Another QRM Nightmare #airspyhfplus #sdrconsolev3


David Jackson
 

Referencing attached picture; top section is my antenna and bottom half is KA1GJU's.

I get this 'curtain' of wideband RFI starting at (fading in) about 7mhz and continuing down all the way through the AM BC band, down to DC.
I have attached a screenshot and am providing a link to a 124Mb mpeg video (recorded with Win10's embedded video recorder as SDRC's 
video recorder "cannot be initialized on this hardware.. error (-10). Just throwin that out there for Simon, I don't even care, It's an Asus GTX860M 
DX11 GPU and every other single video transcoding thing work with it soo... not a feature I use or care about either)

ANYWAY

Here's the Google Drive link for a brief (1:40ish minute) video doing a great trip down the band from where it starts, with a bit of audio (ignore the 
scanner traffic, it's a web page feed, unrelated and only a few seconds in 2 spots): https://drive.google.com/file/d/1Rqem5XXAlo9gysJrN5XE3ngIH9IhxVLD/view?usp=sharing

Note that this RFI is present with very little variance in intensity at all times of the day and whether or not I've powered off the house by switching off all the breakers.
It is also present whether directly attached to the PC or remoted via SDRC server and whether it is grounded or not. Originally it crept up into the 40m band but increasing
height appeared to "shift it down".

Description of my installation:
Airspy HF+ => LDG 1:1 current balun => 30 feet 5D-FB coax => LDG 9:1 unun => 150 feet 18AWG CCA wire.

50 foot counterpoise parallel to antenna wire, approx. 3' AGL and coax shield ground from unun to mains ground (not ideal I know, the RFI is there whether or not it is connected but the ground connection significantly improves reception from 40m down and disconnecting improves 20m reception).

Antenna slopes from feedpoint approx. 8 feet AGL to 25-30 feet in a tree and makes a 45' bend to the right sloping backing down to about 15' AGL (for the last 30 feet or so after the bend).

Is it the season? Last September, with an RTL-SDRV3 and just a homebrew UNUN with that 3 meter RG174 extension cable and the antenna at maybe 10' AGL, I had a very clean waterfall, nothing like that curtain of RFI presenting at all between 6Mhz and 8.35Mhz but appears in December (based on I/Q recordings I have from Sept. and Dec., very low noise floor, S0 and S9+ plus signals).

Is it the length? Too long or too short? Or the counterpoise? Would an isolated 8' copper ground rod kill it (the RFI)?

Is it my location? Perhaps someone has grow lights? Does it look like that to anyone?

I'm stumped, other than seeing mild success with raising the height of the antenna, I don't know what else to do.

Something I haven't tried is recreating the setup (the homebrew, the RG174 and the RTL) from September and doing a comparison, but I need/want the current gear to work. Eventually I want to drop an IC-7300 on it but no way am I spending that kind of money to not be able to use it below 40m.

Any help, pointers, advice, etc would be so welcome. Thank you all. 


Larry Dodd
 

David
It could possibly be an AC power line issue. A bad transformer or bad ground. In warmer weather it may expand and become worse. A call to your power company could be worthwhile to have them check it out. If it is something like that they want to know because it means they are losing power and they will fix it.
Larry

On May 3, 2020, at 12:11 AM, David Jackson <djackson1225@starkstate.net> wrote:

approx. 3' AGL and coax


Stu C <stu@...>
 

A bit of AM audio (background no signals) may help people on here.
To me the repeating signature in the noise does point to a local source but the spread and uniformity does not seem like data or even clean switchmode.
Could be a plasma but if it is on all the time less likely. Plasma TV's show that sort of noise but modulated on scene so often change baseline level on the hour (for example).
Grow lights as you say are a strong maybe, thermal camera anyone?

Here I get to know the individual sources by audio and Mag-loop null.
If you have something you can receive HF with on with a small physical antenna then I'd hold it close to the body and walk round the area under your antenna then back to the receiver.
Headphones on, white noise only, no signals, and  now and then spin round slowly.
If you try that spend a good bit of time looking for a signature (modulating) noise (frequency) that separates the QRM from normal background.
Obviously note where where it is stronger, but also where your body or buildings, vehicles etc. blocks it.
It might be overhead power lines or a transformer, signal level over the day may help on that front.

