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 Flat top Horizontal centre fed dipole for the loft - any top tips?

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hawk657
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hawk657

Call Sign : CT/X 6657
Posts : 30
Times Thanked : 1
Join date : 2020-04-19
QTH or Location : Nuneaton - Warwickshire
Equipment Used : AT5555, Midland PORTAPACK, SIRIO and FIRESTIK mobile antennas. Just building a DIPOLE for the loft as I type and just finished another T2LT.

Flat top Horizontal centre fed dipole for the loft - any top tips? Empty
PostSubject: Flat top Horizontal centre fed dipole for the loft - any top tips?   Flat top Horizontal centre fed dipole for the loft - any top tips? Icon_minitimeSun Apr 19, 2020 10:57 pm

Hi there.

Just moved into a new home and want to get on the air ASAP, so am halfway through building a centre fed horizontal dipole for the loft space.  There isn't enough 'height' to mount my 7 foot Firestik on a mount up there and an outside base antenna needs planning so as not to upset neighbours.

It's being made of RG58 and will have a professional balun in the centre, a 5 turn air choke after the 'drop' lead and will be hung centrally, along the length of the loft space from the wooden rafters using professionally made end insulators.  I have used a dipole calculator and watched a number of builds from Radio Ham's and enthusiastic muppets on YouTube, so have all the basics of the build covered.... However...

Has anyone mounted one before and come across any top tis or advice at all that will help make the dipole work as well as it can up there?  Anything I can do other than the basic build and hanging of it to ensure it works well?

Any guidance at all would be well received - And hopefully when my PSU arrives later this week from Knights, I'll be on the air in the Nuneaton/Hinkley/Tamworth/Coventry area if you're out there for a radio check :-)

Thanks guys

Matt
CT/X 6657
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Victor
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Victor

Call Sign : 26-CT-3228
Posts : 428
Times Thanked : 31
Join date : 2019-11-10
QTH or Location : Bedford
Equipment Used : Various

Flat top Horizontal centre fed dipole for the loft - any top tips? Empty
PostSubject: Re: Flat top Horizontal centre fed dipole for the loft - any top tips?   Flat top Horizontal centre fed dipole for the loft - any top tips? Icon_minitimeMon Apr 20, 2020 7:31 am

Hi Matt,

"Top tips" ....cor are you gonna get some of those Wink

Joking aside, everyone will have an opinion. Some will vary wildly, a majority may have common ground, but remember that even common ground or wideheld beliefs may not always be correct.
You'll get a world of 'technical' tips when it comes to antennas, some based on hypothesis and others on personal observations, yet others regurgitations of someone else's work.

My top tip?......Any antenna is better than no antenna.

So let me congratulate you on building your own antennas, it's all too easy to simply purchase one.
Most importantly of all, have fun doing what you're doing, learn from it and don't be disparaged by others.

Well, there you go, my tuppence worth. Maybe not what you wanted but the secret can often be in the question.

If it helps any, my own experience of a loft antenna system is that it's much better than I expected it to be.
I built a fan dipole array for 80/40/20/10m, (four dipoles), to replace a long wire hanging outside. This massively improved my SWL signals and with the hope of one day transmitting on them I borrowed an antenna analyser from a Ham friend.......considering I simply cut wires to length and ran them around my loft each band was 1:1.5 or lower with impedances hovering around the 50ohm mark. None too shabby.
Recent months have seen me transmitting on 11m CB so the 10m dipole was replaced with longer wire and hung as an inverted V. It's a good 1:1, 50ohm and easily takes up to 100W. Time will tell how good it is Wink
More importantly, not one peep from the neighbours. One must've asked me a hundred times or more "what's that?" when I had the longwire outside!

So my tuppence worth turned into thrupence, but hopefully a good full shilling Smile

Have fun. All the best,
Victor
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Mitch
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Mitch

Posts : 23
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Join date : 2020-01-02
QTH or Location : Leicester
Equipment Used : FT-857D, Formac 88, 5/8 silver rod & Diamond V2000.

Flat top Horizontal centre fed dipole for the loft - any top tips? Empty
PostSubject: Re: Flat top Horizontal centre fed dipole for the loft - any top tips?   Flat top Horizontal centre fed dipole for the loft - any top tips? Icon_minitimeMon Apr 20, 2020 3:08 pm

The only problem I can see is the fact the aerial is horizontal, most people have vertical aerials so your receive will be a lot less for local breakers, but may well be really good for DX when the skip's about. I don't think a balun will do much good though for a dipole, the impedence will be about 75 ohms without so SWR will be 1.5:1 or so, that's good enough. Air choke, yes, stops common mode current and does increase bandwidth. You can only try, it's what this hobby is all about Very Happy
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hawk657
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hawk657

Call Sign : CT/X 6657
Posts : 30
Times Thanked : 1
Join date : 2020-04-19
QTH or Location : Nuneaton - Warwickshire
Equipment Used : AT5555, Midland PORTAPACK, SIRIO and FIRESTIK mobile antennas. Just building a DIPOLE for the loft as I type and just finished another T2LT.

