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Call Sign : 18-CT-002 Posts : 4 Times Thanked : 0 Join date : 2020-05-03 QTH or Location : Monemvasia. Equipment Used : President Grant 2 premium, CRT SS6900N, Solarcon A99, Sigma Skip Master Age : 48
Subject: Sigma Skip Master Mon May 04, 2020 2:22 pm
I am wondering if anyone have tested the Sigma 5/8 Skip Master fiberglass antenna. I am using one this time but i am not sure if this antenna works better than an λ/2 aluminium antenna. Does anyone know????
Not that you'll be able to tell. Whether it's a quarter wave, half wave, 5/8 wave or whatever the gain difference between them all is next to nothing. This ie even more so when you consider that whereas people install quarter waves with proper ground planes they don't with 1/2 waves and 5/8 waves which need them just as much due to a common misconception that half wave and longer end fed antennas don't need a ground plane. Unfortunately for them physics, in particular Kirchoffs Law, requires they do and if you don't use radials then it's the mast and your coax being used as one.
Looking at the stated theoretic gain between a 1/4, 1/2 and 5/8 doesn't always give the best picture. In my location I found that the performance between a 1/2 wave A99 and a 5/8 Sirio GPE was much larger than 1 or 2db.
Obviously location is a factor but bigger is generally better.
It's not theoretical gain, it can be modelled and it's actually measurable. However that's only looking at the maximum gain and not the entire gain over the elevation pattern of the antenna. There will be lobes and nulls at different take off angles on each of those which will affect whether or not you'll receive a signal stronger from station X on one antenna than another.
Even the RF grounding can affect the angles of those lobes and nulls so a 5/8 wave that comes with radials, such as a Sirio 2016, may appear to work better or worse to station X than a 5/8 wave that doesn't come with any. That may explain the difference you saw between using a 5/8 wave with ground planes and the A99.
In regards to the mast and the coax and not worrying about it, "it depends". If you're lucky enough that the mast is carrying the majority of the workload as a RF ground then no you don't need to. However if you're unlucky that the mast length presents a higher impedance on 27MHz than your coax is then you'll have some issues with common mode RFI and all the negatives that come with that including higher noise on receive. At that point yes you need to be worried about it if it's negatively impacting you.
If however you're only interested in decent performance for local contacts talking across the same town/city pretty much none of the above matters a hill of beans. Neither what the wavelength of the antenna you use is nor how good the ground plane is makes much difference and it's how high you can get it up which will be what makes it much better or worse. For local contacts being able to double the height from say 10ft to 20ft at the base will more than compensate any other shortcomings of antenna A compared to antenna B.