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MEGLOTRON
Registered: 06-2011
Posts: 7
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Re: CB antenna radial myths and Legends!
You can coil-load just about anything, including radials, but for the best performance, in this case; better isolation from RFI and freedom from unnecessary additional inductive reactance, full 1/4 wave radials should be used, however, if an antenna is designed for shorter radials you will have to retune the matching network to keep the reactance near zero and SWR low.
The 30° downward radials do set the load right at 50ohms when operating a 1/2 wave dipole but typically the best isolation and performance from a bottom fed 5/8 is found when using 90° radials, though you can set the match for any length or downward angle radials.
If you wanted to increase the length of the radials on the Sirio 827 you would need to remove some inductance from the bottom of the coil and relocate the feed point tap for the new 50Ω location on the coil. A friend of mine did this to his Spectrum 1600 about 5 years ago and I seem to recall he said he had to remove a turn or a turn and a half, and the tap went up a turn or so.
I have read of getting improved performance from the Imax 2000 by adding 5/8-3/4 wave long insulated guy-wire radials to the top u-bolt, but whether or not retuning was necessary wasn't mentioned. It's looking for a 1/4 wave counterpoise mast beneath it so I would presume it might not need much retuning of the rings.
The new Sirio Gain Master doesn't want radials because it's center-fed design already has the one it needs in the bottom half of the antenna, and adding more would upset the balanced design and actually degrade it's performance.
 Sorry about the edit, I was being hollered at when I was posting yesterday and hit submit before I had finished.
Last edited by MEGLOTRON, 25/Jun/2011, 1:37 pm
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24/Jun/2011, 8:56 pm
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yamanx1
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Registered: 09-2007
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Re: CB antenna radial myths and Legends!
Thanks and welcome 
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By all means think yourself big, but never think others small.... R.F.Scott |
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24/Jun/2011, 9:17 pm
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electronica special
Registered: 05-2010
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Re: CB antenna radial myths and Legends!
interesting reading,i plan to import a maco v5000 antenna soon,lets just say that a 5/8 wave with full size radials floats my boat ! (electronica special-sigma 2)
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24/Jun/2011, 10:50 pm
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CraigOWL
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Registered: 06-2010
Location: Sheffield. The Steel City.
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Re: CB antenna radial myths and Legends!
Just as a footnote guys,i had a radial on my mobile antenna (Red Devil,or long coil modulator) and it brought the swr down by 1.2.
Also it seems to bring in groundwave signals a bit better than it did without the radial on.
I have noticed 2 types for sale,a 3 point and a 5 point.Mine is a 3.
They are around £6 on Ebay,or Nights shop,and well worth trying out if your swr is high and wont come down.
I find it interesting that some people think that adding a radial will take the swr rading up,due to altering the legth of the antenna,but to be honest,its only around 1.5 inches difference,if that.
Anyway,it worked fine for me,but ive changed to a Sirio 5000 turbo which works well,wonder if i can get a radial on that somehow to see if groundwave improves?
Not having a homebase set up,i cant comment on your posts above.
---
26FB79 26FI79 26SY351 26OK64
"Women are like old Lambrettas,you can only push them so far"
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25/Jun/2011, 12:33 pm
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MEGLOTRON
Registered: 06-2011
Posts: 7
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Re: CB antenna radial myths and Legends!
quote:
CraigOWL wrote:
Just as a footnote guys,i had a radial on my mobile antenna (Red Devil,or long coil modulator) and it brought the swr down by 1.2...
Not having a homebase set up,i cant comment on your posts above.
I haven't played with those mobile radial kits but I've seen some on Wilson 1000s and thought it a gimmick due to the non-resonant shortness, but I have wondered what would happen to the performance if 2'-5' Firesticks were used in place of the short stubs those kits come with.
Last edited by MEGLOTRON, 25/Jun/2011, 1:46 pm
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25/Jun/2011, 1:45 pm
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John193
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Registered: 11-2008
Location: South Glos
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Re: CB antenna radial myths and Legends!
Radials or cointerpoise as they are being used as are better the longer they are. Longer is best its got little to do with matching and more to do with radiation angle.
1/4's will just match out a g-plane antenna but the longer the radials are the lower the angle of radiation will get. bending them down draws up the resistance as the antenna becomes more like a centre fed diploe ie 70-75 ohms ish. Efficiency increases with more radials as the plane image becomes more like a true perfect earth. its about 72% with four 85% with eight and about 90% with sixteen so the laws of diminishing returns starts to kick in a bit here. A 5/8 can theoretically give 1.4dB over a 1/2 but as the feed impedance becomes more critical this is rarely achieved in practice.
So a 5/8 with massive feed matching coils and about 16 radials is about as good as a cointerpoise antenna can get in practice.
john193
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12/Aug/2011, 11:09 pm
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Hot Fusion
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Registered: 03-2008
Location: South West England
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Re: CB antenna radial myths and Legends!
I understood that these 'radial' kits were not ground radials at all, but rather capacity hats of a kind?
After all, they seem to be fitted above loading coils on the radiating element.
Not sure what to make of that...
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Andy - FB107
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13/Aug/2011, 11:16 am
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26OD022
Registered: 08-2011
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Re: CB antenna radial myths and Legends!
The mobile antenna radial kit is indeed a type of capacitance hat, and the worst place for it is at the base of the antenna underneath a coil, if you've got one then I suggest you take it off, if it helps with VSWR then take it off and find out the reason why you're having VSWR problems, by their very name a hat is meant to be worn on the head, not the feet 
Some god gen reference radials fitted to 5/8 wave antennas, if you've got a 5/8 wave antenna and it doesn't have radials, I can assure you it will not have any gain over and above that of a 1/2 wave antenna, the manufacturer is selling you short 
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15/Aug/2011, 11:45 pm
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mikefox whiskey
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Registered: 02-2009
Location: Northern Ireland
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Re: CB antenna radial myths and Legends!
I think i will put the radial kit back on my Imax again now that I have a good idea of the local regular signals and watch for any difference, it will mean dropping the antenna height a meter and a half or so as it's a bit cumbersome with the radials on to get up.
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(Forum user name is now SuperNasty)
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16/Aug/2011, 9:26 pm
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Coppernob
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Registered: 02-2011
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Re: CB antenna radial myths and Legends!
As I understand it the purpose of radials on a vertical are for impediance matching as said before the impediance on a vertical without them would present a high vswr miss match.some manafacturers get around the problem by having loading coils in the base or indeed capacity hats.
I have heard all the usual bull on air ie with radials I only recieve better in the direction the radials are pointing etc.
Ask yourself a question...Why do you think does the old sigma 4 ,sirio vector 4000 have the great whacking basket on the bottom?
Its because its a 3/4 wavelength long and the radials are sloped downwards so as to present the right impediance to the transciever,therefore unity is agreed.
Adding the radial kit to a antron imax will ncessitate in the signal leaving the antenna at a much lower angle,great for dx,if however you just want the local chit chat to your friends then it really isnt neccesary to have them...
Hope this is clear.
Best regards Roger-Coppernob,
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25/Aug/2011, 5:41 pm
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