RDA1846

SP5WWP · Oct 28, 2018

Hi there!
I'm looking for RDA1846 replacement. I'm mostly interested in 430-470MHz band.
I've found an interesting IC - SA58646 - but I'm unsure if it works on mentioned band.
The requirement i have is that it should provide analogue FM demod input and output.

I've spent all day trying to initialize RDA1846 with different sets of data. I've used Saleae clone to sniff I2C on GD-77 and SA818-U. I also tried with a sequence found on github (phishman/RDA1846). No success.
The most interesting part is that I had disassembled the (working) SA818 module, removed the Renesas microcontroller and performed the same init as the uC does... Also with no success. I have checked the connections, they look correct. Also the RDA acknowledges all the data. One thing I have also found interesting is that I can't write to register 0x2C.

freddaniel · Oct 30, 2018

Why work with the RDA1846 IC directly? There are tons of RDA1846 modules available with eeprom built-in to retain the frequency and other settings, with a TCXO. I put together a summary of what I located several months ago at: OpenLMR is the place for all things in the Land Mobile Radio system world under Tiny Transcievers. The best modules are from Professional RF module & Solution Designer and Manufacturer-NiceRF Wireless as Walke-Talkie Modules and are sold at places like Buy and Sell Maker-Made Hardware Products - Tindie or eBay.

These are OK for link radios or satellite receivers. The analog modules will not pass low-frequency modulation on the analog input or from the audio out. They have high-pass audio filters to eliminate CTCSS tones, so they are not good for connecting to a data modem. However, the DIGITAL module looks very interesting.

SP5WWP · Oct 31, 2018

freddaniel said:
The analog modules will not pass low-frequency modulation on the analog input or from the audio out. They have high-pass audio filters to eliminate CTCSS tones, so they are not good for connecting to a data modem. However, the DIGITAL module looks very interesting.

That's right. Analogue modules can, however, work in digital mode. All you have to do is to modify specific register values and remove DC blocking caps from modulator input and output. That's not trivial though, because there is no complete documentation regarding RDA's registers.

Too bad I can't initialize my RDA... Seems like the GPIOs are causing problems (in SA818-U module, version 1.4).

freddaniel · Oct 31, 2018

For hobby stuff, the RDA series of chips are OK. Even the digital/analog chips work well in the many Chinese handhelds on the market. There are reports the technical support for the RDA chips is lacking. Maybe you should try some western chips with USA support. Look at the TI CC1125 chip for a nice inexpensive digital transceiver. There is a market for inexpensive narrowband VHF or UHF OEM modules for data reporting. A single design could cover all bands. Things like fill-level reporting of vending machines, propane tanks, intrusion alarms, barge & trailer location reporting, and so much more.
The TI LMX2571 would make a good Exciter for digital or analog transmission. So many great chips and so little time.
There is also a market opening for low-speed narrowband data networks to challenge the cellular providers in the bottom of the market. Some of the new narrowband networks simply use OEM cellular modules coupled to their remote receivers to haul their data back to their switch. Cellular carriers like Verizon only charge $5 per SIM plus traffic, which is far better than buying a DSL circuit, and it can all run off a solar panel.

RDA1846

SP5WWP

M17 Project Founder & Lead

freddaniel

Member

SP5WWP

M17 Project Founder & Lead

freddaniel

Member

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