If it is constantly changing channels because there is interference on one
channel, that means we could only have one plane in the sky at one time.
you would think that since this world we live in also shares the 2.4ghz
frequencies with cordless phones and computer wireless networking (802.11b)
that you could possibly get interference from that too.
Not quite Vance. I don't claim to be an expert but I see you don't
understand the way it works. It doesn't change channels because of
interference. It changes channels constantly, regardless of the situation.
Many times a second. It's a form of encryption. It uses 25 channels
essentially all at the same time. It shifts between these channels in a
pattern determined by some algorithm built into the radio. So it doesn't
hit each channel in numerical order but in some pattern known by the Tx and
Read the four levels of protection at the bottom of this page:
The Tx and Rx are in sync with each other. What this means is the Rx also
knows the pattern and is expecting to "hear" from the Tx at the prescribed
time on the prescribed channel. Correct channel at wrong time is ignored as
is correct time on wrong channel. Even another R/C Tx using the same
pattern would not cause interference unless it was in the same exact spot of
the pattern at the same exact instant in time. And instant is the key here
because to our perception it is only an instant that it is on any given
channel. If fact, I suspect it hits each channel several times each second.
And if I remember my math correctly, with 25 channels we end up with well
over 13,000 possible patterns (probably more but hey, do we need more?:)
which would equate to the possibility of 13,000 models in the air at once.
Likewise, any phones or wireless computers would have to be on the same set
of channels and the same pattern to cause any problems. As would the Line
of Site microwave shots and Satellite links that used this band. This is a
proven technology that has been in use for years. It is simply, finally
being implemented in R/C. About time too!
Thats true! These chipsets have been around for a long time. The neat thing
here that hasn't been talked about is the ability of the chipsets to be
transmitters/receivers together, meaning each side can transmit and recieve at
the same time. You standing on the ground sends signals to the plane, the plane
can send signals back using the same frequencys. Instant data back about
airspeed, engine rpm, gps, any thing you can think of to be displayed realtime
on your transmitter! It's closer than you think!
My guess is that the modules will be replaceable. Everyone with "standard"
radios will be out of luck. I also suspect a rather long phase in-out
period to allow the older sets to be either converted or used long enough
that the sting of replacement won't be so bad.
That is always the issue with introducing new technology. IMHO - I do believe
that when this issue comes to the forefront, that the FCC will be happy to help
us! I think there is enough demand for our current frequency allotment by other
interested parties that converting into the 900mhz or other currently used
spread spectrum bands will look like a win/win solution to them. They have
already allowed the Hams to experiment with spread spectrum data transmission
on certain bands.
All I can say is that it will get interesting!
| So Red, what do 'ya think; will existing radios be able to be converted to
| spread spectrum or are all those high-dollar radios in use going to become
| obselete overnight when SS happens?
As mentioned by another poster, radios with modules will probably be
changable by just replacing the module.
As for other radios being obsolete, no. We can't just start using
spread spectrum on 72 mhz -- if people do start switching to spread
spectrum, they'll need to use another frequency range. So radios on
72 mhz will keep working and will be just as good as they are today
... as long as the spectrum isn't sold to the highest bidder. Spread
spectrum does play reasonably nice with other types of radio
emissions, but even the perception of causing problems would be bad.
I'm not sure if 900, 2400 or 5800 mhz is the answer, however. The
power limits on these bands will severely limit the range usable by a
spread-spectrum system. That, and these bands are full of junk.
Spread spectrum does tend to ignore noise, even if the noise isn't
spread spectrum itself, but the noise will reduce performance. Your
plane won't crash (unless the whole band is saturated) but response
speed could drop. Your microwave can easily kill your WiFi network,
as can your 2.4 ghz cordless phone.
Ideally, another band would be allocated just for R/C, just for spread
sprectrum. No need for an air/ground split. The power limits would
be high enough to allow the same range we enjoy. Of course, spectrum
is money, so I'm not holding my breath. :)
I suspect any current radios with Freq Modules will be easily converted.
Those with built in RF decks may prove to be more trouble than they're
worth. But this will probably be on a case by case basis as I'm sure some
designs may lend themselves to easy conversion.