[RFI] 2.4 GHz Phones

Eric Gustafson Eric Gustafson <n7cl@mmsi.com>
Thu, 3 Aug 2000 11:58:38 -0700

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: <dgsvetan@collins.rockwell.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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