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DART-70
=======
In 2023, the 70MHz band became accessible to amateurs in Switzerland. This offers an excuse to build a transciever.
* Separate things a bit more than on Picardy 2020
* One HF SSB/CW exciter PCB with:
* Voltage regulators
* Mic input from Picardy 2020
* AGC measurement like Picardy 2020
* AGC IF amp better than Picardy 2020
* VEXIBITX applies AGC at HF input instead, and uses uBitx amplifiers for IF
* uBitx has no AGC
* Hybrid Cascode? (Implies IF between 8 and 12 MHz)
* Frequency plan:
* What HF intermediate frequency?
* High-side mixing? need low-pass to reject image, also rejects FMBC
* 96MHz oscillator: 26MHz IF
* Low-side mixing (kuhne and anglian do that)
* 42MHz oscillator: 28MHz IF
* Prefer, can't be wrong if others do that
* Reuse Anglian 3L oscillator from lo_board/lo_board.pro
* VFOs Si5351A-B-GT for first two mixers
* Mixers (3 needed: VHF, HF, AF)
* AF: like VEXIBITX
* HF: like uBitx (BAT68-04W ring mixer, see doc/ubitxv6.{txt,pdf})
* VHF: MCL RMS-11X (+7dBm LO) or the macom one? (missing from inventory)
* XTAL filter QER like uBITX at 11.0592 MHz
* One PCB with HF-4m transverter, inspired by Anglian
* One PCB with 4m driver, PA and antenna switching
* We are allowed 25W ERP, aim for 10W PEP
* BCW71 driver, 2SCR573D3 push-pull amp?
* How about STN4NF20L?
* LNA: SPF5189Z
* One PCB for frontend
* Connected by cable to the main board
* Microcontroller, Display, Encoder
* Enclosure: Hammond 1411R or 513-0900?
## To order
* Adafruit 292 and an i2c display
* Enclosure
* Microphone MH34-B4B
## TODO
* Mixer termination
* https://www.qsl.net/g3oou/mixerterminations.html
* https://www.changpuak.ch/electronics/calc_16a.php
* http://land-boards.com/blwiki/index.php?title=Kits_and_Parts_Mixers
* Check LO level for diode mixers
## Notes
SPK click:
LM386 was wired as 46dB gain on Picardy 2020
LM4865 (20dB gain) + gain stage
and volume control like
https://www.mikrocontroller.net/attachment/315502/Zwischenablage01.png
https://mbonnin.net/posts/2011-01-05_bwaaaaaaaaaaaaaaalarm-clock/lm386.png
https://groups.io/g/BITX20/topic/4995877
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