hawk657
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Horizontal loft dipole problem
Hi all.
I have purchased from a reputable UK antenna maker, a 27Mhz dipole and have erected it into my loft as a horizontal.
No metal objects in the loft except for electrical wiring along the rafters and the small metal joints in the Apex of the roof joists. There is no water tank, just a few cardboard and plastic storage boxes.
The antenna is in free air, at the correct length both sides for a 27Mhz build and has insulators on each end, connected by non metallic string to the rafters and a correct sized air choke on the drop lead to the 'shack'.
The SWR's are equal (within 0.1) from 27.601.25 to 27.991.25 (UK 40) at 3.0 which is the start of the red band on the scale.
Down at 26Mhz the needle goes OFF the red max scale.
up at 28Mhz it is half way into the red.
I have continuity tested both the antenna and patch lead to the SWR meter and both appear normal and correct.
I wrote to the manufacture to ask advice before tampering with the length of the sides - but they just said to move it away from metal objects ... even though I had stated there were none in the loft.
I don't know where to turn because the normal formula of lengthening or shortening toward a low SWR doesn't seem to apply here as they are both equal at 3.0.
Can anyone guide me toward a usable solution as I clearly cannot transmit at 3 on the start of the red scale.
Thank you.
Matt
FB1013
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2/May/2020, 6:35 pm
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yamanx1
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Re: Horizontal loft dipole problem
Hi Matt, I read this twice, I would say the bandwidth of the antenna is very narrow and the frequencies you are trying to use are too wide apart.
So depending what you are going to use it for, and if its horizontal, then I suspect its for 27555, then you'll need to tune it for 27555 as the best SWR (Centre), meaning the range of frequencies you can use is narrow.
Loft aerials are ok, but usually for 40-80-160m, at 11m they are just a bit restricted, particularly for TX. RX you may be able to hear some strong stations. But bare in mind we are at solar minimum, so 11m activity is low
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By all means think yourself big, but never think others small.... R.F.Scott |
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2/May/2020, 6:57 pm
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hawk657
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Re: Horizontal loft dipole problem
Hi there.
Indeed, I have the antenna for use on the UK 40 and 27555. I started the SWR process there, but they are just equal at 3.0 (start of the red band on the SWR meter).
I took the other measurements down at 26 and up at 28 simply to try to get an overall picture of it.
I have swapped patch leads, moved the cardboard boxes around, tried another rig and all to no avail.
I simply do not know what to do as the SWR's are equal at 3.0 on the UK 40 1 and 40- so I cannot lengthen nor shorten it...
I just don't know what to do.
If the SWR was either Higher or lower on 1 or 40, I would obviously shorten or lengthen the antenna appropriately - but what do you do when they're both equal and both to high to transmit?
I'm stumped..
Cheers.
Matt
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2/May/2020, 7:59 pm
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2FB059
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Registered: 11-2019
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Re: Horizontal loft dipole problem
Hi Matt,
Is there any chance you might have any sort of metal around the roof? Sorry, I don't know the correct term for this, but there is a sort of metallic material that is sometimes used to cover roofs under the tiles - sort of looks like foil. I've heard of some folks having issues because of that.
Just a thought.
73
Last edited by 2FB059, 11/May/2020, 10:30 pm
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I see many sunspots in your future.
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11/May/2020, 10:29 pm
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hawk657
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Re: Horizontal loft dipole problem
quote:
2FB059 wrote:
Hi Matt,
Is there any chance you might have any sort of metal around the roof? Sorry, I don't know the correct term for this, but there is a sort of metallic material that is sometimes used to cover roofs under the tiles - sort of looks like foil. I've heard of some folks having issues because of that.
Just a thought.
73
Thanks for your reply bud.
No, there is nothing, I can see the felt/plastic underside t the slates. There is literally nothing up there - I have since purchased a new SWR of much better quality, just incase it was that .... with the same results.
I'm totally stumped and cannot use my radio for fear of damage. The SWR's are basically 3 all the way on the UKCB band and I cannot lengthen or shorten the antenna - and when i did, they get worse.
This is driving me mad as I really want to get back on the air.
Cheers.
Matt
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11/May/2020, 11:08 pm
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hawk657
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Re: Horizontal loft dipole problem
Hi there.
After a week of banging my head against a brick wall.... I found the problem.
Made a short video if anyone wants to see what was up - not what you would expect!...
https://youtu.be/bmy_6hYotGs
Cheers all.
Matt.
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17/May/2020, 12:27 am
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