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I am working on making a low latency rf link that will be used as part of a feedback loop on a remote sensor. Because it is real-time the delay needs to be as small as possible (if sub milliseconds are possible I'd leap at it).

Due to the information being transmitted, it only needs to transmit 8 bits at most. In fact if there were an analog rf link (2 frequencies determine the states) that would be suitable for my needs if there was a ready to buy ic.

After reading the questions here and here, then doing my own research, I think there are still better solutions such as found in zigbee.

My question is what is the lowest latency one way rf link?

EDIT: I'm looking for a complete system such as zigbee, wifi, or some other way to incorporate information, with a preference for the lowest latency

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  • \$\begingroup\$ uh, roughly a nanosecond per foot... \$\endgroup\$ – user_1818839 Dec 6 '14 at 20:23
  • \$\begingroup\$ @BrianDrummond while not quite what I thought I had asked, your comment is helpful if I decide to go the purely analog route. I've updated my question to clarify what I'm asking \$\endgroup\$ – Legen Diary Dec 6 '14 at 20:42
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My question is what is the lowest latency one way rf link?

You have to consider what an AM or FM receiver has to do to lock-in to a transmission and then consider how this might affect latency. See the picture below. The left (red) is random demodulated noise due to no transmission being present and, in the centre of the picture the transmission starts. Towards the right, the filtered receiver data slicer (blue) gains lock to the transmitted signal: -

enter image description here

You can't expect instantly to start receiving data unless you are transmitting some form of preamble all the time. This may not be allowed in some countries (at some frequencies) so do your homework and look for RF circuits that "get in lock" in the quickest possible time.

In my experience, locking into a freshly started preamble may take up to 10ms but there may be newer circuits out there that are much better. Clearly you also want to send data as fast as you can.

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  • \$\begingroup\$ thanks for the info. for what I'm working on, it's alright for the system to be always on. The question is more how quickly can a change in the transmit be picked up by the receive. Preferably it would be a pre-built system because we have deadline the would make custom implementation prohibitive \$\endgroup\$ – Legen Diary Dec 9 '14 at 17:35
  • \$\begingroup\$ Get some RF FM modules - they are readily available and cheap. data rates of 9600bps are commonly available and the demodulated output is usually available should you want a more direct connection. The demod output would look like the red curve in my diagram BTW. I've used this company in the past: radiometrix.com/wrx2-0 \$\endgroup\$ – Andy aka Dec 9 '14 at 17:50

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