Home made dipole

[suealw]

Does any one know how to make a dipole just for the uk 40 fm

[jazzsinger]

300 / 27.79125 / 2 X .95 = 5.12m total length / 2 = 2.56m for each leg x 3.28 to convert metres to feet = 8.40 ft or 8ft 5 inches for each leg length,add a little to each side for tuning and trim equal small amounts of either side, and then fit a 1:1 rf choke balun/ugly balun as its a balanced antenna fed with unbalanced coax which will prevent coax radiating.for a dipole centred on ch 20 ukfm (27.79125 mhz)
good luck!!!

p.s if your planning on using zetagi use heavy guage wire.

[ryan_paul]

Dear Suelw

Its dead easy I will assume that your dipole is 1/2 wave length.
first find out what teh middle frequency for UK 40 is and use this frequency in the below formulars

the formular to use is:
for 1/2 wave with no insulators in meters
145.5 devided by frequency in MHz

for 1/2 wave with insulators in meters
143 devided by frequency in MHz

now devide that by 2 and add a couple of cm extra and cut two lengths of wire to this length.

connect one length to the inner of the coax and the other to the out.

insulate against elecrical short and the weather. and erect in a verticaly polarised way.

[Guzzy]

Don't forget a 1:1 RF Choke "balun" in the above.

See Ugly balun

[5thElement]

I use the ugly balun on a simple wire dipole for 20m in my loft, seems to work not bad considering it's indoors and in a V shape to make it fit lol worked allover europe and across the atlantic a few times aswell , no doubt it would be better outside though and in its proper configuration!

[JazzMan]

Hi all,

Quick one - I tried a loft mounted inverted V and achieved a SWR which almost didn't register but the result across town was pretty poor.

I hadn't fabricated an ugly balun but took another point of advice and made a "coil" of coax feeding the aerial.
Does anyone know how much difference a balun makes to the radiation pattern of an inverted V?

Best regards
JM

[Keyboard]

JazzMan - I had some TVI issues when using my homebrew dipole as the coax was radiating rather than the antenna! I quickly knocked up an ugly balun simply by cable tying the coax (as shown in the above link) to an old medicine bottle and the TVI was gone. Well worth a try for practically no money!

[JazzMan]

Been pondering it.. I think you're most probably right Keyboard.

If the feeder is radiating from current in the outer shielding, hence the need for a balun, probably a lot of the transmission is bleeding away before it reaches the antenna which is probably why I read a very low SWR (all out, none back!).

I'll have to try the experiment again and let you know.......(be patient, this might take time!)

[Matt_b]

I've made a few dipoles with good success. These have mainly been for dx though.

I suspect making one for groundwave CB FM would be a bit dissapointing though since most CB stations use vertical polarisation. A horizonatally polarised dipole for local groundwave CB wouldn't yield good results in my opinion.

If you're going to do it, mount it vertically for a good omnidirectional vertically polarised antenna