Дизайн передающей антенны Magnetic Loop на 160 метров (перевод)

Автор: Стив Адлер, vk5sfa@wia.org.au

Примечание переводчика: Данная статья является переводом замечательной статьи о рамочной магнитной антенне, которыми я достаточно давно интересуюсь. Я постарался сохранить оригинальный авторский стиль где это было возможно. Некоторые фразы и идиомы, коенчно же, были адаптированы. Фотографии были взяты из авторской статьи без изменений. Стив Адлер, автор оригинальной статьи, любезно позволил сделать этот перевод и поместить его на моем блоге. Если вам интересно, вы всегда можете прочесть оригинал статьи. Я буду рад любым комментериям относительно правильности перевода - некоторые вещи иногда достаточно сложно перевести так, чтобы оставить и смысл, и ту интонацию, которую в свой текст вкладывал автор.

Shortened dipole. How to design one for 40 meters band.

Sometimes you don't have an opportunity to choose an antenna. You can be either limited in finances or space, but the only antenna you may build is something small. Just imagine you live in a country house and have two 10-meters-tall trees with a distance of 15 meters between them, leaving you only 11-12 meters of free space for your antenna. You want to be present on 40 meters band, where the propagation does live the whole day. Since you don't want to build a ground plane, you have chosen to build the dipole. Good choice: the dipole is a pretty good and easy to build antenna requiring not so many materials. But you have realized you have no space for this antenna: diagrams tell you that the antenna must be 20 meters long. So sad...

But, don't panic! A shortened dipole is your choice. Let's try to design the shortened dipole that could fit the space between your trees!

Shortened dipole. How does it work?

Recently I was asked about the shortened dipole. In a nutshell: the question was pretty simple - is this possible to create a small yet effective antenna for 80 meters band. Below is a result of my thoughts on this topic as well as some number of diagrams, which, as everybody knows, worse one thousand words.

Let's start from basics: the antenna is a wire conducting the RF current. As far as we are talking not about the conducting of the DC, the basic understanding of the RF transmission is a must, although this is out of the scope of this article.

How the height affects the VHF antenna

The previous article caused some amount of questions in respect to the VHF/UHF antennas and how the height of the mast affects the radiation pattern. This is to answer these questions and bring light on this very interesting topic.

We all know that VHF antennas are vulnerable. There is a lot of things which might destroy the antenna - wires, trees, birds, even its own mast. Therefore we try to place the antenna as higher as possible to avoid the impact of the mentioned above objects. For the birds, we have the scarecrow. The practice tells us: the higher antenna is, the farthest QSO you have. This is the true and the false simultaneously. The devil is in details. Two antennas for the 433 MHz GP located on the 20 meters mast and on the top of 20 meters building are very different antennas, even if they are twins. This is because the overall height of the antenna is calculated relative to the nearest more or less flat conductive plane: the ground or the roof. The radiation pattern of the roof-mounted VHF GP is the same as of ground-mounted one.

How the height affects the antenna

After the third article, I decided to perform more general work and calculate the same antenna on the different height. In a nutshell, the antenna parameters depend on the height the antenna is placed at. I stored some number of pictures, looking at which worse thousands of words.

The antenna is a quarter-wave GP with two radials. I know that the number of radials does matter, but this is very quick, thus not very thorough exercise. The antenna is made of aluminum pipe (R=10 mm, 3/8 inches), counterpoises are an aluminum wire (R=0.8 mm). The antenna was designed to be mounted on the 1 meter (3 feet) tall mast.

The twin-lead Marconi antenna

In general, the Marconi antenna is a well-known type of antennas widely used by hams, and, in fact, is a Ground Plane antenna. In comparison to the regular Marconi antenna, the twin-lead modification is a short-circuited one.

The Half-Lambda T-antenna

The half-lambda T-antenna is a specific implementation of the T-antenna. The overall view of the antenna is shown in the picture below. The picture contains formulas as well.

T-antenna

T-antenna is a very simple antenna having the form of the letter T. As shown in the picture below, the antenna seems to be most useful when used with receivers having one single antenna connector (e.g. banana socket).

How to switch Icom IC-706 and PA simultaneously

Some time ago I had to learn how to switch the PA when transmitting on my Icom IC-706MKIIG. Visual observation of the RIG gave nothing - there is no dedicated socket there on the device. I spend some time examining the User Manual and realized that there is an ability to do this using the CI/V cable. But this works only with the PA by Icom. Then I went to the Internet and start looking here and there.

SatNOGS antenna rotator. Part 4. The frame.

The frame is the skeleton of the SatNOGS rotator. And today I have started building it. Yesterday I received the cut T-slot 20x20, ball bearings 6008ZZ, hidden construction corners and T-nuts. Also, I have almost all the plastic parts printed (except ones I have planned to do of nylon).