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Old 26th Apr 2020, 1:48 pm   #1
djsbriscoe
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Default Linsley Hood "Lofty" antenna-Advice on materials please.

I'm considering building a copy of John Linsley Hoods "Lofty" FM antenna.
I have attached the relevant article below.
I can buy 3 foot by 1 foot aluminium for 4.77 (3 off needed) and the other two pieces (1' by 1' 1.59 and 2' by 1' 3.18).
I'm just wondering if aluminium (0.9 mm thick and grade 1050AH14) is OK to use (I want to keep the costs down) and what can I use instead of pop rivets?
I want to be able to dismantle the antenna easily as I live in a rented flat. And also make sure the antenna is sound electrically.
Also is there any advice on the best way to connect the coaxial cable?
Any other advice welcome. Thanks.


PS It will probably be attached to the rear of some Ikea shelving so it needs to be light.
Attached Files
File Type: pdf LOFTY_FM_ANTENNA.pdf (909.4 KB, 144 views)
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Old 26th Apr 2020, 2:09 pm   #2
mhennessy
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Default Re: Linsley Hood "Lofty" antenna-Advice on materials please.

This looks like an interesting idea - I'd be interested to hear feedback from anyone who has tried this, as my current loft aerial (just a "freebie" dipole, mounted at the top of the rafters) is only just acceptable with my better tuners. Something like this could be made to fit fairly easily up there - much more so than a traditional multi-element type.

I'd be tempted to join the aluminium sheets with M3 nuts and bolts, with shakeproof washers to help improve the contact. For the connection to the downlead, the same nuts and bolts could be used to attach some solder tags. The co-ax could be soldered directly to these, or short wires could lead to an intermediate connector, like a terminal block or a socket of some form. Easy to build and take apart
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Old 26th Apr 2020, 2:13 pm   #3
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Default Re: Linsley Hood "Lofty" antenna-Advice on materials please.

I would go for the cardboard and ali foil, soldering or using a choc block will do for the co-ax connexions.
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Old 26th Apr 2020, 2:57 pm   #4
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Default Re: Linsley Hood "Lofty" antenna-Advice on materials please.

Cooking foil on hardboard seems hard to beat. So cheap does it need to be dismantleable?

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Old 26th Apr 2020, 3:30 pm   #5
djsbriscoe
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Default Re: Linsley Hood "Lofty" antenna-Advice on materials please.

Cardboard and hardboard that is 4 foot square is a bit difficult to handle unfortunately. Or I could just stick some tinfoil on the wall.
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Old 26th Apr 2020, 3:53 pm   #6
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Default Re: Linsley Hood "Lofty" antenna-Advice on materials please.

Quote:
Or I could just stick some tinfoil on the wall.
The "walltenna" Wireless World I think
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Old 26th Apr 2020, 5:49 pm   #7
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Default Re: Linsley Hood "Lofty" antenna-Advice on materials please.

Quote:
Originally Posted by mhennessy View Post
I'd be tempted to join the aluminium sheets with M3 nuts and bolts, with shakeproof washers to help improve the contact. For the connection to the downlead, the same nuts and bolts could be used to attach some solder tags. The co-ax could be soldered directly to these, or short wires could lead to an intermediate connector, like a terminal block or a socket of some form. Easy to build and take apart
Just a follow-up - as I was writing this, I was wondering if aluminium foil tape might be of use. I've got a few rolls of 3M stuff, which probably came from Lidl, of all places!

Sadly, from a quick test that I've just done, the glue does not appear to be conductive. OK, there'll be some pretty reasonable capacitive coupling, but it won't connect together the various bits of metal together as well as I hoped. The possibility of making the whole thing from this tape also crossed my mind, but I think that's probably out.

Another thought would be foil-backed plasterboard. Easily found in DIY stores. It would be easy to remove the foil from the inner square and the section where the cable connects, and connections again can be made using standard solder tags and shake-proof washers. I'd mount a bit of timber behind to take the screws, but penny washers would probably spread the load on the other side of the plasterboard well enough.

The edges (and bits where the foil was removed) would need to be taped over to stop them shedding white dust, but otherwise, that seems like the easiest solution to me. When you don't need it any more, just break it down and chuck it away.

How well does solder take to aluminium foil, MM?
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Old 26th Apr 2020, 5:56 pm   #8
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Default Re: Linsley Hood "Lofty" antenna-Advice on materials please.

You are right in the capacitive coupling, you can solder to ali foil using the right stuff but all to soon it eats through it, a choc block will do with a crunched end of the tape. All ali tape antenna, very feasible.
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Old 26th Apr 2020, 7:29 pm   #9
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Default Re: Linsley Hood "Lofty" antenna-Advice on materials please.

Thanks for all the replies, I like the plasterboard idea. Before I start spending any money can anyone explain a bit of the theory behind the dimensions used in this design and why does the Original author call it a "Quad"? Just some due diligence. Thanks.
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Old 26th Apr 2020, 9:18 pm   #10
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Default Re: Linsley Hood "Lofty" antenna-Advice on materials please.

Trawl the amateur radio field looking for 'cubical quad' and you'll find a lot of two element ones usually for the HF bands, but the maths scales them.

Quagi will find you yagi antennae where some or all elements are quads.

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Old 26th Apr 2020, 10:01 pm   #11
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Default Re: Linsley Hood "Lofty" antenna-Advice on materials please.

Quad, it's got four sides, other (the majority) are a straight line with a bit of thickness.
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Old 26th Apr 2020, 11:13 pm   #12
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Default Re: Linsley Hood "Lofty" antenna-Advice on materials please.

A religious transmitting station in the tropics had trouble with corona eating the ends of a yagi aerial so the cubical quad was born without high voltage ends. I have a book somewhere detailing this.

I made a two element 20m quad with bamboo speaders and flexible wire loops. I used this to talk to my sister weely, Shropshire to Halifax Nova Scotia. Heathkit DX100 AM transmitter.

There has been a lot of papers saying how superb the quads are, much of the claims seem to me to wishful thinking.

If the aerial is wanted for portable use, I would go for a two element yagi which could be folded easily. Indoor aerials are compromised by adjacent conductive equipment.

Indoors (Derbyshire) I use a vertical folded dipole made from 300 ohm ribbon held up with a drawing pin and a 4 element yagi pointing at Sutton Coldfield.
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Old 29th Apr 2020, 1:18 pm   #13
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Default Re: Linsley Hood "Lofty" antenna-Advice on materials please.

So, I've bought all the aluminium pieces (5 in total) and 2 pieces of 6" x 12" 3 mm hardboard. Awaiting delivery and will update later.
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Old 14th May 2020, 10:53 am   #14
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Default Re: Linsley Hood "Lofty" antenna-Advice on materials please.

Aluminium arriving today. I bought it from Aluminium Warehouse in Hatfield, Herts. Still waiting for the hardboard as it was sent 2nd class by royal mail.
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