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Low band chasing and interference in the shack

If you are going to fit in a dipole, you might consider a doublet fed with twin line of some kind, rather than an 80m dipole - it could be more versatile.

I’m pondering a new wire antenna as mine had to be removed recently to facillitate a rebuild of the chimney that supported it. I’ve been using the spreadsheet linked in an earlier thread, and posted by Armin @DL6GCA. Armin’s translation, together with a bit of Google translate action clarified how to use it to calculate the length of the “legs” together with the length of feeder. (I also picked up a tip from Owen Duffy’s website to avoid copper covered steel conductors as used in many commercial ladderline feeders, as they can be very lossy at LF due to skin effect)

I have nothing in the air yet, and less room than you have to play with - but I do have high noise on 160m and 80m!

Anyway, just a thought. I’ll be interested to hear how you get on, and will update when I have something working…

Link to spreadsheet

Andy,

The main information you really need before making decisions about antennas is “what and where is the source of the noise?” Without that, you cannot know whether putting an antenna closer to the power lines, the house or near the neighbours will increase the noise pickup or reduce it. Some dedicated hunting with a portable radio could help you to answer that question.

Good luck
Andrew VK1DA/VK2UH

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I’ve just been wandering round our plot and the road by our driveway with a KX2 with a telescopic whip listening to a quiet frequency about 3700kHz on SSB with a wide filter (~3500Hz). The high-band whip was ill matched for 80m and signals were very weak but I hoped the setup would be good enough to pick up any local source of noise.

There was an increase in noise as I got within a few metres under the overhead power and telephone cables in the street and it became a maximum when standing directly underneath them. Without a cherrypicker to raise me and the KX2 vertically 8m or so, it wasn’t possible to say if the noise was from the mains cables at around 8m up or the telephone cables at around 6m up. It was very localised to the line of the cables and the noise dropped to ‘normal’ before getting to the other side of the road.

There was a small increase in noise when holding the top of the whip within a few cm’s of our own overhead telephone cable. There was no increase doing the same with the overhead mains electricity cable running to our house.

The rest of my survey around the house, shack, gardens back and front, near the neighbour’s house, etc was uneventful.

I’m not sure if any firm conclusion can be drawn between the noise detected from the overhead roadside cables and the high noise on the low bands using the long wire antenna whose ends are located between 15m and 45m away from the cables and mostly at right angles to the cables. In other words, yes, the overhead cables are a noise source but how localised is it? Do they extend enough to affect the LW antenna? Not possible to answer without being able to change the separation distance.

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Even indoor antenna can hear pretty well with modest receiver like FT817ND. Below my test on 30 m with second floor Buddipole September 2020. 160 m and 80 m are difficult due to antenna size. Indoor 80 m magnetic loop is big or needs large capacitor and has some safety concerns. I would check reception and propagation first on https://pskreporter.info/pskmap.html.

73, Jaakko ac1bb/oh7bf

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OH, I Wish!! We have to pay through the nose each quarter for a TV/Radio licence in Germany and what is worse - the government-owned national TV stations that this is supposed to pay for now have lots of commercial adverts on them! So we are “paying” twice. No need for the vans here though. You have to register where you live and for every property, there has to be a TV licence. Whether you own or rent no difference. If you don’t have a TV in the house - no difference - “you can get our stations over the Internet” - so you still have to pay the licence fee.
73 Ed.

I guess you’ve seen this video have you Andy (since you have an SDR Play - this process would seem to be a good match for you).

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In my case I replaced the tv antenna amplifier swiching supply with a 230/15vac trasformer and linear lm7812.
You might have benefit with a good ground system in the shack.

73

Can you use a fishing pole to set up a temporary dipole/doublet? This would be an easy way to see if it helps before going to the trouble of a permanent installation. Also make sure you have good common mode choking. GM3SEK has good advice. I have the low, mid and high band chokes in series and it does help.

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I’ve pretty much concluded that’s the next step. If I hadn’t cannibalized my portable 80m dipole (to make a 20/10/6 linked dipole), I would have tried it yesterday. No matter, I’ll make another and erect it on my 10m SOTAbeam pole.

Thanks, Richard. I’ve downloaded the PDF. I’ld prefer to read it rather than get back to doing the wallpapering but my wife will have expected ‘progress’ when she’s gets home. Doing QRP portable most of the time, it’s never been a problem but it’s time to bone up on chokes.

I mentioned K9YC’s articles before. He has a choke cookbook with construction details for different chokes.

http://k9yc.com/2018Cookbook.pdf

His longer article, “A Ham’s Guide to RFI, Ferrites, Baluns, and Audio Interfacing”, goes into the detail behind the chokes, plus guides on reducing RFI in the rest of the shack, not just the antenna.

http://www.audiosystemsgroup.com/RFI-Ham.pdf

Last year, the ARRL gave him their Technical Service Award for all his contributions.

wunder

Thanks for the various links.

