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26fb010 Profile
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Accomplished DX-er

Registered: 01-2009
Location: BLACK COUNTRY
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Re: CB antenna radial myths and Legends!


But, the fact is that adding ground planes in one direction only will make the antenna more directional in that direction. As mounting an antenna on the rear of a car will make it directional forward.
14/Oct/2011, 7:56 pm Link to this post Send Email to 26fb010   Send PM to 26fb010
 
148 Profile
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New Kid On The Block

Registered: 01-2012
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Re: CB antenna radial myths and Legends!


A capacity hat is a misnomer.

What you are in fact doing is adding inductance to the antenna and in most cases this will lower the resonant frequency of the antenna.

One must not confuse resonance with impedance matching of the antenna.

Vertical CB antennas, both base and mobile allow for adjusting the length and therefore resonant frequency of the antenna but most all commercially made antennas do not offer any adjustment for optimum impedance matching at the feedpoint.

Manufacturers usually implement a small inductor or fixed capacitor to effect a 50 ohm impedance.

If you run high power then an open coil is probably best but both work.

Many different views on groundplanes and radials.

Broadcasters on medium wave or AM as the Americans like to call the band use 1/4 wavelength buried radials spaced at 3 degrees apart over 360 degrees making 120. Close in to the base out to typically 30' all radials are brazed together where most current is flowing.

See some of Kevin's work in the US here www.amgroundsystems.com.

Now if you scale this up to 11m you can see that a number of 1/4 wave radials will work as well and in the case of a mobile station the larger the vehicle chassis (which acts against ground) the better.

In a past life I transferred a QRO mobile station from your average saloon car to a VW LT truck and increased field strength by over 10db (this is not gain) at a fixed site on a calibrated spectrum analyzer. That larger chassis improved the efficiency of the antenna system as a whole.

Just my 2p - your mileage may vary.

148
Broadcast engineer that knows just enough to be dangerous.
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yamanx1 Profile
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Registered: 09-2007
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Re: CB antenna radial myths and Legends!


Interesting information, you and John 193 would get along emoticon

I have recently, and over time, put in some large radials buried as suggested. This had the effect of reducing noise by a noticeable amount. But it also started to cause rfi elsewhere. So it benefited my station, by a big margin, but made a problem elsewhere.

Which I am always trying to limit. It takes ages, and gradual movements to get optimum set up for good radiation and low rfi emoticon

A balance emoticon

---

By all means think yourself big, but never think others small.... R.F.Scott
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whitestick Profile
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Registered: 06-2012
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Re: CB antenna radial myths and Legends!


never bother with radials on verticals myself - but what i DO have is an 8x4 sheet of ally as a GROUND PLATE - which according to theory forms a capacitve ground - and seems to work rather well in a restricted plot ( concrete yard ) - obviously only really usefull for near ground mounted antenna

i use a couple of plates for ALL my "grounds " there is a smaller one near the shack that is tied in with a couple of ground rods

this may be of interest :www.bencher.com/pdfs/00361ZZV.pdf - related

and of course always use a coax choke on the feed lead

any hoo thats how i do it - i think that one mistake a lot of people make is trying to fit the SITE to the system ( antenna - feed -ground - etc ) rather than the SYSTEM to the site - each site is different - and each will throw up new challenges - so whilst THEORY is fine as a STARTING POINT with antenna systems - never be afraid to go against "perceived wisdom " - and try something a bit different - you may just be surprised emoticon

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"my reputation proceeds me " ..... "right lets fire up the quattro "
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criswat Profile
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Registered: 08-2012
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Re: CB antenna radial myths and Legends!


This thread is very useful to me as I was looking for such resource. I am glad I visited here and gathered so many facts. It's always great to learn something new about the antennas.
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BOOTYMONSTER Profile
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Registered: 08-2014
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Re: CB antenna radial myths and Legends!


i've built a few CB base antennas and i've compared four 9 ft horizontal ground elements to four 4 1/2 ft horizontals and four 4 1/2 ft 45ish degreed slopped ground elements and got better performance from the full length ground elements .

