2.4GHz radio and cellular phone masts

[Peter Smith 12]

Does anyone know if there have been any proven instances of mobile phone base stations in the UK perhaps on 2.1Ghz interfering with 2.4Ghz model control
planes in the form of blocking the receiver when flying near a mast? My local
flying field has some such masts close by all on 2.1Ghz and a number of recent
crashes of models are being blamed possibly on such interference.

[Daithi O Buitigh]

It sounds like the 2.1 GHz transmission is de-sensitising the receivers - 300 MHz may seem a large amount, but up in the top end of the UHF segment it's close enough.

 

What is possibly happening is that the AGC on the receiver is simply being swamped and unable to reject the signal which then blocks the weaker signal from the hand held transmitter.

 

It happens a lot to me on the HF bands - where a very strong signal in the same segmant on, say, the 10 MHz band, that is 5 KHz away from me simply wipes out any weaker signals .

 

Daithi, GI7OMY

[Allan Bennett]

There's a phone mast on our field -- don't know what frequency it's on -- but we've had no known instances of radio problems.

[Peter Jenkins]

I thought that mobile phones were either in the 900 MHz or 1.8 GHz bands. I was not aware of the 2.1 GHz band being used by mobile phones. Does anyone know for sure what are the bands used by mobile phones?

[Peter Smith 12]

Posted by Allan Bennett on 24/08/2011 20:12:54:
There's a phone mast on our field -- don't know what frequency it's on -- but we've had no known instances of radio problems.

But is it on 2.1G...it could be a 900MHz one. Do you know the post code for the site?

[Peter Smith 12]

Posted by Peter Jenkins on 24/08/2011 21:26:28:
I thought that mobile phones were either in the 900 MHz or 1.8 GHz bands. I was not aware of the 2.1 GHz band being used by mobile phones. Does anyone know for sure what are the bands used by mobile phones?

I believe phone-to-base station in 1.8G and base -to-phone can be as high as 2.1G

Posted by Allan Bennett on 24/08/2011 20:12:54:
There's a phone mast on our field -- don't know what frequency it's on -- but we've had no known instances of radio problems.

But is it on 2.1G...it could be a 900MHz one. Do you know the post code for the site?

[Peter Smith 12]

Posted by Daithi O Buitigh on 24/08/2011 13:31:20:

It sounds like the 2.1 GHz transmission is de-sensitising the receivers - 300 MHz may seem a large amount, but up in the top end of the UHF segment it's close enough.

 

What is possibly happening is that the AGC on the receiver is simply being swamped and unable to reject the signal which then blocks the weaker signal from the hand held transmitter.

 

It happens a lot to me on the HF bands - where a very strong signal in the same segmant on, say, the 10 MHz band, that is 5 KHz away from me simply wipes out any weaker signals .

 

Daithi, GI7OMY

Yes this is the sort of action I was thinking of. It all depends on how good the filtering is in the receiver and how well it rejects unwanted signals. I don't ever recall seeing figures like that for a 2.4G receiver?

[Biggles' Elder Brother - Moderator]

We have a major regional hospital immediately adjacent to our fyling site. Frankly you name it they are probably pumping it out - pagers, wireless systems, networks, ambulance comms etc. But I've never noticed any adverse effects on any 2.4GHz system from any manufacturer. Can't say the same about 35MHz though!

 

BEB

[Daithi O Buitigh]

There's one possibility - is there a military base in the area?

 

We had a lot of problems on VHF (I live in Belfast) and the army pumped out a lot of hash on the IF frequency of 10.7 MHz (to jam any two way communications and/or radio contyrol bombs).

 

If that is pumping out on the IF frequency it will wipe out any reception

[Tim Kearsley]

Take a look at this in Wikipedia - I don't think there are any cellular phone transmissions as high as 2.1 GHz.

 

Also, I don't believe spread-spectrum receivers are afected in quite the same way as conventional receivers, as descrobed by Daithi.

