70MHz antenna

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Werthers
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70MHz antenna

Post by Werthers » 12 Oct 2019, 16:36

I'm planning on building a 70MHz antenna for 4 meters and I'm not allowed to install any antennas outside neither do I have access to my roof whatsoever and I do not have a garden.

I use to have an indoor dipole indoors which pretty much dominated the room it was in and wasn't really a permanent setup anyway not to mention being a pain as it got in the way of everything, however it did perform well. I don't have that dipole anymore as my ex girlfriend snapped it up a while back.

I have a small loft so I'm limited for space and I have done some measurements of the loft to see what is possible.

A half wavelength is just under 7 foot although the loft is only about 5 foot high so putting a dipole up vertical wont fit so it will have to be somewhat horizontal and I'm thinking of a V or L shaped dipole antenna which will fit. I'll mainly be working FM.

Here is a few bits I've ordered to start things off.

I'd really appreciate any ideas or advice.
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Werthers
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Re: 70MHz antenna

Post by Werthers » 12 Oct 2019, 19:17

Well after doing some thinking my idea of the 70MHz dipole in the loft probably wont perform that well if at all unless its a standard vertical dipole which still wont be the best but will work ok, but as I don't have the height in the loft I need for a vertical dipole for 70MHz its not going to happen.

I've been looking at a few antenna designs but they all require to be lengthy in order to be half decent.

There is the Viper Antenna which is available for 70MHz and its a wire antenna so its more practical for indoors and easy to take down and put away when I'm not using it and offers a 3.0 dbi gain however the only problem with the Viper antenna is that its just over 12 foot in length and my ceiling is 10 foot high from the floor... I could build a smaller version of the Viper antenna of course it wont fit in the loft and building a smaller version I'd lose some gain but would be easier to pin up. If I can achieve a 1.5 to 2 dbi gain then it be better than my other idea.

Also the only other antenna designs I've seen are the J-Pole and Slim-Jim designs which I don't like.

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Re: 70MHz antenna

Post by DX-Digger » 12 Oct 2019, 19:37

You could go for a 1/4 vertical with 4 x 1/4 radials that would work.
Or could you fit a Delta loop in the loft?
I use one on 6mtrs ok its outside but works very well.
Or a magnetic loop or a halo type antenna.
Anyway Just a few idea's
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ch25
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Re: 70MHz antenna

Post by ch25 » 12 Oct 2019, 20:05

Werthers wrote:
12 Oct 2019, 16:36
I'm planning on building a 70MHz antenna for 4 meters and I'm not allowed to install any antennas outside neither do I have access to my roof whatsoever and I do not have a garden.
Don't bother than.
Chris
You can't have too many antennas...

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Werthers
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Re: 70MHz antenna

Post by Werthers » 13 Oct 2019, 09:05

DX-Digger wrote:
12 Oct 2019, 19:37
You could go for a 1/4 vertical with 4 x 1/4 radials that would work.
Or could you fit a Delta loop in the loft?
I use one on 6mtrs ok its outside but works very well.
Or a magnetic loop or a halo type antenna.
Anyway Just a few idea's
:thumbup:
The Delta loop sounds like the one to go for, I may even just about get away with a 1/2 wave Delta loop in a 5 foot high spacing :think:

I'll build a few antennas. The 1/2 Viper is easy to make as well which is basically a coax dipole that I could string up somewhere temporary while I work on a permanent setup for the loft. I will build the Delta loop as well and see how each antenna performs.

Luckily where I live I have got a good take off point with reasonably high elevation hence why I do well with indoor antennas.

I'll also need to find some half decent coax for the Viper build otherwise I could end up with this situation...
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Last edited by Werthers on 13 Oct 2019, 09:44, edited 2 times in total.

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Werthers
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Re: 70MHz antenna

Post by Werthers » 13 Oct 2019, 09:12

ch25 wrote:
12 Oct 2019, 20:05
Werthers wrote:
12 Oct 2019, 16:36
I'm planning on building a 70MHz antenna for 4 meters and I'm not allowed to install any antennas outside neither do I have access to my roof whatsoever and I do not have a garden.
Don't bother than.
Chris
Thats not very positive now is it :D

Giving up is not an option, besides I could never give up my 4 Meters.

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Re: 70MHz antenna

Post by mr_m3 » 13 Oct 2019, 19:31

1/4 wave and a ideal ground plane may work in your loft as already stated or a coil shortened dipole but it really depends on how much power you plan to run through it i suppose, a delta loop sounds appealing too
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