I’ve changed my mind (fickle or flexible?) about making an 80m 1/2-wave dipole [because of its poorer performance on many higher bands even with a good ATU] and instead I’m gonna make an 80-10m OCFD. My home QTH antenna for donkey’s years was a [USA-made] heavy-duty QRO 80m windom and it always gave good performance on most bands [this all predated 60m].

I still need to have the balun (now a 4:1 current balun) supported by the aforementioned mature tree 7m from the shack so I’ll need to run a longer support cord at the ‘short wire’ end to reach the other tree due to the 36%-64% split in the wire lengths (compared to the 50%-50% for the dipole).

I understand, if I use a current balun comprising a twin-core [rather than the cheaper but less effective single core], I shouldn’t need any further choking (loops of coax, ferrite rings etc).

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Yes, the full size 80m and down OCFD is a good compromise if you can fit it in Andy. If you get the feedpoint into the 7m tree and then run the ends out as an inverted vee and it works well at that height - great! I’ve been using a similar arrangement since Jan 2017 here and have no desire to change it, albeit I only use it on 30-40-60-80m. As mine is higher than yours I have a 6:1 balun at the feedpoint and believing the theory, I chose to choke the feeder again at around 20-22 feet below the feedpoint with a stack of ferrite rods. The theory supposedly says this will produce some vertical radiation from the feeder, (according to the article I copied the design from). The feeder starts out in my case as mini 8 down to the choke, so I get plenty of turns on that, I then go into RG-213 down to ground level and then buried Ecoflex 15 for the lions share of the cable run back to my shack. How the extra choking supposedly works with a balun at the feedpoint above it only the Lord knows, but that’s how I made mine up and I haven’t been minded to change it since it went up, as it works quite well. I resonated it perfectly for the 40m band by tweaking the lengths of the top a little, proportionately each side. 40m for me is the most important band in terms of SOTA chasing. The 80m match is acceptable without an ATU in the CW/FT8 part of the band, but if I go up to SSB above 3600 KHZ the auto ATU in the radio will take care of it. The only band the AUTO ATU will not tune the antenna to a perfect match is 60m, so when using the OCFD there I use an external tuner.

Tree mounted aerials at G4OBK: YouTube

If you can obtain permission or sneak a strongish fibreglass pole into the tree (if it is climbable) then more hieght above the branches will make the aerial more effective and would probably help reduce your local noise level. I use 25 or 55mm wide X 600mm long velcro straps obtainable from ebay sellers, to secure my three antenna poles into the upper branches of a beech tree. The velcro straps are then backed up with very large tyrwaps to make the strapping more secure. You may still think that your noise level is high, but the best comparision would be to see what you can hear of the stations that others may be working and then hopefully you will also manage to work them yourself. Good luck with the project.

Phil

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And - which is more - you’ll be a man my son!
(With thanks to Rudyard Kippling)

Braver than me :grin:

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Phil, I watched your YouTube video with your poles ‘growing’ out of the top of your beech tree. I know that a similar arrangement here would be aesthetically displeasing to my wife. Striking a balance between my hobby interests and my wife’s (gardening) is a tricky balance. I think any small improvement in the antenna performance by raising its height from where it’s virtually invisible to where the rest of the village can see it is not worth it.

I’m hoping merely going from an end-fed LW with no counterpoise to a dipole [thereby not requiring a ground plane] will reduce the noise from local sources even if the height of the wires is about the same as before.

I won’t need to make the OCFD an inverted V due to the relative heights of the three support trees. However, my plot is on a hill [actually the whole village is - first settled by Norsemen as a defensive position over the Kent estuary] and the ground drops away towards the end of the back garden. So, whilst the wires will be roughly horizontal, the heights above the ground will increase going from the short end to the balun to the long end.

P.S. The balun tree is climbable but I’m not sure I want to try going up to the higher branches. I might try a hook taped to the end of my SOTAbeam pole to get a lanyard over a high branch.

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What you propose sounds perfectly acceptable for SOTA Chasing if that is your main interest Andy. I am confident your noise level / signal to noise ratio against an end fed without a counterpoise will improve significantly as a start point, then you need to look at your shack and the local environs, but getting inside peoples homes to investigate specific issues you may find by DFing is difficult. If you do any electrical work in their homes it is a gamble as if something goes wrong with something electrical in their home you may be held responsible. Its tricky. Where I lived before I detected some terrible interference in one of the nearest homes to where we lived, in the green belt just outside of the town. I found the source by going down the road with a small medium wave radio until I found the strongest source. The interference was spoiling reception in the 160 and 80 metre bands over a radius of over 400m in every direction. The people allowed me in to their home to investigate. They allowed me to turn off their circuit breakers one by one until we found the ring main concerned. Then we started swtiching off appliances. The source turned out to be a Thomson TV digi-box / HDD recorder. The unit case was very hot to the touch even when it was on standby and not recording. The digibox had been in service for some years, yet the interference just started out of the blue and was affecting my reception. They were happy to take it out of service and give it to me for investigation. I scrapped it on their behalf and they thanked me for alerting them of the defective equipment. I was lucky as they were good people.

