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Home brew base ant!!!

Dear All i a have allready make each experiment regarding matching antenna on 5/8 with 4 nos ground with each methode matching, the first experiment is using Gamma Match but i can't get lower SWR (1:2.5)

Detail Connection on Connector
http://www.4shared.com/file/193711041/668b3e1a/Foto0404.html

Gamma Match Assembly

http://www.4shared.com/file/193713443/25853f61/Foto0409.html
/media/KOEN/Images/Foto0404.jpg

Detail Gamma Match and Gama Root
http://www.4shared.com/file/193714201/36bddf42/Foto0407.html

I experiment with Coil to... but VSWR can't Get Lower SWR (1:2)
http://www.4shared.com/file/193717526/8d159108/Foto0419.html

My Daughter Help me to read SWR iam at roof :oops:
http://www.4shared.com/file/193721529/7f61a995/Foto0413.html

please adise me, tho change like Mr BOOTY MONSTER and Mr Rob KI6USW change to http://www.worldwidedx.com/cb-antennas/36898-pics-progress-homebrew-5-8-a.html

Sorry i can't take picture for all assembly 5/8 because in my town every day rainy

Thanks maybe next week i can get picture...

ok can you are advise me regarding my homebrew 5/8 ???
 
How high is the antenna off of the ground surface?
20 or 30 feet up?

You might have to change the location of the tap on the coil.
Are the ground plane about 3 meters long?
 
CDX-007 said:
Hey 15minigrass, Nice job of home-brewing an antenna! Feels FANTASTIC to talk on your own creation, doesn't it!?!

OK, I'll try to shed a tiny sparkle of info that I know 'bout dat 'ting.

You should maybe bend your radial down 30* more. - Why?

OK, two 1/4waves at 90*(degrees) like you have it, makes it about a 37ohm impedance antenna, not 50 ohms like your radio wants for a 1:1 swr, that's why you have 1.5:1.

Since 25 goes into 50 twice, if it was a 25ohm impedance you would have a 2:1 swr, and since 37ohms is ~1/2 way from 25ohms to 50ohms you are half way to 2:1 swr.

At 180* (one straight up & one straight down) you would have about 75 ohms which is also 1.5:1 because it's 1/2 way to 100ohms from 50ohms. 100 ohms would be a 2:1 since 50ohms is 1/2 of 100ohms and 50 goes into 100 twice.

BUT - at 120* it should be right about 50ohms where you would get that beloved 1:1 swr!
- So, you can bend down the radial on the side to about a 30* down angle and watch the swr fall close to 1:1!

...or you can try a shunt to ground.

To build a shunt just take two 9" pieces of copper or brass welding rod and connect one to the top 1/4 wave and the other to the radial or ground on the box near the top 1/4wave element.

- Try to keep the two rods parallel to each other and about 1.5" apart.

You might find it needs to be more like 1" or maybe even 2" apart, but it should end up around 7"-8" long and ~1.5" apart.

Then:

Cut a little piece of copper wire about 2.5" long and bend around about 1/2" on each end so it becomes 1.5" long with a little loop on each end, to connect over each of the rods making a long U-turn.

It's a shorting bar - to short the rods together in such a way that you can slide it from the outer ends of the two rods closer and closer to the 1/4 wave element & ground until your swr goes flat.

You should be able to cut off the overlapping ends once you find the 1:1 tuning point and solder it there.

Your basically tuning out the reactance by making a little 5" to 9" U-turn out of the two rods and the copper slider, which basically shorts the top radiator to ground.

It looks like it would be a dead short to your wattage but it isn't, because RF isn't going to act like DC.

Your wattage will prefer the 50ohm antenna to the weird impedance U-turn to ground so your wattage will get radiated but your antenna reactance will flatten out - which is a good thing.

Plus, you should find this sends more of the static to ground instead of down the coax to your radio!

+++++++++++++++++

Another observation, in the direction the radial points you should get a lower take-off angle for your signal and that would help you to talk longer distances locally.

