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 HF Noise Floor 
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Post HF Noise Floor
Hopefully I am not covering old ground here, I have done a search and could not find a lot so here goes...

I appear to have quite a high noise floor on 20m - around S4-5 and it appears to be across the whole band. The antenna I am using is a 2 element Mosley for 20/15/10m. If I monitor 40m this appears to be around an S6. 10m appears to be quiet at around an S1.

I followed this blog and thought it would be worth trying:

http://www.m0nwk.co.uk/audio-video/main ... reduction/

I purchased a large 31 mix ferrite:

https://uk.rs-online.com/web/p/ferrite-sleeves/4669164/

Unfortunately that did not appear to make a difference. I have systematically turned off everything in the house with no effect. I went as far as turning the main breaker off and running the radio off of a battery, it was still the same. I have the antenna on a rotator and have tried all directions, the does not appear to be a noticeable null in the noise.

Earlier on after trying the large ferrite on the mains the noise disappeared, the scope went black from a steady shade of blue and I thought "great", after transmitting to call CQ on 20 the noise returned to default leaving me mystified!

The only thing I can think of now is that I have long run of earthing cable between the radio and some earth rods. I know this is not ideal but I have no choice as the shack is upstairs at the front of the house but I wanted to earth the shack as best I could thinking that something is better than nothing. I wonder if the noise could be being picked up through there(?) - I will disconnect this tomorrow and report back.

I have been scratching my head over this for some time now, and would be grateful for any help. I suspect I am going to have to use something to detect the noise and go for a walk...


Wed Aug 29, 2018 10:04 pm
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 HF Noise Floor 
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Location: Markyate, St Albans, IO91ST
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Post Re: HF Noise Floor
40m noise sounds about normal for the average location, but 20m does sound a bit high and when you said it vanished then returned when you transmitted it has got me wondering if it's the dreaded VDSL syndrome.

An easy way to confirm that is to tune 12.05MHz and see if the noise drops just below that frequency, that is the 50KHz transition point between one of the upload and download bands for VDSL

At least if it isn't that, it is one thing that is eliminated.

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Thu Aug 30, 2018 6:19 am
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 HF Noise Floor 
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Post Re: HF Noise Floor
Thanks Paul, I just tried the frequency you mentioned and the noise does not appear to drop off lower down. I will upload a photo of the scope later on, it's very frustrating as I saw it all disappear briefly yesterday. It was almost as if there was a glitch in the radio where the attenuator was on at --12db!


Thu Aug 30, 2018 6:48 am
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 HF Noise Floor 
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Post Re: HF Noise Floor
If you have got an SDR I found it quite handy to look at a large amount of the spectrum each side of the noise.

I used an SDR Play and you could see a noise pattern,you could also see where the noise peaked which helped me find the problem

In my case its solar panels to my east which cause me problems on 50Mhz


Thu Aug 30, 2018 7:00 am
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 HF Noise Floor 
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Post Re: HF Noise Floor
VDSL is an easy one to identify, so it isn't that. So a bit of leg work will be involved walking around the district looking for it, doing what G4RRA says is a good start.

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Thu Aug 30, 2018 8:15 am
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 HF Noise Floor 
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Post Re: HF Noise Floor
Thanks for your replies, I just sold an SDR device as I thought I didn't need it anymore!

I do have a KX3, battery and 2m dipole that I could connect to the HF antenna socket for receiving...

Once I have found the source I dread the next step "knock knock, please can I come into your house and turn everything off please...".


Thu Aug 30, 2018 9:38 am
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 HF Noise Floor 
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Post Re: HF Noise Floor
You really need to make a small shielded loop that has nulls broadside to it, the 2m dipole won't give you that.

That are plenty of designs on the internet like this one although for 1.8MHz for 20m it probably won't need to be more the a foot in diameter to work well.

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Thu Aug 30, 2018 9:57 am
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 HF Noise Floor 
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Post Re: HF Noise Floor
By the way, there is an EMC section on this forum now that would probably be more appropriate for this.

viewforum.php?f=66

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Thu Aug 30, 2018 10:01 am
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 HF Noise Floor 
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Post Re: HF Noise Floor
G4LNA wrote:
By the way, there is an EMC section on this forum now that would probably be more appropriate for this.

viewforum.php?f=66


Ah yes, so there is. If it can be moved that would be great.

I will look into the loop antenna option - I wonder if there is something commercially available as getting the time to build such things these days is very difficult with work and a young child!


Thu Aug 30, 2018 10:05 am
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 HF Noise Floor 
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Post Re: HF Noise Floor
Well, there is, but how deep is your pocket?

https://www.radioworld.co.uk/aor-la-400 ... op-antenna

That is really overkill for what you need it for, it's only a bit of coaxial cable, if I get time over the weekend I'll make one for you and post it to you. You just need to confirm what frequency the noise peaks on, just be aware it might not peak in an amateur band.

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Thu Aug 30, 2018 10:20 am
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 HF Noise Floor 
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Post Re: HF Noise Floor
Ouch indeed! That would be very kind of you, happy to pay you for it if it will help locate the issue. With regards to the noise itself, this is what the scope looks like:

Attachment:
IMG_20180830_074330.jpg
IMG_20180830_074330.jpg [ 121.84 KiB | Viewed 573 times ]


I have also uploaded a couple of videos that demonstrates what I am referring to:

https://youtu.be/g2ehK3EXCU0

https://youtu.be/R7YIfKcORVE

I am trying to provide as much information as possible as any help to at least identify the issue is gratefully received.


Thu Aug 30, 2018 10:40 am
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 HF Noise Floor 
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Post Re: HF Noise Floor
It is really difficult to tell what it is, at first I would have said atmospheric noise, but earlier you said that it did vanish for a short period, it might have just been coincidence the noise appeared again after you transmitted.

Does the noise vary as you turn the beam?

It could be a PLT device or solar panels, from what I've heard from other sources is that solar panels make the most noise when the sun is at it's brightest, which makes sense as that is when they working the hardest, so does it vary from day to night?

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Thu Aug 30, 2018 11:10 am
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 HF Noise Floor 
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Post Re: HF Noise Floor
Thanks Paul, I don't recall that it varies at day/night.

The noise very slightly varies when I turn the beam - I will get another video later tonight whilst turning the beam.

I do wonder if my earthing system is not sufficient and it is just picking up noise rather than doing some good and the distance is 6-8m between shack and earth rods. The mast itself is not grounded either.


Thu Aug 30, 2018 11:21 am
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 HF Noise Floor 
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Post Re: HF Noise Floor
You are using a balanced antenna, so the additional earthing would have no affect whatsoever. Just be careful with earth rods, you might create an electrical hazard by providing parallel earth paths with the mains safety earth. It's best to remove the earth rod system and rely on the electrical safety earth.

Keep safe mate.

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Thu Aug 30, 2018 11:27 am
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 HF Noise Floor 
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Post Re: HF Noise Floor
this is a helpful site as well.
https://www.ukqrm.org.uk/

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Thu Aug 30, 2018 12:00 pm
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