Questions tagged [rfi]

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

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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
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 ...
0 votes
1 answer
86 views

How does inductive coupling between transmitter amplifier stages reduce harmonics

In some notes on transmitters I have found the statement that "inductive coupling between transmitter amplifier stages reduces the generation of harmonics", with no further explanation. Can anyone ...
2 votes
3 answers
616 views

Can you jam jam?

Is it possible to jam the jammer signal, to disrupt its jamming of the owned RF signal?
2 votes
4 answers
700 views

Measuring a device's 2.4 GHz RF signal in an open field/indoors

How can I measure/what instrument should I use to identify/measure the RF signal strength in a "noisy" environment? For example, I want to measure the RF signal strength of my device at a particular ...
  • 121
3 votes
1 answer
567 views

What might this "spreading" interference be?

Any idea what might be causing this signal to appear in the "panadapter" spectrogram of my Omnia SDR around the 40m band? Every twenty seconds, I get a strong "focused" signal that then rapidly ...
0 votes
2 answers
186 views

How can I find out if a particular LED light bulb model is known to cause RFI before buying?

With «green» electricity bills amounting to ever more greenbacks, I am in the process of gradually replacing my incandescent light bulbs with LED light bulbs. However, my efforts met with mixed ...
  • 1,277
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 ...
1 vote
1 answer
131 views

Transmitter won't transmit with antenna installed

I built a node for my friend out of a baofeng BF-888s UHF transceiver. I am powering the radio with a voltage regulator, and a few caps with a wall wart power supply. The radio will transmit fine ...
  • 7,500
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
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
3 votes
4 answers
3k views

Why did I lose my FM radio signal?

My lady and I were driving on the interstate recently when we noticed an unusual phenomenon. We were listening to the radio (an FM signal), and only over a couple of bridges did we entirely lose our ...
  • 133
1 vote
2 answers
549 views

Inverter noise on my signal

I recently built a sound card packet TNC and it is working fine under my standard laptop power supply when I hook it into the wall. When I plug my computer in via a car inverter (12VDC to 120VAC), ...
  • 7,500
2 votes
1 answer
205 views

Computer cables in shack — what to do with them?

What should I do with all the cables connecting this to that? Coiled, folded, cut-to-length, wound on ferrite? Anyone have the definitive answer to this? My rat's nest is getting more messy. The ...
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
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 ...
2 votes
1 answer
445 views

Low frequency noise on ground line. Why?

I'm currently experiencing what I think is induced coupling on my ground line. Can someone explain how this is possible? I live on the third floor of an apartment block and my only grounding option ...
  • 23
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 ...
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
3 votes
1 answer
1k views

Steps for eliminating RF interference

I built a little USB dongle I put on my radio. This dongle interfaces audio and PTT to my radio so it can use AllStar link. The problem is interference. When the radio transmits, I heard a high ...
  • 7,500
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
2 votes
2 answers
5k views

How to eliminate alternator whine?

On my car's LW receiver, I have a severe case of alternator whine, especially when the headlights are on. It has become worse over time. I have read that capacitors might help. However, two things ...
  • 1,277
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
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
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
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
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 ...
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
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 ...
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 ...
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 ...
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' ...
3 votes
2 answers
361 views

Do electronic ballasts for fluorescent tube lamps cause HF interference?

I am going to build a new home and I would like to use energy-saving fluorescent tube lamps in some rooms. Manufacturers are currently pushing electronic ballasts a lot in favour of switchstart series ...
  • 1,277
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
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?...
2 votes
1 answer
124 views

Interference generated by antenna placement?

I'm thinking about putting up a 80m dipole in the back yard, the only place I have to put this (can't do inverted V since I don't have a high enough location) is close to a overhead telephone wire. ...
  • 817
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. ...

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