GW4ALG's QRP Radio Pages

[ GW4ALG went QRT in February 2007 ]

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Vertical Antenna for  80 & 160 m

This page describes the simple vertical antenna used at GW4ALG.   This page describes a 12 m 'experimental' vertical (i.e. not a permanent structure) located away from the house; and the occasional use of balloon-supported extensions to the basic 12 m antenna.

Experimental Vertical
Balloon-supported Vertical

Experimental Vertical Antenna

The general arrangement of the basic 12 m vertical antenna occasionally used at GW4ALG is shown below.  This antenna is located away from the house, thereby reducing the dielectric losses caused by proximity to nearby 'earthy' objects. 

Also shown is the method used for extending the vertical with a balloon-supported wire: more about that later . . . .

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Construction of the radiator

The main part of the vertical uses a 10 m fibre glass pole to which insulated wire has been taped.  At the top of the wire, a loop of about 6 cm in diameter has been made by folding the wire back on itself and soldering it in position before taping the joint with insulating tape.  The purpose of the small loop of wire is to help prevent corona discharge from the top of the vertical.  The base of the fibre glass pole is mounted on a wooden base assembly, which slides into a wooden upright that is fixed to the frame of our children's garden swing.  (As our children have got older, the homemade swing frame had been falling into disuse in recent years - until now, that is!)

The picture at lower-left shows the wooden upright with its 'slide' made of two lengths of aluminium angle.  At lower-right is a picture of the base assembly for the fibre-glass pole.

Experimental Vertical

Wooden Upright

Base Assembly


This free-standing antenna is not strong enough to withstand high winds.  So this is definitely a 'fair weather' antenna.  The antenna is taken down at the end of each operating period.


 

Balloon-supported vertical

Using balloons to raise lengths of wire can be great fun - as well as making it possible to work the DX on 160 m and 80 m from small gardens.

When mounted on the base assembly, the vertical is about 12 m tall.  To increase its height, additional wire has, on occasions, been supported using helium-filled balloons. 

The maximum height that I have achieved using balloons has been 27 m, but, typically, I will use a balloon height of  20 or 24 m.

Balloon-supported Vertical

Balloon information:
- I started by using 'Punchball' type balloons, as used at childrens parties. They will inflate to about 400 mm diameter and each balloon costs about 40p.  Depending on the quality of such balloons (which is very variable), each balloon can be re-used about 3 times, if not over-inflated;
- These days I use better quality balloons purchased from Everts International Limited (Tel: 01724 282525).  Two of their 24" Giant Balloons (Part number 001700, costing about one pound each) will easily lift 15m of plastic-covered hook-up wire.
- the neck of the balloon may be folded over and held with a small cable tie to seal the balloon;
- I use two 400 mm balloons to lift 8 m of insulated, multi-strand wire;
- you must use at least 300 mm of nylon cord (e.g. thick kite string or similar insulating material) between the top of the wire and the balloon. (If you don't, you may get arcing between the balloon and the wire - a 400 mm balloon makes a very big bang when it bursts!!)  It took me three 'bangs' to figure out why the balloons were bursting;
- consult 'yellow pages' for details of balloon suppliers (who will also be very willing to supply the balloon gas);

Balloon gas information
- each 400 mm balloon will cost about 50p to inflate with balloon gas;
- balloon gas may be purchased from a bottled gas specialist - again, see yellow pages;
- helium leaks out of most types of balloon quite quickly - expect to have to 'top up' the balloon about 8 hours after inflation.  
- suppliers of balloon gas will be able to supply a special fitting for the gas cylinder to provide an easy and controlled method for filling the balloon - be sure to buy or rent one!;
- According to BOC Safety Data Sheets 300-00-0037 (balloon gas) and 300-00-0015 (helium), the relative density of their helium (Grade 'A'), and balloon gas is 0.14 for both products (air = 1.0).  So, when compared with balloon gas, there appears to be no advantage in using pure helium for this application.

Happy ballooning, and good DX!