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 Help my swr had gone loopy

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Big Massey
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Help my swr had gone loopy Empty
PostSubject: Help my swr had gone loopy   Help my swr had gone loopy Icon_minitimeTue Apr 13, 2021 4:53 pm

Hi I've got a 1/2wave silver rod it's currently mounted to side of house on a 3meter pole so is essentially 4.5foot above gutter, now this is giving me swr reading 1 1.2  ,today I purchased another pole to raise it a further 3meter above gutter and my swr jumped to 2.8 , why is this and how can I fix it , or will it be bringing rod down and adjusting top section????? Thanks for reading
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Alan Pilot
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Alan Pilot

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Help my swr had gone loopy Empty
PostSubject: Re: Help my swr had gone loopy   Help my swr had gone loopy Icon_minitimeTue Apr 13, 2021 9:09 pm

How old is the aerial.
What is the SWR on 1 and 40 ?.
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BigTone
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Call Sign : G8YMW or 26CT4498
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Help my swr had gone loopy Empty
PostSubject: Re: Help my swr had gone loopy   Help my swr had gone loopy Icon_minitimeWed Apr 14, 2021 12:02 pm

Sounds like it's using your poles as a counterpoise.
3 metres is 10ft-ish. A quarter wave at  11 metres is 8.5ft so at that will not be far off.
At 6 metres (20ft) it will be slightly longer than a half wave so the impedance will be very high.
Now I'm clutching at straws.
Wind a choke in the coax as close to the aerial as possible.
Clip 5ft of wire to the base of your mast and let it dangle (hoping that takes the overall length of the mast (electrically) to 3/4 wave which would bring it back down to low impedance

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Victor
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Help my swr had gone loopy Empty
PostSubject: Re: Help my swr had gone loopy   Help my swr had gone loopy Icon_minitimeWed Apr 14, 2021 3:33 pm

Where's Conor, our Mr Northern Crusader? He'll be telling you all about 'common mode', end feds, grounds and such. Wink

The 'choke' idea suggested by BigTone, (hiya Tony), is a good one. What was that 27MHz coax choke? Think it's five turns of coax at 110mm, (4.25 inches old money), or something like that.....about the same diameter as a soil pipe, (the big pipe from the loo). Wind that as suggested at the base of the antenna.

Ain't antennas fun? Very Happy


You'll only be pulling it down, SWR, adjust, back up, damn, back down, etc. etc. otherwise. Wink

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BigTone
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Call Sign : G8YMW or 26CT4498
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Equipment Used : CRT 9900, Yaesu FT817, Kenwood TS570, Icom 910
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Help my swr had gone loopy Empty
PostSubject: Re: Help my swr had gone loopy   Help my swr had gone loopy Icon_minitimeWed Apr 14, 2021 5:50 pm

Hi Victor.
Yes, that sounds about right.
A choke, more often than not, is good practice and my other suggestion is also a quick install

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Victor
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Help my swr had gone loopy Empty
PostSubject: Re: Help my swr had gone loopy   Help my swr had gone loopy Icon_minitimeWed Apr 14, 2021 6:44 pm

Hi Tony,

I agree mate and a good quick fix that's worth trying.

Usually I only muck around with balanced dipoles but recently built a colinear for 2m/70cms so end fed. Despite the coax stub match it was only after remembering coaxial choke discussions here at Charlie Tango that I gave it a go and that antenna now works beautifully.

Sure is a helpful bunch here. Smile
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Help my swr had gone loopy Empty
PostSubject: Re: Help my swr had gone loopy   Help my swr had gone loopy Icon_minitime

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