DCF77 reception interference due to pulse power supply operation

TechEkspert 08 Dec 2024 22:00 46 4419 Cool? (+12)

📢 Listen (AI):

TL;DR

A DCF77 watch reception problem turned out to be local interference from an SMPS power supply replacing a faulty unit.
A longwave receiver pinpointed the noise source, and the interference varied with inverter operation and the current drawn from the supply.
The noisy unit was an EA 10850D1 MW Power supply, while the quieter replacement was a GSM36B12 MW MEAN WELL supply.
The first PSU showed distorted input current with repeated spikes and no active PFC, while the second drew a more sine-like current.
SMPS supplies can produce strong RF interference and disrupt weak radio signals, even though they offer high efficiency and compact size.

Generated by the language model.

When I noticed for a long time that the watch was out of sync with the DCF receiver, at first I suspected problems with the strength of the DCF77 signal transmitted from German territory. After contacting a ham radio operator who has a similar watch at his operating station, it became clear that the cause must be some local interference or a failure of the watch. I got the hint to try to detect the source of possible interference with a longwave receiver. This was a hoot, the source of the strong interference was the SMPS power supply with which I replaced the faulty unit. The power supply visible in the photo, by the way, replaced several other plug-in power supplies that arrived around the ONT device, switch, router, i.e. the devices that provide internet access in the house. It is a model EA 10850D1 MW Power power supply.

.

The interference generated by the power supply was strong and modulated by the operation of the inverter and also depended on the current drawn from the power supply.

.

I looked through the box of power supplies and through selection using a receiver managed to find a specimen with low levels of radio interference. This is the model GSM36B12 MW MEAN WELL power supply.

.

The interference has a smaller range and is more like a hum than a whirr.

.

The current waveform (blue) at the input of the first PSU reveals that this is a design without active PFC correction. At this power this is not mandatory and with the low price of the product it is not possible. The yellow trace is obviously the mains voltage sine wave.

.

There are "pins" superimposed on the current waveform this is probably the result of operating at a certain frequency of the inverter circuit.

The waveforms are quite complex they are repetitive double current pins.

A power supply that generates less distortion also does not have an active PFC circuit, but no additional spikes are imposed on the current waveform.

.

At idle, the first power supply also generates cyclic current spikes.

The second power supply at idle draws a current that resembles a sine wave.

The output voltage of the first supply is more strongly noisy,

compared to a power supply that generates a lower level of interference.

.

I managed to eliminate the source of DCF signal interference. SMPS power supplies offer high efficiency, high currents, small dimensions but sometimes generate strong radio interference. The current drawn by such power supplies is strongly distorted, in power supplies with higher power we find active PFC systems and the current drawn has a chance to resemble a sine wave.

Comparison of input current of power supplies without and with active PFC:

.

Have you encountered electronic devices that, by their level of interference, impeded the reception of radio signals?

When PLC (power line comunication) appeared ham radio operators were concerned about strong interference on the amateur bands. It turned out that PLC did not become that popular, while SMPS are often enough to cover weak radio signals with their whirring. It used to be that TV receivers and ~15KHz deflection drew a strong mark on the FFT in the software receivers of VLF band listeners. Now it is common for the LED 'bulb' to generate interference in the wider band. The amount of RF interference has increased quite strongly over the years.

Here is more about active PFC correction with oscillograms and internal design of power supplies:

About Author

TechEkspert wrote 7181 posts with rating 5547 , helped 16 times. Been with us since 2014 year.

Comments

Add a comment

prosiak_wej 09 Dec 2024 00:51

Article showing that: - A cheap power supply is worth g. - MW Power is not Mean Well (and I once encountered such a statement in an electronics shop) By the way, I like to buy power supplies from... [Read more]

szymon122 09 Dec 2024 06:17

Can such a PFC module exist as an external module connected from the 230V side? It is not always possible to replace the power supply. [Read more]

Janusz_kk 09 Dec 2024 10:29

. But why? It is not the lack of PFC that makes noise and interference. The PFC itself also generates interference independently of the inverter. It's better to use a filter, except that it's live on... [Read more]