 

Tim.

 

[James40]

It's all too easy to blame a crash on anything other than human error.
The chances of the mast hitting the same frequency devision and time burst your bound tx/rx are operating on is almost non existent and even if it did get lucky, it would be a micro second of interference, not enough to cause any harm.

If you made a phone call from under a phone mast, you don't receive all the other phone calls travelling through that mast, the phone locks on to a particular carrier wave and a particular time slot within that carrier wave, just as a tx/rx works when it's bound.

I fly on an RAF base with 2 phone masts, a radar, ILS, TACAN and god knows how many high power radios transmitting, the only crashes I've had is through my own lack of skill.

[Steve Houghton 1]

A lot of the mountains I go sloping off in S Wales have masts on them but I haven't experienced any problems. However, my two flying buddies have on Machen when they have both experienced loss of control whilst flying, and it's only ever happened to them on that mountain.

[James M]

Hi all

At our flying site we have a couple of mobile phone masts and have lost a plane or two when flying near the mast - we think. One possibly was receiver battery failure plane was never recovered, the other was flying close to the mast and we lost control, recovered and all ok when tested.

 

The way to think about it is the signals from the transmitter are 150/500 mW (milliwatts) and a phone mast operates at around 20watts but when you get through the antenna gains and the rest it becomes about 800 watts outputting from the aerial.

 

If you fly close enough to it you your signal will be lost, imagine standing next to a baby screaming for food, whilst trying to hear someone, talking to you in a low whisper from the other side of the room, you can't.

 

Similar sort of thing will be happening to the receiver in the aircraft, there will be some form isolation from foreign radio signals but at some point it will be over loaded and fail!

 

Same principles are used for radio jamming, you don't need to know the exact frequency if you can drown out a lot of the surrounding spectrum - and 1.8 to 2.4 GHz isn't a big jump when the power difference is so big!

[Peter Smith 12]

Posted by James40 on 25/08/2011 07:48:19:
It's all too easy to blame a crash on anything other than human error.
The chances of the mast hitting the same frequency devision and time burst your bound tx/rx are operating on is almost non existent and even if it did get lucky, it would be a micro second of interference, not enough to cause any harm.

If you made a phone call from under a phone mast, you don't receive all the other phone calls travelling through that mast, the phone locks on to a particular carrier wave and a particular time slot within that carrier wave, just as a tx/rx works when it's bound.

I fly on an RAF base with 2 phone masts, a radar, ILS, TACAN and god knows how many high power radios transmitting, the only crashes I've had is through my own lack of skill.

But if the signal is big enough it will make the receiver deaf momentarily no matter what frequency its hopping too?

[Peter Smith 12]

Posted by Daithi O Buitigh on 25/08/2011 00:50:10:

There's one possibility - is there a military base in the area?

 

We had a lot of problems on VHF (I live in Belfast) and the army pumped out a lot of hash on the IF frequency of 10.7 MHz (to jam any two way communications and/or radio contyrol bombs).

 

If that is pumping out on the IF frequency it will wipe out any reception

No we are well away from military bases, but yes they could pump out lots of rubbish.

[James M]

Posted by Peter Smith 12 on 25/08/2011 08:21:26:

But if the signal is big enough it will make the receiver deaf momentarily no matter what frequency its hopping too?

Yes, in a fashion.

If you have interference with in a frequency band, as with the 35 MHz systems frequency clashes, this is 1st/primary harmonic interference. As you go further away from the frequency you go to 2nd/secondary harmonic interference, then 3rd/tertiary harmonic interference and so on down the orders.

 

Also as you move to the lower orders there will need significantly more power to cause the interference.

 

This is taking me back to my uni days and looking at wave synthesis!

 

Also as 2.4 GHz uses packet data, like the internet, so as more and more packets are lost the signal will eventually collaps!

 

No system is perfect!

