RF switch power supply noise - Page 1
Forum section: electronics / rf-microwave

author: sadboi
author_rank: Newbie
timestamp: February 23, 2024, 06:43:57 am
content: Hey,I'm looking to use the SKYA21003 RF switch for sharing an antenna with a GNSS module and RF transmitter.Just wondering if the power for an RF switch requires low noise. Will power supply noise from a switching converter couple onto the RF signals?Cheers.

author: radiolistener
author_rank: Super Contributor
timestamp: February 23, 2024, 10:19:21 am
content: yes, noise leakage can happens even if you put single ground wire to SMPS, it will be enough to get noise interference

author: p.larner
author_rank: Frequent Contributor
timestamp: February 25, 2024, 03:56:46 am
content: imho any switching psu is bad news anywhere near a radio!.they belong in landfill.

author: radiogeek381
author_rank: Regular Contributor
timestamp: February 27, 2024, 11:00:28 pm
content: Modern switch mode power supplies can be quite suited to high performance radios. I have several on my desk right now - an Ettus B210, B200mini, N200, and a N321. All with switch mode power supplies. Some with several. The ADALM-PLUTO has one too. I do a whole lot of work looking for spurs. The power supplies aren’t contributing in any perceptible way.In the 70’s it was hard to find quiet supplies. It still is if we’re talking down-market PC supplies and such. But well designed switch mode supplies can be quite good.In any case the RF devices should be mounted over an appropriate ground plane, with appropriate decoupling between power and ground, and careful layout. The app note from the vendor is often very helpful here. Some notes even suggest various RF choke schemes. Such practices are important whether the power source is a battery or a wall wart.p.larner: Have you encountered actual problems in a modern radio with a purpose-designed SMPS? I have not. And I have more than a few modern radios.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: February 28, 2024, 09:27:21 am
content: Considering the supply current is <1mA, I'd use a RC filter to get rid of most of the noise.Something like a 200 ohm resistor and a 100nF capacitor should do the trick.

author: pdenisowski
author_rank: Super Contributor
timestamp: February 28, 2024, 09:43:24 am
content: Quote from: radiogeek381 on February 27, 2024, 11:00:28 pmI work in RF Test and Measurement (and am an active amateur radio operator) and I agree with this statement completely. I have very few concerns about using a modern, high-quality SMPS in applications where EMI is a potential issue.Yes, there are still some noisy SMPS out there, but they have come a long way since the 70s and 80s in terms of emissions (and, frankly, a lot of other things as well).

author: radiolistener
author_rank: Super Contributor
timestamp: February 28, 2024, 11:01:48 am
content: Quote from: radiogeek381 on February 27, 2024, 11:00:28 pmAny switching mode DC/DC or PSU has negative effect on radio receiver and you can see their spurs. The good switching mode PSU has less noise power and their noise is less spreaded across spectrum, it is more narrow bandwidth or even synchronized with ADC clock with large steps between harmonics (500-1000 kHz for example) and usually it is tuned in such way to appear at frequency which is not critical for the radio receiver. Professional SMPS for radio has a knob which allows to change noise frequency, so you can tune it in such way to shift noise away from the receiving station frequency. But if radio receiver is good, it can still see spurs from SMPS and it is very much perceptible and noticeable.For modem it may not be critical, because modem works with pretty high signal level, so using SMPS just reduce working distance, but not prevent its function completely. But if you want to work with weak signals it is critical for the radio receivers.There is also another issue, modern city has a lot of SMPS, so they produce high noise floor. So if you use good quality designed SMPS with filters, it's noise effect may not be critical on the background of modern city noisefloor.But if you go away from city and buildings full of modern digital electronics with SMPS, you will get very low environment noise floor and in this case even very good SMPS noise will be extreme high on the background of low environment noise floor.For example when we had power outage, I was able to listen FM stations with high quality from neighbor cities at about 150 km. But when I tried to plug my phone to a power bank, its DC/DC flooded FM station with high noise even if I put power bank in another room at 10 meter distance through 2-3 brick walls. But when mains is present I tested this power bank and cannot even notice noise from it even if put receiver close to powerbank... This is because environment noise floor from neighbors electronics exceed noise produced with power bank, its still there and can be very noticeable on receiver if I use it far away from buildings.