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Re: Sirio 827 Radials

Posted: 14 Feb 2021, 21:35
by thundercat
bigpimp347 wrote: ā†‘14 Feb 2021, 21:23
thundercat wrote: ā†‘14 Feb 2021, 20:58
bigpimp347 wrote: ā†‘14 Feb 2021, 19:56 the 827 will work perfectly fine without radials.
they are mostly there for show and to help radiate the signal across the ground
if you mount it at it's correct height, a 5/8th off ground so around 20ft it will use the ground as it's ground plane.
Is that 20ft to the tip of the aerial?

no to the base..
the idea is use an antenna (without radials) a wavelength it is off ground,
so if it's a half wave, then 17ft, a 5/8th then around 20ft.

Cushcraft used the idea years ago on various VHF antennas where line of sight is more important
they just made the antennas ground a matched wavelength below it.
Cheers for that, I dare say Iā€™m not far off 20ft to the base of my antenna now šŸ‘

Re: Sirio 827 Radials

Posted: 14 Feb 2021, 21:38
by stanogs68
bigpimp347 wrote: ā†‘14 Feb 2021, 21:23
thundercat wrote: ā†‘14 Feb 2021, 20:58
bigpimp347 wrote: ā†‘14 Feb 2021, 19:56 the 827 will work perfectly fine without radials.
they are mostly there for show and to help radiate the signal across the ground
if you mount it at it's correct height, a 5/8th off ground so around 20ft it will use the ground as it's ground plane.
Is that 20ft to the tip of the aerial?

no to the base..
the idea is use an antenna (without radials) a wavelength it is off ground,
so if it's a half wave, then 17ft, a 5/8th then around 20ft.

Cushcraft used the idea years ago on various VHF antennas where line of sight is more important
they just made the antennas ground a matched wavelength below it.
[/quote :thumbup: :thumbup: :thumbup: :thumbup:

Re: Sirio 827 Radials

Posted: 14 Feb 2021, 22:04
by ch25
bigpimp347 wrote: ā†‘14 Feb 2021, 21:21 get an 827 remove the useless there for show radials and see what happens..
it still works.. what do you think the coil is for ? , it's matching system as you described in the 'silver rod' post.
the radials, like on a lot of Sirio antennas pretty much do bugger all..
I don't have 827 here, but I have Mmana, pretty accurate software. Almost as good as Eznec i use too.
I created 827 and made a simulation with and without radials for antenna 20m over the ground.
Images are self explanatory.
radials.jpg
no radials.jpg
Coil parameters are dependent from Z and jX which vary from radiating element and radials length. Easy to spot on Smith chart.
There is one possibility, when you remove radials and SWR in OK: you have dummy load connected.

Re: Sirio 827 Radials

Posted: 14 Feb 2021, 23:30
by The Collector
So, does that equate to just 1/3 of a dbi loss? I'm not up on techy stuff.
Would that even be measurable on someone's signal meter on non-skip AM/FM/SSB?

I think if the poster can't physically get the aerial up any higher...which would be nice and beneficial but maybe not practical.. he can just plug in as many legs as he's able to and it won't really make any measureable difference.

And how come it's only got 5.odd dbi gain when an Antron's got 9.9? Lol ;)

Re: Sirio 827 Radials

Posted: 15 Feb 2021, 07:01
by ch25
SWR value...

Re: Sirio 827 Radials

Posted: 17 Feb 2021, 10:56
by bigpimp347
20m from the ground ???
so you're using computer generated maths but not actually tried it physically ??

anyone can claim something works because they use a program to tell them, doesn't mean it does.
if you remove the radials you get a dummy load ??
wow, how does that work then ??
a dummy load that only resonates on one frequency, has resonance on one frequency and is a 50ohm resistance on one frequency
you know what a dummy load is right ??

Re: Sirio 827 Radials

Posted: 17 Feb 2021, 11:08
by bigpimp347
The Collector wrote: ā†‘14 Feb 2021, 23:30 So, does that equate to just 1/3 of a dbi loss? I'm not up on techy stuff.
Would that even be measurable on someone's signal meter on non-skip AM/FM/SSB?

