Questions tagged [rfi]
Use this tag for questions regarding RFI (Radio Frequency Interference).
160 questions
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Building a low-power simple RF frequency (433MHz or 900MHz (but not both)) detector effective at 5m with a 10mW signal
I am looking for a simple schematic for building an effective RF detector which can trigger a GPIO. The goal is to (passively?) detect a 10 mW RF signal (10% duty cycle) and have that raise voltage on ...
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Checklist for QRO remote setup
In a few weeks I'm hoping to set up a solid state linear amplifier at a remote shack that I've set up at the house of a friend who lives in a rural area. I've been connecting to this shack remotely ...
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Receiving an Coded Odd Signal at 137.25MHz but don't know what it might be. It can affect my detection on NOAA 19. Need help
I am a newbie trying to detect NOAA 15, 18, and 19 satellites, which have downlink frequencies between 137 MHz and 138 MHz. I am using an SDR dongle and attached a photo of it to this post.
Of course,...
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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 ...
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RFI from radials
Helping a friend with his RFI problem.
He has a SDR HF radio and Hustler BTV antenna with a toroid choke and about 32-radials. He has vertical bars on his panadaptor around 20 khz apart, mainly on 40M....
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Hunting RFI with bars every 61 khz
I realise there have been many great posts on hunting RFI, i've got pretty close to tracking mine down, but would appreciate some insights from the ham.se experts :)
I've done quite a lot of work to ...
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What is the maximum antenna cable length allowed in GNSS application?
I am beginner in designing GNSS receiver design and facing concern while testing the high precision GNSS survey.I am using GNSS survey grade antenna for my GNSS receiver application testing, the ...
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Do chokes at the antenna feedpoint stop the coax from receiving signals as well, or just transmitting?
It seems common knowledge that a choke at the antenna feedpoint stops the outside of the coax shield from radiating when transmitting into the antenna. But what about stopping the outside of the coax ...
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What kind of RFI is this?
I'm getting a lot of noise now that I have a dipole higher up. The pattern on the waterfall makes it seem man made.
Could it be power line? Or is it some kind of motor?
Here's a short video of the ...
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What is the name of a device used to detect noisy appliances?
I live in an apartment. I don't have control over all of the appliances but perhaps I can mitigate if I know where the noise is coming from and under what circumstances.
If I'm shopping for such a ...
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How Duty cycle affects transmission rate in RF module?
I planning to use RF module for communication of high precision GNSS module. So I am doing detail study on RF module. In one of the datasheets of RF module (part no: RFD868ux) mentioned that 'Duty ...
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Buzzing FM interference
What kind of interference or other receiver issues can cause a constant buzzing noise (picket fence lines in the audio spectrum) in the demodulated audio of a received NFM VHF signal?
With AM, it ...
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Method to generate PIM
I would like to have a go at measuring PIM. ( Passive Intermodulation ) in UHF.
To test my ability to measure PIM, I need to find something that generates PIM.
I either envision a 50Ω device that ...
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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) ...
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The whole neighborhood's internet drops when I transmit on 40M
I recently built a vertical. It's 6M radiator, a coil, and 1.2M more of radiator. It sits on my roof, which is metal, and acts as a ground plane (GND from the feedline is connected to it). There is a ...
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How does FM station have fixed frequency when FM modulation changes the frequency?
I am not sure if this question fits better in physics.stackexchange or ham.stackexchange, feel free to correct me. I am new to studying RF and SDR in general, I was looking up how modulation works and ...
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144Hz monitor with freesync noise on 40m
When I tune on 40 m (7.074 MHz USB as test frequency for there's FT8) and turn on my PC with a monitor that's 144 Hz refresh rate and has freesync on, it starts to make noise and makes signals almost ...
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HDMI to VGA adapter interference with 138.5 MHz carrier
(sorry for my English)
I'm using the HDMI to VGA adapter on my pc, and receiving weather satellites on ~137 MHz with RTL-SDR V3. There was a problem: my VGA adapter creates a powerful signal, who ...
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What causes my direct conversion 80m receiver to receive AM broadcasts?
I am making a Direct conversion receiver from this circuit at this website.
I made it for the 80m band and I changed:
The frequency of VFO to about 1.75 MHz
L1 and L2 to a bandpass filter for 80m
...
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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 ...
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What are the most common EMI blockers for household computer cords, monitors, etc.?