In the other directions you should have a higher angle which might help you to DX if the DX is closer than further, like maybe Calif or other even closer DX contacts.

High angle is good for 'Sporadic E' like maybe 500-1000 miles, where low angle will get you longer DX like into the East Coast of the USA, or Europe.

Personally, I'd prefer a bent down radial (to about 120* down from the top element) for what is a little more gain than the 90* 1/4 wave ground plane you've got there, and an overall lower take-off radiation angle.

- At 120* it becomes a 'Center-fed 1/2 wave Dipole'.

And you can still experiment with a ground shunt if you want to try to make a quieter 120* DIPOLE antenna.

I hope you're now less confused after you read this than I am after writing it...
icon12.gif


73!
Click to expand...

Dear CDX-007 i am interest with your explanation on the Top... but iam confuse regarding my bad in english, sorry can you explain by sketch ? i have problem regarding matching antenna on 5/8 with 1/4 ground with 4 radial horisontal (90 degree), i allready experiment with 2 matching system, 1 by Gamma Match , 2 by Loading (Coil) but i can't get lower VSWR , the VSWR aaround 1: 2.5 until 1:3 we need get 1:1 but we need the ground in posisition horisontal (90 degree) can you advise me ?
the picture you can see on this thread....

Thanks for your kind attention
 
Dear Rob..

For Tab Coil is allready change from 1st tap until 9 , but is still can get better VSWR, i use Coil 9 Turn on 1.25" Wooden with 1.5 mm Cu , for height i try to get higher than now but no different VSWR , VSWR is same with now
 
Bejo,

I built a homemade 5/8 wave antenna last Spring. So many of the guys here helped me get it done and I was finally successful with my project.

The thread where we worked it out has some info that may help you. There are some photos linked on the thread. Perhaps that will help. You are in good hands with these fellows helping you.

Here is the thread: my first attempt to build a 5/8 wave homemade
 
Last edited:
Hello Bejo,

For some reason I didn't get an email letting me know you had posted here, even though I set it to...? - But I did get your PM.

Make certain your radiator length is right about 23' for ~27.350mHz and 9' for the radials.

Then move the tap until you find 1:1 or so. I usually see it about 35% of the way up from ground. You may need another turn or two, or already have too many. If I remember correctly, I believe there was about 9 turns to the radiator and maybe 5-6 to the radials / ground at 1.5" diameter for the full .64.

- If it still won't tune, tell us what reading you are getting at higher and lower frequencies, including Reactance if you have an MFJ-259 analyzer or equivalent.

But if you do not have one then don't worry about it.

I'd sure love to get hold of some of those radial brackets! Where did that one come from?

73
 
Last edited:
CDX-007 said:
Hello Bejo,

If I remember correctly, I believe there was about 9 turns to the radiator and maybe 5-6 to the radials / ground at 1.5" diameter for the full .64.

73
Click to expand...

Are you referring to the diameter of the coil here? I had to use that size diameter core for the coil to get a match on my antenna.
I know less than many of you guys here, but I found this advice useful:

"I calculate that you need about 10 turns of #12 wire on a 1 1/2 inch form, spaced out over about 2 3/4 inches.

You connect the coil top end to the base of the vertical radiator and coil bottom end to the radials' common point. I know it might sound weird to put a coil *across* the feedpoint, but trust me!

The shield of the coax cable connects to the radial common point/bottom of the coil. Then you take the center conductor on the coax and attach it a *couple turns up* from the bottom of the coil... I think 2 turns up should do it.

|
|
|
|
|
|
|
|
| vert
|
|
|
|
x
x coil (10 turns #12, 1.5 inch form, 2.75 inch long)
x
x
x -- center coax tapped 2 turns from bottom of coil
x
O -- radials and coax shield meet here, coil bottom

It's a nice design because it keeps static from building up on the vertical radiator.

There are two ways you can adjust it.

Spreading and compressing the coil length will change the resonant frequency, and that will be the frequency where you get lowest SWR. If you find the SWR is lowest at the bottom of the band, spread the coil. If lowest at the high end of the band, compress it. You can also trim or lengthen the vertical radiator instead.

