Low band chasing and interference in the shack

On the Bands
61

Hi Patrick, I have already done a survey of the area using my KX2 / whip antenna on 80m [see my post #42 above]. However, taking your advice I repeated it using my Sony ICF-SW7600GR tuned to 1630kHz and it was more sensitive (and directional) than the KX2 set up.

Results were pretty much as before. The noise went up a lot under the overhead electricity / telephone cables that go up the road and up a bit under the phone cable running to my house.

I could get very high noise if I held the MW/AM radio 5 cm away from the large bunch of cables going vertically up the telegraph pole (see photo) to join the horizontal cables 8m up. But the noise dropped rapidly as I moved the radio away.

telegraph pole cables
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I could create other loud [and weird sounding] noises holding the radio next to my iPad or laptop, but again it’s very localized. There is no increased noise level from any of these sources anywhere near my shack or the end-fed long wire.

As I said [at post #42] I’m not convinced one can draw any firm connection between the noise sources detected by the handheld radio and the spatial distribution of those noises (which must be very dependent on the radio and antenna used). The KX2 /whip and the MW-AM radio / internal ferrite antenna are very different from my FT857 / EFLW.

Another point I haven’t mentioned the background noise is highest during the day and lowest evenings & night time.

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62

If that period is 4 years then it’s too late for the council to take enforcement action and your aerials can stay.

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63

?? Solar panels ?? The invertors can cause problems and as they are ona roof they tend to radiate well - and are connecfted to quite a lot of wire ??? Just a thought. Paul

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64

Two neighbours across the road have solar panels on their roofs but they are about 50m and 80m away. My MW-AM radio survey didn’t show any increase in noise near their houses.

I suspect a component of the high wide-spectrum white noise I get on 160m and 80m [and on 60m and 40m to a lesser extend] during the day / summer [c.f. after dark / winter months] is due to D-layer absorption.

I also suspect [but have no expert knowledge to confirm] that some of the noise is due, not to a single source [though the overhead power / phone lines in the street remain a suspect], but to many sources and made worse by using an end-fed inverted-L long wire which has no adequate ground plane.

I’ve already got the components for my new stealthy 80m-10m OCFD [i.e. twin ferrite core 4:1 current balun, lightweight antenna wire, bungee support cord, dark-green nylon cord to make lanyards for the three tree-based hoisting points]. I might even paint the top part of the coax feeder light brown to look like yet another ivy branch going up the tree with the balun.

I’m just waiting until this untypically hot weather [hot for Cumbria] passes before attempting to get stuff up in the trees.

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65

For what its worth, Andy, you are not alone! My antenna for the lower bands is a 40metre long doublet fed with 300 ohm window line and tuned with an MFJ-949E. My noise registers S8 on 80m and 60m, and S6 on 160m and 40m. I find it best to operate with the attenuator on, which seems to help the operation of the audio DSP, but weak signal chasing is very much a thing of the past. Fortunately when those bands are working well there are plenty of strong activator signals to chase (well, perhaps not on 160m!) At this time of the year they are pretty rubbish! :frowning_face:

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66

Hi Andy,
To improve the ground plane - take a look at the loop counterpoise for HF vertical antennas system from G4HYG covered in the October 2020 RadCom - I works well for me in a small space and being buried it’s not visible.

73 Ed.

67

Hi Ed,

Thanks for the suggestion but I foresee a problem or two. As I said previously [post #39 above] my garden consists of very shallow soil over ancient limestone [A few months ago it took me many backbreaking hours just to plant a dozen small saplings and I had to remove more rocks and boulders than soil to make each hole in the ground]. I would rather have all my teeth pulled out than attempt to dig a large trench there to bury a counterpoise.

I doubt how effective such a ground plane would be in such rocky ground. In any case my wife would be very unhappy if I destroyed the rockery garden, pond, etc that the counterpoise would have to take under the existing long wire. I guess I’m saying it’s not really an option for me.

I’m committed now to an antenna solution that does not require a ground plane to be effective. I continue to research [or wot we used to say ‘read up on’] OCFDs and there’s a lot of contradictory info on the internet, so difficult to know which source to trust.

However, it confirms what I knew from having an 80-10m one in the past: an OCFD is a multi-band antenna but not an all-bands antenna. One can change the ratio of the lengths of the short and long legs to optimize performance on some bands at the expense of other bands. Here’s a chart I made that summarizes the performance of HF bands for three ‘short leg’ percentage lengths (20%, 25% and 33%) of the total length (the 50% line is for a 1/2-wave dipole]:-

image
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For me, 60m, 40, 30, 20m and 10m are my favourite bands so a short leg of 20% [long leg 80%] seems best but at the expense of 17m. A pity but there we are.

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68

An OFCD is also good at turning nearby common mode noise into differential mode noise, because the two elements pick up different amounts of noise. That differential mode noise won’t be rejected by a common mode choke.

wunder

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69

I hope less so than my current end-fed long wire against a poor or non-existent ground plane. I used my previous OCFD for several decades at my old QTH which was surrounded by houses much closer than here, and was not troubled by high noise on the low bands. So, despite its limitations I’m hoping another OCFD at this QTH will be an improvement over the current antenna.

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70

No large trench needed. The wire can simply lay on the ground. My suggestion to bury it was purely for the WAF (Wife acceptance factor). Even 1/2" under the surface should be enough that it’s no longer visible. The shape is not critical, in fact you can even put multiple loops down and connect them together and it doesn’t have to be under the antenna - it’s all explained in the article.
73 Ed.

