An article by I5NZR (SK)
Antenna Dimensions :
A) VHF element 147 cm
B) radiator 49 cm
C) UHF element 17 cm
Element distances :
A to C 11,5 cm
B to C 4 cm
Feeding is applied directly to element B
MAST (D) :
Rectangular aluminium profile 4 x 6 cm, 18 cm long, and rounded at the end at element B (see photo) to fit the radiator connector and drilled to fit the other elements and drilled to insert the other elements.
Homebrewing the J-Pole Dual Band Antenna
To feed the radiator I used a special panel connector. I disassembled the central pin and soldered it to the radiating element made of 8 mm diameter copper pipe, which was then reassembled in the connector, insulating the initial part for a few centimetres using a piece of nylon pipe.
This type of connector, which really meet very well our needs, is unfortunately not easy to find.
The power supply to the radiator, which must be isolated from the support, can be easily realised with a car antenna base, designed for mounting on the bodywork through a hole.
In the realisation of the antenna, the measurements of the elements are not critical and can be adapted with minimal variations depending on their diameter, while the distance between them can be critical
To find the correct impedance adaptation, not being able to move the feed point, as happens in the classic J, after drilling the support I had to ovalise the holes themselves, creating slots, to be able to move the elements away from each other or closer together, especially as regards the distance between the radiating element and the UHF one.
I do not think there is any need to dwell on explaining the characteristics of the “J” antenna. In any manual for amateur radio antennas and in all the magazines for OM the subject has been treated several times extensively: F
inally, just type “J pole antenna” into Google and you will find numerous pages on the subject.
In fact, this creation was the result of research carried out among the various projects available on the Internet, with the aim of having a single feed and improve the performance of the “J” antenna in UHF, since the performance of the VHF version is not satisfactory, when the antenna is used in 70 cm., even in the presence of acceptable SWR.
Article by I5NZR Sergio (now SK) and freely translated by IW5EDI Simone
Hi. Are the distance measurements of the elements taken from the centre point of the elements or are these absolute values? Thanks for sharing and all the best.