| Author |
Message |
    
Kwhubby
Junior Member
Username: Kwhubby
Post Number: 20
Registered: 12-2004
| | Posted on Wednesday, May 17, 2006 - 1:20 am: | 
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Hello, I am planning on constructing a homemade base antenna, but am having problems deciding which. I am considering either a dipole, vertical dipole, 1/2 wave vertical or 5/8 wave vertical. I am trying to figure out which will give the best performance (lowest takeoff angle and highest gain). Reading all over the internet, I believe that the 5/8 wave vertical, mounted at least 1/2 wave above ground with the proper radials (4 1/4 wave radials?!?! angled how??? anybody know?) will work the best. I have been confused by articles claiming dipoles will outperform 5/8 waves and articles claiming 5/8 waves will outperform dipoles... which is it? I also can't seem to find any simple ARRL-antenna-book-like plans for those vertical antennas when Not ground mounted with a hundred radials.
Anyways I plan to build this antenna either from wire (dipole or vertical dipole up a tall tree) or riged copper tubing. One of the trickiest things I am trying to figure out is how the radials are to be configured for those verticals (how many and at what angle relative to the ground for both 1/2 and 5/8) I basically would like to replicate the design used with antron 99 / imax 2000 but with copper tubing.
Any help? In terms of groundplain/radials/counterpose whatever u call it, anybody with one of those vertical antennas could probobly tell me real quick simply by looking at the antenna. Anyways I don't want to purchase one of those great antennas because I want the fun of building it myself, and saving money at the same time.
Thanks! |
Bruce
Senior Member
Username: Bruce
Post Number: 3851
Registered: 9-2003
| | Posted on Wednesday, May 17, 2006 - 8:20 am: |
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a 5/8 wave with 4 1/4 wave radials is hard to beat |
Tech237
Moderator
Username: Tech237
Post Number: 350
Registered: 4-2004
| | Posted on Wednesday, May 17, 2006 - 9:19 am: |
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KW - 5/8 will beat a halfwave dipole anytime, mainly as the angle of radiatioin is lower. I will email you some CB antenna plans over the next couple fo days just to give you a few ideas. |
Wildrat
Advanced Member
Username: Wildrat
Post Number: 880
Registered: 12-2003
| | Posted on Wednesday, May 17, 2006 - 4:46 pm: |
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go to signal engineering and do some reading. He also has a couple of calculators out there. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1621
Registered: 9-2004
| | Posted on Wednesday, May 17, 2006 - 4:50 pm: |
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kw,
i was researching this very project some months ago.
i think there is even a thread where tech833 lent me some advice.
a search should find it.
anyway, here's what i learned so far:
the best vertical design for what you and i want is a .64 wave vertical antenna.
this would be about 23' long.
here's the key, the feedpoint of the antenna will not be 50 ohms, so we need to feed the vertical radiator with a coil.
take a look at mr. coily's design.
i drew up plans to basically replicate that design, but with simpler construction.
the radials should be 102" long and stick out at 90*. four of them.
the vertical radiator has to be separated from the groundplane by some sort of insulator, which would have the coil going around it.
marconi also had some very helpful input and pics.
check his pictures for some of coils at the base of an antenna.
matt |
Kwhubby
Junior Member
Username: Kwhubby
Post Number: 21
Registered: 12-2004
| | Posted on Thursday, May 18, 2006 - 1:29 am: |
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Wow, thanks for the fast replies. I was pretty sure the 5/8 (or extremely close to that) was going to be the winner. One note on the .64 wave antenna, a 5/8 wave is .625 so a .64 should be extremely close. I read that if the radials are braught to a 45 degree angle from ground, instead of completely horizontal, that the impedence can be lowered closer to 50 ohms (wouldn't that be a better solution then loading an antenna...lossy). But anyways, why the tiny additional length? is this do to velocity factor or whatever of the metal, or is this just a little tweak that affects takeoff angle. Anyways, what about height? Is the elevation thing as I posted earlier?
