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Low band chasing and interference in the shack

HI Andy

I would start by turning the pre-amp off on your radio’s on 40m and down. I run the LF bands from 40m to 160m with the RX in IPO - low gain on the input of the receiver. Good tips from Paul G4IPB I would say, you only get out what you put in, and its often a case of trial and error. I have done the same things here, but didn’t go wifi on the two shack desktop PCs and have probably spent the same or more on ferrites as Paul, I used 2 X screened CAT 6 cables to the router 20 feet from my shack just off the house hallway downstairs and built two mains filters for the shack so all mains power to the 15 devices plugged in comes via the mains filters, built to the G3SEK designs found on line. The parts for the filters alone cost £80. Get your antenna feeds and the antennas themselves as high and as far as you can within the constraints of your property and away as far as you can from masonry and overhead lines such as mains or telephone cables.

73 Phil

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Although I’m using the KX2 for this test, in real life I use it only for portable activations and have the pre-amp turned off on 40m and down and (nearly) always turned on for 30m and up. I ignore the KX2 S-meter reading in the pre-amp off case and make my own judgment as to his/her signal strength. I know the other guy isn’t S1 when it sounds stronger to me. But I know at least one person who will object to that approach.

You are probably talking about the FT817 / FT857 here. I just turned on IPO on the FT817 and the noise dropped from S8 to S5 on 80m. I’ll try using both rigs with IPO on for the lower bands and see how it goes.

An 80m Skyloop would be a quieter antenna for Andy if he has room for it but if this turns out to be VDSL interference as I think most of us are thinking - I would not expect a sufficient reduction in interference to justify the work involved in changing antennas.

One suggestion Andy - see if you can find a sound sample of VDSL interference on the Internet and see if it sounds the same as what you are hearing. I think that you said it was almost like white noise, which is not what I’ve heard about VDSL noise.

73 Ed.

No Andy, bigger radio’s at home. FT101MP and FT991A. Fortunate to have an 100 feet X 75 feet square back garden and a large beech tree which houses three antennae from 40 feet to 61 feet AGL (above top branches). Coax feeders are buried underground to the tree 60 feet from the house. Guess I am luckier than most to have the tree, but two of the aerials and OCFD and top band inverted L run back to the house and terminate at a metal TV aerial pole on the gable end at around 30 feet AGL.

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I think you said you have an SDR? Have you checked the noise in the VSDL guard-band frequencies? per http://rsgb.org/main/files/2019/01/EMC-Leaflet-15-VSDL-v2-January-2018.pdf

If you have powered down your house and removed the coax, it sounds like the easy options within your control are running out and an RX antenna might be worth trying.

In my quest for low noise on LF I’ve tried both a cross country wireless loop amplifier (with a copper loop) and a LoG. The loop is effective at nulling out local noise. The LoG is surprisingly good (on 160/80 if possible, increase the loop size compared with web page dimensions), but not very directive and with a major local noise problem may still have problems. Depending on your radio an RX antenna can cause extra logistical complications.

73 Matthew M5EVT.

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Thanks for the reference to the EMC PDF, Matthew. I’ll check the guardbands with my SDRplay RSPdx hooked to the existing inverted-L

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Hi Andy, Well I’ll put my 2 penorth in. I run an end fed long wire, something similar to what you run and my noise level on 80m has always been between s1 and s2 that is until Wednesday this week, and I say Wednesday because I had contact with Neil (G0WPO/P) in the lake district on Tuesday.on 80m. But for the last couple of days the noise level is between s5 and s7, and like you I thought it was due to the different conditions outside, and I still do.
Best 73

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I’ve now checked around each of those frequencies and looking at the SDR spectrum display there’s not a hint of any sudden change in the noise floor. So, I think VSDL isn’t the cause of the high noise level on the low bands.

Unfortunately not. The house and shack are not near the centre of the plot (and erecting a centre support pole for a dipole would spoil our lovely view of the garden and the Lake District hills on the horizon - unthinkable!).

Even an off-centre fed dipole (windom) couldn’t be properly supported. As it is, I’m having to use the chimney of our bungalow as a support between the vertical and horizontal sections of the end-fed long wire.

I think I read about an end fed windom??? Might be worth a Google?

Andy,

One approach I have read about (but not used as I don’t have the problem) is to use a magnetic loop for receiving, but retain your existing antenna for transmitting as it is more efficient that a loop. Some 160m ops use this combination to avoid noise pickup.

Somehow it is hard to shake the impression that you have an antenna positioned nearby some wires that may be radiating noise caused by birds nests hundreds of metres away but is still very strong.

I have used a vhf sniffer to find where a birds nest was, bridging two of the phases of a high voltage line and radiating noise all the way up the spectrum.

Good luck isolating and eliminating.

Andrew VK1DA/VK2UH

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I can second M5EVT’s suggestion; a loop on the ground worked wonders here for the low bands receiving (including 40m) - much of my noise interference comes from the nursing home next door (right up to 70cm) and I don’t think any approach from me would be too welcome :innocent:

Just don’t try using it for transmit, even with a bigger ferrite transformer in circuit, it is useless!!!

https://youtu.be/e0WvIxoU0LI may be of interest.

