On Thu, Oct 19, 2006 at 11:55:57AM -0700, [EMAIL PROTECTED] wrote:
| I have to question this too, because 2.4ghz is limited in power output
Yes, in the US it's limited to one watt with a dipole TX antenna (or
another 2.3 dBi antenna) by the part 15 rules.
For comparison, I think our 72 MHz R/C gear is limited to 0.750 watts.
I believe the DX6 only transmitted with 50 mW, but they could do more
if they wanted to. I don't know how much the DX7 transmits with.
| and it doesn't travel (propagate) well.
It doesn't? Could you expand on this? 2.4 GHz are attenuated by air
at 0.01 dB/mile -- perhaps signifigant for a many mile video link, but
utterly insignifigant for our purposes. Even pouring rain won't
attenuate the siganal too much for us (and who flies in pouring rain?)
| I have personal experience with video feeds on both 2.4ghz and
| 1.2ghz. and 1.2 has much better range, but both freqs. will not go
| through trees, so if you fly behind a tree and the radio doesn't
| have "last frame hold" you could completely go out of control.
It's a pretty good guess that all SS systems will have `last frame
hold' or full fail-safes. The DX6 system does. It would be silly to
make a system with all the smarts needed to do SS, and to not actually
use these smarts to add these simple features.
2.4 GHz will go through trees to a small degree, but you're right --
trees (and buildings and other things) will attenuate it. Of course,
as a general rule of thumb, you can't fly your plane if you can't see
it, so this shouldn't be a big limitation.
| real world use will decide if this is an issue or not, but the
| bottom line is that high frequencies at low power have poor range
| and there is a lot of stuff on 2.4ghz to screw up your signal when
| the primary signal is lost.
Well, when the primary signal is lost, you're not flying your plane
anymore. And as I said, I'm quite sure that all commercial SS
implementations (both present and future) will not respond to spurious
signals -- at worst, noise will drown out your TX (making you lose
control), but it won't make your servos move.
| I would really like to see spread spectrum on 72mhz. but it probably
| isn't a high enough frequency to work at a high resolution........
There's no technical reason why you can't do spread spectrum on 72
MHz. You'd pretty much need to use the whole R/C part of the band,
but it could be done.
Practically/politically, there's some big reasons why you can't, and
they're both show-stoppers --
1) the FCC regulations don't permit it.
2) a SS implementation on 72 MHz would interfere with all non-SS R/C
receivers on the band. Yes, SS can co-exist with non-SS applications
to a degree, but it does raise the noise floor, and is therefore
likely to cause problems.
| All of that being said, if they made a module for my 9C, I would buy it in a
| heart beat...
The XtremeLink people are promising just such a module. See
http://www.rcgroups.com/forums/showthread.php?t=566018 and
http://www.xtremepowersystems.net/xtremelink.php.
Of course, unlike Spektrum, they have no track record. In fact, they
have no products of any sort available for sale at all, so we'll just
have to wait and see how this turns out.
--
Doug McLaren, [EMAIL PROTECTED]
If you were from Earth, you would be home now!
RCSE-List facilities provided by Model Airplane News. Send "subscribe" and
"unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and
unsubscribe messages must be sent in text only format with MIME turned off.
Email sent from web based email such as Hotmail and AOL are generally NOT in
text format