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71

If you are interested in experimenting, The Sept 2019 QST, pages 30-32, has an article “A slightly off-center-fed-dipole” by Brian Machesney K1LI/J75Y. The dipole is split 45:55 and claims operation on 8 bands.
I am suggesting this, as the idea was to use a balanced antenna to help reject noise and this design is less unbalanced than the usual designs.

Ian
VE6IXD

72

You mean just lying there on my lawn and garden where my wife [a keen gardener] will see it ten times a day and she and the dogs will trip over it?

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That’s why I said bury it!
The point is you don’t need a deep trench, just enough so that it’s out of site. Now the problem you might have of course is that the dog or the wife, while digging holes my dig into it, but putting it as far out as possible, should reduce that chance.

I take it you don’t have any radials buried at the moment - as that would be a far, far bigger problem!

73 Ed.

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74

Think we’re going round in circles now, Ed. I can’t bury or lay a counterpoise on the ground. I’ve ruled out an antenna requiring a good ground plane for that reason

75

OK, to be clear the system can be buried or simply laid on the ground it works the same. In your situation I would bury it just under the surface to keep it out of the dog and wife’s sight.

I think you’ve decided on trying an OCF in any case, so it’ll be interesting to see how quiet that is compared to the long wire.

73 Ed.

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76

Ian, I wish I had access to an antenna analyzer which would probably help me optimize the wire lengths. The analysis I summarized in the chart above gives me 8 bands including the 5 bands I use mainly from the home QTH. So, I’m going to try the 20%-80% ratio first.

Just to put this whole thing into prospective, the vast majority of my operating is up on the hills as a SOTA activator. At home, it’s mainly chasing on HF and VHF. I don’t do contests or special events from home so I don’t need [and could not erect] a high performance DX antenna system. My existing antenna is adequate except for the high low-band noise. If the planned OCFD improves the low-band performance that will be just fine and - with my stealthy implementation - won’t cause friction with family or neighbours.

Thanks everyone for your suggestions and advice. I’ll report back on this thread once the new antenna is up and I’ve had enough time to evaluate it.

73 Andy

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77

Two months ago, I said I would report back when I had the new antenna working. Well, my first two attempts at making and positioning a homemade Off-Centre Fed Dipole for 80m-10m were not very satisfactory and, feeling downcast after my efforts, was even thinking of reinstalling the old end-fed long wire despite the high background noise that prompted me to create this thread in the first place.

Also, moving the house-end antenna support point from the bungalow chimney to a mature tree at the edge of the property [to be near the outside shack] meant the wires getting entangled in leafy branches and the antenna wires being less out in the open.

This morning I decided to try yet another short leg to long leg length ratio (19.5% to 80.5%) and move the 4:1 current balun from the tree branch to the chimney. I choose a total length to suit the CW section of 80m (and higher bands). The long leg (33.25m) fits perfectly in the distance to a high tree at the bottom of the garden and the short leg (now reduced to 8.06m) needs to run only to the corner of the roof rather than a messy highly-visible run over my wife’s car to the neighbour’s overhanging tree branch.

Armed with my brand-new Rig Expert AA-35 antenna analyser [funded through the recent sale of some radio gear] I quickly did an all-bands SWR scan followed by ones for individual bands.
image

The author of the on-line article in which I read about the 19.5%-80.5% split warned that the SWR for 17m was poor so that came as no surprise. The bad SWR for 60m was a big disappointment – as it’s one of my favourite bands – but as it’s not harmonically related to the main A.R. bands, you often read about this problem with multi-band antennas.

My LDG Z11 Pro 2 ATU does a good job of matching the OCFD on the ‘bad SWR’ bands (80m and 15m) [only the CW sub-bands tried so far] indicating an SWR from 1:1.0 to 1:1.5. It even does the same for the 60m UK CW sub-band (around 2560kHz). But it complains about 17m by rattling its relays forever.

The background noise on all bands is much better (quieter). For example, even with lightning QRN today, noise was S7-S8 on 40m where as it was consistently S9 +5 to +10 with my old end-fed long wire. Even the 3s cyclic ‘ticking’ noise on 6m is much reduced and I can clearly hear the GB3NGI 6m beacon in N.I.

I had time this afternoon and evening only for a few CW QSOs - on 80, 60, 40 and 30m getting excellent reports [except on 60m] running 15W or 25W.

Well, more tests to be done in the coming weeks but I don’t expect any big surprises. I think I’m all set to do a bit of chasing from home now.

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78

Well done on all the work Andy.

As you rightly say multi-band antennas have to be a compromise.

I don’t know if you have the room (most of us in Europe/UK don’t I think) but as you say the main issue with this antenna is 60 metres not being resonant (and whether or not the ATU manages to match it, it still won’t radiate well) - have you considered putting up a single band dipole for 60m in addition to the OCF? I know even if you have the space, the WAF (Wife acceptance factor) factor may be an issue but that may be the best technical solution. Who knows in some way the ATU might even match a 60m dipole better than this OCF on 17m?
In any case, WELL DONE on what you have achieved so far.

73 Ed.

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79

Thanks Ed. I’m very lucky to enjoy a high WAF but another overhead wire in the garden would be pushing my luck.

80

Hi Andy

have you considered a loop-on-ground receiving antenna for the low bands ? See for example http://www.kk5jy.net/LoG/

I have tried one briefly and was surprised how effectively it cancels local noise. From my tests with the wire laid on the grass, signals are typically 10dB down but noise is 20dB down. I haven’t yet worked out how to do Tx/Rx switching - I am considering buying a separator adapter for my IC-7300.

If you have a sensitive receiver you don’t need a preamp.

Cheers

Rick