Note that at the time of writing this article this information is captured incorrectly in the data sheets. The following minimum preambe length requiements are needed for packet loss free reception and no sensitivity loss compared to non antenna diversity applications (less the the insertion loss of the T/R switch and the longer traces obviously).
When AFC is not enabled antenna diversity requires 80 bits of preamble.
When AFC is enabled antenna diversity requires 88 bits of preamble.
Si446x revC2A and A2A devices support antenna diversity with DSA. This operation requitres 64 bits of preamble. Note however that co-channel rejection with DSA in antenna diversity mode is poor so this configuration is not recommended.
Leave all the antenna diversity parameter calculations to WDS. Make sure you transmit the minimum length of preamble and Rx will just work.
The auto frequency hopping feature on EZRadioPro (Si4x6x) devices is an Rx feature only where the receiver autonomously scans through a predefined channel table for the expected packet.
It is primarily meant for applications where the transmitter changes its frequency channel between packets but stays on the currently selected channel for the duration of the whole packet transmission. In auto frequency hopping mode the receiver has no prior knowledge where to expect the next packet so it duly keeps scanning all the possible channels until it finally “finds” the signal. This mode of frequency hopping operation may be referred to as asynchronous hopping as the Tx and Rx nodes have no knowledge which frequency channel the other is staying at at any given time.
Typically in such asynchronous hopping applications the Tx node has to transmit a relatively long preamble to allow the Rx node enough time to find the right frequency channel.
To sum it up what the auto frequency hopping feature supports is asynchronous hopping operation in the receive node.
Now, if the receiver knows at what frequency and at what point in time the Tx will transmit there is no need for it to scan a wide range of frequency channels. It “simply” has to be on the right channel at the right time to receive the packet. This mode of frequency hopping operation may be referred to as synchronous hopping as the Tx and Rx nodes are moving together both in frequency and time.
Now, the auto frequency hopping feature does not support synchronous frequency hopping in neither the Tx nor the Rx node.
This does not mean however, that synchronous hopping systems cannot be built with EZRadioPro devices. It is, however the task of the host MCU to direct the Tx and Rx nodes to the right frequency at the right time. It is important to note, however that the auto frequency hopping feature is of no help whatsoever in synchronous hopping applications.
This article is part of a series that discusses various aspects of auto frequency hopping. Find the links to the other articles below.