73 Stu


Brent Seres/ VE3CUS
 


It could be AC powerline.  When I worked for Department of communications years ago we dealt with all kinds of power line interference issues. In many cases, it was loose hardware on 27 kv and 44 kv lines. The noise would propagate further as you went lower in frequency. 

Several clues :
Does the noise diminish when things are wet? Although it might seem counter intuitive,  wooden poles would swell slightly in wet weather,  and the hardware would tighten up and the noise would be reduced or absent.

If you have a nearby hv line, drive down it with the car radio tuned to the top of the AM band and see if you hear any increased buzzing at a specific location. If you have a wideband receiver, you can zero in on the location be progressively increasing frequency. 

Not recommended for the layman (people will think you're crazy and you might get arrested), but we carried a big wooden mallet in the vehicle.  When we thought we found the spot, we would hit the pole with it, and listen for variations in the noise.

As someone else mentioned   if you find it, call the power company. 


Sent from my Samsung Galaxy smartphone.


Kriss Kliegle KA1GJU
 

I was hoping to hear the 'real' sound of the RFI at 0:52, but the NR4 was on and (as usual) it sounds like its under water. LOL

Questions/comments going forward:
1) Where are you? No call sign in your post to even guess. Closest neighbors are how far away? Industrial park nearby?
2) Connecting to service entrance ground can introduce QRM from devices in the building. I have success with a just a half of a ground rod (4') at the Unun.         Gives me 1-S unit of noise floor reduction on the lower bands.
3) The LDG 1:1 Current balun? You have balanced line in there too? Are you sure that's not a typo and its an 1:1 unun?


4) Did you try RXR'ing w/o the counterpoise? There's some info on the last page of this file, but some of it contradicts what worked for me:
https://www.balundesigns.com/content/Wire%20Lengths%20for%204%20and%209-1%20ununs.pdf
Such as unun at just a few feet above ground and grounding the ground stud of the 9:1 unun (physically connected to coax shield BTW)

5) Can you remotely post some IQ recordings (as to not flood the inbox of the complainers here using 1200baud AOL service) and allow us to hear some of the affected bands?


Tom Crosbie G6PZZ
 

Brent has just reminded me of something else: Make sure of your ground connections. If you are using earth rods outside, water them regularly to maintain a good connection. We often forget about this in the UK because it rains every other day (!) but in a hot, dry climate it becomes important. A friend of mine Told his wife one summer it was about time they invested in an irrigation system for their vegetable patch. It would be gravity fed mainly from rain water collected from the roof.  She agreed but didn’t notice when he started lifting slabs to run pipework underneath to “water” his earth rods. Together they grow fruit, veg and salad plants and the DX keeps rolling in.

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Brent Seres/ VE3CUS
Sent: 03 May 2020 11:49
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] Another QRM Nightmare #airspyhfplus #sdrconsolev3

 

 

It could be AC powerline.  When I worked for Department of communications years ago we dealt with all kinds of power line interference issues. In many cases, it was loose hardware on 27 kv and 44 kv lines. The noise would propagate further as you went lower in frequency. 

 

Several clues :

Does the noise diminish when things are wet? Although it might seem counter intuitive,  wooden poles would swell slightly in wet weather,  and the hardware would tighten up and the noise would be reduced or absent.

 

If you have a nearby hv line, drive down it with the car radio tuned to the top of the AM band and see if you hear any increased buzzing at a specific location. If you have a wideband receiver, you can zero in on the location be progressively increasing frequency. 

 

Not recommended for the layman (people will think you're crazy and you might get arrested), but we carried a big wooden mallet in the vehicle.  When we thought we found the spot, we would hit the pole with it, and listen for variations in the noise.

 

As someone else mentioned   if you find it, call the power company. 

 

 

Sent from my Samsung Galaxy smartphone.

