Advice on a 2.4 GHz radio

On Sun, 16 Sep 2007 20:19:13 -0500, Slent thndr wrote in :
I don't own one yet, but I'm planning to go that route some day.
The 2.4 GHz stuff is vastly superior to what we have now. The receivers will only act on correctly signed and formatted data. They won't respond to noise.
Of course, stuff happens and I do expect the technology will improve over the years.
I've heard of as many as 15 planes flying at the same time. It was done as a demo. I can't imagine any club allowing that much noise and confusion.
If I were starting out this year, I'd buy SS. I have lots of old equipment in good working order, so I'm going to bide my time.
Marty

::nods::

wrote in : Thats not really the OP's question is it?
2.4 is no more or less relaible than any other band (ie 35 in the UK) when considered against non RC signals.
At the end of the day Tx's are limed to 100mW output (again here in the UK) , if you have a big transmittter ie a cell tower then no matter what your frequency you are on there is likely to be swamping if you get close enough to it. 2.4 is better at rejection than others but it's like the olod PPM / PCM failsafe argument , would you prefer to know you have interference and the plane be jittery to warn you, or have the PCM lock it out and you fly through the interference without knowing. PCM is a digital format just like the 2.4, it won't respond to noise, but if the signal is rejected you have no control, analog PPM you get some responose it's just very jittery...
2.4 has some great features, the model memory lock out so you have to have the right model selected, and the only respond to it's own TX are great, but they are more geared to acidental mistakes, I always check I'm on the right model before trying to take off before I start, and also check a fequency scanner before I start to check my freqency is clear (despite the fact I have the peg) , but not everyones does, (I've seen enough shoot downs to be cautious) and I've seen crashes where someone taken off to find they are on a heli model with a plane. It's more a case of adopting a right minded attitude and sticking to a procedure until it becomes second nature to you.
2.4 does not mean you can be lax with safety procedures, but it does seem to be encouraging lazyness to wards some preflight checks, Why should I check x, y, z when the TX will do it for me is asking for trouble when you use someone elses TX for any reason, as you'll be out of a safe habit.

2.4Ghz is far less susceptible out on te field as against in the home.
There are issues with wet air (fog) and trees though.

On Mon, 17 Sep 2007 06:43:02 GMT, Gavin wrote in :
wrote in :
I thought it was. That's why I answered the way I did.
The thing that, in my estimation, makes 2.4 GHz "much more reliable than our old radios" is the way that the receivers listen for a signed and formatted packet and reject everything else as noise.
If you're arguing that the same kind of technology could be implemented elsewhere in the spectrum, you may be right--if the gummint wanted to allow the same number of channels elsewhere in the spectrum.
But if we're comparing currently-available 6-meter (U.S. HAM) and 72 MHz equipment (U.S. RC bands), then, in my view, the answer to the question of whether the new radios are "much more reliable than our old radios" is, in my view, yes.
The fact that any system can be defeated by a person choosing to fly close to cell towers does not mean that the two different design philosophies are equal in merit.
There. We agree.
We agree again.
Some of the systems block the signal--will not let you take off at all--if you have the wrong model chosen. That's a huge plus for the new systems.
Checking frequency pegs is not required with 2.4 GHz, because the whole point of spread spectrum is that the channels to be used are chosen in real time in response to what's already on the air at the field at that time. That's a huge plus for the new systems.
Thanks for the reminder that we need to stay on our toes.
But the next TX module and RX that I buy will be for 2.4 GHz (some day).
Marty

On Mon, 17 Sep 2007 10:59:42 +0100, The Natural Philosopher wrote in :
As a general rule, I try not to fly in fog and trees.
I admit that I have broken this rule on occasion, mostly with unfortunate but not unforeseeable results.
Marty

Around trees anyway.
This is all WiFi spectrum. It is definitely poor when line of sight is interrupted by almost anything..including a bank of trees you may dip below.
Multipath when flying over them is also an issue. The technology does its best using multiple recievers and error correction, but even so, you may get some odd effects. Its a bit too soon to say how good it really is. But in terms of an open flying field, its certainly BETTER than HF band.

On Mon, 17 Sep 2007 14:43:09 +0100, The Natural Philosopher wrote in :
OK.
One more reason not to fly our planes where we can't see them.
I tried this one (1) time in my career when trying to land in a small field we were using for some exhibition flying. I exhibited what happens when one of our planes tries to occupy the same space as tree branches.
The branches are still there.
The fuselage is still flying with two new wings (also recovered from crashes) added on by a fellow who likes to rebuild other people's wrecks. :o(
As an interested observer, that is my impression, too.
Marty

-------------
Yeah, me too, Marty. It is amazing how much longer the models last when you stop flying them in fog and trees.
At the ranges that we normally fly, what little signal attenuation there is shouldn't be of any consequence.
However, I have measured some far sighted pilots flying their giant scale models as far away as a half a mile at times. When confronted with the evidence, video tape, they were completely non plussed. I've never been plussed, so being non plussed is my normal state.
Ed Cregger

On Mon, 17 Sep 2007 22:33:03 -0400, "Ed Cregger" wrote in :
My heavens--that sends shivers down my spine!
I have taken some risks vertically with a glider and with a camera plane, but I wouldn't put my biggest and best plane (not that big--a GP Extra 300 with your MVVS 2.15 on it) that far out.
Sincere, heartfelt condolences. Deeply sincere. :-P
Marty

