Following the frequent demands on the topic here is detailed with picture the construction of an Yagi antenna calculated for the FM broadcasting band 88 - 108 MHz. The central frequency used for our calculations is 100MHz. You can extrapolate easily below for others frequency grace to values of diagrams. This antenna is less difficult to construct than the one presented on the previous page.
Click on image to enlarge.
Short description :
The goal of this page is to help you to construct an antenna, not to make the theory of this one, theory complex strong to staying it. Here are some definitions of basis therefore. The name of axis of an antenna call the BOOM. The antenna uses a dipole says " trombone " that is the only element a few delicate to achieve. Contrary to what lets believe diagrams above the two tubes of the trombone are not to dish " but disposed perpendicularly to the axis of the antenna. On the photo below taken perpendicularly to the antenna one doesn't see the two tubes, but in " alone appearance " one. Directors increase the directivity of the antenna (sense of the arrow) but as the gain, it is because of them that with 4 elements the antenna to a Gain of 6dB and 5 elements procures a Gain of 8dB. The reflector return the bundle of wave " collected " by directors toward the dipole, but his major role is to protect the antenna against the parasitic signals coming from the rear. In any case an antenna must be raised in relation to background to work well. 1 to 2 length of work wave is counseled. For F = 100 MHz, the Length of wave is 3Meters (9.85 feet) ...
|To meet the material :
In a store of tinkering buy:
4 Round tubes in aluminum length 1Meter (3.28 feet) diameter 8mm (0.31 inch)
4 round full of 6mm (0.24 inch) length 1Meter (3.28 feet)
1 batten of wood (Pine) of section breve 28x28 mm (1.10 inch) (not critical) length 2Meters (6.56 feet).
1 electric derivation box WEATHERPROOF square of dimension 75mm (2.95 inch ) (Legrand manufacturer)
1 box of screw metal type diameter 4mm (0.16 inch) length 30mm ( 1.18 inch) more 4 nuts type " butterfly " diameter 4 mm (0.16 inch) .
If you choose " the option " 5 elements stay up to add a tube in addition round 8mm (0.31 inch) and 1 of 6mm (0.24 inch) because you should build one elements besides that in our example.
|IMPORTANT REMARK: If you find the tube of 8mm (0.31 inch) in length of 2M (6.56 feet) you don't have need of full round of 6mm (0.24 inch) , that serves to " to lengthen " tubes of 1M (3.28 feet) . You won't have in this case need that of 2 full round to achieve the " dipole Trombone ".|
|10 necklaces to set diameter 10mm (0.39 inch) or 10 necklaces adjustable
type (dearer but more convenient)
With necklaces to set you won't be able to disassemble your antenna anymore whereas with adjustable will be himself the case.
( 4 elements Antenna )
|The BOOM in our case it is in wood but one little also to use an another
insulating, the PVC for example. If you decide to use a square or a
U of aluminum stay up to isolate elements of the antenna of the BOOM.
After his building it will be necessary to protect it by a varnish, the painting or the silicone so that he doesn't distort itself to inclemencies.
Start per drawing on one face a first reference mark to 3 cm (1.18 inch) of the beginning of the batten, draw 3 other distant reference marks of 45 cm (17.71 inch) then the some of others. Mark the intersection to the middle of the batten on every reference mark. If you choose " the option " 5 elements stay up to pierce the BOOM with a first interval to 60/F = 60cm (23.62 inch) for 100MHz.
|Pierce 4 holes of diameter 8,5mm (0.33 inch) while using reference
marks previously tracings. Council: Pierce a before-hole first to 4 or 5
mms (0.15 or 0.19 inch) of diameter. Attention to the perpendicularity.
Pierce a hole of 4 mm (0.15 inch) of diameter then on the opposite face in order to cross the hole preceding perpendicularly. This hole will serve to pass a bolt of 4mm x 30mm (0.15 x 1.18 inch) to immobilize and to center elements on the boom.
Pierce a hole of 4mm (0.15 inch) of diameter also to the middle (50cm - 19.68 inch) of every diameter tube 8mm (0.31 inch) length 1M (3.28 feet).Conseil: made one before hole with a wick of 2 or 2,5mm (0.07 or 0.09 inch) of diameter.
To permit the liaison of the coaxial cable to extremities of the dipole you have two solutions:
|After the drill came the time of the saw...
Do a slash of 1 cm (0.39 inch) of depth (split) to surroundings of every extremities of tubes of 8mm (0.31 inch). It will permit a better tightening by necklaces, of Circles of 6mm (0.23 inch) that will slip inside himself.
Cut with the saw to metals one of round of 6mm (0.23 inch) to the middle (50 cm 19.68 inch) . Is going to permit you to lengthen one of diameter 8mm (0.31 inch) tubes in order to get the 1,5M (59 inch) of the reflector. For it slip each of pieces of Circle of 6mm 0.23 inch) in extremities of the 8 mm (0.31 inch) tube and adjust an overtaking of 25cm (9.84 inch). 25 cm of part is other deal 50cm (19.68 inch). The tube of 8mm (0.31 inch) measure 1M (39.37 inch) one adds him 50cm (19.68 inch), veiled our reflector of 1,5M (59 inch). Below final aspect of the assembly with a set necklace.
Proceed thus for each of the DIRECTORS elements. For the first quotes it out all is of 1,38M(54.33 inch), the second is 1,34M (52.75 inch).
In the version 5 elements 1,38M - 1,30M and 1,20M. (54,33 inch - 51.18 inch and 47.24 inch)
Bring up your Reflective elements and Directors on the BOOM fix the center with bolts of 4mm (0.15 inch) and set necklaces in order to block extension pieces, if it is the solution that you chose. With necklaces adjustable you will be able to bring up them at the end.
Realization of the Dipole
|He must remain you only one tube of diameter Round 8mm (0.31 inch) and
two of 6mm (0.23 inch) of diameter.
Insert on a depth of 6cm (2.36 inch), one of 6 mm (0.23 inch) round in the tube of 8mm (0.31 inch). Fix the with the help of a necklace. Since this tip of the tube of 8mm (0.31 inch) measure 18,5cm (7.28 inch) on the round of 6mm (0.23inch) and draw this point. You can also draw a feature to 21,5 cm (8.46 inch) (length of the extension).
Procure you a fall of tube of a diameter of 30mm (1.18 inch) (PVC PIPE 32mm 1.25 inch). Place it vertically in one stalls as on the photo opposite.
Bend each of the 2 bars of round of 6mm (0.23 inch) to dish from the reference mark 18,5cm (7.28 inch). (cf photo).
Slip the tube of 8mm (0.31 inch) in the BOOM and immobilize it with a bolt.
After have slip the round of 6 mm (0.23inch) in the tube of 8mm (0.31 inch) you have a dimension out all of 1,43 Meter (56.30 inch). Set necklaces.
|To pass extremities of the Trombone in weatherproof box. To fix this
box to the BOOM use one bolt + 1 screw.
To pass wires coaxial 75 ohms type TV. To fix his extremities (Mind of a quoted and Twist the other) on every extremities of the trombone is by necklaces, either by pods screwed in the trombone. Verify the continuity of sons, fill then box it of SILICONE in order to assure his tightness.