I need my aerials as high as I could get them, in fact I’ve just bought a “DX Challenger Extra Long Telescopic Antenna Support Mini-eXteme Nebula” from M0MCX:
NEBULA

Its 41 feet long (12.5m) long to fix in the tree in place of the 7m Lifes a Breeze pole, so that will give me 61 feet in the vertical for 80m DXing in the winter months. When I got married in 1996 the XYL knew what she was getting as I had an 18m versatower in my garden where I lived in Scarborough at that time (much to the chagrin of some of my neighbours!). Some believe in live and let live and some don’t :face_with_raised_eyebrow:

73 Phil

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Hi,

Have you a portable battery operated radio set that has the LW/MW bands ?

If yes, i would take it outside and with the help of the directivity given by the ferrite antenna try to find the source of the problem before trying to find a cure !

Set it at the end of the MW band 1620 kHz and if the QRM is not that sharp in frequency you will be able to track it until you find the source.

Good fox hunting !
73, Patrick.

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As an example of my efforts to make my antennas as low profile as possible: when we moved here I took down the TV and VHF-FM radio aerials on my chimney put up by previous owners [now redundant as we have FreeSat TV] and replaced them by my Diamond X50 2m/70cm colinear. I spray-painted the ‘white stick’ portion in a disrupted pattern of matt blue, grey and matt white.

Of course, the Cumbrian skies can range from dark grey to sky blue so it’s rarely perfectly camouflaged - at best, it doesn’t attract attention.

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If it doesn’t look like the other TV antennas in the area then you are high profile not low profile :slight_smile:

Hah! My house used to be one of two in the village with a collinear. Sadly, since the other ham went SK, his has been taken down.

According to the AoONB rules on aerials / dishes, one is not supposed to have an antenna on the road-facing side of your house [BTW: the whole village is bestrewn with ugly overhead electricity and phone cables]. Whilst walking the dog round the village one day, I reckon almost half the properties I saw violated this [well thought out?] rule.

Can you imagine the council knocking on some poor villager’s door to demand they take down their satellite dish because their south-facing house wall overlooks the road?

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I live full time in an RV and also have pretty server RFI. I quickly eliminated my RV by hooking up IC7300 to small 12vdc battery and shutting all power. RFI level didn’t change. Here in the US we’re dogged by tons of RFI generating devices. A year ago I pulled my “home on 4 wheels” out to the Arizona desert and miles from civilization and my noise floor dropped next to nothing, almost like the rig wasn’t working…what a treat!!!

GL/73

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Fortunately me and some of my neighbours like to receive Yorkshire TV from Emley Moor 70 miles away rather than the nearer Tyne Tees / BBC North East from Bilsdale 20 miles away. This means a good number of my neighbours have 5m+ poles on their gable ends with high gain aerials and masthead preamps, including me. This assisting the planning officer in the acceptance of my two planning proposals and she ending up saying to me that they were only interested in the free standing Tennamast and not the TV and DAB aerials and long poles, the three wire aerials and the three poles in the tree in my garden.

Several neighbours pleaded in letters to the council that I shouldn’t have the poles in the tree and the wires in the garden. Their pleas were ignored and were never taken into account in the final anyalysis, before permission was granted for the 12m Tennamast and then later, the two aerials fixed to it. The RSGB Planning Committee Chairman was a great help in giving me useful advice. You have to be a member to take advantage of the service of course.

I imagine if you draw a line or get a map of the AONB boundary you could catalogue 100s of breaches of the AONB planning guidance - its probably not law in fact, just guidance. You really need to test them out in my opinion and so long as it is not incurring high expense if you were forced to remove the aerials, then you could put them up and see what happens. Then after a prolonged period of time, if pressured, you may have to decide whether to give in and remove them, make them less obvious or apply for retrospective planning permission to avoid an enforcement notice being issued. To get to that stage usually takes eons, but in the meantime you have to live through the stress and pressure of it all, as will your XYL. Having been through it, it isnt pleasant, I wouldn’t wish it on anybody, but when you win the day in the end, it could be considered worthwhile. It depends what you want out of the hobby I guess. Just to have a station you can enjoy for SOTA Chasing it probably isn’t necessary, but if want to chase DX and winkle out the rare stations on HF and VHF and SOTA Chase with a greater degree of success, I’m afraid higher gain aerials well above ground are essential tools in your armoury whether you have chronic QRM/QRN or not. Better antennas will improve the reception of short wave signals at the expense of the interference in most cases, even if the interference persists throughout the upgrade of your station.

73 Phil

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