LeszekBytom1 09 Dec 2024 10:29

Hello, I had a very similar problem with an active TV antenna and a Mi scooter charger of type BCTA 71420-1791. Switching on the charger effectively disabled TV reception. Only moving the charger about... [Read more]

szeryf3 09 Dec 2024 10:37

I put up a Christmas tree on Saturday. There is a router under it. Well, and the problem started with receiving TV using Wi-Fi when the Christmas tree lights up. [Read more]

Janusz_kk 09 Dec 2024 10:39

Do they flicker? if so block them (there is a tips topic) and see if it helps :) . [Read more]

szeryf3 09 Dec 2024 10:42

Not when they are on all the time because blinking makes me slightly nervous [Read more]

gulson 09 Dec 2024 10:50

The manufacturer of such power supplies should be punished! This is unthinkable. How is a non-technical person supposed to function in this world, how is he supposed to know why a watch goes out of sync... [Read more]

TechEkspert 09 Dec 2024 11:00

@simon122 the question about active PFC in front of the PSU surprised me, it's usually a built-in module that increases the voltage on the capacitor already behind the PSU bridge. As external devices... [Read more]

ArturAVS 09 Dec 2024 11:06

. Especially since the PFC is sized/and designed for the specific power supply.... [Read more]

Janusz_kk 09 Dec 2024 11:11

. But that doesn't mean at all that they are nicely sine powered, it could still be a triac that only starts from a certain sine voltage, we can't see it but the interference it generates. Only shorting... [Read more]

prosiak_wej 09 Dec 2024 16:30

And such filters, either as stand-alone modules or integrated into the socket, can be bought without any problem: https://obrazki.elektroda.pl/1068740400_1733758196_thumb.jpg https://obrazki.elektroda.pl/3573199700_1733758196_thumb.jpg... [Read more]

acctr 09 Dec 2024 17:03

DCF synchronised watches have the disadvantage that they do not continuously signal the quality of the signal reception and there is no chance of finding the optimum location for it. . . As far... [Read more]

kris8888 09 Dec 2024 18:01

. It is worthwhile selecting power supplies for themselves in terms of ripple and noise values at the output. Test under some kind of constant load. A standby test can also be useful. You can be really... [Read more]

LEDówki 09 Dec 2024 18:19

If the inverters are able to interfere with UKF, BT and TV, then they are very bad. I've got some pads that interfere just like that. [Read more]

Janusz_kk 09 Dec 2024 19:12

. Because such power supplies are built that way, class 2 protection, i.e. with double insulation, PE is unnecessary for them, only that then unfortunately they 'sow'. [Read more]

TechEkspert 09 Dec 2024 19:50

Good observation, in fact these power supplies do not have a PE connection, the C7 radio plug used is the so-called figure eight. [Read more]

Anonymous 09 Dec 2024 21:40

. E.g. Panasonic heat pump - it sows all the way - I wonder how it is that they pass EMI/EMC approval? - I have a quandary here as the currents and powers require a non-trivial filter (30A). Another... [Read more]

LEDówki 09 Dec 2024 22:02

DaoLong battery charger. Model YH-2120 - chaffs mainly PR1 on 225 kHz. When switched on it noises the radio in the other room beautifully. A charger that comes with a Zundapp bike. This one manages to... [Read more]

FAQ

TL;DR: If a DCF77 clock stops syncing, a 230 V plug-in SMPS may be the cause; one expert found “the source of the strong interference was the SMPS power supply” and fixed reception by swapping adapters. This FAQ helps clock, radio, router, and LED users identify noisy supplies, compare models, and choose filters or placement that restore stable reception. [#21339333]

Why it matters: Local RF noise from chargers, LED drivers, and cheap adapters can break time sync, TV, Wi‑Fi, and longwave reception even when the original radio signal is fine.

Feature	EA 10850D1 MW Power	GSM36B12 Mean Well
Observed DCF77 impact	Strong interference blocked sync	Much lower interference
Interference character	Whirr, load-dependent, inverter-modulated	Shorter-range hum
Mains input waveform	Repeated double current spikes	No extra spikes superimposed
Idle behavior	Cyclic current spikes	Current resembles a sine wave
Output noise	Higher ripple/noise	Lower ripple/noise

Key insight: Replacing a noisy power supply usually works faster than adding complexity. If replacement is impossible, a properly enclosed 230 V EMI filter can reduce conducted noise, but it will not fully cure direct radiation from a badly designed adapter.

