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Addressing issues with an SWR meter and the Nextion display

Joel KD6AGW has been working on his UBiTx V5 for a few months now and added the KD8CEC update with Nextion screen and the I2C update.  He had all the features working (CW decode etc) except the SWR meter.

Joel also built a Kits and Parts SWR bridge and hooked it up to the second Arduino.  However, the meter never operated correctly.  The home brew Stockton bridge that Ian (CEC) used apparently did not have this problem.

After hooking up an oscilloscope to the forward and reverse outputs, Joel noticed that the reverse voltage would bounce up to 4 volts or so before settling down after a few seconds.  This was while the uBITx RX input was hooked to a 50 ohm dummy load.  When the probe was hooked up, the meter on the Nextion display would go high, and then settle down to a good swr reading.   However, as soon as he removed the probe to the oscilloscope, the meter would just stay pegged at very high SWR.

He ran across a blog item here (http://www.kk5jy.net/swr-meter-v1/)  about building a digital SWR meter and noted that:

“In order to prevent stray RF from getting into the A/D circuits,  a 0.05uF ceramic disc capacitor was placed between each line and the GND pin.  Since the A/D inputs are very high-impedance, and the SWR sensor outputs were meant to drive current devices (e.g., analog meters), a 75k resistor was placed across each of the 0.05uF caps, to drain the accumulated charge when no RF was applied”.

After doing these modifications, Joel has found the SWR meter to work great.

For information, here is a sketch of the circuit modification:

Following a question about power wastage in the Stockton Bridge SWR circuit Joel checked the output with the bridge in and out.   There was no perceptible difference in power out on the oscilloscope.

Reference
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A couple of uBITx

Each year the Dutch radio society VERON organises a ham fair known as the “Day of the Amateur”.  The Netherlands is only a small country so it’s an easy journey for most hams in the Netherlands to get to the fair.

Cor PA4Q posted a couple of pictures of µBITx rigs on display at the fair.

The first is from PA0MBE:

And the second is from PH2LB:

These interesting examples may prompt others to add features to their µBITx.

Reference

 

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New version of Allard’s firmware for BITx40

Just as the BITx40 goes out of production, Allard PE1NW has released a new version of his acclaimed firmware for the BITx40.

This is known as the Raduino v1.29 version, and can be downloaded from here: https://github.com/amunters/bitx40

New in this release:

  • Added Roger Beep (NASA style “Quindar Tone” as used in Apollo missions).
Note that the PTT sense, RX/TX and CW Carrier mods must be installed for this feature to work.
Press Function Button 7 times to toggle this function on/off.  It’s OFF by default as some find it annoying. Others find it helpful in pile-up situations though.
Allard says “Use responsibly!”

Allison KB1GMX commented that the “Roger Beep” was not a common thing until the CB mess broke down in the early 80s and it was often accompanied with other electronic noise makers and profanity. Then that mess started moved into the lower (CW) sections of the 10M band and they got tired of freebanding.

Most of us back when that used CB found it annoying and unneeded especially for SSB. The general feeling is it was those that were disruptive or trying to feel like they were running something important doing it initially. It was especially noxious when it appeared in the 80s. Then it became a feature on CB radios (a signal that those that were modified for non CB allocated frequencies) and later Chinese made HTs.

For the Space activities (Mercury and later) it was needed as the communications were actually full duplex on the data links and you had to have some way of knowing when the other guy was done as in really did release the button and it was also to confirm the button didn’t stick as in heard in the astronauts headphone when he released  the button (or VOX). Until CB adopted it if you heard a over beep is was likely a repeater (usually ham) or space based radio (space program).

To date I know of the use of “over beep” appearing is standard communications systems, those being Space program, Repeaters, military systems that use satellite links, and CB.

It does however represent what one can do with a MPU of reasonable power and some programming skills!

Reference
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End of road for the BITX40

Ashhar Farhan VU2ESE has just announced that HF Signals has had to pull the plug on the bitx40 run.  Ashhar said, “The sales were sparse and frankly it had become a bit of a frankenstein.”

“There were too many connectors that one could plug in the wrong place.  We moved from analog VFO (that drifted due to heating of the pre-driver stage) to a raduino which wasn’t well integrated into the motherboard.”

“However, it was a big deal for us all.”

HF Signals was able to ship a full SSB transceiver for just US$50 dollars. This went over and above the ARRL challenge for a kit of parts for US$50.

