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 Help please with Delta Loop antenna. 
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Post Help please with Delta Loop antenna.
OK I need some help to try and understand what is happening here. I have just built my first ever Delta Loop antenna. Following online instructions from different websites I cut the wire to 6.10m. I then cut 99cm of what I am almost certain is 75ohm coax for the matching section. Now for the confusing part. SWR is sky high on 50Mhz but the Analyser shows a perfect match on 95mhz. I could understand it being a bit off or not working at all. But 95 MHz... ???? So far off.. Any ideas?? 73 Adrian.


Sun Jul 08, 2018 1:10 pm
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 Help please with Delta Loop antenna. 
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Post Re: Help please with Delta Loop antenna.
Have you checked at 47.5mHz? You be picking up the second harmonic of the antenna at 95mHz.

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Sun Jul 08, 2018 1:56 pm
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 Help please with Delta Loop antenna. 
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Post Re: Help please with Delta Loop antenna.
I need to set it up again and double check as it would make sense. But I dont think it did.. I will update the forum once I have checked again.


Sun Jul 08, 2018 2:00 pm
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 Help please with Delta Loop antenna. 
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Post Re: Help please with Delta Loop antenna.
Hi I built on for 6m works great with a swr at 1.2.1

Attachment:
6m loop.jpg
6m loop.jpg [ 30.96 KiB | Viewed 521 times ]


Mark 2w0jmk

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Sun Jul 08, 2018 6:14 pm
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 Help please with Delta Loop antenna. 
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Post Re: Help please with Delta Loop antenna.
Mark, how did you make the matching section.. ??


Sun Jul 08, 2018 6:41 pm
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 Help please with Delta Loop antenna. 
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Post Re: Help please with Delta Loop antenna.
105cm of 75ohm tv coax cut 3cm off each end to connect to the wire and 50ohm coax.

I coiled the matching stub up and put it inside a piece of wast pipe and used to caps to water proof it all.

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Sun Jul 08, 2018 6:46 pm
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 Help please with Delta Loop antenna. 
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Post Re: Help please with Delta Loop antenna.
Well, I made a new matching section and still have the same problem. I have also confirmed it does not tune anywhere up to 95 MHz.. but 95mhz is a great match... Arrghhh...


Tue Jul 10, 2018 8:09 pm
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 Help please with Delta Loop antenna. 
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Post Re: Help please with Delta Loop antenna.
Is the antenna mounted on a non metallic pole?
I am using a fibre class pole to mount it in the air.
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Tue Jul 10, 2018 8:13 pm
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 Help please with Delta Loop antenna. 
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Post Re: Help please with Delta Loop antenna.
Don't want to sound like a numpty but when I ran an inverted 17m delta loop I just fed it at the bottom with normal 50 ohm coax via a 1:1 current balun.

The loop wasn't quite symmetrical but similar to your photo having the shorter top side and one of the two long sides being about 2ft longer than the other, almost an inverted right angle triangle, pretty well a straight 50 ohm match.

Cheers, Dave.


Tue Jul 10, 2018 9:51 pm
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 Help please with Delta Loop antenna. 
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Post Re: Help please with Delta Loop antenna.
I can't seemed to puzzle out why it's not working, when I modelled it even without the matching stub the worst VSWR is 2:1.

Forget the analyser for a moment, what does it show when you connect the rig to it and measure the VSWR? Just in case the analyser is telling lies.

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Wed Jul 11, 2018 8:31 am
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 Help please with Delta Loop antenna. 
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Post Re: Help please with Delta Loop antenna.
I have an issue with the antenna analyser telling lies.
Been adjusting my GAP Titan vertical antenna and the minimum SWR on the analyser (MFJ 259) are vastly different to the SWR readings on my external SWR meter when the antenna is connected to the rig (Kenwood TS870). Is there an explanation for this?
Sorry if I appear to be hijacking the thread but it could have a bearing.
73 de Ken G3RFH


Thu Jul 12, 2018 1:53 pm
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 Help please with Delta Loop antenna. 
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Post Re: Help please with Delta Loop antenna.
Manufacturers always state not to set up screwdriver antennas with an analyser and this has borne out for me. Bit of power and an SWR meter.

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Thu Jul 12, 2018 2:56 pm
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 Help please with Delta Loop antenna. 
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Post Re: Help please with Delta Loop antenna.
Ken, try measuring a dummy load, if R=50 and X=0 across the range then you can be pretty sure the analyser is working.

The trouble with analysers is they work fine under perfect conditions, but you are connecting to an antenna which picks up signals, some of the BC signals on the shortwave are mighty strong at times and that can mess with the internals in the analyser and affect the readings, it is a known problem with them.

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Thu Jul 12, 2018 3:37 pm
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 Help please with Delta Loop antenna. 
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Post Re: Help please with Delta Loop antenna.
You say you're "almost certain" the tuning stub is 75ohm, are there no markings on the coax?

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Thu Jul 12, 2018 4:29 pm
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 Help please with Delta Loop antenna. 
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Post Re: Help please with Delta Loop antenna.
You said 105 cms of 75ohm cable but I had a look at a version on t'internet and apparently the matching stub needs to be a quarter wave long

:scratch: It should not make such a massive difference though. As already suggested perhaps check the quality of the cable or check for any shorts ?

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Thu Jul 12, 2018 5:36 pm
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