(plans after DC7BJ)
The HB9CV+3 is a fullfeeded directional antenna with 2 active plus 3 passive elements. One might call this array "HB9CV-Yagi". This adds about 3dBd over a pure HB9CV and eliminates the squint of the classical 2-element HB9CV.
If higher gain is needed this is a good solution. Obviously a better front/back ratio is achived too.
Having built the aerial myself, I'm very satisfied with its performance using it as a pure TX-antenna for a telemetry device. Very recommendable!
Dimensions:
|
element:
|
remarks:
|
431 MHz
|
435MHz
|
|
length (mm)
|
length (mm)
|
||
|
1
|
director (passive) |
295
|
280.25
|
|
2
|
director (passive) |
300
|
285
|
|
3
|
HB9CV (active)
|
320
|
336.85
|
|
4
|
HB9CV (active)
|
350
|
332.5
|
|
5
|
reflector (passive)
|
400
|
380
|
|
between:
|
431 MHz
|
435MHz
|
|
|
spacing (mm)
|
spacing (mm)
|
||
|
a
|
element 1+2 |
125
|
118.75
|
|
b
|
element 2+3 |
125
|
118.75
|
|
c
|
element 3+4
|
90
|
85.5
|
|
d
|
element 4+5
|
80
|
76
|
This type of matching is called gamma-match. A 50-ohm coaxcable can be connectet straight without a balun. Easier to handle than Yagis. But it is recommendable to insert a capacitor in series to centre conductor and the feeding point of the gamma-match. This is necessary to minimize the SWR.
|
@ element
|
431 MHz
|
435MHz
|
|
|
length (mm)
|
lenght (mm)
|
||
|
e
|
3
|
50
|
47.5
|
|
f
|
4
|
60
|
57
|
Spacing of the gamma-match to elements and boom is 3-4mm.
Fix e.g. a BNC-flange-connector at the intersection of element 3 and the boom. Use a 5pf trimming capacitor - as seen in the drawing - to adjust minimum SWR. Replace the trimming capacitor with a fixed capacitor (remove + measure carefully) to guarantee long-time stability and weatherproofness.
HOME TOP (by DL2NET/OH4JZJ Sept.2000)