ESB with different frequency

RE: ESB with different frequency

niebert — Sat, 03 Aug 2019 08:11:19 GMT

I know this is a very old post, but I stumbled over the phenomenon (receiving at channel 0 packets from channel 80, so here is my interpretation:

The radio listens on a channel and tries to capture an address event. As long as it does not capture an address event from the wrong channel, a packet from the chosen channel will almost always be strong enough to dominate the crosstalk and will be received. But once an expected address is parsed from a crosstalk channel, the receiver clock is running and the radio will not be available for reception from the chosen channel.

As to the example, an RSSI of -23 in channel 2 and -22 in channel 3 suggests a crystal that may be a bit off, but in any case it means that you have a VERY short distance between the sender and the receiver. At any reasonable distance, your RSSI would have fallen somewhat and with it, the chances of receiving in the other channels. The spec says -56dB attenuation when you are more than 3 MHz away.

However, this does not explain why you capture crosstalk better on some channels, even far away, than on other channels. The explanation to this is probably in the GFSK modulation and the sampling of the radio, in particular when the sampling and the modulation are in some favourable harmonic relationship. You certainly observe that all distant channels in the list are in multiples of 8MHz distance from the base channel and that the best group (66/67) is in a 64MHz distance. If you sample at 8MHz without anti-aliasing, you see the same phase relations of samples if you are a multiple of 8Mhz off. The antialiasing filter (if there is one) does not reduce these phase relations to the noise level and you can still capture packets.

In summary, there is no simple way to chose channels to avoid crosstalk. The best advice was not only to select different channels but also use different addresses in the different channels in a proprietary protocol in order to avoid collisions.

RE: ESB with different frequency

Hung Bui — Fri, 14 Jul 2017 14:52:29 GMT

I'm not entirely sure on how channel crosstalk works but I would suggest to divide the 100 channel into X (=5) equal parts and then uses the channel at the start of each part.

RE: ESB with different frequency

Vlad Mokhnachov — Fri, 14 Jul 2017 11:50:24 GMT

Ok, I try make this. But there are channels, which haven't interference. It is possible find, for example, five independent channels for minimize crosstalk and noise?

RE: ESB with different frequency

Hung Bui — Fri, 14 Jul 2017 11:37:09 GMT

I think what butch suggested is correct. You use different channel and different address for each pair. Doesn't matter which pipe you use on each of the pair, it's the address (Base address 0 for example) that's matter. There will be crosstalk between channels. But if you use channels that's far enough from each other, you can reduce crosstalk. The signal on the correct channel on the receive will be stronger than the crosstalk signal from other channel.

You should also try to reduce the on-air time as much as possible to avoid interference.

If you use different address for each pair, there shouldn't be any crosstalk (but there still interference causing packet loss)

RE: ESB with different frequency

Vlad Mokhnachov — Thu, 13 Jul 2017 13:25:24 GMT

All pairs use logical address(pipe) for self. I can't give different pipe for each pair, unfortunately.

RE: ESB with different frequency

butch — Thu, 13 Jul 2017 13:18:05 GMT

So each pair would have a unique (rfchannel, addr.) There would still be crosstalk between the rf channels, but the addresses would not match. If your question is: why is there so much crosstalk, I can't answer that.

RE: ESB with different frequency

butch — Thu, 13 Jul 2017 13:15:39 GMT

We are not understanding each other. The address is different from the rf channel. An address is an ID that is sent in the payload. You tell the receiver what addresses to match. If an OTA packet does not contain the address in the payload, the receiver ignores the OTA packet. I could be wrong, maybe ESB doesn't provide address matching capability. But in general, the Nordic radio does.

RE: ESB with different frequency

Vlad Mokhnachov — Thu, 13 Jul 2017 12:14:56 GMT

NRF_RADIO->FREQUENCY = m_esb_addr.rf_channel;

My test work without pair, but I want use different channel for each pair. For example: pair1 at 2-th channel, pair2 at 36-th, etc.

RE: ESB with different frequency

butch — Thu, 13 Jul 2017 12:07:50 GMT

Have you considered using an address? Each pair use a distinct address. I am not very familiar with ESB or RF channel crosstalk.