Antenna coupler simulator

D'après une idée de Kevin Schmidt W9CF, modestement traduit par TK5EP avec l'autorisation de l'auteur.

Voici un simulateur pour le populaire coupleur d'antenne en T avec capacités série et inductance parallèle. Les trois boutons au bas du dessin permettent d'ajuster les trois composants. Ils peuvent être réglés en déplaçant la souris sur un bouton, en cliquant et en maintenant le bouton gauche de la souris appuyé et en faisant tourner le curseur autour du bouton. Le bouton devrait alors tourner et faire varier la valeur du composant choisi. Les boutons des condensateurs ont une course de 10 tours et la self 30.

No java tuner.gif

 

Le ROS est  affiché simultanément de manière digitale en haut à gauche du "coupleur" ainsi qu'analogiquement sur le ROS-mètre. La perte provoquée par le coupleur est affichée en pourcentage par rapport à la puissance d'entrée ainsi qu'en dB. En cliquant sur le bouton "Autotune", l'ordinateur calculera la valeur exacte des composants qui adapteraient parfaitement la charge en limitant au minimum la perte dans le coupleur en supposant que les condensateurs variables ont un Q nettement plus élevé que la self.

L'algorithme de calcul Autotune tente de minimiser la valeur de l'inductance à utiliser en commençant par essayer de trouver un accord  en affectant une valeur maximum à un des condensateurs variable, puis si cela échoue, il essaye chacun des composants avec sa valeur actuelle. Si aucun accord initial n'est trouvé, il abandonne et affiche "Tune failed" dans le panneau des messages. Si un accord initial est trouvé, il effectue une recherche dichotomique entre la valeur de départ de l'inductance et zéro afin de trouver la valeur minimum de l'inductance pour un accord.

Notez qu'il est simple de programmer un algorithme qui trouve le minimum de perte, alors que nos coupleurs n'ont pas d'indicateur de perte, une règle comme "trouver un accord avec un minimum de self" est bien plus utile. Dans tous les cas, le Q des véritables composants varient pendant qu'ils sont ajustés.

Le bouton Set Up vous permet de changer la valeur maximum des trois composants et leurs Q. Initialement les condensateurs ont une valeur de 250pF, un Q de 2000 et la self une valeur de 30 uH et un Q de 100.

Les trois champs à droite vous permettent de changer la charge et la fréquence en MHz.

Une façon d'utiliser cette applet est de sélectionner une valeur de résistance et réactance de la charge, puis d'ajuster les boutons pour trouver une adaptation, comme vous le feriez avec une vrai coupleur. Notez le pourcentage de pertes dans le coupleur pour votre réglage et cliquez ensuite le bouton "Autotune" et vérifiez si l'ordinateur a trouvé un meilleur réglage.

Veuillez prendre note que si vous cherchez un logiciel pour déterminer les valeurs optimums des composants d'un coupleur en T, vous devriez chercher ailleurs !

Pour utiliser ce logiciel localement sur votre ordinateur, téléchargez le fichier tuner.jar et le fichier que vous visualisez actuellement tuner.html et copiez les dans le répertoire de votre choix, puis visualisez le fichier tuner.html à l'aide de votre navigateur.

Le code source Java de l'applet est distribuée sous licence GNU general public. la source est disponible dans l'archive tunersrc.zip.

La page de l'auteur est disponible ici. Vous y trouverez quantité d'informations intéressantes d'un niveau technique parfois élevé !

The vertical for dummies

This page has no pretention and is not a complete description of the vertical antenna, it only is intended to help you understand the most important things about this antenna and to how make it work !

vert1The simplest of all antennas is the vertical, also called the Marconi antenna. It has a quarter wave electrical length and has its base connected to earth.

This antenna vibrates with a intensity node (minimum) at his top, so at a voltage antinode (maximum).

Simple in its operation, it is by cons not the easiest to understand and handle.

Picture : The 1/2 wave antenna and it's equivalent mounted on ground. The missing 1/4 wave can be considered as its image in the ground.

 

 

6 Beverage remote ant. switch

1During our multi-multi contest operation, we came against a problem while using low band receiving antennas.

There were 3 low band stations, one on 160m, another on 80m and one on 40m.

The problem was simple : how could we share the Beverage antennas on all of these 3 stations ?

The first solution was to split each antenna in 3 directions with coaxial T's and to use a coax switch on each station, so that each station could select a different antenna. That proved to be not very satisfying, the impedance seen by the receivers and antennas were changing a lot depending on the position of the different switches.

