Slim Jim aerial for DAB radio

[beeman]

I got fed up with the warbling/burbling from my DAB radio so went browsing - always dangerous. Anyway I came up with a couple of antennae designs that I could make with bits in the garage. One was a J-pole design which I made from a spare Link Stake (used for supporting flowers in the garden). Worked OK but not for distant stations.

My second attempt was a "Slim Jim" made from some overflow pipe and the copper core pulled out from some spare mains cable. It worked a lot better with distant stations coming in strongly.

OK, my question. The designs I've seen on the net suggest using 15mm copper tubing. Will the thicker material give better reception? Is it worth me having a go or should I give up now? I can pick up stations from 40+ Km away with no distortion.

PS. I know nothing about aerials so be gentle

[Orion]

In my ham radio days i used to make slim jims out of 300 Ohm ribbon cable fitted into a plastic pipe very easy to make

Found this easy to follow guide
http://dl.dropbox.com/u/19393276/SlimJimDab.pdf

[beeman]

Hi Orion, that's exactly what I've made but without the waterproof coat. The antenna is hanging from the ceiling. Not pretty but it works fine.

So do you reckon I won't gain anything by making a copper pipe version?
Does the thickness of the wire have any effect on reception?

Regards

[Orion]

For a receiving antenna wire gauge will not matter

[beeman]

OK, many thanks

[werribee_au]

In my ham radio days i used to make slim jims out of 300 Ohm ribbon cable fitted into a plastic pipe very easy to make

Found this easy to follow guide
http://dl.dropbox.com/u/19393276/SlimJimDab.pdf

This looks like it is resonant at about 220MHz which is good for the UK where the transmitting bands cover between 218-224MHz.
In Australia the bands cover 202-206Mhz (Eastern states). Here is a calculator for Jim Slim or J Pole dimensions that can be used to make the antenna more resonant to the frequencies used in your local area which may help pull in those weaker stations if you are in a fringe area.
A little hint. When connecting the cable to the antenna, before soldering it, set your dab radio to the signal strength and from the dimension where the drawing indicated the connection, just move that point where they connect up and down and observe the signal strength. When you have the maximum strength that is where you should solder the permanent connection. Your dab radio may also display the frequency of your favourite station so you can use the calculator below to customize the resonant frequency of the antenna. I know we are talking about a receiving antenna here, but if you are in a fringe area every little bit of gain helps.
http://www.m0ukd.com/Calculators/Slim_Jim/index.php
Also at these frequencies, transmission/reception is predominately line-of-sight, so the higher the antenna (to a point), the better the reception.

[beeman]

Hi Gerard,
That's what I did to get the best signal. The calculator is also the one I used to work out the lengths of wire.

The antenna is now dangling from the rafters in the loft of the garage. My local transmitter won't be starting DAB transmissions until later this year