A closer look at the strength and shape of 2.4 GHz radio signals

[redbird300]

Thank you all for the kind words, I really do appreciate it. I consider this payback time for me, a lot of people helped me here as well when I started this superb hobby, and I learned a lot, included some knowledge of Shakespeare’s language, which I needed badly.

To be honest, I couldn’t decide where to post all this in the beginning, the Futaba or Spektrum subforum didn’t seem the best place, as the post is about both these systems and more. Silently hoping that this info won’t be lost, the sticky suggestion is very nice to hear, and I hope to add more graphs in the future, as more people at our local club will be prepared without a doubt to let me measure their Multiplex, Aurora, dual ACT S3D (2 x 100 mW!) and other brands of transmitters or plug in modules.

Back to business, and as promised, a graph of a Spektrum DX8 in DSMX mode, at normal power. The system will now switch between 23 randomly selected channels all the time, instead of using only two channels in DSM2 mode, so after a very short while we get this picture on the analyzer screen when it’s set to memorize max values:



The peaks measure around -10 dbm or 0,1 mW, exactly the same as in DSM2 mode.

[skunkworx]

Very nice write-up Redbird. While it's a lot to take in (I would imagine it's somewhat indecipherable for non-electronics backgrounded people), it's very honest and very un-biased, which is pretty tough to do. Like you said in the beginning, there will be the fanboys who like to use the info about their system to magnify just how great it is, but that's to be expected. In reality, they're all very, VERY good and solid systems and the problems people have are typically related to user error or power supply system on the individual models themselves. It's a truly rare case when it's 100% the radio's fault, so it's funny to see some of the animosity on both sides of the fence.

Anways, the best antenna position is roughly 90* to the surface you are modulating to. Very little of the signal come straight out of the tip of the antenna, so it's best to bend it off to one side. You can leave it at a bit of an angle if you'd like, but the majority of your flying should be done as cloe to perpendicular to the antenna as possible to ensure maximum signal strength.

[jperkosk]

Interesting, Raf. It gives me an impression that S FHSS uses narrower channels compared to F. Could this explain why my DX8 goes through its stock NiMH battery pack 2-2.5 times slower than the 8FG?

Would the wider channels (more energy pumped in the air) have any bearing on the maximum range, or it's just a plain and pure waste of radio energy, defined by the SS algorithm in use? The peak power is exactly the same...

[Finless]

We are working on sticking this somewhere. GREAT POST! It's just where to stick it. I proposed my tech forum but what do you all think?

Bob

[Redlight11]

Originally Posted by Finless

We are working on sticking this somewhere. GREAT POST! It's just where to stick it. I proposed my tech forum but what do you all think?

Bob

(chanting) sticky..sticky..sticky!! I think the tech forum is a perfect spot for the post.

[Finless]

So be it!

Bob

[Jazzjohn]

Nice post. So that nobody gets confused, there are a couple of typos (or probably font symbol issues) here:

"The formulae to calculate x [dbm] as a function of P [Watt] is:
x= 10log10(1000P) or x = 10log10P + 30

And the formulae to calculate P [Watt] as a function of x [dbm] is:
P = 10(x/10)/1000 or P = 10(x-30)/10"

The first formula should be
x = 10logP + 30, where "log" is the base 10 logarithm
The second should be
P = 10 ^ [ (x-30)/10 ], where "^" is read "raised to the power of"

[daveapplemotors]

Thanks,
A basic lesson on how to set up the transmitter antenna was sorely needed. And I really enjoyed the explanations of the different signal patterns.
I learn a lot on this form.

[Jason O'Connell]