DK4VW, Uli told me that the BCC (Bavarian Contest Club) crew was using a Beverage switching box that proved to be very efficient and i began to build such a box with his precious help.

Informations below given with permission of DK4VW.

A 7el 144MHz yagi

groupe7elyagiSince almost 30 years, for my portable VHF activities, i used a F9FT 9el yagi. This one was the best i've found for this purpose, it was leigthweight, relatively cumbersome and performed quite well. Unfortunately, it broke during a contest when falling down from 7m...

To replace my beloved antenna, i decided to build something and not to buy one. After searching some design on internet, i finaly adopted DK7ZB's one. He offers several designs, and i chosed a 7 element yagi in 28 Ohms technology.

The advantages of DK7Zbs antennas are :

- Computer optimized
- Great reproductibility
- Easily assembled and dismantled. Ideal for portable operations.
- Excellent electrical characteristics, gain, pattern, F/B ratio.

The original version described on DK7ZB's page has a 3.26 m boomlength. So, i asked him if he could calculate it for a 3m boom. Aluminium tubing are sold in 6m length, and with 3m booms i would be able to build 2 antennas. The new calculated antennas have a small gain drop (about 0.35 dB)

Another advantage of this 7el is that with a 6m long alu tubing, you have enough for all elements and build 2 antennas.

4 square vertical system

80m-4sqThis page is a short description of the four phased verticals system i've build and used. It is primarily intendend to be used on the lower bands 160m, 80m, 40m. All the principles stated here are of course valid for any other bands, but you can achieve the same game with yagi antennas easily. It is mainly built around the Collins hybrid phasing system wound on toroids.

Other feeding methods are possible and certainly better, but this one is rather simple to build and use on the battlefield. (contests, fieldays, expeditions)

Many stations use this system all around the world and it has proven his effectiveness.

  Four phased verticals on 80m (click to enlarge)


 

 4sq diagram

Diagram of the phaser and control box

 
Directions, phasing and relay powering
Direction
K1
K2
K3
Ant 1
Ant 2
Ant 3
Ant 4
NW
1
1
1
180°
-90°
-90°
NE*
0
0
0
-90°
180°
-90°
SE
1
1
0
0
-90°
180°
-90°
SW
0
0
1
-90°
-90°
180°

(*) is the default position, with no supply. It should be your favorite working direction.

RADIATION PATTERNS

azplot

Azimuth and position of antennas, system in NW position.

elplot

Elevation pattern.

The hybrid coupler, if well built, will deliver equal voltages on the 2 output ports as well as negligible voltage on the isolation port. The phase shift between both outputs is 90°.

This is only true if the impedances of the loads on all ports are the same as the one for which the system has been calculated. And this is in practice never the case ! So, the complete system is a compromise...

A 4 square array needs equals currents on each antenna to work properly. Unfortunately, the antenna impedances are NOT equal, varying on each antenna due to mutual coupling as well as during beam direction change. Feeding the antennas through feed lines that are 1/4 wave long or an odd multiple of a 1/4 wave long, will force the the antennnas to have the same currents in them even though they do not have the same feed point impedance. That's called current forcing.

Feeding the antennas with 1/4 wave long feed lines is very important !

 

The switching box can drive a 4 or 2 antennas phased array.

With 4 antennas, arrays are mounted in a perfect square with 0.25 lambda side, the beam directions are along the diagonals.

The phasing lines are quarter wave of 75 Ohm coaxial cable. Use at least a cable with 0.76 velocity factor, otherwise with 0.66 factor the lines will be too short to run to the center of the square (where the phasing box should be) with a quarter wave. Otherwise, you will have to cut the lines 3/4 lambda long.

I used CATV distribution coaxial cable with foam dielectric which can be easily found.

With 2 antennas, use antenna outputs 1 and 4. The corresponding position on the control box are NE and SE.

In this case, the phasing lines are quarter wave of 50 Ohm coaxial cable. Same remarks as above concerning the dielectric. Preferably use foam dielectric cables, this will make the lines a bit longer, enabling an easier connection.

Beam directions are in the alignment of the antennas and only 2 directions are possible.

The feeding line to the station is a 50 Ohm coaxial of any length.

CONSTRUCTION DETAILS

Calculating the values of the hybrid coupler.

