Here's my 2 cents...
NO!!! ? You can't do that kind of rate on HF! ? ?
1) ? The transmission time is much longer on VARA than on the usual 1200-baud 2M VHF. ?A simple beacon, especially if it is not in a compressed format like Mic-E, ?can take 20-30 seconds. ? At a two-minute repetition rate, you are occupying 1/5 th to 1/4 of the total capacity of the channel.?
Note that on a random-access channel with no coordinated timing of the users, that if the channel is occupied more than 18-20% of the time, the probability of data collisions between stations goes up sharply. (The so-called Aloha" limit.)
Let's start with this. Not all beacons are alike. Data saving measures are hidden within VARA modems code. Uncompressed beacons are actually compressed within VARA, which is why the math doesn't add up when you look at the data sizes. VARA uses tricks to reduce the tocall, digi paths, acks, and other things. It balances the slowest speed possible with data length, and the compressed tricks it has hidden within. This is why an uncompressed beacon is more data, but uses a slower speed. It was designed this way to allow the most robust signal and lowest speed with a simple beacon.
- An uncompressed beacon (no speed or alt) takes 2 VARA packets at speed 1. (~12 seconds)
- Mic-E beacon with no speed or alt takes 1 VARA packet at speed 2. (speed 1 isn't possible with Mic-E, ~6 seconds)
- Mic-E with speed and alt is 2 VARA packet at speed 2. (~12 seconds).
- Compressed with no speed or alt is 1 VARA packet at speed 2 (speed 1 isn't possible with compressed, ~6 seconds)
- Compressed with speed and alt is 1-2 VARA packets (~6-12 seconds)
- Some uncompressed beacons WITH comments OR speed and altitude can use speed 1 with 3 VARA packets (~18 seconds)
Every user is different, so how they operate their beacons will greatly vary. So the above should help determine what's best for you speed and time wise, and the air time consideration. Whether you utilize the 1/4 or 1/5 of the air time definitely matters.... but only if the airwaves are actually being used.?
I've been using 30m for 3 weeks 5 days a week or more in the mornings and evenings. I've been the only one mobile during that entire time that I've seen or heard. So what's best practice for my usage and consideration of the network? Easily 2 minute +/- intervals using smart beaconing. There's no problem doing such either. Even if we had a couple other stations, it still wouldn't be a problem. We've tested multiple stations in our 1 year of operations on 40m. It's rare you'll see more than 1 mobile station at any given time.
With that, you are now pointing out a crucial flaw of 30m. The band skips across too much of an area, meaning it could see congestion much quicker. Though unlikely, as basically no one seems to go mobile on the band.
As you said,
"On HF, a reasonable beacon rate is around 15-20 minutes for a mobile, if the channel is being used with multiple users."
I find that just ridiculous unless the band is congested or heavily used. Which is never. So 2-4 minute smart beaconing intervals are perfectly sufficient. Whether on 30m or 40m.
I'm more concerned with the base stations spewing out all the crap "DX" beacons every 30 seconds. Or those who push out the "grid position". Or stations who's messaging is off, but they beacon every 2 minutes with their base station.?
"I think there needs to be some consensus on beacon intervals. I would propose a base station I-Gate beacon on RF at no more than 20 munities intervals. Mobile stations on short trips no more than 4 minutes and long road trips no more than 8 minutes.
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"As far as the beacon length, I started out with PinPoint with a length of about 20 seconds. I understand PinPoint is not compressed. This may change with a new release. Today I changed to APRSIS32 and the beacon length, which is compressed, is about 10 seconds. I will give this some time to see how this works out."
One problem you're missing here is how VARA works. Compressed or not, it's about the speed when using uncompressed, not the time or length like other packet types. This is why VARA uses speed 1 with uncompressed, because it's specifically designed to use the lowest speed for uncompressed packets. If it didn't, it would use speed 2 exactly like compressed or Mic-E due to the length of data.
So with that, 2-3 minutes and smart beaconing is an acceptable interval WHEN the band isn't being heavily used. Which seems to be never. We adjust as we go, not based on something that isn't happening or never happens.
When stationary (as a mobile), 15-30 minutes is acceptable and best practice. When a base only, 30 is best.
Pinpoint doesn't support smart beaconing, so this requires being a little more diligent with operations and changing it based on how you are travelling.
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