ARROW uBITX Group Purchase
Jump to navigation
Jump to search
Things related to the uBITX radio group purchase made by a number of ARROW members.
Mailing list for all BITx radios
Problems, Issues and Glitches - significant issues reported by builders
- TDA2822 stereo amplifier high failure rate
- Reported on the mailing list, Some ideas discussed there:
- Replace with 8-pin socket and NJM2073D
- LM386 + adaptor
- Voltage regulator + capacitor (Ron's solution ... see mailing list archives)
- <link(s) to best discussion(s), fix(es), etc(es)>
- Reported on the mailing list, Some ideas discussed there:
- Power output differences across bands
- http://ubitx.net/fix-fix-uneven-tx-output-across-bands/
- The PA is reported to be quite sensitive to SWR / reflected power. Make sure to use a good dummy load for power measurement.
- It has been reported that the schematic has an error: <one of the diodes> is shown backwards.
- Audio "pops"
Building Hints and Tips
Operating Hints, Tips and Warnings
- DO NOT insert a mono plug into the stereo audio jack -- this shorts the output of the audio amp and will likely blow it up
Recommended Mods
Advanced Mods
- AGC circuit
- VK2ETA simple software AGC mod (see mailing list)
- AGC circuit built into Omega transceiver
- G7JUR used an audio AGC board by Walford Electronics (G3PCJ).
- Disconnected the yellow wire from the top of the Volume pot. Yellow wire to the input of the AGC board via a 10 K resistor.
- Output to the top of the Volume pot. Removed R235 and connected top of C252, to top of the Volume pot via 1 K resistor and 0.1 microfarad in series (Cap stops DC on the input of the audio amp ) This now puts the CW side tone in after the AGC board.
- also replaced the TDA2822M with a LM380-8 will need a bit of jiggling with the pin connections. hint turn it upside down. The LM380-8 will work from 10 to 18 volts, and has built in thermal protection.
- K9HZ summary of options
- ... audio range passband...Benefit: saves your ears, $0.02 diode, trivially easy to implement.Bad: only protects your ears... not RF sections from excessive signal and overload. Not a true AGC signal for "s" meter, only an audio strength.Comment: Save the $0.02 diode, turn the damn volume down and live with the IF overload.
- ... IF range passband...Benefit: Saves ears, prevents IF overload, AGC signal for "s" meter (can be calibrated to real signal strength by reference).Bad: More complicated/ more parts, RF level attenuator and AGC response, more expensive than the $0.02 diode,Comment: can be triggered by anything in the passband and that can be good and bad.
- ... Full range integrated Passband (front end through audio section)...Benefit: True AGC on all levels, no overload or distortion of any stage. AGC signal for "s" meter (can be calibrated to real signal strength by reference).Bad: Very complicated, impacts every RF/IF/Audio stage. Lots of mods and parts.Comment: A CW ops dream.
- KD2NDR port to Teensy
- VK4PLN AM broadcast filter (3.5 MHz high-pass filter)
- VK4PLN Raduino board replacement {fixes and I2C)
Enclosure Ideas
ARROW Rig Showcase