The T1 transformer is the "key" of the system. It is a Collins hybrid coupler build on a toroid core. Any core dimension can be used depending of the power you want to use. The colour must be red as it determines the permeablilty and frequency range.

The values of the hybrid coupler are :

2 3

Where Xc = 100 ohm, XL = 50 ohm , L in µH, C in pF, F in Mhz, C1=C2 and L1=L2

From this, we can calculate the components for the different bands :

Freq. C L
1,850 MHz 860 pF 4,30 uH
3,650 MHz 436 pF 2,18 uH
7,050 MHz 225 pF 1,13 uH


Now, we have to build the T1 transformer.

The number of turns for a toroid coil is calculated with the formula :

So, for the above calculated value of 1.13 µH and a T225-2 which has a AL value of 12 nH/turn, it gives : 9.7 turns. (in practice 10 turns)
For an T225-2B core and an Al=21.5 nH/turn it gives 7.25 turns. (i practice 7 turns)

A turn is when the wire goes through the center hole of the core.

4

CAUTION : Be carefull, some manufacturers give the AL in uH/100 turns !


In this case, you must use the following formula and units :
4-2

 You can find a nice free tore calculator written by DL5SWB on his page that will help you to calculate the right number of turns depending of your toroid choice.

The first step is to wind the coils with the 2 wires tighten together and measure their values. Solder the ends of both wires, and start to wind one turn of the first wire, then the 1st turn ot the second wire, and repeat for all turns. I've found that it's easier to make 1 of 2 more turns and measure the inductance. You can then easily adjust the coil to the right value by removing a turn or 2 and stretch or compress the windings on the core. Once you have the right value, lock the wires with varnish or tape.

Then, you must measure the capacitance between both wires. This value has to be substracted by half from the above calculated value of C1 and C2.

Then solder the 2 capacitors C1 and C2 of this calculated value. I generaly use 2 or 3 capacitors in parallel for C1 and C2, by choosing the right values and tolerances, you can trim to the the right value.

Finaly, using at least an oscilloscope (dual trace) and a wattmeter you can check if the phase shift of 90Ý is correct between both outputs, and if the power are the same. You can of course use better instruments if you have them !

Don't forget the load all ports with 50 ohms loads !

In practice, the 90 degree phase shift remains relatively constant over a large bandwith while the coupling energy of -3dB equal split between the output ports occurs only within a relatively narrow bandwith.(few percent of the design frequency)

The T2 transformer serves as a 180° shift line and is the same as T1.

Wind the transformer with 2 wires tighten together. Ground one end of one wire and the opposite end of the other one. This will make a 180° phase shift.

The 180° phase shift can also be made with a half wave long coax cable. When cutting the coax, don't forget the velocity factor which will make the cable much shorter. (See the coaxial page of this site for coaxial datas)

I used ceramic capacitors of 1kV rating and Teflon insulated wire for a 1.5kW level. The relays must be able to handle your output power.

CHARACTERISTICS of the FERRITE CORE used in this SWITCH

DIMENSIONS
MICROMETALS
Part No.
AL
nH/N²
OD
mm
ID
mm
Ht
mm

cm
A
cm2
V
cm3
T225-2
12.0
57.2
35.7
14
14.6
1.42
20.7

T225-2B

21.5
57.2
35.7
25.4
14.6
2.59
37.8

tcore
Datas taken from Micrometals, Inc. © 1998. A lot of information about cores can be found there !

RECOMMANDATIONS

- Make the 4 antennas as similar as possible, use the same number of radials, same tubing diameter, etc...

- Carefully cut the 4 quarter wave phasing lines in the same 75 Ohm coax cable and as accurate as possible. Don't forget the velocity factor which depends of the cable you are using. I've measured some non neglegible differences between several manufacturers. I used a spectrum analyser with tracking generator to cut the cables to accurate phasing angle, but simpler methods are possible.

- Be sure to mount your system in the right shape and direction, don't forget the antennas fire along the diagonals. You can of course shift the whole system to have 4 other directions.

RESULTS

If you take care on all the above points, you will have very nice results with this antenna.

The F/B ratio is at certain time well over 25-30dB depending of the signals incoming radiation angle. The noise level on this antenna is much lower than with a single vertical and beam switching is done in a second.

The power dissipated in the load is at resonance, only a few percent of the input power. We found 15W for more than a kW !

Plots have been made with the freeware software MMANA by JE3HHT which can be found here.

 

Last products !