Φαίνεται το δίπολο να έχει σχεδιαστεί για λειτουργία λίγο κοντά στους108 - 110 MHz, αν και οι υπολογισμοί ανακλαστήρα και κατευθυντήρα είναι για χαμηλότερες συχνότητες και κανονικά ο κατευθυντήρας θα έπρεπε να έχει μικρότερο μήκος από το δίπολο. Ένα παράδειγμα σχεδίασης yagi τριών στοιχείων, με μήκος (αναδιπλωμένου) διπόλου περίπου στα 132 εκ . (το πρόγραμμα που χρησιμοποιήσα ήταν το
Yagi Calculator)
VK5DJ's YAGI CALCULATOR
Yagi design frequency =110,00 MHz
Wavelength =2725 mm
Parasitic elements contacting a square section metal boom 25 mm across.
Folded dipole fully insulated from boom
Director/reflector diam =7 mm
Radiator diam =10 mm
REFLECTOR
1341,5 mm long at boom position = 30 mm (IT = 658,0 mm)
RADIATOR
Single dipole 1288,1 mm tip to tip, spaced 545 mm from reflector at boom posn 575 mm (IT = 631,5 mm)
Folded dipole 1313,8 mm tip to tip, spaced 545 mm from reflector at boom posn 575 mm (IT = 644,5 mm)
DIRECTORS
Dir Length Spaced Boom position IT Gain Gain
(no.) (mm) (mm) (mm) (mm) (dBd) (dBi)
1 1234,6 204,4 779,5 605,0 4,8 6,9
COMMENTS
The abbreviation "IT" means "Insert To", it is the construction distance from the element tip to the edge of the boom for through boom mounting
Spacings measured centre to centre from previous element
Tolerance for element lengths is +/- 8 mm
Boom position is the mounting point for each element as measured from the rear of the boom and includes the 30 mm overhang.The total boom length is 809 mm including two overhangs of 30 mm
The beam's estimated 3dB beamwidth is 92 deg
A half wave 4:1 balun uses 0,66 velocity factor RG-11 (PE) and is 899 mm long plus leads
FOLDED DIPOLE CONSTRUCTION
Measurements are taken from the inside of bends
Folded dipole length measured tip to tip = 1314mm
Total rod length =2670mm
Centre of rod=1335mm
Distance BC=CD=632mm
Distance HI=GF=624mm
Distance HA=GE=664mm
Distance HB=GD=703mm
Distance HC=GC=1335mm
Gap at HG=15mm
Bend diameter BI=DF=50mm
If the folded dipole is considered as a flat plane (see ARRL Antenna Handbook) then its resonant frequency is 108,2MHz and K is 0,948
MATERIALS GUIDE for purchase. Allow extra, do NOT use these figures for cutting
NO allowance for saw cuts or purchased lengths resulting in waste
1) Length used by directors and reflector 2576mm of round 7mm rod
2) Length used by single dipole 1288mm or folded dipole 2670mm of round 10mm rod
3) Length used for boom 809mm (allows for 30mm each end) square section 25mm