Quick Facts

A longwave receiver quickly exposed the DCF77 problem source: a replacement SMPS near the ONT, switch, and router, not weak signal from Germany. [#21339333]
Moving a noisy scooter charger about 3 m away from an active TV antenna restored reception, which shows distance alone can cut coupling sharply. [#21339795]
A DIY DCF setup used a 1 Hz LED signal indicator, while a CRT TV only 2 m from the antenna fully blocked reception. [#21342897]
Reported interferers covered several bands and use cases: 225 kHz longwave, 443 MHz garage remotes, TV antenna amplifiers, Wi‑Fi video links, and UKF/FM radios. [#21341525]
High-power equipment can also be involved: one heat-pump case discussed a 9 kW monoblock and the difficulty of filtering currents around 30 A. [#21344182]

How can I find which switching power supply is interfering with DCF77 clock reception using a longwave receiver?

Use a longwave receiver as a sniffer and compare devices one by one. 1. Tune near the DCF77 longwave area and walk the receiver around each adapter. 2. Unplug or swap one supply at a time. 3. Keep the unit that produces the weakest buzz or hum. This method identified a replacement SMPS feeding internet gear as the actual source, while the DCF77 transmitter itself was not the problem. [#21339333]

Why would an EA 10850D1 MW Power supply disrupt DCF77 reception while a GSM36B12 Mean Well supply causes much less radio interference?

The EA 10850D1 showed stronger switching artifacts on both the mains current and the DC output. Its interference changed with load, sounded like a whirr, and its input waveform had repeated double spikes plus cyclic spikes at idle. The GSM36B12 still lacked active PFC, but it produced a shorter-range hum, no added spike train on the input waveform, and cleaner output noise. [#21339333]

What is active PFC in a switching power supply, and how does it relate to input current waveform distortion?

“Active PFC” is a power-factor-correction circuit that shapes mains input current to follow the AC voltage more closely, reducing distortion and improving power factor. In the thread, both compared adapters lacked active PFC, but the noisier one drew a more distorted current with extra spikes. The cleaner adapter also had no active PFC, which shows PFC is not the only factor controlling RF noise. [#21339333]

What is an EMI filter, and how can it help reduce radio interference from plug-in power supplies or LED luminaires?

“EMI filter” is a mains-side suppression network that blocks high-frequency noise from traveling between a device and the 230 V line, usually using chokes and capacitors. In practice, forum users bought standalone modules, inlet-integrated filters, or reused ATX filter boards. One added filter heavily reduced shortwave interference from an LED luminaire, especially by stopping the house wiring from acting like a long antenna. [#21343863]

Mean Well vs MW Power power supplies — which is usually the better choice for low RF interference and cleaner output noise?

In this thread, the Mean Well unit was clearly the better choice. The GSM36B12 Mean Well adapter produced less RF interference, had a more benign input-current shape, and showed lower output noise than the EA 10850D1 MW Power supply. One commenter summarized the practical lesson bluntly: “MW Power is not Mean Well,” after seeing the measurement results and brand confusion in shops. [#21339502]

What do repeated current spikes on the mains input waveform of a non-PFC SMPS indicate about its operation and interference behavior?

They indicate pulsed energy draw tied to the switching stage, not smooth sine-like current consumption. In the measured EA 10850D1, repeated double spikes rode on the mains current waveform and remained visible even at idle as cyclic spikes. That matched the audible whirr on the longwave receiver and the stronger DC output noise, so the spike pattern was a practical warning sign for higher interference. [#21339333]

How should I test a power supply for output ripple and RF noise under load before using it with radios, routers, or sensitive devices?

Test it under a steady load and again at idle. Measure output ripple on the DC side, listen for RF noise with a nearby radio, and compare more than one adapter before installation. One experienced commenter stressed that even reputable supplies can generate surprising “garbage” at the output, and that routers, switches, Bluetooth audio adapters, video intercoms, and radio receivers do not all tolerate that noise equally well. [#21340445]

Which filters can be added externally on the 230 V side to suppress interference when I cannot replace a noisy power supply?