Edited By James M on 25/08/2011 09:25:05

[Allan Bennett]

Posted by Peter Smith 12 on 24/08/2011 22:34:23:

Posted by Allan Bennett on 24/08/2011 20:12:54:
There's a phone mast on our field -- don't know what frequency it's on -- but we've had no known instances of radio problems.

But is it on 2.1G...it could be a 900MHz one. Do you know the post code for the site?

I've just check on the internet, and it's an Orange mast operating on 2100MHz (2.1GHz) at 29.5dBW.

 

I see there's also three others on 2100MHz within a couple of hundred yards of us, plus one on 1800MHz and one on 900MHz -- none of which I've ever noticed.

Edited By Allan Bennett on 25/08/2011 11:47:06

[Daithi O Buitigh]

Ouch!!!!!

 

29.5 dBW is almost a 900 Watts of RF

[Peter Smith 12]

Posted by Daithi O Buitigh on 25/08/2011 12:27:34:

Ouch!!!!!

 

29.5 dBW is almost a 900 Watts of RF

 

But the antenna gain is 16dB so it only represents about 20 watts into the antenna

[Erfolg]

Just had a look at the local phone mast sites, and most were on 2.1 and in the region of 30 dBW region. I am amazed how many there are in the suburbs.

 

I do not think we have a problem at our site though, which appears to have no local masts.

[Daithi O Buitigh]

It's still a whopping 900 Watts being pumped out of it (aerial gain is included because that's the amount of RF actually in the air)

 

Even at 20 Watts RF - consider a CB only puts out 4 Watts and your hand-held Tx is putting out a lot less.

 

I have a hand-held VHF/UHF rig with 5 Watts output into a rubber duck and that will still function two-way over several miles at 430 MHz.

[GONZO]

The 2.4gHz band (2.4000gHz to 2.4835gHz) is an ISM licence free band and as part of the terms (OFCOM) of it being licence free all users must accept interference from all other users. It is not just for RC. There are many other legitimate, legal and higher power users of the band not just internet routers etc. For instance, a full licence radio ham can transmit at up to 400W in the band 2.4000gHz to 2.4500gHz using any modulation type (IIRC). My understanding is that both analogue and digital ATV transmissions take place, amongst others, within this ham band. It's just hard luck if you get shot down by a more powerful user of the band because thats the terms under which we are allowed to use it. The only dedicated RC aircraft band is 35mHz as even the un used 459mHz band is shared with other users.

Food for thought.

HTH

[Chris Channon]

Hi all, glad i got rid of my 2.4 gear and stuck with good old 35 !!!!

I lost two aircraft on 2.4 NOT pilot error, only ever lost one on 35, genuine radio failure but one loss in 30 odd years is ok by me.

( lost lots BY pilot error though !!!!)

Regards

Chris.

[Daithi O Buitigh]

Actually amateurs are only primary users for the 24.000 to 24.050 section of the band and we must accept interference from ISM users

 

We are secondary users for the segments of 24.050 to 24.150 and 24.150 to 24.250

 

However, to operate in the 24.050 to 24.150 segment requires written approval fron the Secretary of State for Trade and Industry (and the ISM caveat also applies but not to the remaining upper secton)

[GONZO]

D O B,

You are quite correct on the detail (my mistake on the upper limit, I may have confussed it with the French 2.4gHz RC band?). I didn't want to cloud my point with too much info as the ham radio user was just an example. The point is not that ham users may suffer from interference from RC users rather that IMHO the use of the band is not as 'safe' for RC, especially if used in an urban environment (sportsfield etc near houseing/ industrial park/hospital) as is generally assumed. A sentiment, false I believe, that I often detect is that 2.4gHz systems are immune from external influence. There could quite easily be a high power legitimate user in the local vacinity whos transmissions could, as you previously stated, block a RC Rx front end and cause loss of control. I can not find the site at the moment but did ,in the past, come across a company hirering out very high power equipment for outside broadcast use. The RC fraternity should, I believe, be more aware of what RF polution may be about and his thread has gone some way towards this.