Isolated antenna assembly

An isolator assembly for isolating a transmitting and receiving communications antenna member from a mast and connector. The isolator assembly electrically couples an antenna member to a connector for passage of radio frequency energy but also electrically isolates the antenna member from the connector and the mast from a high voltage on the antenna member.

BACKGROUND OF THE INVENTION 
Long antenna assemblies, such as those typically used as home base station 
antennas by C.B. operators, when being erected, and occasionally in use, 
present safety hazards to installers and users. Contact with power lines 
which sometimes accidentally occurs results in serious injury and 
sometimes death to those in contact with the connecting cable or mast. 
Warnings and cautions are insufficient to assure absolute safety in use 
and installation. 
SUMMARY OF THE INVENTION 
In accordance with the present invention there is provided a communications 
antenna which is provided with an isolater assembly for isolating the 
metal radiator or antenna member from the mast and coaxial conductor. The 
isolator assembly allows for effective transmission of the radio frequency 
energy between the antenna member and the coaxial conductor, but 
electrically isolates the radiator from the coaxial conductor and mast up 
to a designed maximum breakdown voltage which is set at a level high 
enough effectively to insulate the installer or user from the effect of 
contact with power lines carrying a normally encountered voltage in 
environments in which CB base stations are installed and used. 
A transmitting and receiving communications antenna assembly for 
electrically isolating a radiator from a mast and a connector in 
accordance with this invention comprises an elongate radiator adapted for 
mounting on a mast and an isolator assembly for electrically coupling the 
antenna member to the connector, for mounting the radiator on a mast and 
for electrically isolating the antenna member from the mast and the 
connector. 
The isolator assembly comprises a radiator mount comprising a gap defining 
means, capacitor plate means mounted adjacent the gap defining means to 
confront in spaced relation to the radiator to define a capacitor 
therewith, and a tuning circuit means electrically connected to the 
capacitor plate means for connecting the capacitor plate means to the 
connector. The capacitor couples the radiator to the tuning circuit means 
to isolate the connector and a mast from a high voltage on said radiator 
and electrically couple radio frequency energy between the connector and 
the radiator. 
The isolator assembly may further comprise a second capacitor plate means 
spaced from the first plate means to define a second capacitor with gap 
defining means therebetween. The radiator and first capacitor plate means 
define a first capacitor and the first capacitor plate means and the 
second capacitor plate means define a second capacitor for the two 
capacities coupling the radiator to said tuning circuit means. The 
isolator assembly may also include the tuning circuit which comprise a 
coil connected to the second capacitor plate to the connector and circuit 
means for tuning the antenna assembly and for matching the impedance of 
the atenna assembly to the impedance of a load, such as a coaxial cable, 
connected to said connector. 
The circuit means includes an adjustable tuning plate mounted on the 
isolator assembly which define a third capacitor with the second capacitor 
plate means. 
In its preferred form the radiator mount comprises a tubular insulating 
form for receiving the base of an antenna member, the first capacitor 
plate means is curved and is mounted on the tubular form and is spaced 
away from said antenna member to define a first capacitor therewith, and 
the second plate means is mounted to the tubular form, is displaced from 
the antenna member and is spaced away from the curved plate member to 
define a second capacitor therewith. 
The second capacitor means comprises a first sleeve member confronting the 
curved plate means and a second sleeve member axially spaced therefrom, 
each electrically connected to the coil, and a tuning capacitor plate 
spaced from and confronting the second capacitor means to define a third 
capacitor which is a tuning capacitor to match the impedance of the 
antenna assembly to that of a cable connected to the connector. 
Numerous other advantages and features of the present invention will become 
readily apparent from the following detailed description of the invention 
and of one embodiment thereof, from the claims and from the accompanying 
drawing in which each and every detail shown is fully and completely 
disclosed as a part of this specification in which like numerals refer to 
like parts.

