Bent dipole question

Low VHF antenna discussion
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Paul_Logan
Posts: 106
Joined: 24 Sep 2014 12:58
Location: County Fermanagh, Ireland

Bent dipole question

Post by Paul_Logan » 29 Oct 2014 14:14

Heres a question for all of you antenna gurus. What will the radiation pattern be like from a dipole which has its top half vertical and its bottom half @ 45 degrees to vertical. Will it behave just like a vertical dipole?

Any answers / ideas would be great. just hooked such a configuration up for CB / 10m. On 10 it seems to be working well, but i'd love to know where the signals is headed.
Paul Logan
Lisnaskea, Fermanagh, N. Ireland IO64GG

FMDX: Elad FDM-S2 with 5 el Yagi by K6STI, Andy Bolin Phaser.
MW / SW: Perseus / Elad FDM-S2 with Inverted L wire / Wellbrook Loop.

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Julian Hardstone
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Re: Bent dipole question

Post by Julian Hardstone » 29 Oct 2014 15:07

It's essentially a Vee, or Inverted Vee as used on the HF bands
The feed impedance will be reactive with lower R, and basically it will radiate as a dipole set at 45° to horizontal

daveB
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Joined: 07 Oct 2014 16:49

Re: Bent dipole question

Post by daveB » 29 Oct 2014 15:54

Just modelled it on 4nec2. The signal will tend to be best in the direction the 45 deg leg is pointing - but there is not a huge difference. If you add a second sloped lower half you'll get a nice circular pattern and you'll have a ground-plane antenna with a 2.5:1 SWR bandwidth of around 27-31 MHz. Element length was 8.25ft. If you read the history - the original GP aerial only had a single horizontal half-wave ground plane but the manufacturer had to add a second at right angles as people wouldn't believe it gave an omni-direction pattern. Of course with software like 4nec2 you can show it.

I actually used an elevated 16ft vertical with single sloped 'ground' wires cut for 20m, 15m and 10m for HF transmitting back in 1982-1988. I had a switched LC network and was able to load it nicely for 10-15-20-and even 40m - and it proved quite effective. All those years ago I was contacted by a Russian ham who wanted to work RTTY on 30m - seemed to be he was the first station licenced on that band - fortunately I had read how to set up my FT101E to transmit on 30m and managed the contact! (Good grief - that's 40 years ago!).

Rgds

David
Sittingbourne
SDRPlay, AirSpyMini, RTL dongles, SB920s, Yamaha TX930. 5 ele compact yagi on rotator at 18ft agl. FM5 facing east, FM5 facing south, FM3 facing NE, OIRT dipole, 3-ele Moxon vertical facing east.

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Paul_Logan
Posts: 106
Joined: 24 Sep 2014 12:58
Location: County Fermanagh, Ireland

Re: Bent dipole question

Post by Paul_Logan » 29 Oct 2014 19:56

Thanks Julian and David. So it works out like a sloping dipole with a tad more signal in the sloping direction. Very interesting. Can you post a graphic from the 4nec2 David? So with extra ground plane bandwidth will increase?
Paul Logan
Lisnaskea, Fermanagh, N. Ireland IO64GG

FMDX: Elad FDM-S2 with 5 el Yagi by K6STI, Andy Bolin Phaser.
MW / SW: Perseus / Elad FDM-S2 with Inverted L wire / Wellbrook Loop.

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