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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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25th Jul 2020, 12:40 am | #1 |
Heptode
Join Date: May 2015
Location: Chatham, Kent, UK.
Posts: 947
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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. |
25th Jul 2020, 10:57 am | #2 |
Nonode
Join Date: Jun 2013
Location: Surbiton, SW London, UK.
Posts: 2,801
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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 ? |
25th Jul 2020, 1:43 pm | #3 |
Guest
Posts: n/a
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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
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25th Jul 2020, 1:58 pm | #4 |
Dekatron
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 8,923
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Re: Multiband vertical
Same price too on Ebay and in the UK.
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25th Jul 2020, 3:03 pm | #5 |
Heptode
Join Date: May 2015
Location: Chatham, Kent, UK.
Posts: 947
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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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25th Jul 2020, 5:06 pm | #6 | |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,923
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Re: Multiband vertical
Quote:
I may yet have to admit the a VNA beats a GDO. B
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Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch. |
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25th Jul 2020, 5:11 pm | #7 |
Heptode
Join Date: Sep 2009
Location: Tonbridge, Kent, UK.
Posts: 684
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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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