.
Dave G4UF has another method that he uses. You don’t have to be as careful with the LCD cutting 🙂
http://projectcasedesignandbuild.blogspot.co.uk/2017/07/printed-facia.html?m=1
And then Dan, W2DLC told us that he printed his out on with an inkjet printer on regular photo paper and then put some clear tape over it to preserve it with a pretty amazing result:
AA9GG adheres his printout to the case using a sheet of 3M adhesive. Basically, it’s a large sheet of double sided tape.
Daniel W2DLC uses “Loktite” spray adhesive.
Mike ZL1AXG (editor of ubitx.net) has taken a different approach to mounting a BCI filter. The high pass filter design and mounting point are the same as that documented here. However, the mounting system has been modified to make the filter easily removable.
Mike has other filters that plug into the QRP-Labs LPF filter board so his filter takes the same dimensions (1.5 x 0.5 inches or 38.1 x 12.7mm) and uses the same mounting system (two four pin male dupont header connectors.) The protruding centre pins of the DuPont connector were cut off, and the outside pins bent over (in opposite directions) to improve stability of the mount. The pins were soldered to the empty pads to ground on C216 and C210 on one end (RHS in the photo below) and to the RX signal rail on the other end (LHS below). A cut was made to the track mid-way between the dupont connectors (not shown here).
The BCI filter as mounted can be seen below. It makes a tidy looking unit that can be substituted or bypassed later.
Don ND6T has recently installed a 20 dB RF AGC modification in the BITX40.
He has not installed it in the uBITX yet but intends to do so soon. It’s a simple circuit and replaces the S meter circuitry, too.
Most BITX automatic gain control schemes use the audio output to apply control of the input of the audio power amplifier. This depends upon the volume control setting and introduces considerable distortion on high level signals. By using a signal source before the control then we can use the constant fixed gain of the receiver as a good indicator of signal strength and still adjust the speaker or headphone levels for the best comfort.
This simple project uses a single stage amplifier to tap into the audio at the input of the volume control, rectify it to a DC level, filter it, and use it to control a MOSFET as a shunt across the receive RF path. This project assumes that you have already installed the RF gain control described here (for the BITX40 or here (for the uBITX) and bridges across it at the control potentiometer.
R3 and C3 are used to not only filter out the audio component, but to form a “fast attack, slow release” control signal. That means that, when a strong signal appears, RF gain will be quickly reduced but will take a second or so to restore to full gain after the signal stops. This avoids “pumping” during a single sideband transmission but is fast to react to very loud signals.
Nearly any general purpose NPN bipolar junction transistor will work as Q1 as long as it has a beta of more than 100. 2N2222, 2N3904, etc. will work quite well. Q2 can be a 2N7000 or a BS170. None of the component values are critical. The 5 volt supply makes it easy to use any part with more than a working limit of just 6 volts and the current drain is low enough to be negligible.
I have found that most 2N7002 transistors will yield at least 20 dB of RF attenuation across the HF spectrum at 50 ohm impedance. Attenuation begins around 1.4 volt bias on the gate referenced to the source and provides maximum action at around the 3.7 volt level. Very effective for a single, simple, and inexpensive device. A great first step.
A more fulsome article with construction details (using surface mount components) is posted on nd6t.com.
This simple circuit led to a discussion on the BITX20 IO Group list, started by Jerry KE7ER, about the BAP64Q pin diode attenuator. This gives 60dB of dynamic range: https://groups.io/g/BITX20/message/32066
Attenuating back in RF gets around the limited dynamic range that Henning points out in the first post of that thread. Note that the control voltage is inverted with respect to the 2n7002 FET, higher voltages give less attenuation. You could get a slightly lower noise figure for the receiver if the attenuator was inserted at a later stage of the RF chain.
Jerry observes, “The BAP64Q is relatively expensive at $0.50 single piece,
the frugal among us will note it’s down at $0.20 if you buy a few thousand.
Mouser and Digikey both stock it, Mouser points you to the wrong BAP64* datasheet. There are other similar small signal pin diode attenuators out there from other manufacturers.”
Mike WB8VGE claims, “mounting any LCD on a front panel is a pain”. Probably most constructors would agree. Here’s how Mike does it without drilling holes in the corners to hold the display.
Tom AB7WT has also tried this out. He used shorter standoffs and put the JB weld on screws instead of longer standoffs. This way he could still unscrew the standoffs. It worked well and the screws were solid. The display and bezel look nice.
