446 beam

[ballores]

anyone point me in the right direction want to make one for the dx weekend will be transmitting from chichester beaming towards Wales by the look of things probably sunday ch8

[M0JSW]

http://www.lightandcolours.com/delboy/p ... t_yagi.htm

Google pmr yagi and see what u come up with.

[bigpimp347]

or just try a 433 70cms beam, the bandwidth on say a jaybeam built commercial type will easily work or tune upto 446..

even some jaybeam taxi stuff will be ok on 446.

[littlemo]

Why not try building your own Hybrid Double Quad. I build one for 2m and they work brill !! Great gain figures, static can't build up on the antenna and they will be quite compact for 446. They are available to buy too for 70cm that will probably do the job

[Andy]

I've been a fan of the double quad, or bi-quad for a very long time, and I've used them on bands from 70cm to 13cm. They're fairly easy to make and don't seem too fussy.
I've even made one for broadcast TV. We have a digital (Freeview) TV in our bedroom, and on a standard 'set-top' antenna it's a bit 'on the edge'. So I made a biquad centred on 750 MHz and reception is now solid.

[JOHN,YORK]

Andy.
Have you ever tried building a double bi quad.I think it gives an extra 2-3 db gain over the bi quad.Problem is that it is twice the size.

Regards,John.

[Andy]

Yes John. It's just got four quads instead of two, crossed over at the mid-point of each pair. Certainly better, but bigger as usual.
What I like about bi-quads is that they are quick to construct and can be made very solid for slinging in the car. Carefully lifting a ten ele yagi in and out of the car is a pain.

[JOHN,YORK]

Andy.
How would you rate the bi quad against the Moxon or the CJU.

Regards,John.

[Andy]

Phew, just got back from Morrisons, God those pensioners sure know how to dawdle...
Well, the Moxon is only a 'bent' 2-ele beam, so it's never going to have the gain of a bi-quad which has effectively 5 elements.
I use a horizontal Moxon on 4 mtres. It works and it matches and it 'points', but it doesn't set the world on fire.
I don't know much about the CJU... I must find out. Isn't it a kind of Moxon +1?

[JOHN,YORK]

Andy.
The Moxon seems popular due to its easy build and wide bandwidth,gain is somewhat mediocre (3-4)dbd.
I have got the MOXGEN CALCULATOR,but it will only accept diameters.I have some aluminium strip that I would like to use,I have searched all over the web for a Moxon with strip elements,but no luck.Would it work by converting the end surface area into a diameter.I did ask this question some months ago,but I did not get much feedback.
The CJU antenna is popular with amateur satellite work.Just 2 elements,but this can be increased to more elements.If it is running with several elements,it is similar to the ARROW antenna.It can also be made into a dual bander.I believe that it works by having a full wave loop in front of a reflector.Constructional details can be found at........

CJU,EA4CYQ.

If you decide to give the CJU a go,the dimensions are for 435.300mhz,satellite downlink FX.

Regards,John.

[Andy]

John, thanks for the pointer. I'll take a look at the details of the CJU, as I'm always up for a bit of wire-bending.
I wouldn't get too involved with wire-size or strip calculations. My Moxon is made from bog-standard wire stretched around a wooden frame. The wire lengths were scaled up from a 2-metre design.
The wire lengths are just a bit shorter than you would use for a normal two-ele, because the ends are quite close and the elements de-tune LF. A bit of trimming of the driven ele got a good match and it seems to work OK. It 'points' in the right direction and has nice deep nulls off the sides. I think theres a picture of it on my website somewhere.

http://www.freewebs.com/g1hbe

Yup, just checked - first page, bottom. The ends of the elements are held together under slight tension with nylon thread.

[JOHN,YORK]

Andy.
Thanks for the reply.When you say that you are using dimensions for a 70 mhz Moxon from scaled measurements from a 145 mhz Moxon,you can find yourself with errors,especially the gap measurement.For example,I have done some calculations on the MOXGEN CALC,using an element diameter of 1/8 inch.To make it simple,I will only use length,width and gap dimensions.The dimensions are in mm.

145.5..............70.250mhz.......scaled.......ERROR in mm
length....741.7.......1542...........1536.............6
width.....274.9.......568.8..........569.36..........0.56
gap.........32.7........58.2......... .67.72...........9.52

As you will have noticed,the scaled measurements are out,the width and length are not too bad,but the gap is not too good.It is the gap measurement that is very important.
Regarding the diameters of elements,the dimensions alter again.I will use 70.25 mhz.

2.5 sq.mm....................1/8".................3/8"
length....1546.6...........1542.3............1532.9
width......568.2.............568.8.............569.9
gap..........51.7..............58.2...............73.2

As you will notice again,the gap measurement alters quite considerably.


Regards,John.

[Andy]

Thanks John, those errors are eye-openers!
But I still say they don't matter too much if you are prepared to do a spot of trimming. I reckon even if you stuck to the 'proper' calculated lengths, you'd still have to do a final cut-and-try.
Anyhow, good luck with the 446 beam , it's not something I've ever tried myself. A 70cm beam would probably work well on RX, but the match would be on its way out for TX.

[JOHN,YORK]

Andy.
Thanks for the reply.As you say,you can make an aerial to the text book,but still find a tweak here and there will improve things.
The aerial is not for me,the member who posted this article is BALLORES,I hope that he has been reading these comments.
I keep meaning to get going on 446 again.I have a 5050 with mods done,also another 5050 that I won last year in a competition in the RU magazine,which as yet is still unopened.Also I have a KG-UVD1P and several 500 mw sets.Several VHF JINGTONGS and a UHF one.A ft817nd,which I have had for 3 years,but never got around to do my foundation course,it has only been out of its box about a dozen times.

Regards,John.

[adds666]

Sorry to bring up an old thread but I too have the 5050 with mods and use the KA505 antenna aswell as a magmounted antenna double the size of the KA505.

I am wanting to make my own antenna and was curious as to how you guys know the dimensions? For instance If I wanted to make a simple di-pole for the 446 Frequencies?

I would also like to make the bi quad you posted in the thread Andy but dont know the dimensions/know how to calculate the dimensions. Presumably the core of the coax is attached to the "bowtie" and the sheath to the deflector?

Is there a simple book out there on antenna principles/dimensions/connections that I've missed??

((Or should I get myself along to my local HAM club and start learning and moving on from PMR446? Which I do intend on doing))

Thanks in advance

Adam