HFU HF Underground
Technical Topics => Equipment => Topic started by: NJQA on March 04, 2022, 1251 UTC
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Some noise sources you might not suspect:
https://youtu.be/ewcemoXLzcU
I use switches like this to turn off noisy items (like my Keurig) when I am not using them:
https://www.amazon.com/Oviitech-Grounded-Outlet-Adapter-Indicator/dp/B0747N2Z66/ref=sr_1_4_sspa?
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Some noise sources you might not suspect:
https://youtu.be/ewcemoXLzcU
I use switches like this to turn off noisy items (like my Keurig) when I am not using them:
https://www.amazon.com/Oviitech-Grounded-Outlet-Adapter-Indicator/dp/B0747N2Z66/ref=sr_1_4_sspa?
Unfortunately, there are way too many noise sources in my home, and probably most homes for that to be practical.
If your antenna is on your home or close to it, you have a multitude of single frequency and wide band noise sources to content with... and of course, then there are your neighbors. I had a reminder of this recently during an ice storm that hit here a couple of months ago. A wide spread power outage gave me a chance to do some DX'ing with my trusty Icom 705 on battery power. WOW..... SO QUIET!!! it was unbelievable 8) You can certainly do that in your own home by throwing the main breaker but when the entire area is out... that's a real "local noise test"
So what's the solution? I gave up years ago in the fight to locate and eliminate all my local noise sources. I discovered an easier way to a lower my noise floor was to use one of the noise cancelling phasing devices. This is a device that goes between your main antenna and receiver. There is a "noise antenna" input that you connect to a shorter wire very close to your house. I use an 8ft piece of wire taped vertically against the side of my house. The idea is noise that arrives on your main antenna AND the noise antenna (local noise) can be phased out sometimes almost completely. It's amazing, it works. There are some disadvantages like it has to be re-tuned when you make a big change in frequency... Having several noise antennas to choose from makes it really effective.
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Getting back into the hobby after a few years, I found many sources in my house and neighborhood. I found dimmable LED light bulbs are much more noisy than non dimmable ones. The non-dimmable LED version are tolerable if you can keep 3 feet or more from your antenna. The four foot LED light fixtures, which are replacing older fluorescent ones are terrible. My solution keep them off during listening sessions. Most portable computer supplies are very bad. I had to use several clamp on ferrite cores to tame mine. USB phone chargers and some tablet chargers are very bad. I went through all of mine to find the lowest noise ones.
A real surprise was my neighbor's solar panel installation was a major source of HF noise. The good news for me, I found a location far enough away from the power lines for my HF antenna, which minimized the noise pickup.
Most of the high efficiency power supplies are great EMI generators. Part of the problem is the FCC has decided that those devices have no radiation limits for frequencies less than 30 MHz. Now you know why the medium wave and short wave bands are so noisy.
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Hi Finman -
I live in a tall building and have a high level of disruption.
Shielded antenna cables, grounding cables, ferrite rings, power filters do not help much.
Your method is probably the only good solution to the problem!
Write something more closely about how you couple the antennas together, how you phase them, and how you adjust the attenuation level.
Thank you in advance on behalf of all the oppressed!
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Hi Finman -
I live in a tall building and have a high level of disruption.
Shielded antenna cables, grounding cables, ferrite rings, power filters do not help much.
Your method is probably the only good solution to the problem!
Write something more closely about how you couple the antennas together, how you phase them, and how you adjust the attenuation level.
Thank you in advance on behalf of all the oppressed!
Hi Chris;
Glad to help!. here's a few links to some of the available noise cancelling phasing units.
https://www.dxengineering.com/search/part-type/antenna-phasing-and-noise-cancelling (https://www.dxengineering.com/search/part-type/antenna-phasing-and-noise-cancelling)
https://www.hamradio.com/detail.cfm?pid=H0-002235 (https://www.hamradio.com/detail.cfm?pid=H0-002235)
https://www.ka6wke.net/projects/hf-noise-reduction (https://www.ka6wke.net/projects/hf-noise-reduction)
There are more of these devices than are listed in these links. There was a kit being offered on E-bay a while back but it's no longer available. I only have experience with the MFJ-1026 and the Timewave ANC-4. Download the manual for the MFJ unit, that will give you a better idea of what's required for an install. You basically adjust the Main antenna gain, the noise antenna gain and phasing controls while you watch your S-meter (or just listen) to null out the noise. You will need to experiment with different noise antennas to get the best results.