Ferrite beaded cords, and especially double-sided ferrite beaded cords, seem especially uncommon. Are there other, perhaps more effective ways, which I should be minimizing the EMI of my overcrowded ...
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Will my neighbor's amateur RF antennas effect my own utilities?
I am buying a house in the UK and the property next door has two poles for antennas.
The next door lady seems to be very nice person and said her husband is an RF engineer and he used these on ...
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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 ...
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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 ...
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New quad-band mobile receives while transmitting?
I've got a week-old TYT TH-9800, a quad-band (10/6/2/70cm) mobile, Chinese knock-off of a Yaesu HT-8900. So far, I love it -- several times the power of my HT, and a better antenna actually outside ...
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Audio being sent over ground pin on audio jack
I just bought a QYT KT-8900D mobile radio. One of the first things I've noticed is that I cannot use my mixer to completely lower the volume of the radio's 3.5mm TRRS output. When the fader is all the ...
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Can my neighbors ham radio station be preventing my TV antenna from proper reception? [duplicate]
I have a winegard 8200 series antenna and it worked flawlessly in getting me reception of more than 70 stations. The wind blew it down and I couldn't replace it for about 6 months due to the fact that ...
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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 ...
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Should I run RG8x / mini8 zip tied to a cat 5e ethernet cable?
I'm running a feed line from the end of my amplifier to the antenna for HF transmissions. I'm using RG8x / mini 8. There's an existing pathway through my house I'd like to use that has a cat 5e ...
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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 ...
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Tips for HF Antenna with house near AM transmitter
My back garden is very small - about 500sqft. I also live near an AM transmitter and requires an AM filter. I would appreciate some general tips on the best approach to receiving HF signals (Ham and ...
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Where does this common spurious transmission come from? Is there a quality difference?
I decided to see what my ham transmissions look like on an SDR and was kind of shocked to see how much leaks out. The waterfall display is split between two handhelds during transmit. There are a ...
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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. ...
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Can an indoor antenna damage unshielded electronics?
I have a 25w radio running through a ~4.5db gain antenna. If I use a 4W HT indoors, I can hear a loud buzzing noise emmanating from my computer speakers.
If I used the 25w mobile with the 4.5db gain ...
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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 ...
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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 ...
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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 ...
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High Noise Floor on 40/80m at Night
I've notice a couple of times over the past couple of weeks that the noise floor, particularly on 40 and 80, is exceptionally high as the grayline passes me into night. I'm looking at the general band ...
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What's the Noise Floor?
What's the noise floor according to this picture?
Is the noise floor S5 as it shows in the Signal meter at the top right or is it S1 as it shows on the panadapter?
The reason why I ask is I'm trying ...
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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 ...
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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 ...
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What can I do about my strong RF noise?
I have a problem with strong and constant received noise, from S7 to S9+20.
I've shut off the power, both in my house and two neighbors' houses.
I took my portable rig with a Hustler antenna and ...
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What has happened to HF?
Has the HF spectrum become noisier over the decades due to man-made interference? Is this a reason why HF band activity appears to be declining?
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What is this odd data/screeching/fuzzy signal?
I was listening to a commercial FM radio station on 100.9 MHz, and this intermittent weird sound kept coming through it.
Here is a recording of it. The audio starts at about 15 seconds.
It sounded ...
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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 ...
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Benefit to remote antenna tuner for end-fed non-resonant antenna?
Does addition of a remote feed-point antenna tuner affect the use of the coax braid as a radiator? If it no longer "radiates" in such a setup, what does? Is a shack or remote tuner better for ...
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How do active loop vs. passive loop differ in terms of noise rejection?
As a urban ham (Harvard Square, Cambridge MA), I'm on the hunt for RFI rejecting antenna configurations. After hours of research, I've come across many strong recommendations for loop antennas, since ...
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Interference difference: fixed and mobile wireless systems
I am answering some questions about my course of radio links and I came across with the question about explaining interference in fixed and mobile wireless systems. As far as I know ALL wireless ...
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How should I measure RFI on the headset cable from a hand-talkie?
I'd like to build an audio interface cable from my smartphone to my Yaesu FT-60 which incorporates VOX (since the Yaesu doesn't have VOX functionality) for APRS apps on the phone.
I'm having problems ...
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Can jamming a channel with white noise be detected?
If somebody were to setup a pirate radio signal that was broadcasting static would the people tuned in to that frequency be able to tell?
Assuming that there was nothing already on that frequency ...
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