GW4ALG's 136 kHz Pages

[ GW4ALG went QRT in February 2007 ]

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Vertical Antennas for 136 kHz

This page describes the simple vertical antennas used at GW4ALG.   This page starts by summarising my attempts to tune up a pole mounted on the back wall of our house, through to the use of 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.

Prototype Vertical
Experimental Vertical
Balloon-supported Vertical

Prototype Vertical Antenna

The first vertical antenna at GW4ALG was installed on the gable-end wall at the back of our (brick-built) house.

A lower loading coil was wound on a plastic bucket and wall-mounted about 3 m high.   The coil, included a 25-turn link winding for connection, via 50 ohm coax, to the TX/RX.   A wire from the top of the lower coil went up the side of the house, and through a hole in the wall into the loft [attic] to a variometer (using another bucket for the outer coil, and a short length of plastic pipe for the rotatable inner coil).   The 'hot' side of the variometer was then connected to a good many turns wound on a plastic laundry basket, and a wire then went back through the hole in the wall, and up to a 1.2 mH loading coil mounted on a short length of 2" x 2" hardwood. The top of the 1.2 mH loading coil was then connected to 5 m of aluminium pole mounted on the hardwood support.

Two outrigger wires (spaced about 0.5 m from the aluminium pole), and a small capacity hat, attempted to increase the top capacitance, but there were no top hat wires (because there were no suitable supports).  The 'cold' end of the lower coil was connected to the outside water tap.  Later, short earth spikes were installed at three corners of the back garden, and also connected to the water tap.

Successes with prototype
On receive, it was an excellent omni-directional antenna. On transmit, using 40 W RF, the vertical was used to make the first 2-way GM-GW QSO (to Dave, GM3YXM/P) over a distance of 395 km. 

Observations
1) The major problem with the prototype vertical was achieving enough insulation - there's a lot of volts up there - even when running just 15 W of RF 'barefoot' from the transverter.  So I had to grapple with compromises of mechanical stability (supporting/guying the 5 m pole) and achieving the required electrical insulation.  Car ignition HT lead (copper conductor) would break down at 100 W RF, causing a fantastic light display between itself, and where it passed through the brickwork!
2) The proximity of the antenna to the house, and the resulting shunt path to ground, meant that the RF losses were high.  On wet days, the vertical would be detuned, and the increased losses caused by the shunt path became more significant.
3) The number of turns on the link coupling was difficult to get right. Also, about 30 nF of series capacitance was required to tune out the reactance of the link winding.  The whole system was time-consuming to adjust - both to maintain resonance, and to obtain a good match.  Even coping with hour-to-hour, and day-to-day variation in the resonant frequency was difficult due to poor access to the loft space (where the variometer had been installed).
4) The addition of the three earth spikes made no measureable improvement in antenna performance, relative to the water tap connection only.



Experimental Vertical Antenna

The general arrangement of the basic 12 m vertical antenna currently used at GW4ALG is shown below.  Unlike the prototype, 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 . . . .

Sketch of Experimental Vertical

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

Successes with the experimental vertical
With the basic 12 m antenna I was able to work Reino OH1TN (1916 km) - which, at the time, set the world DX record on 136 kHz; and remained the UK distance record for over 12 months.  Another exciting QSO was with Dave GM3YXM/P when he was located at Gairloch, Highland Region. At 703 km, this QSO established the intra-UK distance record for many months.

Other early contacts include those with Finbar EI0CF, 508 km; Toni HB9ASB, 902 km; Rik ON7YD, 521 km; and Harry PA0LQ, 495 km.  

Problems with the experimental vertical
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.

Related information

Loading Coils (including variometers)
Matching Transformer

 

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 136 kHz 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 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 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 will 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;
- as noted elsewhere by Mike G3XDV, nylon cord - even clean nylon cord - becomes a poor insulator if it gets wet.  On damp or foggy days, you will need to use an additional insulator between the wire and the nylon cord used to attach the balloons;
- 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!

 

 

 


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