Superheterodyne ASK (Digital AM) Receiver With Design Issues But Good Reception

The RXB8 breakout board is based on the SYN4126/HB4126 single-chip solution.

Design Weaknesses

SYN4126 seems to be out of production for a long time (or might have originally been a non-public custom-made batch for a specific product): no data sheets or other information about seem to exist. What seems evident though is that this chip was originally designed to receive FM modulation.

In this board, the RSSI output is used instead to decode ASK (AM) signals. One could speculate that the vendor got its hands on a large batch of surplus FM receiver chips and came up with a creative solution to use them in AM ASK receivers. The chosen implementation has one important backdraw, though: it limits the minimum detectable impulse widths (and thus the data rate that can be received): impulses of 350us duration and less become accidentally widened by the way how RSSI signals are processed, and communication fails at these speeds.

For simple remote control scenarios where only small amounts of data need to be transmitted at low speed, this receiver is excellent: its very good sensitivity can pick up a signal even through walls or at greater distances where other and more simplistic receivers would not be able to.

In use cases where large amounts of data need to be received quickly, this receiver chip fails though, and you better switch to a receiver using a dedicated ASK receiver chip.


The board exposes five pins, two on the left side and three on the right side. Pins are labeled on the front side of the board:

Pin Label Description
1 ANT Antenna
2 GND Ground
3 GND Ground
4 DATA Data Out
5 +5V 4.5-5.5V

Make sure the power supply is properly filtered and carries no exceptional noise which could interfere and distort reception.

The pins on this module do not fit the common 2.54mm pin grid. This makes it difficult to plug the board into bread boards for testing.


There is no antenna mounted. Make sure to add an antenna or else the board will have poor reception.

For example, solder a wire to the ANT pin (17cm for 433MHz).

Technical Data

Item Description
Voltage 4.5V-5.5V
Current fully operational 12mA
Frequency 300-440MHz, breakout boards are set to one specific frequency via a crystal
RX Sensitivity -111dBm
Modulation ASK (AM)
Chip SYN4126
Data rate 10kbps
Size 31.5x14x7mm


Please do leave comments below. I am using utteran.ce, an open-source and ad-free light-weight commenting system.

Here is how your comments are stored

Whenever you leave a comment, a new github issue is created on your behalf.

  • All comments become trackable issues in the Github Issues section, and I (and you) can follow up on them.

  • There is no third-party provider, no disrupting ads, and everything remains transparent inside github.

Github Users Yes, Spammers No

To keep spammers out and comments attributable, all you do is log in using your (free) github account and grant utteranc.es the permission to submit issues on your behalf.

If you don’t have a github account yet, go get yourself one - it’s free and simple.

If for any reason you do not feel comfortable with letting the commenting system submit issues for you, then visit Github Issues directly, i.e. by clicking the red button Submit Issue at the bottom of each page, and submit your issue manually. You control everything.


For chit-chat and quick questions, feel free to visit and participate in Discussions. They work much like classic forums or bulletin boards. Just keep in mind: your valued input isn’t equally well trackable there.

  Show on Github    Submit Issue

(content created Apr 19, 2024)