Cordless phone RFI


Alan Higbie
 

Interesting coincidence that you are discussing how you used SDR-Console / SDRPlay to track RFI from DECT cordless phones.

For the first time - I did just that this week while helping a friend.

We are tracking 2 RFI sources:
(1) powerline source causing RFI on HF has been located &
(2) some (as yet) unknown source causing interference to his AT&T and Panasonic DECT phones.

These DECT phones operate in the 1.9 GHz range.  The exact frequencies were in the user manuals. 

In investigating this phone RFI problem, we used SDR-Console with an SDRPlay RSPDx.  It was very interesting to visualize the transmissions from the base unit and the handsets.
His phone RFI is interference TO HIS PHONE - - vs. Allan's RFI from a DECT phone.

I have tried other SDR software - but for RFI sleuthing, SDR-C is the best.  Its Signal History feature is most helpful. 

For anyone interested in locating and mitigating RFI sources, be sure to search archives of the RFI reflector:
http://lists.contesting.com/mailman/listinfo/rfi

Also, the ARRL's website has a very good RFI page:
http://www.arrl.org/radio-frequency-interference-rfi

Earlier this year, WD8DSB developed a small UNIDIRECTIONAL and BROADBANDED portable loop antenna for RFI hunting. It was the cover story in QST March, 2021.
To me, it seems like a breakthrough.
It pairs very well with SDR-Console, SDR receiver, and a laptop.

73, Alan K0AV


 


David De Coons
 

Very interesting. Last night I noticed what looked like waves in the panadapter on 80m. Also groups of horizontal lines spaced close to each other.

I’ll need to look closer to my Panasonic Dect phones. 

The other thing I was thinking is we had a LOT of rain from tropical storms Henri. My next door neighbor closest to my 80m antenna has a sump pump that is normally off.
Hmmm..

I do have a very short video of it I can post on Dropbox.

Dave wo2x


On Aug 23, 2021, at 6:38 AM, Siegfried Jackstien <siegfried.jackstien@...> wrote:



GOOD CATCH ... especially the cordless phone (i never thought that a dect phone on 1.8 gig wipes out shortwave on 160 and 80)

also look for the psu of the base unit (those switchers can be noisy) ... either try to filter it out ... or replace the switcher

greetz sigi dg9bfc

Am 23.08.2021 um 12:11 schrieb Allan Isaacs:
I've been plagued by interference on the 80m band for ages and decided to have yet another attempt at tracing its source.
For the test I used an SDR PLay sitting on my desk connected via a USB cable (A plug to B plug) to a computer USB3 socket and a long wire antenna.
I initially looked at narrow spikes every 8KHz from 1.7MHz to 3.752MHz. These were very stable across the range and roughly equal in strength at about -80dBm. I got rid of these by changing the USB lead from a grey one marked Xingong USB Shielded High Speed Revision 2 28AWG/1P + 24AWG/2C to an ancient one, orange in colour with GP on one end. The second cable is fitted with a ferrite ring and reduced the spikes by 18dB to -98dBm. The same ferrite ring had no effect on the first cable.
The next problem was a really annoying pulsing sound producing regular horizontal lines on the waterfall a bit like noise from an electric fence. This was at a rate of 7 pulses per second and I eventually found it was emanating from my cordless phone base unit. Lifting the phone (Siemens Gigaset C430) stopped the pulsing and after replacing it the pulsing restarted after about 30 seconds.
Looking for an RF signal I found this at 1.887GHz. This was relatively stable but slight pulsing was apparent.
A second identical handset in another room was also radiating and pulsing.
The solution was really easy. On the first phone I selected settings, ECO DECT, ticked No Radiation and unticked Maximum Range.
The RF signal disappeared, the trace went completely flat and the pulsing vanished.
I'm now left with just general background mush from countless switching power supplies and the phone but this is now at a fairly low level.
Lifting the phone reduces the level of mush from -98dBm to -104dBm so the next step might be to fit ferrite rings to the base unit power cable and telephone line...
Allan G3PIY


Siegfried Jackstien
 

GOOD CATCH ... especially the cordless phone (i never thought that a dect phone on 1.8 gig wipes out shortwave on 160 and 80)

also look for the psu of the base unit (those switchers can be noisy) ... either try to filter it out ... or replace the switcher

greetz sigi dg9bfc

Am 23.08.2021 um 12:11 schrieb Allan Isaacs:

I've been plagued by interference on the 80m band for ages and decided to have yet another attempt at tracing its source.
For the test I used an SDR PLay sitting on my desk connected via a USB cable (A plug to B plug) to a computer USB3 socket and a long wire antenna.
I initially looked at narrow spikes every 8KHz from 1.7MHz to 3.752MHz. These were very stable across the range and roughly equal in strength at about -80dBm. I got rid of these by changing the USB lead from a grey one marked Xingong USB Shielded High Speed Revision 2 28AWG/1P + 24AWG/2C to an ancient one, orange in colour with GP on one end. The second cable is fitted with a ferrite ring and reduced the spikes by 18dB to -98dBm. The same ferrite ring had no effect on the first cable.
The next problem was a really annoying pulsing sound producing regular horizontal lines on the waterfall a bit like noise from an electric fence. This was at a rate of 7 pulses per second and I eventually found it was emanating from my cordless phone base unit. Lifting the phone (Siemens Gigaset C430) stopped the pulsing and after replacing it the pulsing restarted after about 30 seconds.
Looking for an RF signal I found this at 1.887GHz. This was relatively stable but slight pulsing was apparent.
A second identical handset in another room was also radiating and pulsing.
The solution was really easy. On the first phone I selected settings, ECO DECT, ticked No Radiation and unticked Maximum Range.
The RF signal disappeared, the trace went completely flat and the pulsing vanished.
I'm now left with just general background mush from countless switching power supplies and the phone but this is now at a fairly low level.
Lifting the phone reduces the level of mush from -98dBm to -104dBm so the next step might be to fit ferrite rings to the base unit power cable and telephone line...
Allan G3PIY


Allan Isaacs
 

I've been plagued by interference on the 80m band for ages and decided to have yet another attempt at tracing its source.
For the test I used an SDR PLay sitting on my desk connected via a USB cable (A plug to B plug) to a computer USB3 socket and a long wire antenna.
I initially looked at narrow spikes every 8KHz from 1.7MHz to 3.752MHz. These were very stable across the range and roughly equal in strength at about -80dBm. I got rid of these by changing the USB lead from a grey one marked Xingong USB Shielded High Speed Revision 2 28AWG/1P + 24AWG/2C to an ancient one, orange in colour with GP on one end. The second cable is fitted with a ferrite ring and reduced the spikes by 18dB to -98dBm. The same ferrite ring had no effect on the first cable.
The next problem was a really annoying pulsing sound producing regular horizontal lines on the waterfall a bit like noise from an electric fence. This was at a rate of 7 pulses per second and I eventually found it was emanating from my cordless phone base unit. Lifting the phone (Siemens Gigaset C430) stopped the pulsing and after replacing it the pulsing restarted after about 30 seconds.
Looking for an RF signal I found this at 1.887GHz. This was relatively stable but slight pulsing was apparent.
A second identical handset in another room was also radiating and pulsing.
The solution was really easy. On the first phone I selected settings, ECO DECT, ticked No Radiation and unticked Maximum Range.
The RF signal disappeared, the trace went completely flat and the pulsing vanished.
I'm now left with just general background mush from countless switching power supplies and the phone but this is now at a fairly low level.
Lifting the phone reduces the level of mush from -98dBm to -104dBm so the next step might be to fit ferrite rings to the base unit power cable and telephone line...
Allan G3PIY