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Nov 06, 2018, 07:26 AM
Registered User
Discussion

Cell Towers..


Can somebody explain how exactly interference from a cell tower works?

I just lost a plane due to a loss of radio connection. I lost one in the same field(albeit 300-400 yards further away) earlier this summer. I had thought it was the radio protocol, so I phased out all of my D8 receivers. The plane today though - my Funjet - has a new RX6R - D16, and supposedly %40 more range than a normal X16 receiver. The antennas are fed out through the fuse, one on bottom, one on top, with the ends at 90-degree angles, taped to the wings, away from carbon fiber. I have flown this plane numerous times, without issue. And even at this precise location.

This field is huge. The F-27 I lost in June was being flown at the opposite far end. Today I was flying at the bottom of a hill, on top of which is a cell tower. Still, it's probably 400-500 yards away as the crow flies? And, I had flown a bunch of planes just before, including up over the hill closer to the tower. I have also flown here numerous times since the crash in June. I still feel queasy about flying here sometimes - even at the very far end where the F-27 crash happened(while buzzing a metal pedestrian bridge over the river..), but once you pile up so many successful flights, you start to shrug it off... That, of course, is precisely when it bites you...

Anyway, IF it is the cell tower, do they just shoot out cosmic radio-signal devouring gamma rays sporadically, or is it constant, or what?
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Nov 06, 2018, 09:55 AM
Registered User
Can't be the cell phone tower - had to have been pilot error, bad equipment, or aliens (or at least that's what some will say!)

Depends on the tower. In Theory, the RF spectrums that Cellular uses are different than our 2.5ghz (cell is usually 1700, 1900, 2300 and 5200)
It also may depend on what protocol you are using - some have better channel hopping abilities than others.

Now, RF interference doesn't always have to be "in band" to cause problems - if there is enough radiated RF energy "around" our frequency, bad things start happening. Enough "noise" at a higher power than your radio will drown out your signal, which, is very plausible. Cell phone towers generally broadcast in the WATTS range - where we operating in the ~100milliWatt range - orders of magnitude, so, from a technical standpoint, yes, it could be interfering.

I'm positive that we have problems, especially with DSM2 (I can't comment personally on other protocols) but we get interference and dead spots due to WiFi from an apartment complex by our field. DSMX is more robust.

Hell I'm about ready to go back to good old FM :-)
Nov 06, 2018, 10:13 AM
Registered User
I used to fly at a field in the city where I lived until last year, and the Spektrum guys had all kinds of brown outs and crashes. Including me, with my Orange module… ( this field was next to a police storage depot of some kind or something… The suspicion was that it was shooting out weird signals of some kind or whatever… ) My non -EU Taranis though never had problems. Out here though, some of this stuff has just been weird..

I actually had a couple crashes at the beginning of the summer, and I assumed it was all down to faulty antenna placement, or receivers getting banged up in the battery bays. With this plane though, I was very careful about everything. And again, I had flown there with no issues before.

BTW, how do power lines affect our signals?
Nov 06, 2018, 10:30 AM
Registered User
Low voltage (regular) power lines aren't too bad.

High Voltage (the big metal ones that buzz) create an EMI field that will block damn near all RF
Nov 06, 2018, 10:38 AM
A man with too many toys
I also fly close to a cell tower. Close in (a hundred yards) it is OK with 2.4 GHz. Telemetry would sometimes drop out even at close range.

I finally got a Dragon Link system and a Taranis transmitter. That combo works really nice and has full telemetry. Now I have a solid connection all 100% of the time. Been flying it for a couple of years with zero problems. https://www.rcgroups.com/forums/show...ner-Data-Modem

http://www.dragonlinkrc.com/

.
Nov 06, 2018, 06:14 PM
Perpetual Noob
BoxCar31's Avatar
As stated, cellular uses different frequencies from RC in the 2.4 GHz ISM band. Cellular sites are also low power as their RF output is generally 10 watts or less due to frequency reuse at nearby towers. Some cellular companies do use microwave links in the 2.4 band for intertower links until land line communications are either installed or upgraded. You would have to fly into that beam in order for it to affect your plane but that beam is only a few meters wide t the distance you cited.
Nov 07, 2018, 03:46 AM
Registered User
So what’s the take away here then?

