Useful Ebay aerial manufacturer

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paulears
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Useful Ebay aerial manufacturer

Postby paulears » 13 Oct 2016, 07:50

I took a punt on this item on ebay.
http://www.ebay.co.uk/itm/Base-antenna-5-8-435-mhz-HAM-430-440-MHZ-70CM-BAND-/302097774644?hash=item46566e3834:g:Xb0AAOSwNsdXRqkT

A vertical 5/8th antenna from Slovakia - sounded a bit odd, but quite cheap. It came really quickly (quicker than some UK purchases) and is clearly made by somebody with some proper machining facilities - not a bodge job. First thing is that it really performs well, does have 3dB gain over a dipole and the design is slim and light weight. VSWR very low and wide enough to transmit on quite a bit either side of centre. He makes quite a lot of useful aerials I note. N type connector, and rather neat design. You thread the cable through the mount, screw up the N type, then slide it back down and secure with one screw. The connection to the mounting pole uses a small offset clamp and is rather neat.

I shall buy more from him if I need similar.

No connection with him, just thought I'd share a reliable ebay foreign seller.

I was tempted to destroy it to find out the internal details and make them myself, but I don't have a lathe or the ability to create threads in aluminium, which he clearly does!

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Re: Useful Ebay aerial manufacturer

Postby wa10 » 13 Oct 2016, 10:35

Open it up but mind you don't spill the fairy dust,

a 5/8wave only has theoretical gain of about 1.2dbd & only when mounted over an infinite groundplane that does not exist in the real world,

5/8waves get their small increase in gain by virtue of their current maxima which is always 1/4wave down from the tip of none loaded antennas been 1/8wave higher above ground than a 1/2wave,
the lower 1/8wave of a 5/8 is out of phase with the upper 1/2wave and cancels some of the gain seen by just raising a 1/2wave to the same tip height,

a 1/2wave dipole or starduster style antenna properly installed at the same tip height as a 5/8wave has a little more low angle gain than a 5/8wave,

to get 2.9dbd you would need a significantly longer antenna with more than one element in phase & vertically spaced wide enough to realise the near full benefit of the extra element,

what this guy is claiming for gain over a dipole is impossible unless your 1/2wave is not installed correctly, its faulty or its endfed with a very lossy matching network.

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Re: Useful Ebay aerial manufacturer

Postby paulears » 13 Oct 2016, 18:30

I'm a little confused here - certainly since 1980 when I first came across 5/8th designs, every manufacture claims 3dB (or the 2.9dB) for their performance over a half-wave dipole. Respected manufacturers too, not fly-by nights or the Chinese manufacturers. I'm wondering why this has become a 'standard' for specs if it isn't true? Over the years, I've trusted the specs from people like Jaybeam - they still have 3dBd gain 5/8th aerials in their inventory. How do I balance this against your theoretical gain of 1.2dBd?

Maybe he is claiming something technically incorrect - but so are much, much larger and well established antenna design companies.

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Re: Useful Ebay aerial manufacturer

Postby wa10 » 13 Oct 2016, 22:08

paulears,

I never saw any respected source claim a 5/8wave with 1/4wave radials has 3dbd, its not an industry standard claim, its the sort of thing some cb antenna makers claim,
1.2dbd when mounted over a perfect groundplane is not my theoretical gain, in the real world of 1/4wave radials its less than that,

3dbi is closer to the truth and that vanishes if you elevate the 1/2wave to the same tip height,
antenna modelling software like EZNEC, 4NEC2, CST, the ARRL guys and actual tests with real antennas confirm it,

The info and history of the 5/8wave is all over the more technical cb & amateur forums,
most of the info on 5/8waves comes from broadcast antenna testing over huge radial systems, Reynolds wrote an article in the 1920's based on broadcast engineers tests,

it is easier to make a low loss matching setup for a 5/8 than it is for an endfed 1/2wave because you are not dealing with such a high end impedance, a dipole or starduster has no matching device to have loss in,

There is no majic 3dbd in a 5/8wave.

can you post a link to the 3dbd 5/8 on jaybeams site, the site is very very slow for me,

Thanks

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Re: Useful Ebay aerial manufacturer

Postby paulears » 15 Oct 2016, 19:59

Ok - here's a few links to the amphenol jaybeam site. Some ⅝ mobiles
http://www.amphenol-antennas.com/getattachment/9ed11ec0-71a5-484c-8952-c7757d598a29//Products/Antennas/Automobile-Antennas/Body-Mount/WL147KN02.aspx
http://www.amphenol-antennas.com/getattachment/ed1521ac-2c6a-486f-ba02-3c11534dbb05//Products/Antennas/Automobile-Antennas/Magnet-Mount/WL127KN01.aspx
These are, of course mobile antenna types - but these too would suffer from having limited ground plane characteristics, wouldn't they?

