Next up is the R909 kit. This kit was developed by JasonKits. JasonKits is running as an e-commerce site by Ham on the island of Malta, which sells a variety of electronic circuit boards and kits. In the area of hams, he is distributing open source boards.
R909 is similar as the RF circuit of R80 V7, and the VFO control part was independently developed using Arduino. The sketch adopts function selection control using a rotary encoder and switch, and incorporates my No. 2 machine sketch. Because of that connection, I cooperated with debugging.
The TA2003 used is a chip that was used in 100 yen shop radios a while ago, and was a favorite among Japanese radio hobbyists. Toragi has published a book about designing radios using TA2003. Written by JA9TTT. AM/FM radio & transmitter production collection (CQ Bunko).
What makes the R909 unique is that it uses a TA2003 instead of a mixer such as the NE602 in the double super first mixer section, and the other TA2003 is configured as an AM/FM radio after the first IF.
There are some problems that have been dragging on since the R80 V7. Two relays are used to switch the AB and FM front end filter sections and to switch the parent radio's AM/FM. However, since the TA2003 switches the AM/FM input using an internal circuit, there is no need to externally switch the TA2003 input signal. Rather than that, the problem is that the external switch is left open when not in use. Especially in the AM position, the high gain FM side circuit input is open, causing oscillation. I found this out when MR.RADIO KITS IN JA pointed out this. Thank you for letting me know.
R909 has a double super radio with 1st IF: 10.7MHz-2nd IF: 455kHz, and a single super with IF: 10.7MHz for FM broadcasting receiver. The first IF is 10.7MHz, which is the case with all Chinese airband receiver kits, R80 and R909. This is caused by the availability of ceramic filters and discriminators for FM broadcasting, but images cannot be removed. In airband reception, if you set the upper heterodyne at 10.7Mhz-IF in the 118-136MHz band, the image will be at 118 + 10.7 * 2 = 139.4Mhz, which cannot be removed by the front-end filter. Therefore, I think it would be better to use an IF such as 21.4MHz for airband receivers.
The R909's display is a 2-line LCD with 16 characters, but I also tried making a modified prototype that switched to OLED 128x256.
