Editing ARROW uBITX Group Purchase

Things related to the uBITX radio group purchase made by a number of ARROW members.

[https://groups.io/g/BITX20 Mailing list for all BITx radios]

[http://ubitx.net/ Huge resource page by ZL1AXG] 

[http://bitxmap.com Map of BITx users]
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'''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)>
* 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"
** http://ubitx.net/2018/03/05/updated-circuit-from-va7at-for-removing-audio-pops/
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'''Building Hints and Tips'''
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'''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
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'''Recommended Mods'''
* [http://www.hamskey.com/ KD8CEC software]
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'''Advanced Mods'''
* AGC circuit
** VK2ETA simple software AGC mod (see mailing list)
** [http://www.lukaszruta.pl/omega_dok/v2/omega2_sch.pdf 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 
* [https://vk4pln.blogspot.com.au/2018/03/ubitx-am-bci-filter-35mhz-high-pass_31.html VK4PLN AM broadcast filter (3.5 MHz high-pass filter)]
* [https://vk4pln.blogspot.com.au/2018/03/raduinoi2c-board.html VK4PLN Raduino board replacement {fixes and I2C)]
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'''Enclosure Ideas'''
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'''ARROW Rig Showcase'''