It has served many well. Once you had it going, it performed pretty well.  With a triple tuned front-end and the favourite ‘down conversion’ to 12 MHz IF.

Many will miss this kit.   However, Sunil (at www.amateurradiokits.in) continues to ship the Bitx20 v3  kits, that can be modded to 40 meters.

Ashhar has indicated that if time permits and some in the group volunteer, we could update the original BITx with a more contemporary design while preserving the original’s bidirectional, single conversion scheme.

Ashhar suggests that “Until then, we will continue to see more scratch built bitxs, a kind of return to the roots.”

Reference
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Variable bandwidth crystal filter

Some time ago we featured a design from Michael N2ZDB that used a Jones filter design from TenTec to produce a variable filter passband for his BITX40.

There has been more recent interest on the IOGroups BITX20 list in variable bandwidth filters in the µBITx.

Karl-Heinz DF9RU completed a build of a µBitx transceiver and found it to be an excellent learning platform. He has been toying with a variable CW filter.

Up until now audio filters have largely been adopted by members:  either active filters with operational amplifiers or DSP filters with microcontrollers.  Karl-Heinz acknowledges that these options represent easy solutions for integration into the µBITx.

Karl-Heinz has a CW transceiver HB-1B from Youkit. This transceiver has a quartz filter of variable bandwidth.  The bandwidth can be continuously changed using varicap diodes.  The circuit diagram of the HB-1B can be found here.

Karl-Heinz was impressed by the acoustic result of the simple circuitry of his HB-1B and wondered why this alternative had not previously been used?

TenTec has patented a filter design which describes the passband curves of this filter.  A German website  also documents results on the bandwidth of these filters, which match with data from the TenTec patent.

Thierry F1HSU suggests taking a look at Tasa’s site for a tunable quartz filter  : http://yu1lm.qrpradio.com/bp%20yu1lm.htm

Ashhar Farhan VU2ESE suggests that these filter designs are merely a variation of the min -loss cohn filters. As only the coupling capacitance is varied without varying the terminating impedance, we must expect high ripple at all settings except one. What does this mean? It means that the filter will exhibit ringing and phase delays.

A better option would be a smooth Butterworth response with minimum ringing at a fixed frequency.  You can vary the BFO for shifting the audio tone. A 400 hz bandwidth will be narrow enough and yet offer a brightness that we miss in more aggressive designs.

Wes wrote a paper on this on his website www.w7zoi.net.
Ted, KX4OM reminded us of the SSB6.1 transceiver, which employs a tuneable SSB filter with tuning diodes in place of the capacitors in a min-loss configuration. The rig is a basic SA612-based design which can be found here:

Allison KB1GMX suggests looking at this design as well.  It is not new and a bit tricky but works best with lower frequency crystals.

Reference

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Monitoring your microphone level

Didier F5NPV notes that many options are possible to tune your AF level. Measurement tools like an ocsilloscope can tap directly at the output of the AF Amplifier.  Alternatively a spectrum analyzer can be very useful in monitoring spectrum quality.

It is also possible to use another RX, a SDR receiver or even WebSDR online to monitor your transmission in quite an accurate manner. When you establish the correct level  of gain required to generate a signal without distortion spikes you just need to calibrate a meter with the appropriate threshold value.

The µBITx does not have an AF level input monitoring system. It is simply impossible to know if the level applied from the microphone preamp is too high or too low.

in the picture above you will notice a little switch just below the vu-meter thatI use to monitor the AGC and AF input level.

Reference
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Large screens, digital modes, and beefy processors

A couple of constructors have been busy pushing the limits …

Digital modes µBITx in a box

Felice IK1ZVJ  project stems from his passion for digital modes. He says “The union between µbitx and raspberry works well”.   Felice combines a µBITx with  a raspberry pi and a large pop-out screen in a single portable package for use with digital modes such as FT8.

The LCD screen is mounted on an old CD mechanism to provide automatic ejection from the enclosure.

The project includes a dual power supply with a built-in power supply and battery power for portable use.  He foresees his pr  ubitx, only being used with the raspberry pi on digital modes. The raspberry pi is loaded with WSTJ-x for use on the FT8 and FT4 modes, and for FL-DIGI for PSK and RTTY.  His enclosure uses a 3U rack  (9 cmx40cmx43cm).

You can see more on his video:  https://youtu.be/TlndGOyNtVc  or you can contact Felice via email.

