CJU antenna

[5thElement]

Thought i'd start a new thread for this following on from here

http://www.transmission1.co.uk/forum/vi ... 34&t=17751

The article with the dimensions etc can be found here
http://personales.ya.com/ea4cax/paginae ... ingles.pdf

Here's the quick one i just knocked up with some stuff out the junk box





I'll report back after i test it.

Does anyone know what the theory behind these antennas is? all i can seem to see is that the radiator is about a full wave - but what about the spacing/length for the reflector? and is there scope to add a director and improve the antenna?

[JOHN,YORK]

5th.
Glad to see that you have made one.Only a suggestion,it might have been more practical to have left some extra conduit next to the radiator,this will give you space to play with a director.Maybe a cut and see approach.(trial and error)
I have tried various calculations to come up with an answer,(984/FX) and (936/FX).
Would it also work if the radiator was mounted at right angles to the reflector.It might be just a design where you leave it as it is.Mind you,I have seen a 3 and 4 element Moxon.
On one site,they give the spacing as 50 mm,but on another site it is 51 mm.I think the latter is to the centre of the wire,if you are using 2 mm wire.
I will give the calculator another go today.
I bet you wished that I had not brought the aerial to your attention.
Nearly forgot,did it work ok for you.
A PL259 on UHF,NAUGHTY,NAUGHTY.

Regards,John.

[crusty]

Nice little project 5th, good luck with the testing.

[5thElement]

Thanks for the replies.

Not had a proper chance to test this yet but initial tests on UHF in general seem to show that it's definitely very directional which is good! i've missed the AO-51 satelite passes for today so i'll need to wait until tomorrow to try. As for the PL-259, it was all i had spare, so it'll have to do for now!

[JOHN,YORK]

5th.
Just joking regarding the PL259.Glad to hear that the CJU lives up to its expectations.It sounds as if you are more pleased with that,than the Yagi you built the other night.
Regarding AO51,on the other topic,I have put a few pass times.Also a couple of sites for pass times.

Regards,John.

[5thElement]

At this moment im definitely pleased with this antenna so far - especially considering it's so small and simple to construct. I just wish there was more information regarding the theory behind it and why the spacing between the driven element and reflector is what it is etc

[fez]

At this moment im definitely pleased with this antenna so far

Knew you would like it

Maybe if the yagi is still together do some comparison tests.

[JOHN,YORK]

5th.
I know exactly how you feel regarding the dimensions etc.For the last 6-9 months I have been looking at various sites to try to gather any information.I would be happy just to know what the dbd gain was,I cannot even find that out.Various people say that it has the gain of a 4 element beam,even that can vary from design to design.
I wonder if it would have any gain by just using the radiator,then feeding it with a balun,a 4:1 or 6:1.
Maybe trying a full wave loop for the radiator using (1005/FX) would have the same results.But still using the same dimensions and spacing for the reflector.If not,it is obvious it is the dimensions,or ratio of the sides of the radiating element that give it the gain.

Regards,John

[5thElement]

Tried to listen to AO-51 today for atleast 3 passes and heard nothing each time which was disapointing - was starting to wonder if i was doing something wrong but everything seems to be okay - not sure why i never received anything (and yes the squelch is set to off)

Here's a photo of the antenna connected to the VX-7R



I've now added a small "handle" which makes it easier to point/swing around.

[fez]

what freq were you monitoring, I think the most active one I rx'ed was 435.300.

start monitoring about 435.310 then when it's 1/4 of its pass go to 435.305 then 435.300 at overhead. then lower as it goes away.

[5thElement]

Yep, 435.300

[5thElement]

Just managed to catch a little of what was probably going to be todays best pass (AO-51) - and the signal was hardly booming in - i would of struggled to attempt any contacts and it was only received for 2-3 minutes with qsb

[YB135]

Theres another name for that antenna, an IoIo beam. Do a google for 2e0hts and check out his blog, lots of info on this antenna

[5thElement]

Yeah i know the one - it was brought up in my 70cm yagi thread and covers 2m/70cm.

[JOHN,YORK]

5th.
It might be of interest to you,

http://www.scribd.com/doc/42750411/QST-February-2009

Polar diagrams of the CJU and SWR graph.Page 41.A bit slow at loading,but persevere.

430 mhz 1:1.9......
440 mhz 1:1.5...... My estimations from graph
436 mhz 1:1.15....

Article mentions a gain of 9.6dbi-12.3dbi

Regards,John.