They have no effect, they always have an effect, or they have sporadic effects?

I guess many people always fly at the same spot so develop a sense for interference or lack of interference. But for people like me, who often fly in different spots, well it kind of feels like you can start developing superstitions almost… It’s very weird how you can have session after session with no problems, then boom!! something goes wrong… And you look around and wonder what happened or caused it, and aha, there’s a cell tower...
Nov 07, 2018, 06:15 AM
A man with too many toys
There is always a difference between theory and real world reality. Theoretically cell towers should not be a problem but in the real world they do cause problems. Maybe there are other devices that are on some towers that are not part of the cell phone network that cause problems with 2.4 GHz RC radios.

Just saying that it's can't be the cell tower is not helpful when everyone in the area is experiencing glitches and crashes.

.
Nov 07, 2018, 06:43 AM
aka: A.Roger Wilfong
gnofliwr's Avatar
So far it's all speculation. You probably have a real problem. But you will never know without real information.

If you have access to an RF spectrum analyzer, you may be able to take some readings around the tower that will show something. But if the source of the interferance is a beamed signal, you may have to get directly into the beam to find it. Also, if it is an intermittant transmission, you may miss it.

Try contacting the tower owner/operator to find out what signals are on the tower. Also, try contacting the local FCC field office - they may be able to do the spectrum tests for you.

But also remember, the 2.4GHz band is not ours. It is a shared chunk of spectrum with rules for its use. No one can intentionally interfere with another service; however, interference is to be expected and technology has to deal with it.

For most of the other services using the spectrum, temporary loss of signal (due to intrrferance) isn't a big deal. One of the next layers in the protocol will recognize the corruption of the link and resend the corrupted packets. We don't have the luxury of resending and have to handle it through fail-safe or hope to reestablish a solid link quickly enough to recover control.

Fortunately, severe interferance is rare, and the manufacturers have been good (and are getting better) at coping with what is encountered.

Like digital proportional, FM and PCM in the past, each advance in our technology, 2.4 Spread Spectrum has been "the answer" to interferance. But, each technology has it's limitations.

If you really want a solid control system, use Control Line. Oh! Wait. Don't fly in a strong wind - the lines will go slack and...

- Roger
Nov 07, 2018, 06:45 AM
Registered User
atreis's Avatar
Sounds like it varies, depending on the configuration of the tower, and whether or not the electronics on it are radiating in an interfering band unintentionally, and potentially, could also vary depending on exactly what's mounted on the tower. (It's not all that common, but community WiFi comes to mind ...)
Nov 07, 2018, 09:03 AM
Registered User
Daren71's Avatar
We used to have a guy in our club swear some sort of “transmission “ occurred everyday between 11-1130. He always claimed he had radio issues then, on 72. We are out in the country, no towers of any kind near by, closest homes are about 1/2km away. But he was the only one that had any problems around that time.

Good times, Daren
Nov 07, 2018, 10:43 AM
Registered User
dalecheek1's Avatar
There is Only one simple thing to do about cell towers if you think you are having issues with them........Do not fly within 5 miles of the them....DUH.....HA....
Nov 07, 2018, 10:57 AM
Registered User
This isn’t freakin’ Alaska. Germany is smaller than the state of Montana, but has 83 million people… Free and open places to fly are few and far between. Furthermore, in some of the spots you can fly there nine times out of 10 without issue. It’s the 10th time that is the problem. But it would appear that, assuming cell towers really are the culprit, there is no regularity or predictability to it.
Nov 07, 2018, 11:13 AM
Registered User
PaulB's Avatar
So only go flying 9 times and then skip the 10th trip??????
Nov 07, 2018, 11:23 AM
Registered User
Yeah.. . On the 10th I fly somewhere else...

Here is me out standing in my field..., with the evil tower of Mordor on the top of the hill in the background. The plane lost contact about 100 yards off to the left…


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