The All-band HF Amateur Radio Transceiver: Just waiting to be modified
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.
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.
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.
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).
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.
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:
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.
Ian KD8CEC has announced a beta version of his firmware (Version 1.12) for the uBITX V5 board. He has written an article about it here.
All existing firmware functions for V3 and V4 are available on the V5 beta.
The same version of uBITX Manager will work with the v5 Board.
Only the LPF control and the frequency control part are changed in the V5 code. Ian has released firmware V1.121 for V5.
Alison KB1GMX counts 5 different schematics for the µBITx, and that is not including the HF1 or minima (2014) designs that came before the µBITx. The design was evolutionary.
The first production boards were labelled “V3”. Two further iterations have been sold since, the “V4” and now “V5”.
V3 and V4 are probably technically not fully compliant with emissions regulations in most countries (at least in the developed world). However, the low power output of the µBITx probably means that emissions will have resulted in few issues with interference in practice.
The effectiveness of harmonics, IMD and spur modifications incorporated in the V5 board have yet to be established across a selection of production boards. There are no doubt improvements, but the degree to which the product could be considered to be 100% compliant on all bands and all modes has yet to be established.
[Edited by uBITx.net]
Jim Sheldon W0EB has done some initial testing of the new µBITx board on his brand new spectrum analyser. The results are CW only (so these results won’t show the impacts of any distortion in the mixers or IF bidi amplifiers that were observed with the v3 and v4 boards.
There are still some bands that would not meet most countries’ spectral purity requirements.
For a full set of graphs for each band click on the reference link below.
