Web Updated;
02/04/2012
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QTH Aerials. (Getting results in a very small QTH!)
Since being licensed in 2008 I have worked all of
Europe with loft based Aerials.
If you look at the homebrew 2 link, you can see some of the stuff I have made.
The Aerials mainly form resonant dipoles at various bands which become a
nightmare when you consider the interaction between them all and of course the
RFI problems.
Also, being only a small loft, without some form of artificial loading or linear
inductance the maximum I can attain is 20m (14MHz).
I have recently been experimenting with outdoor aerials at my home QTH to minimise house bound RFI.
Firstly I must clarify that I live in a standard
3 bedroom semi-detached brick built house with ground and first floors and a
tiled pitched roof.
The garden to the front is not fenced and therefore can not employ any
structures or poles, the garden to the rear is secluded by 6 foot high fencing
and a heavy duty secure gate (for Dukes benefit!)
The total area of the back garden is approx 7.5m width x 5m long and consists of
concrete patio and slabs, so no grass for radials!
I originally developed an off set dipole working
on 20m 15m and 10m with a LDG 4:1 balun at the feed point. This system worked
quite well
draped over the ridge tiles of the house and connected to a small fibreglass telescopic
pole approx 5m in height and the other end of the garden.
This Aerial is the lower one of the two in the photo below. You can clearly see
the LDG 4:1 Balun.
Encouraged by the results of this, I tried a
second experiment using home made ladder line and a dipole making a
"Doublet" antenna.
This proved to be even better in performance and combining my LDG Z11 Pro Auto
Tuner at the base of the ladder line tuned to 30m to 6m.
Homebrew Ladder Line Feeder!
Here is the homebrew ladder line, using
parallel lines of 2mm˛ insulated wire (Kindly donated by Kam M0XXK) and plastic
coat hangers (Free from ASDA) cut with a template to make them all the same length
and drilled with a pillar drill to secure a neat 90° hole.
The plastic coat hanger spacers are centred approx. 100mm (4 Inches).
Using calculations from internet based software this arrangement is approx
550-600 Ohms. The cable will handle 1500 Watts with no problems.
Homebrew 1:1 500watt Balun
Here is the home made 1:1 Balun on a T200-6 core with RG8X coax 8 turns.
This is connected at the end of the ladder line and is fed into the LDG Z11Pro tuner, from here coax feeds to the Radio.
This arrangement worked well but was not long
enough to obtain 80 meters, so a re-think was required.
Also the fact that the wires (although insulated) were laying on the roof tiles
did not help radiation patterns!
These two Aerials came down and the "Mighty Doublet" was designed.
Click here to continue to the "Mighty Doublet"