I think if the poster can't physically get the aerial up any higher...which would be nice and beneficial but maybe not practical.. he can just plug in as many legs as he's able to and it won't really make any measureable difference.

And how come it's only got 5.odd dbi gain when an Antron's got 9.9? Lol ;)
1/3 dBi is miliscule in dB
An isotropic radiator is a fictitious radiator that radiates evenly in all spatial directions. For comparison: 0 dB = 2.15 dBi.

the reason the A-99 uses dBi is because gullibles don't see the 'i' and just see 9.9dB
like with linears people don't see the W pep when they look out out put and just see W,
a very good sales ploy.
i mean would you buy a CB antenna with 3.5dB gain or 9.9dBi ??
when pretty much 9.9dBi is 3.5dB ??

and 3dB is double the power doesn't seem as appealing when you say it only doubles the power,
so 4w at the antenna is 8w out the antenna, hardly worth buying.

also some references are based on a center fed dipole, which has a degree of gain, then there's antennas with unity gain, as in none.
so what do you go for, ?

me, i look at 1/2 wave, 5/8th wave, type of coax, height above ground and use it.

Re: Sirio 827 Radials

Posted: 20 Feb 2021, 14:04
by 5973Laterz
Yes really the Antron has 7.75dBd gain, pure fantasy. It has 0dBd the same as any 1/2 wave antenna yes the Ā£30 silver rod. I will add my two cents. Not having radials with mean 4 things... 1) you probably have to lengthen your antenna a little more 2) you may suffer a little more ground losses i.e. some of your RF energy will be lost in the earth below the antenna 3) you may experience common mode current on your coax that will mess up your radiation pattern 4) your RX may be slightly noisier. None desirable... especially 3 - if common mode currents mess the antenna TX and RX response up as designed you may find your low angle radiation (and reception at low angles) is negatively effected.. that will potentially have a real performance impact.

You may well lose a little of the gain by not having the radials. It will work but not quite to spec. And why an antenna is being modeled at 20m (when few can erect it at such height) when it will be mounted at 20 feet is anyone's guess.

What will happen in the real world when mounted in a completely unknown environment with walls, sheds, gutters, other antennas, real earth/concrete/vegetation etc is anyone's guess. The closest you would get to a model is mounting it 20 feet above the sea... second to that in the middle of a massive playing field with your coax running away by 20m or so so you are out of the close field energy.

It'll still radiate with no radials, but just not as well as an idealized model or actual installation with the radials would suggest.

Get it up in any practical way you can... if you cannot have radials so be it.. you may need a choke in your feed line if you experience any oddities at the radio end, SWR, RF burns, TX audio problems.

Re: Sirio 827 Radials

Posted: 20 Feb 2021, 22:39
by The Collector
You're all talking nonsense. My old Antron clearly had more than 9.9 gain, plus if I painted it pink and put it vertically on a rotator, it'd give me even more ;)

Re: Sirio 827 Radials

Posted: 21 Feb 2021, 20:25
by bigpimp347
The Collector wrote: ā†‘20 Feb 2021, 22:39 You're all talking nonsense. My old Antron clearly had more than 9.9 gain, plus if I painted it pink and put it vertically on a rotator, it'd give me even more ;)
don't forget the ground plane kit
there's another 5dB from the radials that do buggery.

Re: Sirio 827 Radials

Posted: 22 Feb 2021, 10:27
by 5973Laterz
Ground plane radials or counterpoise may well do something, it is metal in the close field of your antenna... it is your antenna, an AC RF electrical system. It will like do something but it will in most cases be a small effect. Points 1-4. It depends on the precise installation, what they may do or may not do. At a guess they may keep cmc's of your line and maybe protect you a little from ground losses from the earth below to an estimated 0.5dB.

Any radials are generally better than no radials... it is just they are generally not acceptable to the eye.