Why do some receivers come with/need a satellite receiver? - RC Groups
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Jul 19, 2012, 08:59 PM
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Why do some receivers come with/need a satellite receiver?

I'm a noob so feel free to laugh and make fun of me, but while you do it could you tell me why the need for a satellite receiver?
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Jul 19, 2012, 09:05 PM
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The answer is, you don't. There is no need for it, I believe its just a plus for extended range and the use of telemetry.
Jul 19, 2012, 11:56 PM
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Piece's Avatar
A lot of bigger planes benefit from having a satellite receiver placed far from the main receiver. In a large aircraft, things like the battery, motor, and even ESC can block the 2.4GHz signal from the transmitter to the receiver which would result in loss of control. Metal and carbon fiber are very good at making shadows in the 2.4GHz range.

Having a satellite ensures that there's always a clear path for the signal, reducing or eliminating the risk of control loss.
Jul 20, 2012, 08:29 AM
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flypaper 2's Avatar
As CH says, it's there so the signal doesn't get blocked by one of the larger metalic objects, motor, batt, etc. Doesn't add to the range. I run up to 40 sized planes without the satelite.

Jul 20, 2012, 09:26 AM
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tacx's Avatar
Some RXs will not bind without the sat RX.
Jul 20, 2012, 01:24 PM
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Originally Posted by tacx
Some RXs will not bind without the sat RX.
Yep, nearly returned my 8000 as faulty for that reason
Jul 21, 2012, 10:42 AM
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As stated above, the satellite does not increase range but it does help in keeping any shadowing effect of conductive objects between the transmitter and receiver plus ( if you have the antenna of the satellite and the antenna of the receive at right angles to one another, you maximize the reception when the linear polarization of the transmitter falls out of phase with one of the receiving antenna as it will still be in alignment with the other one.
Jul 21, 2012, 11:11 AM
Rocket Programmer
jasmine2501's Avatar
OK, you've heard from the Futaba fanboys... now the truth...

With 2.4GHz radio, multi-pathing can be a problem. That's when the receiver gets two signals, one straight from your radio and the other reflected off some surface - these two signals will not be in sync with each other, and sometimes the receiver can't separate them and get a "good" signal. Shading is also a problem - some surface blocks the signal and the RX doesn't get a signal at all.

There are many different ways of dealing with this problem, and the source of the problem is laws of physics, not the design of the system - every system must overcome this problem.

Futaba's method of dealing with the issue is to give you two antennas which you can mount in different locations, and the receiver tries to determine which antenna is getting the best signal and it switches to that one.

Spektrum systems deal with that problem by giving you a whole nother receiver, a complete receiver not just another antenna. Each receiver is able to decode the signal all the way down to packets and do error checking on it. The main receiver decides whether it or the satellite is getting a better signal (fewer errors) and it passes the better signal to the servos.

Both systems are incredibly reliable, to the point where nobody can really say which method is better. Futaba's engineers aren't better than Spektrum's engineers - they are the same guys, but it is not clear if either of these methods are actually better. So, when Futaba guys point at the satellites and say "if the receiver was good in the first place, it wouldn't need that" - they are just being fan boys and not really thinking about what is happening. You must deal with the multi-pathing and shading issues if you want to use 2.4GHz, and the two companies simply chose different methods of doing that.

The quality of the link is amazing in both systems, and that's why it's such a big argument. If one was clearly better than the other, the community would have solved this argument already.
Jul 21, 2012, 12:36 PM
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cwolfe's Avatar
I run Orange RX with Sats in all my planes.
Jul 21, 2012, 01:54 PM
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Piece's Avatar
OK, you've heard from the Futaba fanboys... now the truth...

-snip snip-
... Enter "Toysrme" stage left
Jul 22, 2012, 01:52 PM
Registered User
The use of two antennas, oriented at 90 degrees to one another is NOT for protection against reflections, it is for keeping one of the antennas able to pick up the same polarization of the transmitting antenna. Most of the 2.4GHz transmitters use linear polarization and, if the antenna is in the most unfavorable orientation, you can lose the signal. By having the two antenna at 90 degrees to one another, one will usually be in a favorable attitude to capture the signal. Now, two antenna also help to prevent any shadowing of the signal by any conductive object getting between the transmitter and the receiving antenna as, if the antenna are spaced far enough apart, one will not be in the shadow at the same time as the other is. Now, if you must have protection against reflections, you could use circular polarization (a more difficult physical problem with antenna construction) but reflections will never bother you as the reflection is always polarized in the opposite direction of the transmitted signal and unseeable by the receiver.

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