Hang on are we all missing the obvious? A beverage antenna for receive - as the contest and DXPeditioners use? Of course, you may not have enough room for it to go straight out but how long could it be if you run it around the perimeter of your property Andy? Failing that a LoG (loop on the ground) as suggested by Matthew and Barry suggested should be quieter and if (like here) it didn’t impress (other factors) - it can be converted into a loop on the ground earth system (see RadCom October 2020) and that did reduce noise on my antennas compared to a simple ground stake with radial wires.

73 Ed.

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Yes, they are very good especially is they are terminated and matched at the far end. I had one at my last QTH when my garden was 450 feet long pointing to Carribean / USA. They need to be a least a wavelength long to be effective, so on 40m that is 132 feet. A Beverage will mutually couple in well to your TX antenna though is it is close enough making them less effective for receiving. I have Harold Beverage’s original book here - quite rare to find now. I’m hanging on to it! Some operators have tried “The snake” to good effect. A random piece of wire on the ground in your garden, unmatched and just lying there on the soil. Never tried one, may not work so well here as I have around 2000 feet of buried radials in the soil.

73 Phil

Just one thought - one simple tip I forgot to mention. Avoid earth loops in your shack. Don’t daisy chain earth wires to various pieces of equipment. Best practice is to create a common earth bonding point to your external earth or make an earthed bus bar and earth every piece of equipment to it independently, including PCs. That might help unless you already have it. Again its trial and error. It might make things worse or better - isolating your mains via filters might also affect how effective this measure is. For earth in my shack I use the screen from good quality RG-213 coax with the sheath and dielectric removed and use that to connect the various electronic items chassis to the earth.

73 Phil

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I have an AlexLoop [which I rarely use] mainly cos 1) it doesn’t go down to 80m, and 2) you have to stand next to it to tune the frequency and rotate it for the incoming signal. Our house is at 25m ASL and the take-off at head height in my plot is poor due to surrounding buildings and tall trees.

Our village is in an AoONB (Area of Outstanding Natural Beauty) which places restrictions on type and placement of antennas. My long wire [made of UltraLite thin wire] is practically invisible and my neighbours didn’t notice it until I pointed it out.

If I put a magloop up high enough to be effective my wife - not alone the neighbours or the council - would complain that our house looks like a giant TV detector van [a cultural reference that probably means nothing to folk outside the UK where they don’t have to pay an annual TV license and detector vans drive round the streets looking for non-payers].

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Hi Andy
You need to stand up and assert your rights as a licenced radio amateur Andy - take them on including the XYL LOL… Awkward neighbours do eventually give up once permission is obtained and it can be gained in an AONB although the AONB manager will scrutinise your application and will have his say… It is possible to get councillors on planning committee’s on your side, especially if they get the impression that neighbours are ganging up on you and getting their heads together, writing letters and fabricating reasons such as TV interference, car windows coming down to due RFI, garage doors opening etc as they did with me. The planning officer ended up recommending acceptance of my Hexbeam and 6+6 4m/6m yagi last year, and it was passed unanimously by the planning committee - the Tennamast was passed on appeal to the Planning Inspectorate in 2018. Some neighbours ignore me as a result, no loss to me. I enjoy my radio too much to bother about them, most of them don’t even live in my road and cannot see the aerials.

73 Phil

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I’ve been rethinking about the possibility of a ½-wave 80-m dipole on my plot without the need for a support pole.

I make one some years ago and was very happy with its performance - when portable and at my previous QTH – on 80m and higher bands using an ATU.

But, before I go to the time and trouble of making and erecting one, can I expect - all other things being equal - that a half-wave dipole will be less prone to receive noise than my existing end-fed long wire which has no counterpoise and probably an ineffective ground plane over my plot (consisting of a few cms of soil over 345-million-year-old Dalton limestone) ?

My wife and I have been out with a long tape measure this afternoon [important to get her buy-in up front]. There’s a mature tree on the edge of the property about 7m from the shack and I could attach a ~1m-long nylon cord to one of its branches and a lightweight 1:1 balun at the other end. There would be about 29m from the balun to the existing nylon cord (on a tall tree) at the far end of the back garden where my long wire is currently attached. There’s 20m in the opposite direction from the proposed balun to a tree on the edge of my front driveway. This tree belongs to my neighbour but I think it would be legal to attach something to one of the many branches that protrude well over my side.

One concern: the end of the dipole wire at the driveway end would be 5m away from those previously-mentioned pesky electricity & telephone cables on telegraph poles running up on my side of the road. The dipole wire would be almost at right angle to those cables (say about 80 degrees) so I think the risk of induced EMFs is low.

Another concern: the wire over the driveway would be visible from the road. It may attract attention. But I know from discussion with Phli @G4OBK and others that the low height of the wire (lower than the top of my bungalow roof and the Diamond X50 colinear on 2m pole on the chimney) does not need planning permission. I see nothing in the AoONB regs that would be a problem either.

Any comments before I go ahead?

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The DX wire is quite invisible- difficult to spot even when I am looking for it!!