Hey wildrat, where is this signal engineering thing..link?
Thanks again! |
Wildrat
Advanced Member
Username: Wildrat
Post Number: 885
Registered: 12-2003
| | Posted on Thursday, May 18, 2006 - 9:14 am: |
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type signal engineering into Google it'll show up. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1632
Registered: 9-2004
| | Posted on Thursday, May 18, 2006 - 4:54 pm: |
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i wish i knew enough to explain it better, but its not just the additional length that makes it a .64 wave antenna, i think.
all i remember is that the .64 wave showed a bit of a gain over the 5/8 wave antenna.
tech833 help!
matt |
Georgeodjungle
Intermediate Member
Username: Georgeodjungle
Post Number: 105
Registered: 1-2006
| | Posted on Thursday, May 18, 2006 - 7:18 pm: |
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signal engingeering has a good site.
bigger is better. |
Mrclean
Junior Member
Username: Mrclean
Post Number: 39
Registered: 12-2003
| | Posted on Friday, May 19, 2006 - 7:24 pm: |
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It depends on the distance you want to talk which is better. In theory a 1/4 wave is better for short skip because of higher take off. I have had half wave antennas and 5/8 and even a 1/4 wave Starduster. I could not tell alot of difference. I think conditions have more to do with were you talk than antenna as long as the antenna is a good one and hooked up right. |
Marconi
Advanced Member
Username: Marconi
Post Number: 656
Registered: 11-2001
| | Posted on Friday, May 19, 2006 - 8:50 pm: |
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MrClean is right guys. That is what I find also. |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1471
Registered: 7-2004
| | Posted on Friday, May 19, 2006 - 10:55 pm: |
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Try to get antenna at least to a height of
36ft above the ground.
If mostly used for local talking: 5/8 wave
Mostly talk DX: any design with a low take
off angle should work. Have fun!  |
Ferd1605
Junior Member
Username: Ferd1605
Post Number: 16
Registered: 1-2005
| | Posted on Saturday, May 27, 2006 - 2:29 am: |
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KW .. The radials at a 45 deg. angle you were asking about is to bring the feedpoint to 50 ohms is for 1/4 antenna , NOT for the 5/8 or.64 where you WILL need a coil to do the same thing ... As for working short skip , a 1/4 wave will work good , but a 5/8 or .64 at ground level or low to the ground will work better , being close to the ground will put the takeoff angle higher , same goes for beams . i used to have 2 3 element beams for 10 meters , one up at 55ft. and one at 15 , i used the low one for "in the country" yackin and the high one for DX ... Hope that helps ya a bit KW .. Oh , think about diggin up some aluminum .. copper tubing could get heavey and not alow any flex in the wind which may cause a break ... and maybe , think about 4 di-polls to get some gain and low angle of radiation , i done it and it works ! Good luck ! |
Marconi
Advanced Member
Username: Marconi
Post Number: 658
Registered: 11-2001
| | Posted on Saturday, May 27, 2006 - 9:57 am: |
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1605 is making good remarks for the subject. For a GP longer than a 1/4 wave the radials, if any, probably should be in the horizontal plane, but I have seen them partly slanted down and they work also on 5/8 types (JoeGunn), so I'm not sure how much it really matters. If slanted radials work on these longer antennas like they do on 1/4 waves, then maybe more of the available current at the feed point will be generated in radials that are slanted down a bit when compared to those installed in the horizontal. This could be an advantage.
Problem with antennas longer than the 1/4 wave is you will need an effective matching device to really make it work OK unless you build a 1/2 wave center fed dipole.
If you have the height, co-linear phasing of dipoles, 2 or 3 elements stacked vertically end to end, are very effective for a near omni directional radiation pattern with very good real gain. With 11 meters you probably need to be able to get up a 100' or more however. |