 


David Jackson
 

Kriss, 
I've got the RU-1:1 inline connected direct to the Airspy, then out over coax to the RU-9:1 (I've also got the RBA-1:1, for dipoles and I've alternated between the two, sometimes the 1:1 is a lil better [less noise], sometimes worse [less signal].

I did recreate my original configuration from September today (homebrew UNUN, ferrite choke, crap cable and the RTL) and the RFI is still there. So at least it's not a "fatal flaw" in any of the upgraded configuration.r

I'll work on posting some I/Q, thank you so much for offering to take a listen. I'm leaning towards a bad powerline transformer as suggested by some other posters.
The same noise signature is present regardless of the mains ground connection or counterpoise, it varies in intensity but is always present.


David Jackson
 

On Sun, May 3, 2020 at 11:00 AM, Tom Crosbie G6PZZ wrote:

Brent has just reminded me of something else: Make sure of your ground connections. If you are using earth rods outside, water them regularly to maintain a good connection. We often forget about this in the UK because it rains every other day (!) but in a hot, dry climate it becomes important. A friend of mine Told his wife one summer it was about time they invested in an irrigation system for their vegetable patch. It would be gravity fed mainly from rain water collected from the roof.  She agreed but didn’t notice when he started lifting slabs to run pipework underneath to “water” his earth rods. Together they grow fruit, veg and salad plants and the DX keeps rolling in.

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Brent Seres/ VE3CUS
Sent: 03 May 2020 11:49
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] Another QRM Nightmare #airspyhfplus #sdrconsolev3

 

 

It could be AC powerline.  When I worked for Department of communications years ago we dealt with all kinds of power line interference issues. In many cases, it was loose hardware on 27 kv and 44 kv lines. The noise would propagate further as you went lower in frequency. 

 

Several clues :

Does the noise diminish when things are wet? Although it might seem counter intuitive,  wooden poles would swell slightly in wet weather,  and the hardware would tighten up and the noise would be reduced or absent.

 

If you have a nearby hv line, drive down it with the car radio tuned to the top of the AM band and see if you hear any increased buzzing at a specific location. If you have a wideband receiver, you can zero in on the location be progressively increasing frequency. 

 

Not recommended for the layman (people will think you're crazy and you might get arrested), but we carried a big wooden mallet in the vehicle.  When we thought we found the spot, we would hit the pole with it, and listen for variations in the noise.

 

As someone else mentioned   if you find it, call the power company. 

 

 

Sent from my Samsung Galaxy smartphone.

 

 

Good tip, I'm not sure how much wet I can get the ground though as I've literally got crayfish digging holes in the backyard lol. Thanks for the feedback!


David Jackson
 

On Sun, May 3, 2020 at 06:25 AM, Kriss Kliegle wrote:
I was hoping to hear the 'real' sound of the RFI at 0:52, but the NR4 was on and (as usual) it sounds like its under water. LOL

Questions/comments going forward:
1) Where are you? No call sign in your post to even guess. Closest neighbors are how far away? Industrial park nearby?
           Answered in a PM to you.

2) Connecting to service entrance ground can introduce QRM from devices in the building. I have success with a just a half of a ground rod (4') at the Unun.         Gives me 1-S unit of noise floor reduction on the lower bands.
          RFI still presents regardless of ground connection

3) The LDG 1:1 Current balun? You have balanced line in there too? Are you sure that's not a typo and its an 1:1 unun?
       My mistake, it's the RU-1:1

4) Did you try RXR'ing w/o the counterpoise? There's some info on the last page of this file, but some of it contradicts what worked for me:
https://www.balundesigns.com/content/Wire%20Lengths%20for%204%20and%209-1%20ununs.pdf
Such as unun at just a few feet above ground and grounding the ground stud of the 9:1 unun (physically connected to coax shield BTW)
    Yes, the RFI is still present albeit of lesser intensity. I attached a pigtail to one of the nuts on the SO-239 connector of the 9:1 to attach a ground wire to the coax shield.
 
5) Can you remotely post some IQ recordings (as to not flood the inbox of the complainers here using 1200baud AOL service) and allow us to hear some of the affected bands?
     Will post as time permits. Thanks.