I plan on homebrewing a design based on some online ideas (like the one below) once my new workshop is completed but for right now, the MFJ-1026 works well in my temporary shack.
https://www.qsl.net/va3iul/Receiver_Noise_Canceller/Receiver_Noise_Canceller.htm (https://www.qsl.net/va3iul/Receiver_Noise_Canceller/Receiver_Noise_Canceller.htm)
Hope that helps
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Hi Finnman - you are great! You gave me a great interference eliminator solution, even with PCB drawing! Thank you so much !!! I understood everything immediately. I have no clear idea of the origin of the disturbances in my environment. For example, I was surprised by the fact that sometimes a broadband dipole suspended 35m above the ground picked up more noise than a large Sky Loop hanging from trees 8-12m above the ground.
I explained this to myself with the different directional characteristics of the leaflets, hence it can also be concluded that some of the disturbances come at a small angle from distant regions. I checked it by changing the antennas, which significantly weakened the signals of the annoying but distant OTH radars.
Autumn and winter storms have damaged both of these large antennas, but in the spring I will rebuild the Sky Loop with a circumference of about 200m suspended from trees, and a smaller circumference of about 140m on the roof. I am very convinced of SL antennas, they have a wide reception range with a flat SWR below 2, low noise and high signal level. Better for SWL-ing is just Beverage,but you must have a farm outside your window.
Stay healthy!
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I'm waiting for somewhat drier weather, but before the Spring growth goes crazy, to lay out the W.O.G., (Wire On Ground.), RX'ing Antenna. I have everything I need together for that project, but now waiting upon Mother Nature to cooperate. Getting away from the house isn't enough, but I also need more distance away from the power lines, outside the house.
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Hi Chris;
Glad it was helpful. Yes, depending on frequency, some of the interference you're receiving may be a distant groundwave signal. Again, a selection of different noise antennas with different polarity, direction, would improve your ability to null interference. A very small rotatable loop or mini dipole would also be great, I may try that in the future. 8)
Back in the early 1980's when I lived in NY, i homebrewed a rotatable ferrite stick dipole active antenna for MW DX'ing.
...enabled me to pull in the BBC on I believe it was 838khz.. still have the QSL somewhere.
... another idea for a possible noise antenna
Hi Finnman - you are great! You gave me a great interference eliminator solution, even with PCB drawing! Thank you so much !!! I understood everything immediately. I have no clear idea of the origin of the disturbances in my environment. For example, I was surprised by the fact that sometimes a broadband dipole suspended 35m above the ground picked up more noise than a large Sky Loop hanging from trees 8-12m above the ground.
I explained this to myself with the different directional characteristics of the leaflets, hence it can also be concluded that some of the disturbances come at a small angle from distant regions. I checked it by changing the antennas, which significantly weakened the signals of the annoying but distant OTH radars.
Autumn and winter storms have damaged both of these large antennas, but in the spring I will rebuild the Sky Loop with a circumference of about 200m suspended from trees, and a smaller circumference of about 140m on the roof. I am very convinced of SL antennas, they have a wide reception range with a flat SWR below 2, low noise and high signal level. Better for SWL-ing is just Beverage,but you must have a farm outside your window.
Stay healthy!
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Samsung refrigerators with "Digital Inverter" create spurs all across HF, also large flat screen TV's are another source, some even generate noise even on "stand-by" mode.
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I wanted something a bit bigger for sdr work as far as monitors go so replaced the smallish 1280xWhatever monitor with an hp w2207. OMG the birds this thing has around prime pirate hunting grounds! And not just has from the wobbly switching supply but s5 steady carriers every few kc. Guess it's back to small dual monitors with less noise than a nice fat one that emits from dc to daylight. To check if yours is bcasting, just shut the monitor off while listening to the spectrum of interest.
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I live in a small block of flats & over the years I have noticed more noise on the LF & HF bands. Some of the threats could be HDTVs, wi-fi routers & any unregulated electronics bought online. An example is from around 8500 kHz to 12000 kHz I can see a very high noise floor on my SDR which is there 24/7. When I go outside to the small garden outside my block of flats with my portables the noise is still there. I know they have changed some of the street lighting in the vicinity from the amber type to the white ones which I presume are supposed to be more economical, & around then I noticed more noise although whether that is the cause I don't know.
But it is not only on the lower bands I get noise, I have noticed more starting to appear on the FM band as well. Sometimes I see random noise spikes lasting a few minutes from 65 to around 95 MHz. Again, I can get the same noise outdoors with my portable radios. One suggestion for the cause are solar panels which I am seeing more of on top of buildings in my neighbourhood & further down the road. It seems analogue radio really is at threat from new technologies.