Referring now to the drawings, an antenna assembly 10 in accordance with 
this invention may comprise an antenna rod member or radiator 12, such as 
a one-half wave length radiator for citizen's band use. In accordance with 
this invention, radiator 12 is adapted to be mounted, in electrically 
isolated fashion, upon a mast such as a metal mast 14, via an isolator 
assembly 16. 
In the embodiment illustrated, isolator assembly 16 comprises a 
non-conductive tubular insulating form such as tube 18, as of fiberglass, 
on which is disposed a coil form 20. Coil form 20 is provided with a 
suitable winding or coil 22. Conductive end sleeves 24, 26 are provided at 
each end of the coil. At the upper end, a lug formed with end sleeve 24 is 
connected, as by soldering, to the coil 22. At the lower end, end sleeve 
26 is connected to the other end of the coil 22 and to the outer or shield 
conductor 29 of a coaxial connector 30. The center conductor 31 of the 
connector 30 is connected to the coil 22 at a suitable tap point 22a to 
provide the desired impedance match, such as about 50 ohms. The entire 
isolator assembly is then encapsulated in a suitable encapsulant 36 of 
insulating material, such as a twenty percent glass filled polyethylene. 
It will be apparent that the two-piece coil form and tube may be formed of 
a single piece and that various suitable materials may be substituted for 
those and for the encapsulating medium which in the aggregate, as shown, 
entirely surrounds and encapsulates the coil 22 and sleeves 24, 26 by 
insulating material. 
The radiator 12 is capacitively coupled to the coil 22 and to a 
conventional coaxial cable 32 through the connector 30. To this end, an 
inner conductive sleeve 34 internally of tube 18 is provided and confronts 
and is spaced away from radiator 12. The upper end of curved sleeve 34 and 
lower end or radiator 12 define a coupling capacitor (capacitor 50) 
through tube 18. The lower end of the sleeve 34 and upper end sleeve 24 
confront each other and are spaced away from each other to define a 
further coupling capacitor 52. Capacitors 50, 52 transmit and conduct 
radiation between the antenna radiator and coaxial connector. 
The capacitor coupling allows passage of radio frequency energy to be 
transmitted and received, but blocks or isolates D.C. and low frequency AC 
voltage as high as 50 kv. To complete the tuned circuit 53 and provide for 
fine tuning of the antenna assembly, a slidable tuner plate 40 is provided 
and is disposed in a channel 42 defined by the isolator assembly 16. 
Slidable tuner plate 40 defines a tuning capacitor 54 with upper and lower 
end sleeves 24, 26. 
As best seen in the circuit diagram, FIG. 5, the antenna radiator 12 is 
coupled capacitively through capacitors 50, 52 to the tuned circuit 53. 
Coil 22 is conventionally connected to the coaxial connector 30, hence to 
the coaxial cable 32. 
It will be apparent that the isolator assembly serves to isolate the 
antenna rod from the mast and coaxial cable so that if, in erecting the 
mast and radiator, the antenna contacts power lines, the voltage imressed 
on the rod will not be transmitted to the mast. The gaps provided by the 
capacitive connection between the electrically connected radiator 12 and 
sleeve 34, on the one hand, and the sleeve 34 and the sleeves 24, 26, on 
the other hand, thereby electrically isolates the rod and mast against the 
transmission of high voltage therebetween within design parameters. In the 
embodiment illustrated, the breakdown voltage is about 50 kv, and 
therefore the isolator assembly 16 isolates the radiator from the mast and 
coaxial cable up to an impressed low frequency voltage of about 50 kv. 
Despite warnings and many deaths resulting from the erection of CB antennas 
where carelessness has resulted in contacting power lines, death and 
injury recurs. The use of isolator assemblies in accordance with this 
invention has the potential for reducing the number of such injuries 
dramatically. 
From the foregoing, it will be observed that numerous variations and 
modifications may be effected without departing from the true spirit and 
scope of the noval concept of the invention. It is, of course, intended to 
cover by the appended claims all such modifications as fall within the 
scope of the claims.