1/4 wave coax vertical dipole

sharky · Post by **sharky** » Sun Oct 26, 2014 3:45 pm

Got bored today so I went down the shops to pick up a few bits and decided to have a go at making another one of these to maybe mass produce if the interest was there..

The basics of this antenna are that is is still a dipole ( two poles + and - ) ,but instead of using a boom as stand off, the dipole is end fed and can be mounted at the end of your mast.
Calculate your half wave lengths using the NRG formulae.
Cut a Full Wave length of coax- be it 213 etc ( i've used 58 as the loss at the length i'm going to use is .3dB )
Now from the top of your cable measure your 1/4 wave and mark the coax.
Strip the coax so the outer is still there ( take off the insulating layer only )
So you should be left with the sheath still, on...

Now take the sheath and fold it back down the coax ( turn it in on itself so that it flows back down the unstripped cable ) If you've done it right you should now have a quarter wave up ( the centre still in its jacket ) and the sheath folded over the coax. Does it look familiar yet ???
You now have a basic end fed dipole - with a Balun - as the bottom section is flipped over the transmission line.

Now there are many different ways to do this.
I've gone with cutting the sheath off and replacing it with a length of 15mm copper as it's more stable and you don't have to adjust it's length.
If you dont and use the coax itself, the sheath needs to be trimmed to allow for the velocity factor and in reality that will be shorter than the positive leg.

Now that's as far as i've got as I have no test equip. to match it at the moment.

The whole thing will be enclosed in some PVC for weather-proofing but you dont have to if you don't want to. A quick dab of silicone at the join where the two poles meet would be fine for a temporary measure.

I'll be honest and tell you that I've only used this antenna once in the past, and only because someone walked off with the antenna but left the TX, this got me back on in less than 30 mins.

If you're clever you can also adapt this method for a proper GP antenna.

I will keep you posted. Pics soon.

sharky · Post by **sharky** » Sun Oct 26, 2014 3:47 pm

Oh... Total Cost, less than a tenner

sharky · Post by **sharky** » Sun Oct 26, 2014 3:50 pm

Of course if you're like me and you want the info now NOW NOW.........

http://www.iw5edi.com/ham-radio/?the-ve ... antenna,18

sinus trouble · Post by **sinus trouble** » Sun Oct 26, 2014 10:44 pm

Nice one mr sharky!

Ive seen this configuration in many commercial WiFi antennas before and should be a reasonable performer?

Might give it a go too!

pjeva · Post by **pjeva** » Mon Oct 27, 2014 11:39 am

I am working on similar / modified design, also known as double bazooka or coaxial dipole. Preliminary results are outstanding. First try was with RG58 just to see if math works, and now I'm making two with semi-rigid coax. Will post pictures later...

sinus trouble · Post by **sinus trouble** » Mon Oct 27, 2014 10:24 pm

pjeva wrote:I am working on similar / modified design, also known as double bazooka or coaxial dipole. Preliminary results are outstanding. First try was with RG58 just to see if math works, and now I'm making two with semi-rigid coax. Will post pictures later...

Interesting stuff Mr Pjeva!!

Sounds like some kind of Co linear? or Double stack in a tube?

Matching and balun could be inclosed in the PVC assembly??

pjeva · Post by **pjeva** » Tue Oct 28, 2014 10:34 am

sinus trouble wrote: Interesting stuff Mr Pjeva!!
Sounds like some kind of Co linear? or Double stack in a tube? Matching and balun could be inclosed in the PVC assembly??

It is basically folded dipole modification. Matching part is like stub, and at the same time part of folded dipole.
Here are some pictures. If you're interested, I can put details and calculations...

Pictures are from last to first in each post... don't know why....

pjeva · Post by **pjeva** » Tue Oct 28, 2014 10:35 am

Continued...

midlandswest · Post by **midlandswest** » Thu Oct 30, 2014 12:32 pm

this may sound a daft question but could this be done without chopping off the required length from coax, example 10m coax with this on the end so no joins or plugs (only 1 to go into rig) etc.

pjeva · Post by **pjeva** » Thu Oct 30, 2014 7:28 pm

midlandswest wrote:this may sound a daft question but could this be done without chopping off the required length from coax, example 10m coax with this on the end so no joins or plugs (only 1 to go into rig) etc.

That would be sort ofend-fed design, sinus trouble's variant (with sleeve over coax) is exactly like that. This one on my pictures is center fed, so there is no way to do it without joints.

sharky · Post by **sharky** » Fri Oct 31, 2014 7:09 pm

midlandswest wrote:this may sound a daft question but could this be done without chopping off the required length from coax, example 10m coax with this on the end so no joins or plugs (only 1 to go into rig) etc.

With the one i'm building, Yes.... but remember you should have some kind of isolation from the mast.
Unless you plan to mount it to a fibreglass pole or some other non conductive material.
I do plan to finish the design this weekend, I have everything I need now.

pjeva · Post by **pjeva** » Fri Oct 31, 2014 10:26 pm

pjeva wrote:
midlandswest wrote:this may sound a daft question but could this be done without chopping off the required length from coax, example 10m coax with this on the end so no joins or plugs (only 1 to go into rig) etc.
That would be sort ofend-fed design, sinus trouble's variant (with sleeve over coax) is exactly like that. This one on my pictures is center fed, so there is no way to do it without joints.

Sorry, I meant Sharky's not sinus trouble's....

pjeva · Post by **pjeva** » Fri Oct 31, 2014 10:27 pm

Sorry, I was reffering to sharky's not sinus trouble's variant...

Pants · Post by **Pants** » Mon Nov 24, 2014 8:00 pm

I tried pulling braid over sheaf with 213 and westflex.what a f###king nightmare! Gave up after 2hours.

Exterminator antenna now only £126.69 on pcs electronics.think I'll just purchase one of them for testing things.

teckniqs · Post by **teckniqs** » Tue Nov 25, 2014 11:55 am

I'd rather use a double stack PCS Gamma Matched.

FMEnjoyer · Post by **FMEnjoyer** » Tue Nov 25, 2014 4:14 pm

i tired this wonce and the braid bunched up i canny get it back over the outer cable all the way down to be the ground part i gave up as well... it is look easy until to try and do it even wiv thin stuff

Pants · Post by **Pants** » Sun Nov 30, 2014 10:06 am

teckniqs wrote:I'd rather use a double stack PCS Gamma Matched.

Yeah I got a pair of these worked well but best double I ever used was using 2x mobile dipoles the screw in type only £20 each an all from rocket radio.

teckniqs · Post by **teckniqs** » Sun Nov 30, 2014 11:08 am

They're not as good, they'll just be like 75ohm standard dipoles.

sharky · Post by **sharky** » Sat May 30, 2015 4:40 pm

Bump.... !! For the person who asked me earlier..

P did you ever finish your coll. ??

pjeva · Post by **pjeva** » Thu Jun 11, 2015 2:08 pm

sharky wrote:Bump.... !! For the person who asked me earlier..

P did you ever finish your coll. ??

I didn't saw this post till today...

Yes, I finished it. Not then, but i needed quick solution for one 100w tx and just finished this over night. I didn't post anything about it because at the end I used network analyser to tune it right and didn't have time to take measurements and put them here.

I'll try to make another one and give full description.

1/4 wave coax vertical dipole

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