Month: March 2019

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uBITx v5 Board compatibility with JackAl

 

Jack, W8TEE and Al AC8GY have spent considerable time testing a couple of V5 µBITX boards for use with their JackAl board.  No hardware modifications are required when using their board with the v5 µBITx.

However, Jack is making some minor changes in the software because of the new IF frequency.  They expect to release a new software release for the V5 board in a few days.  They are also expanding the assembly manual with additional photos and narrative.

The JackAl boards are being sold by QRPGuys.com.

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Alison’s audio pop mod prettied up


Mark N7EKU has posted a nice clean schematic and a picture for the audio pop fix he has just completed on his uBITX V3. It works great and saves the ears a lot.

If you check the top part of the photo, you can see that I have done Allison’s fix for harmonics by re-arranging the filters a bit and moving the original relays to the bottom of the board. This worked great too and cleaned up harmonics a lot.

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TSW introduces adapter to protect DC input

Jim W0EB, TSW Project Coordinator,  has announced he has just got the boards and all the kit parts for this little adapter that allows the DC input for your µBITx (or any other kit or homebrew rig) to be protected.

The board allows connections for optional Reverse Polarity (series Schottky diode), a switch on the volume control (or separate power switch) and the switched DC output to whatever item is being powered.  This is achieved t through a small PC board using MOLEX or MOLEX Style male/female connectors. Everything can be plugged in and unplugged for ease of troubleshooting without having to solder or unsolder wires from the rig’s terminals.

TSW is making either the bare board or a full kit of parts available.  The picture shows everything that’s included in the kit.

Full details are on the TSW website

The manual for the SwitchedPowerAdapter is available in PDF form so you can see what it’s all about.

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Q90 blown by strong RF input on antenna line

Further to an earlier post about the vulnerability of Q90 in the µBITx, Gary
W6RAG wrote to uBITx.net today noting that the potential danger to Q90 from nearby strong RF signals is well founded.

Recently Gary was attempting an FT8 contact on 80 meters with his son about 400 miles distant.  Being unsuccessful with the µBITx, he turned off the rig and turned on his TS430 and made contact at about 60 watts output power. The ubitx remained connected to an end fed wire about 10 ft from his dipole that was in use with the TS430.

A few minutes later he tried the ubitx again and it had no output. He traced the failure to Q90. The emitter was shorted to the base just as reported by others.
The diodes in the balanced mixer will not save Q90.

Gary recommends that µBITx users disconnect the antenna if they are going to operate other transmitters with nearby antennas.

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A serial connection from your uBITx

Sascha DL5SMB has soldered some wires to D0 and D1 (RX + TX) and ground on the Raduino nano and then installed a MINI-DIN 8 socket to the uBITX like in an FT817.

“Why?” you may ask!   He is  building a  TF3LJs Magnetic Loop Controller at the moment, which communicates with the transceiver via CAT for tuning the antenna. This interface uses just these three lines. So he needed to make them talk 🙂

After a few hiccups, and a helpful suggestion from John VK2ETA, this solution has now been made to work.   The idea of using D0 and D1 connections on the Nano is to provide a separate serial feed to the Magnetic Loop Controller that is independent of the CAT signals coming out of the USB socket.   This may be a good solution for other potential use cases as well (e.g. driving automatic tuners).

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Warming effect of driver and pre-driver affects spurs

Lawrence Oberman mentioned an issue he has on a v4 board that looks like RF coupling or leakage when testing CW on 20m for FCC compliance.

He doesn’t see it with SSB but if the rig is placed on transmit for long enough spurs will start to show up .  He has only just got Axicom relays to replace the stock relays. Strangely enough he has not seen this behaviour on 15m, 17m or the higher frequency bands, or on the bands below  14MHz.

Others have seen similar phenomena on different bands, some with the spurs appearing on starting TX and then disappearing.

Allison KB1GMX says “Both cases come from the same source, heating in the amplifier usually the pre-driver and driver stages but it can include the finals. These stages are not thermally stable and parts heat up and their bias shifts.”

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v5 board more sensitive

Ashhar Farhan VU2ESE tells us that the µBITx v5 board has more gain on transmit, as well as on receive, than the previous boards.  This is due to the BFR93w transistors in the 45 MHZ IF in place of the 2N3904s.

The carrier and spurs will be appear to be higher if the TX gain (controlled by RV1) is running flat out. it is best to reduce this to about 60% of the full gain. One way of achieving this is to connect a 50 mv audio signal to the mic, and transmit SSB on 7 MHz while reducing the power out until it is around 7 watts.

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Using a 100 PPR encoder with the uBITx

Allison KB1GMX gives details on how to wire up the commonly available 100prr-6 encoder.  These have a nice vernier style dial and cover 100 pulses per 360 degree rotation.  The calibration points line up with these pulses.  They come with either 4 or 6 wire terminals on the back.

The A and B terminals have transistor outputs to ground and are used in connecting to the raduino:

  • Ground is ground (0V) terminal
  • Black and brown to the A and B terminals (reverse if the rotation direction is backward)
  • 5V from raduino 5V reg to the internal LEDs used in the optical encoder  (Vcc terminal)

Allison uses the V4.3 code in her µBITx with here own mods and this encoder worked well. Some firmware for the Raduino will not be sufficiently fast to keep up with the signals being sent from the encoder if you rotate the encoder quickly.

The uBITx.net editor likes the black version better.  These are a classy unit.

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