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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 25th Jul 2020, 12:40 am   #1
mickm3for
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Default Multiband vertical

Hi any advice please I have a vertical 1/4 wave aerial with loading coils in it on a 20 ft ally mast this is earthed, the SWR at say 7.15MHz has been 1.2 to 1 rising if I go up or down in frequency I recently traced my S9 noise level to a length of coax with an open braid somewhere in the middle (S9 with only the coax connected no aerial) having replaced this I find my SWR is full scale to 1 but 1:1 with 50 ohm load. My question is the aerial is 1/4 wave with helical 1/4 wave radials BUT being on a 20 ft earthed mast this is in parallel with the ground plane would it be better to insulate the ground plane/aerial from the mast, the tuning of the radials seems very broad as it is the main vertical being fixed length apart from 80m band.

Help, Mick.
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Old 25th Jul 2020, 10:57 am   #2
Restoration73
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Default Re: Multiband vertical

The aerial data should state info on mounting arrangements etc. The only one I have
used is a Comet CHA250 that benefitted from a ground plane. Can you get hold of an
antenna analyser e.g. MFJ 259 that will allow you to sweep your antenna across the
bands to assess resonance, swr etc ?
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Old 25th Jul 2020, 1:43 pm   #3
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Default Re: Multiband vertical

A Nano VNA is much cheaper than an MFJ 259 and supurb value for money.https://uk.banggood.com/Original-Nan..._warehouse=USA
 
Old 25th Jul 2020, 1:58 pm   #4
HamishBoxer
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Default Re: Multiband vertical

Same price too on Ebay and in the UK.
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Old 25th Jul 2020, 3:03 pm   #5
mickm3for
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Default Re: Multiband vertical

Hi i will reatach this vertical direct to the mast and run a scan when i work out how to use the vna that came today thanks for your help Mick
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Old 25th Jul 2020, 5:06 pm   #6
Bazz4CQJ
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Default Re: Multiband vertical

Quote:
Originally Posted by mickm3for View Post
Hi i will reatach this vertical direct to the mast and run a scan when i work out how to use the vna that came today thanks for your help Mick
If this is your first venture in to the world of nano VNA's and aerials, please report your back on your experience, so that we others who have yet to go down that path can follow your adventure .

I may yet have to admit the a VNA beats a GDO.

B
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Old 25th Jul 2020, 5:11 pm   #7
ex seismic
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Default Re: Multiband vertical

If this is the Sandpiper multi-band vertical with tuned radials sticking out from roughly the middle, the instructions say it should be about four feet above the ground. Takes a while to get the whole thing tuned up on all bands as they interact. Have worked the US with one using an FT817 so cannot be a bad aerial.
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