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Background

My interest in portable Amateur radio operating really took off after I purchased a SOTA 3 Element 2 metre beam at the Leicester Amateur Radio Rally in 2003 weighting less than 200grms. The mast is a light weight blank fishing pole that came complete with guy ropes and pegs. With this portable antenna it is possible to successfully operate portable while in the great outdoors. I have used it many times while at Youlbury our local scout camp site. At Shot over Country Park, And along the Oxfordshire Way long distance foot path near Beckley, And at the WACRAL conference at Swanwick in Derbyshire and many times during Radio Scouting activities for example the communicator badge (Cub Scouts) or Radio communication badge (Boy Scout).

From 2m to HF

Having been successful with the SOTA 2m beam I guess it was only a matter of time before I wondered if it would be possible to continue with the fishing pole theme to support HF dipoles at a modest cost. At first I used the fishing pole that came with my SOTA beam. I found that so long as I kept the weight down by using thin wire and light weight coax. The fishing pole could support a single band 20m dipole.


However I thought it was unrealistic to expected the fishing pole to hold a 40m or 80m dipole in any thing more than a very light breeze. So the hunt began for a portable pole that could support an inverted V-HF antenna. At the Elvaston Castle Amateur Radio Rally 2005. I purchased the Delta International pro 9.00 blank fishing pole for ?19.

  1. The length 9.1m 29.8 feet.
  2. Weight 1.37kg, telescopic.
  3. 10 tapered sections.
  4. Collapsed length 115cm.
  5. Top section width tapers to 2mm.
  6. Base 4.8mm.

I have since found this pole to be ideal. And have used it at the July 2005 Oxford district cub scout camp As a flag pole and again in august for my summer mini dxexpedition in the Scottish highlands. I have since brought a second Delta International pro 9.00 blank fishing pole at the Telford Amateur Radio Rally during september 2005. And on this second pole I made a 160m vertical antenna that I designed for the spot frequency of 1.9750MHZ.

HF Half Wave Dipole Lengths

Just for the record I am fully aware of the science and maths that is required for antennas lengths

The length of a half-wave dipole in space is

150______________ meters

F (MHZ)

The actual length of a half wave dipole is less than this owing to:

  1. The Velocity of propagation in the wire being different from that in space
  2. The presence of insulators at the end of the wire and of nearby objects for example trees or buildings.
  3. The diameter of the wire or element.

The actual length is normally taken to be 5% less than or 0.95 of the electrical length. This is called the correction factor. Hence the actual length is:

150 x 0.95 = 143metres
_________________
F (MHZ F (MHZ)

There are however advantages in designing a half wave dipole antenna for a spot frequency for example:

  1. IOTA
  2. PSK31
  3. RTTY
  4. SSTV
  5. CW
  6. SSB

However by using the data in the chart below I have found that this gives me greater flexibility in my antenna design as I desire to make a single band dipole that is more broadband and with the aid of an ATU I am able to operate across the band

Table

1.8 MHZ

247 feet

3.5 MHZ

129 feet

7 MHZ

67 feet

10 MHZ

46 feet

18 MHZ

26 feet

21 MHZ

22 feet

24 MHZ

18.8 feet

Construction:

I beleive that its very important before you start to assemble your antenna its best to start with some kind of plain I prefer to use a reporters style note book they cost a few pounds. to keep a record of my notes. draw up a list of the diffrent items that are needed for example:

  • type of antenna wire
  • what is the total lenght of wire
  • how many antenna insulators will I need
  • Dipole centre
  • assorted cable ties
  • lanyard or rope.
  • coax or open feeder
  • what will be the over all weight of this antenna
  • what type of fishing pole will I need to hold this antenna up.
  • Only start constructing the antenna when you have all the parts to complete it.

Liner Loaded 80m Inverted V dipole

Liner loading is where you take a full size antenna and fold the elements back into a smaller physical space maintaining four or six inches separation between the folded elements there is some interaction between the folded elements and the main radiator this usually lowers the feed point impedance. However, as this antenna is normally tuned with an antenna tuning unit this is not an issue.



