Keep in mind I am a huge Dynon supporter, I believe in them and love their products. What I say below is just my opinion as I do not understand why the RS-485 standards are not followed with DSAB. This is not an attack on Dynon or their recommendations, just my way of thinking on the subject.
I also love your hubs Vern, they make a neat install out of a mess of wires. If I were building a SV system and was going to follow Dynon's recommendations, I would use em!
Does not matter what label Dynon puts on it, it is a 3 wire RS-485 bus. What it is called does not impact the robustness of the bus.
I would argue that our little airplanes are not that benign with all of the devices with PWM dimmers, PWM constant current sources, Strobe PS's, all kinds of oscillators and DC/DC converters, Stepper servos, brushed DC motors, RF transmitters, HID arcs, etc. that are included even in the simplest RV's these days. Kinda sounds like quite a harsh environment....
Most of the RS232 circuit paths are measured in inches instead of many feet. These are almost always well controlled and behind the panel. They do however occasionally suffer from the same issues that the DSAB bus experiences. It would be better if Dynon did shield these wires but that is not what we are discussing here.
The SV DSAB setup is more critical in nature than the legacy DSAB is. Since without a working DSAB network on the SV renders the system dead. There is no room for a dual DSAB failure on the SV system. If you lose a RS232 link to a handheld GPS, most likely your day is not ruined. If you lose both DSAB networks on a SV system in IMC, your a dead man unless you have a third backup...
I would like to hear Dynon's spill on what error correcting they do with the software on the SV vs the legacy DSAB system. It is hard to correct data from a network that is being swamped by some noise source. It is a well proven fact that the legacy DSAB system is not that immune to noise when installed without following the RS-485 standards. One can find dozens of reports of DSAB failures on the legacy systems in just a few minutes. I would like to know what magic could have been added to the SV system software to prevent these issues.
It is easy to check the signals on the DSAB bus with an O'scope. One day I may do a test by connecting all my devices up in an unterminated "star with long branching arms" arraingement vs one that follows the RS-485 standards for bus construction and termination. I just wonder what that data would show? Hmmm.
Dynon does not claim for it to be an RS-485 bus, which would require compliance to the complete ANSI standard. They may use RS-485 drivers/receivers, but the distance is (obviously) quite limited and the environment (aircraft) is actually quite benign compared to a factory floor or large vessel.
Probably the largest antagonist in an aircraft would be an improperly installed antenna cable. There are a lot of other connections in an aircraft that would be more sensitive to this, including single-ended unshield RS-232 signals that Dynon uses as well.
I'd be very surprised if the SVN is the weak link, even with multiple splitters and hubs.
Of course, I'm sure Dynon is running an error-correcting protocol as well, thats makes the SVN even more resilent.
Perhaps Dynon has an opinion...
V