Image

Image

i used the my copper coil matching network when comparing them but i don't have a pic of the full length ground elements with the copper coil , the pic with the loop.maco matcher is just to show the physical difference of the ground elements . i wouldn't make or use a antenna without ground elements because i am a believer in them .

FWIU 1/4 wave base antennas (like the starduster) need the slopped ground elements to match to 50 ohms , 1/2 , 5/8 and .64 wavelengths don't because the matching network is used to tune the antenna to 50 ohms ... or somewhere there abouts . i never saw any difference between 5/8 vs. .64 wavelength either other than having to slightly having to retune for the 6 inch difference . if i built another 5/8 9or .64) i'd use sloping 9 ft elevated ground elements because of the potential for a longer capture area , smaller diameter footprint and less comfortable perch for birds to sit on and poop from .

then i made a sigma 4 / vector 4000 type antenna and liked it so much better than my previous antennas that i wouldn't bother with them again . if i needed wide bandwidth a gain master would be at the top of my list .....

Image

here's a few links on ground elements that i've found helpful .

http://www.comportco.com/~w5alt/antennas/notes/ant-notes.php?pg=20

http://www.comportco.com/~w5alt/antennas/notes/ant-notes.php?pg=21
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SuperNasty Profile
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Freebander

Registered: 01-2012
Location: NI
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Re: CB antenna radial myths and Legends!


Nice one Booty, good photos though they disappeared way outside my screen size. I'm currently using an imax with 4 horizontal 8.5ft alloy radials. Everything is insulated from the mast though in hindsight as the antenna is DC grounded I don't know if this is the best thing to do, IE where does the static go if it cant get down the mast to ground, well into the radio I guess..?

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(Forum user name was previously - mikefox whiskey) - 68 FB750 - Pat

Kenwood TS870 - Centre fed balanced dipole - HPSD 2 element Moxon for 11m, vertical 'Ringo' for 11m.
22/Aug/2014, 7:11 pm Link to this post Send Email to SuperNasty   Send PM to SuperNasty Blog
 
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Freebander

Registered: 08-2014
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Re: CB antenna radial myths and Legends!


thanks emoticonsorry about the photo size but i'm too lazy to edit them all on PB .
i haven't been on air in a few years due to moving frequently but i still enjoy discussing the hobby and antennas in particularly and i still have my equipment that i hope to put back up .... someday .

sometimes grounding can help reduce static and sometimes it can increase it . if you have a static issue i'd try grounding to earth and vise versa if it was grounded ... try ungrounding it .

if you want to protect your equipment from lightning strikes earth grounding is a necessity . i add a coax choke a few inches below the coax feed point on my base antennas
minimize any CMC's that may be present . i dont have a imax , but according to the forums they are CMC prone so you may want to add one yourself . it probably won't help a static issue though , just minimize any interference to yours or your neighbors electronics .

heres some info on DC grounded antennas you may find interesting .

http://www.iceradioproducts.com/80.html

actually , there's a lot of good articles at ICE that you may find interesting ...... particularly on grounding .

http://www.iceradioproducts.com/10.html
22/Aug/2014, 7:32 pm Link to this post Send Email to BOOTYMONSTER   Send PM to BOOTYMONSTER Blog
 
SuperNasty Profile
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Freebander

Registered: 01-2012
Location: NI
Posts: 59
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Re: CB antenna radial myths and Legends!


Cheers Booty, static is not so bad but there, S2 at least and an S5 at worst. No problem with the unlikely event of lightning here. There is a choke on the coax. I'll maybe short the base of the antenna to the mast and check static then. Sometime I will do that.

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(Forum user name was previously - mikefox whiskey) - 68 FB750 - Pat

Kenwood TS870 - Centre fed balanced dipole - HPSD 2 element Moxon for 11m, vertical 'Ringo' for 11m.
22/Aug/2014, 7:42 pm Link to this post Send Email to SuperNasty   Send PM to SuperNasty Blog
 


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