Antennas..

Today I thought I would give you an insight on my working conditions regarding my HAM radio hobby. This time focusing on the antennas.

The antenna is the inducer that’s allow your signal to travel into open space. It’s also the receptor that allows signals to be detected in your radio. The construction and size of your antenna is vital to how well it works. Also the location and placement is a vital factor.

One could argue that it doesn’t really matter if you use just a random wire as antenna or a fine tuned professional made construction for your station and this is correct. You can use almost anything as an antenna but depending on what expectations and prerequisites you have anything might not do the trick.

One of my interest in the HAM radio hobby is constructing and building antennas. Also understanding the way they work like they do. So far during the three years Iv’e been able to have space enough to try out some different antennas, Iv’e only constructed simple wire antennas and quarter wave verticals. Even though It’s simple antennas, It’s been a learning experience designing, building and verifying them. The fruits of my experiments is now in use as my ordinary antennas.

So what kind of antennas do I have?

Antenna 1

The first main antenna is an triple band dipole for 30, 20 and 15 m band and Is located about 30 m from the house. The location is primarily chosen with the kids outdoor playing in mind. It also has the advantage to be placed as far away from our neighbors houses to minimize interference.

image Figure 1. Main antenna 1. The center isolator and feedpoint can here be seen mounted on top of the mast.

The antenna is constructed by low cost materials not exceeding a total of 70 dollars. The design of the antenna is made out of three tuned dipoles suspended on top of a 5 m mast. The dipoles are, looking from the top down, suspended as an X and depending on space and points of tying the ends configured as a sloping dipole or Inverted V. The dipoles are then connected directly to a 50 ohm feeder via a homemade isolator. The antenna shows a SWR value of 1:1,5-2 on the desired bands. Outside the bands the SWR is typically around 1:3 giving a possibility tuning 17 m, 12 m, 10 m and even the 80 m band. Using the antenna on these bands makes it a bit inefficient but still useful.

This design was tested and verified during the SJ7SOP activity during the summer, then only as an dual band version with 20 and 15 m. The experimental version was suspended to a 5 m fiberglass fishing rod in a portable fashion. This was set up temporarily in the garden and stood the beating from storm winds and hail during the summer months.

Antenna 2

The second main antenna is a dual band dipole for 40 m and 10 m. The philosophy is the same as with the first antenna, a number of tuned dipoles feeded through the same feed point. The dipole is suspended from the attic of the house down in to the garden in a sloping manner.

image Figure 2. Main antenna 2. The 40 dipole is suspended in parallel with the incoming phone line and the 10 m dipole can be seen on It’s front side.

As with the first antenna, this is made out of low price material not costing me more than 30 dollars to build. The 40 m part was the first to come up when as I felt the need for a low band antenna for those dark winter evenings. The 10 m part of the antenna came up just recently as I saw an experimental need for this particular band. The addition of the 10 m dipole also made the SWR come down a bit on 12 m and 15 m why it’s also useful on these bands, even if It’s a bit inefficient. The downside of this antenna is that it’s suspended in parallel with the house phone line and due to It’s proximity to the house, it picks up a lot of man made noise. The phone line and the ADSL modem connected to it seems not to pick up to much of the transmitted signal though.

Feeders

To feed the antennas from the house I´m using different cabling. For the first antenna, wich is located the farthest point from the house, I´m using RG-213 with a length of about 30-35 m. The cable is buried in the lawn about 10 cm down to prevent the kids from tripping over the cable while playing in the garden. The cable length is quite long with attenuation of high frequencies in mind but it´s a calculated trade off for the location of the antenna. For the second antenna, a 15 m length of RG-232 is used to feed the dipoles. As the it was originally constructed as a low band antenna where the attenuation Is´nt that critical, this cable is sufficient. For the 10 m part it generates some attenuation but it can be compensated by utilizing more output power.

Both antennas are actually working quite well and even lets me working DX stations on higher frequencies. Due to It’s surroundings the clearest directions is mainly towards North America, Russia and the Far east. This is why I’ve tried to have the antennas main lobes pointing in these directions. My own experience tells me that you don’t have to invest in expensive premade antennas to work DX. You can make the antennas by your own and at the same time learn and know what you put up. With wire antennas you can easily adapt the antennas shape and suspension to what ever location you got.

This is all for now and the next post I´ll be continuing with giving you an insight of my working conditions.

73 de SM7VRZ

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