Ashhar Farhan is pushing the boundaries

Ashhar Farhan VU2ESE, designer of the µBITx previewed a Raspberry Pi board for HF radios with a high end codec at the FDIM (prior to Dayton Hamfest 2019).

This is for a new radio that he is building to push the limits of what his homelab capability can produce.

The story so far is that there is a very low noise 24 bit codec on a custom board that plugs into the raspberry pi. The display is a 7 inch capacitive touch screen device.

The radio is a single conversion, very low distortion superhet without any amplification before the crystal filter and triple tuned filters for each band.

Ashhar says “Nothing is casual about this radio. Even the power supply had to be included to have low noise rating.”

Reference

 

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Teensy 4.0 adapter board

Jim Sheldon, W0EB, Project Coordinator for the TSW (Triumvirate Skonk Worx) has announced that the team have successfully created an adapter that will allow the new PJRC Teensy 4.0 to directly replace the NANO MPU on their TSW Raduino Clone and on late model HF Signals Raduino boards where the NANO is mounted on the rear of the card.

The Teensy 4.0 is a much faster processor, providing experimenters with plenty of opportunities to add in features to their µBITx, including digital signal processing.   Comments suggest that the Teensy 4.0 is much faster, generates less digital noise and has WAY more programming memory.

The TSW programmer has successfully ported (with only minor modifications) the factory’s V4.3 and V5.1 software to the Teensy 4.0.  You still need to be familiar with HF Signal’s documentation for V4.3 and V5.1  as they have only documented changes in the accompanying manuals for the software.

A bare board and also a complete kit of parts for the plug in adapter is being offered for sale  and kits are also now available.

At present, kits are only being offered to US customers as the pricing includes shipping.    See the TSW website for more information.

Reference
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uBITx HD raduino bracket

Dave K0MBT has beefed up his design of the uBITx HD raduino bracket and added a two line display bracket.   He has also added an audio cable hold down. There is also a small dimensional change.

It is now a 3 part unit that can be used with or without the stock display.

Dave is offering these from his shack to yours for $15 including hardware and shipping.

Order from Ham_Made_Keys

Reference
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Using two nanos to switch firmware

Martin, AJ6CL assembled his uBITx v5 and it seems to work OK.  It is completely stock, with the stock screen and the stock firmware.

He asked two questions:

Exactly what changes in the CEC Firmware v. 1.2 are required before uploading it in order for it to run properly on a stock Ver.5 uBITX?

Evan AC9TU replies, saying it depends on what you want for a display…  “I have the 3.2″ that Dr Lee had already created a full screen TFT file with the link from the web page.  That is what I would use.  This is a personal choice.  If you want bigger, then you will need to find the correct TFT file to match your display.  2.4 and 3.2 I believe are the two that Dr. Lee has programmed.”

“You do not need to compile the code if you use the correct hex file.  Use the uBITXV5 directory and read the FileNameInfo.txt file to help select the correct hex file to load into the Nano.  You will need the Hexloader program to go that route.  I believe that this is where I got the version that worked for me:
https://sourceforge.net/projects/hex-file-loader/

“In case you did not get it, here is the link to the Git Hub repository zip file:

https://github.com/phdlee/ubitx/releases/download/v1.20/uBITX_CEC_V1.200.zip

“For the calibration process, I would do a search on this site to learn the how to do it.  NOTE that the CEC software does not use the same method as the stock (it does not turn on the transmitter to zerobeat wit another receiver.  For the CEC firmware I would download the Memory Manager that Dr. Lee has created to make the adjustments and save the values after a change to be able to backtrack if something goes wrong.”

For the BFO calibration I prefer to use a PC based free audio spectrum analyzer that can be downloaded from here:
http://www.techmind.org/audio/specanaly.html

I connected a mic to the input of my PC, tuned the uBITX to an open frequency with just static, and adjusted the BFO to center the noise spectra between 500 and 2500 Hz.  I then went back and re-calibrated the maser clock, then back to the BFO for a final time.

Can you upload the CEC v. 1.2  firmware to a spare arduino nano processor and  swap out the arduinos with different firmware and still expect the radio to perform normally?

Evan says “Yes, you can use a second Nano to program and keep the first as originally received. There are issues that need to be taken into consideration.

1 – The calibration data is stored on the EEPROM of the Nano, which is not saved in the CEC software. You will need to calibrate before it will work correctly, especially the BFO setting.

2 – The CEC software is different for each display, and the original software only works with the original display. That would mean that you need to change the Nano AND the display if you do not use the original display version of the CEC software.

Reference