Cell Phone

[RC Steve Sterling]

This information fits what I know about field, being first educated as an RF
engineer.

There should not be any problem between a properly designed and operating
cell phone, and a properly designed and operating R/C transmitter. They
operate on widely different frequencies.

Will we find a very few cases where they interfere-- yes.  Either the cell
phone or R/C transmitter can have either tuning system or active component
problems (e.g. a defective RF protective diode or final stage transistor)
such that they spew out interference. How many times have I dropped my cell
phone??? Did that knock the RF deck out of alignment, or knock loose a
solder junction?  In a synthesized RF module (cell phone is full of them),
there are many more mixing frequencies and phase-locking loop signals to be
interfered with if something is not right.

Its also possible, with 800+ cell frequencies and our 50+ frequencies where
the right combination 3rd or 5th order harmonics could mix in the R/C
transmitter's final output stage where it could be amplified enough to cause
trouble. I used to have a computer program around here that would predict
this.  Maybe an interesting exercise.

Its not going to be a every cell phone interfers with every transmitter
thing. Are we talking a 1 in 100 combinations or 1 in 100,000?  There seems
to be enough anecdotal occurances that suggest its more prevelent than
1-100,000, but not enough to suggest its as low as 1-100.

Well, that's my analysis for what it is worth. Whether to ban them or not,
depends on an individual or club's risk adversion.
  -----Original Message-----
  From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org]On
Behalf Of Don Ramsey
  Sent: Saturday, May 03, 2003 4:48 AM
  To: discussion at nsrca.org
  Subject: Re: Cell Phone


  I just got this info about some testing on cell phones.

  Don

  Hi Don,

  I am following the NSRCA mailing list but am not a member. Because of this
I cannot mail on the list without censors reading it first, so I decided to
reply to you directly.

  The use of cell phones with R/C equipment has been discussed on the the
list in August last year, I do not remember the consensus.
  A couple of years ago I found a test report on the Internet, in German.
That page does not exist anymore but the story goes like this:

  An R/C helicopter crashed when the pilots cell phone rang. The phone was
on the belt. The insurance company and DMFV (Deutscher Modellflieger
Verband, German "AMA") got interested. A radio specialist (MSc in RF) and an
R/C pilot himself carried out the tests.

  Results:
  -  Robbe Futaba FC-28 (exactly the same technology as Futaba 9Z) with
synthesized RF module lost control when a cell phone was very close to it,
less than 40 cm distance. It turned out that it was not interference, but
the transmitter was was not able to hold the right frequency, IOW it was
sending with a false frequency.
  -  Same transmitter with a non-synthesized RF module was totally
unaffected by a cell phone
  -  Several other JR and Futaba (probably also Multiplex) transmitters were
tested. No effect at all !
  -  Various brands and types of receivers and servos were also tested. No
effect at all !
  -  Receivers were tested at the flying distance
  -  In these tests the R/C equipment was 35 MHz and cell phones 900 and
1800 MHz. In the USA teh frequencies are different but basic rules against
interference applie the same.

  So the Futaba synth module may be affected by cell phone. It is also
important to avoid close proximity of cell phone at the pits, because the
transmitting frequency is possibly altered. You may shoot someone else down
!
  The sensitivity of other brands i do not know, but why take a chance.

  On the other hand what is the benefit of having a phone close to you while
flying, since you cannot answer it anyway. If you have a hands free, you
still have to concentrate on flying.

  Best regards,

  Iiro Nikkila
  Finland
  F3A, Futaba 9ZAP with TK-FSS module
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