Use a ready-made 230 V EMI mains filter, either as a boxed standalone module, an IEC inlet with integrated filter, or a small board mounted inside the enclosure. The thread explicitly rejected an external active-PFC add-on for single plug-in supplies and recommended filtering instead. The critical condition is safe construction: mains voltage is live, so the filter must be enclosed, insulated, and installed correctly. [#21339793]

How do two-wire Class II power supplies with a C7 'figure-eight' connector compare with grounded supplies in terms of EMI and shielding?

Two-wire Class II supplies can be more difficult to quiet, but they are not automatically bad. The thread noted that many C7 “figure-eight” adapters have no PE connection, and one comment argued that missing PE can worsen interference because the design cannot use Y capacitors to PE in the same way. Another comment added that good topology and shielding still let some ungrounded laptop and DIN-rail SMPS stay acceptably quiet. [#21340342]

What real-world devices most often cause radio and TV reception problems, such as LED bulbs, Christmas lights, scooter chargers, heat pumps, or laptop adapters?

The most frequent offenders in this thread were cheap SMPS adapters, LED lamps, Christmas lights, scooter and battery chargers, CRT TVs, laptops with monitors, heat pumps, shavers, and work-lamp inverters. Reported failures included blocked DCF77 sync, lost TV reception, degraded Wi‑Fi video, interference on 225 kHz longwave, UKF/FM noise, and broken 443 MHz garage remotes. Seasonal holiday lighting was singled out as a major rise in band noise after about 3 pm. [#21353406]

How can I tell whether interference is traveling through the mains wiring or being radiated directly into the air from the power supply?

Check whether a mains filter or physical separation changes the problem. If adding a filter greatly reduces interference, the house wiring was carrying and re-radiating much of the noise. If moving the device several meters away works better than filtering, direct radiation is dominant. The thread showed both cases: a charger needed about 3 m of separation from a TV antenna, while an added mains filter strongly reduced shortwave noise from LED lighting. [#21339795]

What is DCF77, and why are radio-controlled clocks so vulnerable to local interference from chargers and SMPS adapters?

“DCF77” is a longwave time-signal service that radio-controlled clocks decode, using a weak received signal that is easy to mask with nearby electrical noise. These clocks are vulnerable because a charger or adapter only centimeters or meters away can generate stronger local interference than the wanted time signal. In the thread, one noisy SMPS alone was enough to stop sync, while a CRT TV in another room could also block DCF reception completely. [#21342897]

How well do popular HiLink PCB-mount AC-DC modules perform in RF interference and ripple measurements compared with external plug-in adapters?

This thread does not provide measured HiLink results, so it cannot rank them against plug-in adapters. A commenter specifically asked how the popular HiLink soldered modules would perform, but nobody posted ripple plots, RF recordings, or side-by-side measurements. The safe takeaway is narrower: the thread only measured two external supplies, and those results showed large differences even between superficially similar adapters. [#21339502]

What practical alternatives are there when DCF77 reception is poor, such as using a DCF77 Emulator app or building a local mini transmitter synchronized from NTP?

You can emulate DCF77 locally with a phone app or build a local transmitter. One poster recommended a Google Play app called “DCF77 Emulator,” which drives the phone speaker coil; the key limitation is that real DCF77 must be absent, or frames overlap and decoding fails. Another poster said the watch must almost touch the phone, and suggested a mini transmitter synchronized from NTP as the more practical fixed solution. [#21341525]

Where can I place a DCF77 clock or antenna for the best reception when nearby equipment like CRT TVs, routers, monitors, or chargers is generating interference?

Place the clock or antenna as far as possible from noisy electronics and test positions before fixing it permanently. Keep it away from CRT TVs, chargers, routers, laptops, monitors, and LED drivers; in one report, a CRT TV only about 2 m away completely prevented DCF reception. Because many clocks lack continuous signal-quality indication, using a DIY 1 Hz LED indicator or a longwave receiver makes placement much easier. [#21342897]

Generated by the language model.