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Apr 24, 2021, 11:41 PM
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Death of frequency hopping


So there was the problem of phone towers overlapping the 915Mhz ISM which was fixed by adding more power, but there were still occasional losses of signal away from phone towers. There was a software change to send the channel number inside the packet, in case there was crosstalk. This only made the signal losses worse.

It would work perfectly for several minutes, handling errors, then just recieve 1 packet every 2 seconds. It was always a constant rate of reception rather than a total loss of signal. It would scan, immediately get a packet, enter hopping mode & get no more packets. Then it would time out after 2 seconds & scan again, immediately getting a packet. Power cycling either the transmitter or receiver made the problem go away for a few more minutes. It didn't depend on how far away the radios were or the error rate.

It became a lot more reliable just by adding debug statements to the receiver. The debug statements caused the UART receiver to overrun, so the UART had to be reset, which might have been 1 problem. The UART registers showed frequent framing errors, which might have been another problem. This UART scheme had been used for years without getting into a permanent framing error or buffer overflow, though. The mane difference might be those applications didn't turn the radio off between every packet. It could require a software UART on the receiver if it's a permanent framing error.

This was impossible to debug without a spectrum analyzer. There's no way to know if a frequency hopper is transmitting without an instantaneous view of the entire spectrum. It could use an RTL-SDR dongle by squeezing all the channels in a 2.4Mhz test range. Lions just always end up paying twice when they get a cheap option like this.

https://www.amazon.com/RTL-SDR-Blog-.../dp/B0129EBDS2

Another option is hacking the camera mount to receive the truck packets. Then, it would show if the transmitter was transmitting & show more accurate times than a spectrum analyzer.

It's such a hassle for something that every toy does with a $1 off the shelf radio module, the lion kingdom decided to just eliminate any timing errors by using 1 frequency.
Last edited by Jack Crossfire; Apr 24, 2021 at 11:56 PM.
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