[RFI] 2.4 GHz Phones
Hare, Ed, W1RFI
Hare, Ed, W1RFI" <email@example.com
Thu, 3 Aug 2000 16:47:22 -0400
> The 31 V/M field for 2Kw PEP 33 feet away seems a bit
> large to me (high by 20 dB or so - what was the antenna gain assumption?).
By my calculations, 2kW 10 meters away should result in an RMS field of 24.5
V/m, assuming 0 dBi antenna gain. This would be 34.7 V/m peak voltage field.
At the typical angles between antennas and areas where susceptible equipment
may be found, the gain is usually less than 0 dBi. For vertical antennas,
considering real ground losses, about 0 dBi might work. Some beams and
configurations may give higher gain if the beam is low, next to an apartment
building, etc. In that case, 8-12 dBi might be more realistic.
Remember, that figure was for 10 meters distance, pretty close for 2 kW.
Most of the "RF safety" calculations include duty factor, on/off times, etc.
These factors don't apply to RFI; the equipment usually corresponds to the
> Yes, It really would be nice if the FCC requirements
> also specified immunity to EMI fields of 3 V/M or so
> from 500 KHz on up. The vast majority of the Ham's
> EMI complaints would never happen if they did.
The present ANSI standards of immunity for consumer electronics equipment
calls for a radiated immunity level of 3 V/m. More and more equipment has
been being made to this standard and I think there is some reduction in RFI
to consumer equipment as a result. But 3 V/m translates to 100 W to a
dipole 100 feet from the source, nowhere NEAR enough to really offer good
protection from amateur radio.
I once believed that ham radio needed this protection. I have changed my
mind. In Europe, the EU requirements call for such immunity, at around 3
V/m. In Germany, however, the regulators noticed the imbalance -- on one
hand there are regulations about immunity but on the other hand, hams are
allowed up to 200 V/m (depending on frequency). That has changed. German
hams must now be able to demonstrate that their stations don't exceed 3 V/m
in their neighbors' homes. Remember the 100 W and the dipole 100 feet from
the source. There is some distinct advantage to "voluntary immunity."
The real unfortunate part is that many consumer manufacturers do NOT have an
appropriate response to calls about RFI involving their products. There has
been SOME progress in that area, see:
but that is more than offset by the number of times the customer-service
agents at a manufacturer's 800 number, or the service technician, says "the
ham must be using illegal power; call the FCC."
There is still a LOT of work to do in that area. I wish I could clone me.
Ed Hare, W1RFI
ARRL Laboratory Supervisor
225 Main St
Newington, CT 06111
ARRL Web: http://www.arrl.org
ARRL Technical Information Service: http://www.arrl.org/tis/
> -----Original Message-----
> From: Eric Gustafson [mailto:firstname.lastname@example.org]
> Sent: Thursday, August 03, 2000 2:59 PM
> To: email@example.com; firstname.lastname@example.org
> Subject: Re: [RFI] 2.4 GHz Phones
> Hi Dale,
> The 31 V/M field for 2Kw PEP 33 feet away seems a bit large to me
> (high by 20 dB or so - what was the antenna gain assumption?). I
> guess I'll have to get out the books and do a little figgerin' to
> convince myself. I think the last time I did this exercise for a
> typical legal HF station, I got answers mostly in the 2 to 3 V/M
> range. But that is neither here nor there.
> The European specs require immunity to radiated EMI fields of 3
> V/M at frequencies from 27 MHz up. But what is the radiated
> immunity of this particular phone from say 1.7 to 25 MHz? But
> even this is probably not the real issue.
> The real question is: " What is the phone's immunity to
> _conducted_ emissions in the HF frequency range?
> It is very unlikely that the phone is suffering from a direct
> radiated susceptibility problem at HF frequencies. I bet that
> the trouble is really from _conducted_ susceptibility. There is
> probably quite a bit of common mode HF current flowing on both
> the power and signal wiring to the base station for the phone.
> Fortunately, both of these common mode paths are treatable
> external to the phone. Apparently, Uniden has decided to include
> at least some common mode rejection for this type of EMI inside
> the phone.
> Yes, It really would be nice if the FCC requirements also
> specified immunity to EMI fields of 3 V/M or so from 500 KHz on
> up. The vast majority of the Ham's EMI complaints would never
> happen if they did. And the noise generated by many
> "unintentional radiators" would be greatly reduced as well.
> 73, Eric N7CL
> >From: <email@example.com>
> >Date: Thu, 3 Aug 2000 08:25:44 -0500
> >The discussion earlier this week about RFI to Siemens 2.4 GHz
> >cordless phones prompted me to contact a colleague who is
> >affiliated with Siemens for more information. This is his
> >The usual complaints that I see are that our Gigaset 2420 system
> >interferes with video senders and other 2400 MHz devices. I can
> >tell you this, it has been tested to show compliance with IEC/EN
> >61000-4-2, IEC/EN 61000-4-3, IEC/EN 61000-4-4, IEC/EN 61000-4-5,
> >and IEC/EN 61000-4-6. The radiated E-field immunity is at least
> >3 V/m from 27 MHz to 1000 MHz, and greater than 6 V/m in the FM
> >broadcast band.
> >The E-field ten meters away from an antenna driven by a 2 kW PEP
> >transmitter is about 31 V/m, peak. Our phones were never
> >intended to work correctly when exposed to such high field
> >strengths. They should not be damaged by such fields, but it is
> >not astonishing that some users find malfunctions.
> > - - - - - - - - - -
> >Note that there would be no required E-field immunity if the
> >unit complied only with FCC specs. If applying extensive common
> >mode controls, including chokes, does not clear the problem on a
> >given unit, then either the unit needs to be further away from
> >the ham antennas, ham band transmit power reduced, or the unit
> >re-packaged by the owner into a "bullet-proof" shielded housing.
> >If it has an external wall transformer for power, don't forget
> >to apply common mode control to the cord of that power unit.
> >It would be interesting to know what specs the Uniden system is
> >designed to meet. I hope that anyone having the information
> >will pass it along. Thanks.
> >73, Dale, WA9ENA
> > ----- ----- ----- ----- ----- ----- -----
> >Prior messages:
> >I own this phone same system, and I can tell you that it is NOT
> >RF immune in my house during HF all-band contests. Quite the
> >I also have a Uniden cordless phone (900 Mhz?) and it is
> >absolutely quiet during the same periods.
> >Hope this helps.
> >Good luck!
> >73/Jeff K2KV
> >I saw this Siemens Cordless phone system that operates at 2.4 GHz
> >Frequency Hopping Spread Spectrum and wondered if it would have
> >enough noise immunity to operate around my KW station? It uses
> >several cordless phones that operate with the base using a PCM
> >modulation at 2.4GHz. Neat system if it would work in an rf
> >Looked through the archives and didn't find much about really
> >good success with spread spectrum 900 or 2.3Ghz phones. Has
> >anyone had any good luck with these. I used a bunch of torroids
> >on the phone line and still had some interference on a 900 Mhz
> >Uniden phone.
> >Wendell W5FL
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