Re: SWR


K9HZ <bill@...>
 

I think you twisted my words.   I said:

1. If you are resolving variables that are not time dependent between each other (like radio current and s-meter reading), you can let the on board A/D free run and grab and use what ever is in the register for that variable at any time.  Yes they are all muxed but that doesn't matter because all you want is “a number”.

2. You cannot do time dependent resolution of different variables on the Arduino if timing is critical/ the variables are time dependent.  Otherwise its like saying ill take the forward power today and the reverse power tomorrow and calculate swr from non-time related data. You are right, the A/D pins are muxed and that just exacerbates the problem as the number of analog pins used grows. 

3.  If you do have variables where the time relationships are critical (swr, some audio sampling, filters, etc.) then the pest place to do the conversion is off the arduino. Use a sample and hold A/D for critical timed variables so the data time stamps match. It may or may not be critical how long it takes the data to get off the board to inside the Arduino.  For for/rev power for swr it doesnt matter as long as the data pair has the same resolved time stamp. Audio and filters (fft) is more problematic.  The answer is correct but shifted in real time so what you usually see (hear) is the right sound but delayed. 

It appears the temporal issue with sampling causes may people problems. 



Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

 

Owner - Operator

Big Signal Ranch – K9ZC

Staunton, Illinois

 

Owner – Operator

Villa Grand Piton - J68HZ

Soufriere, St. Lucia W.I.

Rent it: www.VillaGrandPiton.com


email:  bill@...

 


On May 7, 2018, at 12:14 PM, Tim Gorman <tgorman2@...> wrote:

Since the ADC on the nano is muxed, i.e. not every channel has its own
ADC, it takes time for the ADC to be connected to a specific channel
and for that channel to settle to a correct reading. So you do lose
time slots while this is occuring. It's why a random read takes 2 to 3
times longer than successive reads from the same channel.

At least that's how I read the specs.

And you are right about letting the ADC in the peripheral just run
continuously. I don't consider SWR to be a critical item. You can
measure reverse power when you need to. And you can do the same for
forward power if you want. SWR isn't going to tell you anything extra
over just the two measurements themselves.

tim ab0wr

On Mon, 7 May 2018 11:40:02 -0500
"K9HZ" <bill@...> wrote:

Correct, but it is more important that, in the case of SWR that the
forward power and the reverse power be synced in time.  Thats where
the Arduino fails and you would want to do it off the Arduino.  With
ten random variables that don't need to be time related, you can just
let the A/D run continuously and just grab data from the conversion
register when you need it. They run in parallel with instruction
processing so no time slots are lost.


Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ
PJ2/K9HZ
Owner - Operator
Big Signal Ranch – K9ZC
Staunton, Illinois

Owner – Operator
Villa Grand Piton - J68HZ
Soufriere, St. Lucia W.I.
Rent it: www.VillaGrandPiton.com

email:  bill@...





Join BITX20@groups.io to automatically receive all group messages.