Is the problem (that I have overlooked) simply that the ground plane elements are simply not sufficient to produce the gain? Does this also mean that a quarter wave vertical on a ground plane performs worse than a half wave dipole? I assumed, perhaps wrongly that they both had a 0dBd gain, but performed as well?

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anyone reckon they have the best ideas ??Re: Useful Ebay aerial manufacturer

Postby stanogs68 » 15 Oct 2016, 20:17

what is the cheapest and best aerial for cb\ham \scanning in everyones mind there is three different bands ????
computers mess with my brain !

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Re: Useful Ebay aerial manufacturer

Postby kr0ne » 15 Oct 2016, 21:43

It depends..................................................

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Re: Useful Ebay aerial manufacturer

Postby wa10 » 16 Oct 2016, 03:41

paulears,
Thanks for posting the jaybeam links,

a 1/4wave with horizontal radials has less gain than a 1/2wave dipole unless you slope the radials down like an old style starduster, then it acts similar to a dipole that's easier to mount and feed,

its not that the radials are too short on your 5/8, they won't make that gain with any sized groundplane,

you possibly did not overlook anything, just looking in the wrong places, cb antenna makers made all sorts of claims about 5/8waves, most of them still do,

have a look for "The 5/8-Wavelength Antenna Mystique" by Ronald K. Reynolds, K7DBA & "The 5/8-Wavelength Mystique" by L.B. CebiK

jaybeam only say "gain 3db", without something to compare against its meaningless but since they are a professional setup id assume they mean 3dbi ( 0.85dbd ),
3dbd for a 5/8 base antenna with 1/4wave radials is nonesense,
im not saying the antenna won't work ok & be easier to mount and feed than a dipole, it just won't give 3dbd.

have a look what jaybeam say is needed for 3dbd http://www.amphenol-antennas.com/getatt ... ssories-(1)/Tri-Sector-UNICELL-Accessories/Mounting-Kits/7533xxx.aspx

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Re: Useful Ebay aerial manufacturer

Postby paulears » 16 Oct 2016, 11:21

Interesting that it's getting on for 100 years later, and still the sources of information cannot quite agree. Clearly from the jaybeam specs, the gain itself is a measurement derived from the polar pattern, but with the lobes and nulls being slightly different for each design, I wonder if it's the ⅝ component making all the difference, or something else. I'm nowhere clever enough to work this one out, but they quote a radiation angle - yet I cannot find anywhere any details on how such a thing is actually calculated? Even though they now produce specific aerial designs that have tilt, to downwards direct the main lobes - this must impact on any calculation they used to measure beam angle too? The physics seems to show that it's the location of the maximum current points in the design that matter most, but is this what causes, or results from other design tweaks?

I do rather like the claim that their antenna can resist lightning strikes of X amps!

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Re: Useful Ebay aerial manufacturer

Postby wa10 » 16 Oct 2016, 14:09

professional antenna firms use modelling software & some use anechoic chambers, some do actual tests to verify the model,

Most cb & some amateur antenna makers just build antennas and make gain figures up,

yes its the height of current maxima above ground, a 5/8 or .64wave raises the current maxima higher than a 1/2wave on the same pole,

bear in mind that a typical uhf antenna install is many wavelengths above ground whereas the 5/8 mystique articles are not.

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Re: Useful Ebay aerial manufacturer

Postby stanogs68 » 17 Oct 2016, 18:57

I want a nice small powerful CB aerial ,( I am high up as land li s ) and a good powerful scanning aerial ,I been told for amateur radio a white stick ??
computers mess with my brain !

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Re: Useful Ebay aerial manufacturer

Postby paulears » 17 Oct 2016, 20:28

Stan - I don't think that small and 'any good' really work when you look at CB, because 11m needs bigger aerials to be efficient. For ham radio, white sticks are popular - although there are rather a lot of different ones.


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