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Updated Audio Receivers (markdown)

Brumi-2021 2024-03-10 11:11:02 +01:00
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Audio-Receivers.md

@ -55,6 +55,17 @@ The Key Items on the App that can be seen or selected with the cursor and change
The next item is the setting of the bin sizes used for the waterfall (0-63) with “0” being the minimum information being the fastest display and “63” the maximum information collected the slowest display. Adjust to give a balance of speed and information seen.
And next right to that field , you will see Rx_IQ_CAL field.It actually can improve (8 to 10 dB's from worse CAL point to the best one ) the receiver Image Reject Ratio only in the Receiver Applications that are using Zero IF-frequency tuning ,like this SPECTRUM mode.
This calibrated value it is stored in the SD card , /settings/rx_audio.ini .
To calibrate it , you will need to try to find some clean isolated continuous carrier , and try to tune it , (example , to the right of the positive frequencies ). Then you will need to start set up to 0 that CAL value (min), to make visible the bare Image mirror frequency in the other symetric left part screen. Then , you will need to adjust AMP , LNA and GAIN to receive strong enough signal to the right part (not so strong to not produce intermodulations , otherwise re-adjust again decreasing AMP, LNA, GAIN) , and not so weak , till just getting the carrier +freq. clean (desired carrier signal) , and its bare visible Image mirror Signal (in the other symetrical -xx mirror freq . (unwanted Image signal to be minimized) . Then, when you got similar situation as left below picture, you can start adjusting Rx IQ phase CAL till minimizing the received Image "mirror" signal (as in the middle below picture).
That below example is calibrating H2+ old r6 version (max2837) that has 31 steps ,(Note , using Hackrf r9 (max2839 ,we will have 64 steps)
![image](https://github.com/portapack-mayhem/mayhem-firmware/assets/86470699/84dc2b51-e265-40aa-a0b8-fb8d9270e6b3)
* **CTCSS:** This Continuous Tone Coded Squelch System is a display at the end of the secondary information line. It is used by many systems and standardised by EIA/TIA, with a description [here.](https://en.wikipedia.org/wiki/Continuous_Tone-Coded_Squelch_System ) In the NFM mode in Audio app, the tone field is increased from 11 to 14 characters.
Now , the CTCSS tone frequency and CTCSS code numbers are displayed at once (if a matching freq was found in the tone_key table). See the Annex to this document below. It should be noted that most of the time the display is jumping around and only clearly displays the received tone when there is a gap in the voice and the Signal is of good quality.