We constructed our liner dipole with a top hat of 100 feet leaving 14.5 feet of wire per leg to be folded back on its self. Using spacers these can be made from fibre glass sheeting, but any water proof and rigid material would be acceptable. However if you suffer from time poverty then making the spacers yourself would not be an option. It would be more convenient in this case to purchase a set of 16 GS-Spacers from W&S. at the centre of the dipole we used a diamond 1:1 balun type BU-50 the balun helps to reduce feed line radiation and radiation pattern distortion and comes fitted with a SO ? 239 socket as standard. Peter and I have been using this antenna as an inverted V for over a year and we have been delighted with the over all performance of this antenna the built in automatic atu in The TS 570DGE transceiver is able to tune the antenna with an swr reading of 1:1.

The estimated cost of this home constructed mono band HF antenna is approximately £49.00


The 80m liner loaded inverted V dipole

The TOP BAND Vertical

Or a budget top band quarter wave vertical, fishing pole antenna for £25.50 pence.

Peter M3PHP and I were very fortunate this year to be invited by Terry G0LUQ to go for the second year running to the Telford Amateur radio Rally as I was able to buy a second Delta International pro 9.00 blank fishing pole. So far I have only experimented with portable beams, and HF dipoles. However I was ready to experiment with a fishing pole vertical antenna. The reality for many radio amateurs in the United Kingdom is the fact that our gardens are some what on the small size often a half size G5RV at a height of 25 feet is about all that can be managed. And unfortunately my Oxford QTH is no exception.

The Need

A year ago Peter and I replaced our half size G5RV with traps for 80m for a nest of dipoles covering 7MHZ-24MHZ fed with a 1:1 diamond balum. Due to the size of the garden the only way around this problem is to construct a Quarter wavelength vertical antenna.

The Design

With my son Peter's M3PHP help we did the maths for the spot frequency for the Oxford Lunch time net on 1.9750 Mhz. We cut the length of wire to 118\' 48". About a foot from the bottom of the fishing pole we started to wind the wire onto the base of the fishing pole slowly winding a few turns of wire on at a time and tying into place with a plastic cable tie. At first we tried to made the turns about half an inch apart and as we progressed up the fishing pole some of the turns we made closer about half of the way up the fishing pole we were able to make the turns much wide however we held the wire in place with a cable tie about every six turns in order to make a neat job.

The perceived wisdom regarding the quarter wave vertical antenna starts off well. Then makes for depressing reading when it covers the problem with earth rods and ground plains etc. The big plus for us was the fact that the vertical antenna offers the attraction of low-angle, omni directional radiation and is popular where space does not allow a long horizontal antenna. The simplest form is a vertical radiator one quarter of a wave length long the impedance at the bottom is 30- 40 ohms and can be fed by a 50 ohm coaxial cable.

That was the good part the down side follows It is difficult to produce a satisfactory earth which is needed when a vertical antenna is to be used. A single earth rod, say of 2m long, is unlikely to be satisfactory unless the soil has exceptional conductivity.


About two hours later we were ready to try our new topband vertical antenna. Peter ran the coax feeder to the MFJ 948 ATU and powered up the ICOM 718 rig. Peter said that he was able to get a 1:1 SWR this was very promising. I nearly for got to add that unfortunately we are not able to run wires out along the garden path. Instead Peter used an old 2m element from a beam as the earth rod and added a couple of feet of wire to it and pushed the rod into the ground then with the aid of a cable tie he was able to fix the other end to the earth side of the PL259.

Well the antenna was up. The rig was tuned up and ready. I put out a test call for M3BQX who gave me a report of 5/9 the following day Peter was able to take part in the topband net and he received 5/5 from G3DQC and 5/9 from G4AZN. Later in the week I worked G4AZN on topband and received a signal report of 5/9.