If you sweep across the channels and find the lowest SWR is in the middle of the band but it's not very low... like the lowest SWR is 2:1 but it happens on channel 20 or so, adjust the location of the coax center conductor tap on the coil.

You can change the coil a little bit but don't make huge changes... the diameter, number of turns and length should be about right."

This info is at: http://www.eham.net/forums/HomeBrew/4665
 
CDX-007 said:
Hello Bejo,

For some reason I didn't get an email letting me know you had posted here, even though I set it to...? - But I did get your PM.

Make certain your radiator length is right about 23' for ~27.350mHz and 9' for the radials.

Then move the tap until you find 1:1 or so. I usually see it about 35% of the way up from ground. You may need another turn or two, or already have too many. If I remember correctly, I believe there was about 9 turns to the radiator and maybe 5-6 to the radials / ground at 1.5" diameter for the full .64.

- If it still won't tune, tell us what reading you are getting at higher and lower frequencies, including Reactance if you have an MFJ-259 analyzer or equivalent.

But if you do not have one then don't worry about it.

I'd sure love to get hold of some of those radial brackets! Where did that one come from?

73
Click to expand...


Dear CDX

Thanks for your advise hope work , sorry for late reply to you iam working and reply to you after working at office, by the way on saturday i want repair my antenna and we will report or post in this thread... (included Picture) an all the thing regarding VSWR .

by the way , i use Barcket Cubical Quad , and i get from market in surabaya. if you want this bracket i can buy for you and send to you by mail or anything

thanks for your kind attention
 
HomerBB said:
Are you referring to the diameter of the coil here? I had to use that size diameter core for the coil to get a match on my antenna.
I know less than many of you guys here, but I found this advice useful:

"I calculate that you need about 10 turns of #12 wire on a 1 1/2 inch form, spaced out over about 2 3/4 inches.

You connect the coil top end to the base of the vertical radiator and coil bottom end to the radials' common point. I know it might sound weird to put a coil *across* the feedpoint, but trust me!

The shield of the coax cable connects to the radial common point/bottom of the coil. Then you take the center conductor on the coax and attach it a *couple turns up* from the bottom of the coil... I think 2 turns up should do it.

|
|
|
|
|
|
|
|
| vert
|
|
|
|
x
x coil (10 turns #12, 1.5 inch form, 2.75 inch long)
x
x
x -- center coax tapped 2 turns from bottom of coil
x
O -- radials and coax shield meet here, coil bottom

It's a nice design because it keeps static from building up on the vertical radiator.

There are two ways you can adjust it.

Spreading and compressing the coil length will change the resonant frequency, and that will be the frequency where you get lowest SWR. If you find the SWR is lowest at the bottom of the band, spread the coil. If lowest at the high end of the band, compress it. You can also trim or lengthen the vertical radiator instead.

If you sweep across the channels and find the lowest SWR is in the middle of the band but it's not very low... like the lowest SWR is 2:1 but it happens on channel 20 or so, adjust the location of the coax center conductor tap on the coil.

You can change the coil a little bit but don't make huge changes... the diameter, number of turns and length should be about right."

This info is at: http://www.eham.net/forums/HomeBrew/4665
Click to expand...

Dear Mr Hoomer BB

Thanks for your advice and assitance, i wil try at saturday too and will reply to you after change

one question

we must be matching the antenna with Horisontal Ground attached or not attached, please reply

Thanks for your kind attention
 
I wonder if those brackets are available in the USA?

What is the cost in USD? $hipping co$t to California?

Thanks Homer for your reply too, that was an inspired guess from my waning memory.

Another thing, you can make it either a 5/8 wave .625 (22.5') or about 6" longer for a .64 (23') which is a little higher gain and a little lower TOA (Take Off Angle) so the performance will be slightly better at distance, but you'll find the tap point on the coil a little different and perhaps you would need a little less overall coil for the .64.

'73
 

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