...it is my understanding that (for example) all the grey ones have the same transmit frequency. So, if you turn multiple of them on and they are not interfering with each other before you start a dive, then they will continue to not interfere with each other during the dive.
Is that correct?
Theoretically, that sounds correct. In the real world, each of those components has a tolerance range, so some may be slightly faster than others. So while they might not interfere at the start of the dive, they could creep up on each other after some time. That could take a while to clear depending on the duration of the transmission and the timing differences between the two.
Having two very different timings means that at some point, they will probably interfere, but by the next transmit cycle, all should be clear again.
Hi Stuart and thank you for the kind words. Brian is correct in his response.
Frequency vs Interval
I just wanted to clarify some semantics that might bring confusion. While you are technically correct when you use the word "frequency" (because it can be measured in cycles over time) we try to use the word "interval" when referring to what you are referring in your question. This is to differentiate from the wireless radio frequency that is used to transmit the information.
All the transmitters in this discussion are fixed at a
frequency of 38 kHz. The transmission
interval varies to avoid interference. Average transmit interval is 5.0 seconds, and the Swift can vary its interval randomly between 4.8 and 5.2 seconds to help avoid interference. Additionally, the Swift contains a receiver to help avoid interfering with other nearby transmitters, delaying transmission if other activity is detected.
Contrast this with fixed-interval transmitters that lack receivers and cannot dynamically listen or avoid collisions from nearby transmitters. Fixed interval transmitters can interfere even if they start at different times due to clock drift. When the drift is slow, they can stay in interfering timing for several minutes or more.
FCC ID
Please note that the FCC ID of the Swift is NOT MH8A for these transmitters, but
2AO24-17001. The FCC ID is different since the Swift is our own design (does not use anyone else's chip or code) and we must apply for our own FCC ID. However, the Swift is compatible with our legacy and future AI computers and our new computer firmware retains compatibility with transmitters with the FCC ID of MH8A.
Also, while I'm asking, can you tell us the total time a single transmission takes? It transmits every 5 seconds. Does that transmission take 1.0 seconds? 0.1 seconds?
Transmit time is
roughly 0.15 seconds. This corresponds to around 3% of available bandwidth.
Chance of Collision between Fixed-Interval Transmitters
The random turn-on chance of two fixed-interval transmitters interfering is
very roughly 3%, however, this chance increases substantially if more fixed-interval transmitters are added. Using Swift transmitters, the interference chance is greatly reduced (but not completely eliminated). Interference likelihood will be higher with a mix of fixed-interval and Swift transmitters since the fixed-interval units do not avoid collisions.
I was very lucky to scoop up a new green transmitter a few years ago. I have a grey and the green on my rEvo. Works flawlessly with my NERD2. I sure hope the green one never dies!
Excellent. These are hard to find. I believe their interval is fixed at 4.8 seconds. I currently have a yellow and a Swift in the rEvo I dive. I've setup my son with a fixed grey (he's on OC single tank) and monitor his pressure on my computers. I have this combination on purpose trying to see if things break (dropped comms). We have a robust battery of lab tests done at the factory, but we also do a good amount of formal and informal tests under real life conditions. So far I have not experience drops that I can attribute to collisions.
Using 38 kHz transmitters for Buddy Checks
While I just confessed that I monitor my son's pressure on my computer, I have to clarify that these transmitters are not meant for buddy checking. Until last Sunday, my son was not aware that I was monitoring his transmitter on my computer and he was very diligent monitoring his own pressure, responding to my tank pressure queries and signaling for turnarounds at the appropriate pressures in accordance to his gas planning. His own responsibility for managing his own gas was never relinquished away.
These transmitters were not designed for buddy checking because of the limited range the 38 kHz frequency has underwater. I do get frequent dropped comms from my son's transmitter when we separate for more than approx 5ft.
Is anyone else experiencing a degradation of the start-up image quality when uploading it?
Hi Mark. Please keep in mind that the screen resolution of the Perdix AI is 320 x 240 pixels. Most cameras these days take images at a much higher resolution. Displaying a high resolution image in a Perdix screen requires resizing of the image. Before uploading your images to the Perdix you can try using an image editor to resize it to 320 x 240 to see if your choice of image has an acceptable appearance at the lower resolution of 320 x 240.
