Recently I knew ATS-25+ AIR at YOUTUBE. There is the HIZ-AIR unit of the option for the current ATS-25. Also ATS-25+ AIR may be combined the HIT-AIR with ATS-25. I'm muh interedted in HIZ-AIR inside.
You shall wind the front end filter coils for R909-DSP1. There are two examples, as the one is the stagger type and the other is the 3 stages Chebyshev style. You shall wind two coils of one kind for the stagger type and three coils of two kinds for Chebyshev style. Please refer the list for those.
I will introduce how to combine the degital VFO with the Chinese airband receiver kit. The tiny R909-VFO is suitable for remodeling the kit to incorporate the digital LO. If you would like to know more information in English, please visit below GITHUB or Hackster.
The sensitivity specificattion for VHF AM radios is measured by 10dBSN method. I tried to get the value by using tiny SA ultra, Adruino oscilloscope, and connecting circuit. I described the note how to check the value.
10dBSN法による感度測定をまとめようとしたきっかけはtiny SA ultraにSG機能が付いていたことでしょうか。nanoVNAはゼロスパンにして周波数を自由に指定できる発振器として使えました。tiny SA ultraでは1dB単位の出力設定ができ、変調のON/OFFまで付いています。(ちょいバグがあり-60、-100dB近辺でレベル増減がおかしくなったり、110dBm以下では画面設定できるが、出力信号レベルは変わらない、AM変調度は80%固定など注意事項はあります。)
I could not find the cause of backgound noise from TA2003 or the former section. I shall compare the measuring value with the TA2003 data sheet listed. I measured all nodes of R909-DSP1 and R909-DSP2. However I could not claer this isuue.
After then I finally noticed that the trace of i2c-SDA was neibouring BGA2851. I cut it, dropped it on ground, and changed i2c-SDA trace into jumper line. I could decrease the backgound noise from the RF section.
The R909-DSP1 sketch is programmed into the ATmega328P using the Arduino UNO loader. There is a 6-pin header for a USB Serial module that connects to the ArduinoIDE, allowing you to drop programs into the ATmega via USB Serial. In this article I will explain the operation reffering the display.
Currently R909-DSP1 is a best my DIY airband receiver. R909-DSP1 is made of TA2003+Si5351a+Si4732+LM386. I would like to introduce it in details. I uploaded the nessesary data on GITHUB.