I think I recall someone noting about interference from celluar phone towers: How close do the towers have to be to cause interference with older, but still functional, 72 mhz TX/RX? The towers seem to be everywhere anymore.
Thanks,
Ray

On Tue, 18 Sep 2007 09:08:36 -0400, "RayB" wrote in :
I seem to remember someone reporting on an experiment where they carried a 72 MHz plane as close as they could to a tower and found no interference at a ridiculously long range.
BUT I can't find that post right now.
Folks argued about how much power cellular tower transmitters use on various frequencies. Whatever the facts may be (and the power output seems to vary), it's almost certainly a lot more power than we have in our transmitters.
So, as a precaution, I wouldn't fly too close to a cellphone tower myself. But I'm not going to worry too much about it, either. Finding a good space to fly is a normal part of the hobby.
Marty

The chief issue with mobile phones is that right up against a TRANSMITTER they can corrupt its memory and make mincemeat of its running code.
I can't remember where I saw it, but some recent test were done inside a hospital operating theater to see what kit responded to mobiles. Within 3ft about half of it did, withing a few inches nearly ALL of it did.
I have issue with even stronger microwave sources..I fly across the beams of some pretty powerful cross country microwave relays.
I am not totally sure, but I think that its actually stuff from mobile radio in the 100Mhz type area that screws me. Not microwaves. But screwed I get for sure. Thats on 35Mhz.
I wouldn't expect a mobile mast to be much of an issue with 2.4Ghz stuff, The ERP whilst large, is not SUPER large. Ther is very little point as teh phone has to transmit back to the mast before the link works, and whilst the mast antennae are better than the phone, they are not SO much better that stuffing a 100W transmitter in a tower is going to render a 600mW phone to be able to send back to it. In fact it may even swamp itself.
No the danger from mobile phones is the *phone*, which is likely to be a whole lot closer..

: Not much. See my last post.
The phones themselves are in the 50mW to 1.2W level
The towers are not much more. No int, since they can't puck up the phones anyway.
If the plane is OK next to the phone with someone talking in it, it will be fine 15 feet away from a tower.

On Tue, 18 Sep 2007 18:50:30 +0100, The Natural Philosopher wrote in :
The estimate from a fellow who had worked in the industry was that the towers might put out 30 to 100 watts (up to 100x the ouput from a cell phone).
Here's the post. Sorry for the long link. Gotta run to class. More stuff in the thread:
"I once designed cullular telephone stuff (both mobile and cellsite). The cellsites pump out _way_ more power than the mobiles. Mobiles put out somewhere between 0.1 and 3 watts. Handhelds only get up to about 0.3W. Cellsite transmitters are putting out a hundred times that."
That makes sense to me.
I'm not a good enough pilot to be challenging towers up close and personal like that anyway. :-O
Marty

Ok wait...
*paranoid expression*
So now we're going to have to ban cell phones from our flying fields? :-P
If you're telling me that if someone flips our their cell phone at flying field it could glitch my model with a 2.4 radio, then I'm prett scared... O.o
And I'm still confused about the whole cell tower thing. So basicall how dangerous is it? If I can't see a tower near a field (meaning tha if there is one its probably far away) then I'm fine, right? =
-- Slent thnd ----------------------------------------------------------------------- Slent thndr's Profile: this thread:

----------
As TNP said, you have more to worry about from the phone in your belt hook fouling up your TX's programming than you have to worry about a nearby cell site swamping/desensing the receiver in your model, regardless of the band it is operating on. IF the cell tower is only carrying 800-900 MHz normal cell traffic, that is.
Some towers share their antenna holding capability with Tx/Rx from other radio services, so it is possible, not likely, to have a 72 MHz paging Tx on the tower also.
I would not be overly concerned unless I was opening up a new flying site and noticed interference. It would then bear further investigation.
Ed Cregger

On Thu, 20 Sep 2007 14:23:51 -0500, Slent thndr wrote in :
*pained scorn*
Oh, nooooooooooooooooo, Mr. Bill!
Theoretically, all 2.4 GHz systems should operate in such a way that all others are left unaffected.
In our case, the packets are signed and sent in 10 numbers (not sure how many bits per number). The chances of a cell phone accidentally sending ONE correctly formatted packet are vanishingly small, let alone taking control of the plane or preventing packets from getting through.
With 72 MHz systems, someone did find a way to generate interference with one brand (I think). It involved a ringing cell phone on or near the TX. If a cell phone rings and you start having control problems, the cure is to get away from the cell phone.
If you want to MAKE a cell phone call, land first, make the call, stow the phone, and then go back to flying.
Basically, we don't have a definite consensus.
My amateur opinion is "not too dangerous."
I think so.
The intensity of a transmission falls off with distance. If you climbed a radio tower and got near an antenna, you might get seriously injured by the power being emitted from it; on the ground at a reasonable distance, you're safe. The power that the body (or the receiver) can absorb from the transmission falls off with the square of the distance.
To me, it makes sense to steer clear of transmission towers and power lines.
Those who get tech licenses so that they can fly on ham bands are supposed to know this stuff--well, at least long enough to pass the exam.
Marty KC2NEB

So seriously, do I need to turn off my cell phone when I'm flying?
Or is it one of those things where there 'could' be a problem but it really not that dangerous
-- Slent thnd ----------------------------------------------------------------------- Slent thndr's Profile: this thread: