Questions tagged [rfi]

Use this tag for questions regarding RFI (Radio Frequency Interference).

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35 votes
14 answers
37k views

Can my neighbor's ham radio antenna be interfering with my internet signal or is my internet provider just throwing blame elsewhere?

My internet provider is telling me that an antenna on my neighbor's house, which he called a ham radio antenna, is interfering with my DSL internet signal. I'm not tech savvy at all, beyond what's ...
  • 351
31 votes
6 answers
37k views

Can I reduce RFI/noise at the antenna?

Recently, the power was out in my neighborhood for an extended period of time. I fired up my HF rig using battery power and was amazed at the lack of noise across the HF bands. When the power grid ...
20 votes
2 answers
12k views

How to detect common-mode currents or “RF in the shack”?

Let's say we already know that if your antenna is not suitably constructed or connected then you can get current on the shield of your coaxial feed line which will flow through the shielding/grounding ...
  • 23.4k
13 votes
3 answers
9k views

How do I prevent radio signals from tripping a GFCI?

My wife woke up several nights by a metallic "thunk". It happened to be while I was talking on 10 meters and turned out to be the ground fault circuit interrupter (GFCI) on her hair dryer cord. ...
11 votes
2 answers
4k views

How to reduce RF in the shack when using vertical HF antenna (no radials)

What can be done to reduce RF in the shack (riding back along the coax) when using a vertical 10M antenna (without radials due to space constraints)? The antenna is an IMax-2000 at 32' elevation (20' ...
11 votes
3 answers
4k views

How can I get rid of RFI coming from my house solar panel inverter?

The solar system on my house creates horrible rfi on all hf bands during the day when the sun is out, it goes away when it's not sunny. Any one got any ideas how to get rid of the rfi ? I already ...
  • 3,550
10 votes
4 answers
5k views

Real world performance of magnetic loop antennas?

I was investigating about magnetic loop antennas. In a paper about them I found some bold claims: and This almost sounds too good to be true, considering a lot of us hams are surronded by city noise ...
  • 1,179
10 votes
3 answers
3k views

My neighbor is complaining about my transmissions, what can I do?

My neighbor has indicated that they can hear noise from their computer amplified speakers when I'm transmitting. We've done a few tests and it does appear that it's my transmitter that's causing the ...
10 votes
4 answers
465 views

How to operate on HF if an AM transmitter is only 540 feet away?

I'm a General Class Licensee, and due to pulmonary disease I cannot operate voice. I am also about 540 feet from a 24/7 1 kW AM station. The signal is so pronounced that most audio devices in the ...
  • 101
9 votes
3 answers
1k views

Attic Dipole - Impact of Ethernet over CAT5/6

I've been thinking about putting 20m and 10m dipoles up in my attic (HOA), but I also intend to soon put some Ethernet cable to a WAP (with PoE) through the attic. I was intending to feed this with ...
  • 773
9 votes
3 answers
17k views

How can I reduce the noise coming in from an RTL-SDR dongle?

I've recently received an RTL-SDR dongle, and I'm picking up a lot of noise that is probably coming from my PC, especially a lot of "spikes" on the 2M band. I've already started using a USB extension ...
8 votes
3 answers
2k views

What is the proper way to ground your station's antenna?

I don't understand how you would go about giving an RF ground to your antenna. Would it not become an additional radial and affect the signal? What is the proper way to ground your station's antenna?...
8 votes
1 answer
186 views

Identifying regulations for interfering stations

I'm working on tracking down some 2m repeater interference, and I have identified that the offending signal is a spur transmission on a commercial pager service (that lands right on our repeater input ...
  • 1,881
8 votes
1 answer
117 views

S Parameters in HFSS

I'm new to HFSS Software and I'm trying to plot Scattering parameters for a dielectric resonator excited by a probe (shown in image). I know that the top cylinder has a higher dielectric than the ...
  • 81
7 votes
3 answers
5k views

Is 20m noisy, or do I have a lot of local interference?

I'm making my first ventures into HF with a Yaesu FT-450D and a homebrew 20 Meter inverted-V antenna a local ham helped me set up. I've noticed that the 20 Meterm band seems to have lots of ...
7 votes
2 answers
3k views

Understanding coax radiation and "current on the shield"

I'm having trouble understanding what seems to be the fundamental principle behind baluns (and probably other related topics). Perhaps some of my confusion comes from an audio background, where one ...
7 votes
2 answers
171 views

Apps and or equipment needed to document local interference?

A neighbor ham user recently started doing something that causes very noticeable feedback/buzzing in AM radio as well as any device that uses a wired microphone (such as a gopro with wired mic). ...
  • 171
7 votes
4 answers
1k views

DIY SA612 + RTL-SDR HF receiver: good on laptop, but huge wideband noise on Raspberry Pi

I recently built a SA612 mixer for HF reception. I used an USB-frequency oscilator to shift the incoming frequency up by 28.8 MHz. I used a random wire antenna outside my balcony and connected it to ...
7 votes
1 answer
528 views

Super-low-tech VHF low-pass filter construction?

Related to this question: Is it legal to broadcast an FM radio signal with a Raspberry Pi Zero? Is it possible to build a super-low-tech low-pass filter for VHF harmonic suppression without a PCB or ...
  • 12.8k
6 votes
3 answers
2k views

Noise & shielding, SDR Dongle

First, I'm very new to SDR. This may turn out to be really obvious. I just want to verify my thoughts before I spend more dollars. I have a USB dongle with the RT28xx in it. Works great. Side by ...
  • 909
6 votes
2 answers
5k views

How would operating a ham radio affect other wireless devices in my house?

I am interested in getting into ham radio however one of my concerns is could a ham radio affect current wireless communications in my house. I am particularly concerned when it comes to WiFi signals. ...
  • 225
6 votes
3 answers
1k views

"Coaxial capacitors in line” in E4E04?

I've been studying the U.S. license examination question pools. For the most part, it is reasonably obvious what the questions and answers mean even when I am not yet able to come up with the answers ...
  • 23.4k
6 votes
2 answers
1k views

Feed-through Capacitors

I'm in the "information gathering" phase of a RF Power Meter project and the design I fancy (W7ZOI Power Meter) calls for a feed-through capacitor at the output port. I understand that a feed-through ...
  • 967
6 votes
4 answers
28k views

Advantages of using Digital Code Squelch

I am trying to decide whether or not I should use a CTCSS (Continuous Tone-Coded Squelch System) or a DCS (Digital Coded Squelch) for my mini repeater I just set up. What are the advantages of using ...
  • 7,500
6 votes
2 answers
98 views

Can an ultra-wideband system transfer data at high speed without precise clock synchronization?

Recently, ultra-wideband technology has been in the news again. From the Wikipedia article: UWB transmissions transmit information by generating radio energy at specific time intervals and ...
6 votes
2 answers
654 views

Choosing capacitor for high-pass filter with cutoff of about 160 MHz

A strong (100 kW) local FM transmitter causes interference to or overloading of receivers in the VHF/UHF bands. It seems like a single, properly chosen, capacitor could make an effective passive high-...
  • 163
6 votes
3 answers
2k views

How to stop interference on shortwave radio when connecting to a computer

I have a Tecsun PL-600 and when I can receive clear signals, and they come through just fine on headphones, and through the speaker. If I'm trying to receive RTTY or fax, when I connect the radio to ...
6 votes
2 answers
3k views

Do ethernet-over-power adapters interfere with radios?

I remember not long ago seeing a lot of chatter in the ham community about large-scale "Broadband over Powerline" (BPL) systems causing harmful interference across several bands. Does similar ...
  • 161
6 votes
1 answer
666 views

FM radio in car gets interference from APRS beacon

The FM broadcast radio, factory installed in my car and usually tuned to 88.6 MHz, gets some interference from the 5W APRS transmitter on 144.800 MHz. It sounds like if the sensitivity of the ...
  • 2,351
5 votes
5 answers
5k views

HF Noise Level S5 to S9+18

Since I got my HF radio a year and change ago, I've been able to hear very little except noise and the WWV time station on 10MHz. Noise seems to vary by band, but not how I'd expect: 80m: S7-S9 40m: ...
  • 773
5 votes
5 answers
832 views

Signal path to maximize RFI rejection in an urban environment

Urban ham here (Cambridge, MA - FN42ki - KC1JZE) looking for tips to make this hobby possible in the city. I rarely can hear both sides of HF phone transmissions, and have yet to make contacts despite ...
5 votes
2 answers
2k views

What is the purpose of limiting radio output power?

According to article 25, section I, § 4 (25.7) ITU's Radio Regulations: The maximum power of amateur stations shall be fixed by the administrations concerned. In my country this is 500W for CEPT ...
  • 153
5 votes
2 answers
102 views

How does a digital demodulator know which level it is reading?

I have recently started getting into wireless digital communications and I read about QAM modulation. But I am a little confused as to how the receiving demodulator would know which symbol it is ...
5 votes
1 answer
510 views

Can my laptop pick up CB radio frequencies?