Flat top Horizontal centre fed dipole for the loft - any top tips? Empty
PostSubject: Re: Flat top Horizontal centre fed dipole for the loft - any top tips?   Flat top Horizontal centre fed dipole for the loft - any top tips? Icon_minitimeTue Apr 21, 2020 3:33 am

Thank you so much for the great input.  cheers

I have measured today the exact lengths on either side of the inner roof pitch and it 'may' just fit in an inverted V pattern, but it'll be very tight.  The length for the Horizontal fit is no problem as the space up there is plenty.  

I have finished the Dipole build but am awaiting the PSU from Knights, which should be delivered tomorrow, so hopefully be On Air tomorrow at some point - if the radio still works after being in a Peli Case for 3 years!!....... We'll see.

Thanks fellas!
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26TC62
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26TC62

Call Sign : 26TC62, 26CT2817
Posts : 142
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Join date : 2019-06-27
QTH or Location : Portsmouth
Equipment Used : Yaesu 891, 10m pole, wire 5/8, T2LT

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PostSubject: Re: Flat top Horizontal centre fed dipole for the loft - any top tips?   Flat top Horizontal centre fed dipole for the loft - any top tips? Icon_minitimeWed Apr 22, 2020 7:53 am

The further away you can keep it from any conducting surfaces the better is about the only rule with loft antennas, and if you can't do that, don't worry. Indoor antennas tend to tune up at shorter lengths than outdoor ones.

Horizontal polarisation will be fine for working skip because the ionosphere scrambles polarisation anyway. You will see a bit of loss working local vertical stations because of the opposite polarisation, but it won't be as bad as the textbooks predict because they are looking at "free space" models and not real world ones.

I've forgotten who it is on the forum who uses an indoor bazooka up near Sheffield, but we had a great QSO last year on the short skip with me portable over on the Isle of Wight.
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Pagan
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Pagan

Call Sign : 26CT2069
Posts : 105
Times Thanked : 20
Join date : 2019-08-09
QTH or Location : Pendle, Lancashire
Equipment Used : CRT-SS9900

Flat top Horizontal centre fed dipole for the loft - any top tips? Empty
PostSubject: Re: Flat top Horizontal centre fed dipole for the loft - any top tips?   Flat top Horizontal centre fed dipole for the loft - any top tips? Icon_minitimeWed Apr 22, 2020 1:50 pm

26TC62 wrote:
The further away you can keep it from any conducting surfaces the better is about the only rule with loft antennas, and if you can't do that, don't worry. Indoor antennas tend to tune up at shorter lengths than outdoor ones.

Horizontal polarisation will be fine for working skip because the ionosphere scrambles polarisation anyway. You will see a bit of loss working local vertical stations because of the opposite polarisation, but it won't be as bad as the textbooks predict because they are looking at "free space" models and not real world ones.

I've forgotten who it is on the forum who uses an indoor bazooka up near Sheffield, but we had a great QSO last year on the short skip with me portable over on the Isle of Wight.



Hi Stuart....that was me (near Burnley, not Sheffield) on August 26th last year. I also had a short QSO with 26DC01 in Bickington, Devon (235 miles), just before talking to you. The double bazooka works very well for skip and although the S-levels are slightly down for local contacts it makes little difference. The noise levels are also much lower with a horizontal antenna and the bazooka is very "broad-banded" so the SWR is low all the way from the bottom of low-band to the "muppets" channels. Photo of my antenna below.

Flat top Horizontal centre fed dipole for the loft - any top tips? MLKT1nkb
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listener85
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listener85

Call Sign : 26-CT-3477
Posts : 9
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Join date : 2020-04-19
QTH or Location : Worthing, West Sussex
Equipment Used : CRT Superstar 3900
Age : 59

Flat top Horizontal centre fed dipole for the loft - any top tips? Empty
PostSubject: Re: Flat top Horizontal centre fed dipole for the loft - any top tips?   Flat top Horizontal centre fed dipole for the loft - any top tips? Icon_minitimeThu Apr 23, 2020 5:47 pm

Ahhhh, lockdown lockdown! We all need things to tinker with during these stay at home times and I thought I would try to knock together a loft antenna too, so with the shape of the roof an inverted V seemed the obvious choice.

It is a bit of a lash up at the moment (not sure drawing pins into the roof timbers are the approved way of fixing the ends!) but it is picking up more signal than the Stinger whip I initially got from eBay for this old Superstar 3900 CB rig I am trying out after a slight absence of just over 40 years from the CB radio scene!

I have treated myself to one of these cute little NanoVNA toys too (and a lovely cross needle SWR/Power meter), so once I had pinned everything in place and drilled another hole in the spare bedroom ceiling I tried connecting it up.... the dipole initially resonated around 24.5MHz so a few trips back into the loft snipping the ends off bit by bit and rechecking brought it up to somewhere in the middle of the CB bands with an SWR of around 1:1.3 mid bands, OK to experiment with I think.

My loft is full of diagonal timbers that have to be climbed through to get from one end to the other and my body is telling me it does not appreciate bending into the shapes required for that so many times these days! Still, at least I managed not to fall through the bedroom ceiling!

I will have a listen on the Southern Net channel this evening and find out if I can hear anything, assuming it is still happening to some degree.
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