I was on my laptop watching a show and I paused to look something up and since there was no sound I could hear a voice talking. It sounded distorted like it was coming over a radio and I couldn't make ...
5 votes
1 answer
2k views

How to find something disrupting car key fobs across a parking lot?

Apparently there's a parking lot in which car key fobs are messing up: Key fobs that suddenly won't unlock vehicles. Cars that won't start. Alarms that go off for no reason and can't be quieted. ...
  • 153
5 votes
3 answers
2k views

Is this the Correct Ferrite Core to Reduce RFI as a Common Mode Choke?

I have a Flex 3000 connected via RG-11 coax to a inverted V fan dipole tuned for 40m and 20m on my roof. I have an "ugly" balun up on the mast by the antenna. I further have the feed-line going into a ...
5 votes
3 answers
877 views

Only noise, no signals whatsoever on HF

Last night there was a power outage at home. I was able to see a LOT of stations on 20M (FT8). As soon power returned, all of them disappeared. You can see in the waterfall very clearly when power ...
  • 1,179
5 votes
2 answers
220 views

Will a HF beam antenna on rooftop building interfere with other antennas there

I am moving into an apartment on the top floor of a building and I intend to install a HF beam antenna for 20 to 10 meters, on the rooftop of the building. I notice that there are already some ...
5 votes
2 answers
845 views

Using an SDR on a Laptop with Noisy Power Supply

I'm going to start this off by saying I'm very new to this and I don't really know a lot so any detailed information would be much appreciated. I have just started using an SDR (a cheap RTL model) ...
5 votes
2 answers
354 views

Eliminating RFI from raspberry pi

I am trying to eliminate RFI coming from a raspberry pi 4. The Rtlsdr(enclosed in a metal case) is directly plugged into the pi without any USB extension cable. The frequency of interest is at 1420....
5 votes
1 answer
144 views

OK for S/RF light to be illuminated at engine idle?

I just installed a mobile CB (Uniden) into my Jeep. When the key is in auxiliary (car off, accessories on) and the squelch turned all the way down, no S/RF lights are illuminated and the background ...
5 votes
2 answers
1k views

How to choose right inductors for a matching circuit

I would like to chose an inductor to make a matching circuit. Operating frequency is 6.1 GHz. I am more concerned with self resonance frequency and Q of an inductor. Would an inductor with SRF > 7 ...
5 votes
2 answers
581 views

Wide band TX capable band-pass filter for VHF and Airband

I want to share the same antenna for VHF (TX/RX 144-148 MHz) and for Airband RX-only (116-136 MHz). I live on a very congested area where filter is a must, so I'm looking for the best solution for my ...
  • 51
5 votes
1 answer
630 views

How can I counter DC-DC inverter noise / ground noise in an electric-vehicle mobile setup?

So, I'm relatively new to all this; and I've gotten an ICOM IC-7100 on sale, which looks like an excellent transceiver … unfortunately, this very specific line shows up in the manual: The ...
4 votes
6 answers
669 views

Cordless phone consistently experiencing RFI

I've tried several cordless phones (most recently KX-TG570), and all seem to frequently pick up terrible RF interference. I have a neighbor that is a ham enthusiast, with large antenna masts on the ...
  • 41
4 votes
7 answers
1k views

QRN: How to chase down a solid S9 noise floor on 40m only

I am new to this, having just set up my station. I have "very bad" QRN on 40m: S9. Here is the setup: High density suburb with flats and houses Yaesu FT450D with fan dipole at 6m-9m above ...
4 votes
4 answers
869 views

My radio in the garage is temporarily shutting down the wifi when I key up

I have a Yaesu FT-101EE, D-104 Mike, MFJ-929 Antenna Tuner, 80-10 OCF Dipole Antenna with a MFJ balun. When ever I key up for more than a few seconds, the wifi network goes down for a couple of ...
4 votes
3 answers
918 views

Suggestions for mounting a mini-whip as high as possible

I've ordered two mini whip antennas from Ebay (Russia) for HF and MW. As power lines cross my city property in a L shape - the only way to get away from them is to go up. So I'm hoping that going 5-...
4 votes
1 answer
913 views

Cellular VHF Interference

I just got my license a week ago. Installed a new VHF/UHF radio in my car and everything seems to be working great. I've been heard at distant locations and picked up signals from repeaters that are ...
4 votes
1 answer
499 views

How to avoid Bluetooth intereference?

I'm thinking about dropping a bluetooth module into my Softrock receiver so I can use it with my computers and portable devices wirelessly. The receiver runs from 1.8MHz to 30MHz, and the bluetooth ...