Another ¼ λ Ground Plane for 70 cm

The elements of this antenna are cut from 3/8" aluminium tubing. The length of the driven element is 6½" and that of the the radials 6¾".

The connector is SO-239.

Another ¼ λ Ground Plane for 70 cm

The radials are fastened to the connector flange after their mounting ends are flattened and drilled. They are then bent, making an angle of 30 degrees to vertical, with the connector flange corners taking the bend.

The driven element is fixed to the SO-239 centre terminal using a brass bush. A plastic sleeve makes the joint water-tight. The open end of the driven element is then sealed with rubber compound.

SWR at 435MHz is 1.5:1.

Related post: Twin-Radial ¼ λ Ground Plane for 70 cm
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Twin-Radial ¼ λ Ground Plane for 70 cm

The driven element of this antenna is a telescopic whip. It is mounted in a tubular aluminium pill box using polythene end-caps as insulators. A BNC flange-type socket is mounted on the bottom end-cap, with its centre pin soldered to the whip.

Twin-Radial ¼ λ 70 cm Ground Plane

Two aluminium-strip radials are bolted on to an aluminium base plate, beneath which the driven element assembly is attached. The whip clears the base plate through a central hole.

Mounting screws ensure that the base plate and the BNC flange make contact with the pill box.

SWR at 435MHz is better than 1.5:1.

Related post: A ¼ λ Ground Plane for 70 cm
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Open-stub J-Pole for 70cm

Telescopic whips and an old terminal block insulator make this open-stub J-pole for 70cm.

70cm open-stub J-Pole Antenna

The stub portion of the driven element is of 3/16" copper tubing (if only to make up for the shortage in length!).

The dimensions are: Driven Element - 495mm, Stub - 165mm and Spacing - 16.5mm.

70cm open-stub J-Pole Antenna - Schematic

The elements are wired to a BNC socket mounted on the block.

SWR at 435MHz is less than 1.5:1.

Related post: End-fed Sleeve Antenna for 70cm
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½ λ End-fed Sleeve Antenna for 70cm

One of the well-known end-fed ½ λ vertical antennas is the J-Pole. It's ¼ λ stub may be closed and fed at the point of lowest SWR or be kept open and fed at the ends (ARRL Handbook). A closed stub is first choice as it ensures DC ground and static-free operation. The sleeve variant of this is the Sperrtopf Antenna.

Notwithstanding the above, ease of construction prompted homebrewing of an end-fed sleeve antenna with an open-stub.

OE7OPJ OM Peter's plans for a 'Beer Can Antenna' fitted the bill.

 The 19¼" long driven element is cut from a length of 3/16" scrap copper tubing. A 2" diameter aluminium can, 6½" long, is used for the sleeve. Two PVC door buffers with 3/16" bores are used to hold the driven element centrally insulated from the can. One is press-fitted into the mouth and the other fastened with screws to the base of the can. A BNC socket is similarly fixed after it's centre pin is soldered to the driven element pushed out through a hole in the base of the can.

70 cm End-fed Sleeve Antenna

A tapered bakelite tube and a plastic end-cap complete the picture.

SWR at 435MHz is around 1.5:1.

Related post: A ¾ λ Ground Plane for 70cm
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Sleeve Dipole Antenna for 2m

The elements for this Sleeve Dipole Antenna are cut from copper tube scrap (3/16" diameter for the driven element and 5/8" for the sleeve).

2m Sleeve Dipole Antenna

The driven element is pushed into a 2" long rubber hose and fitted 1" deep into the sleeve. A tapered bakelite tube gives rigidity to the joint. For an overall length of ½ λ (39" at 145MHz), the sleeve is 19½" long and the driven element 20½".

2m Sleeve Dipole Antenna details

The ends are closed with plastic caps. A BNC socket is mounted on the sleeve end-cap and wired with RG-59/U coaxial cable. The centre conductor is soldered to the driven element and the braid to the sleeve. Care is taken to ensure that the BNC socket does not touch the sleeve.

A good weekend project, awaiting tests for effectiveness.

Related post: Wire Slim Jim for 2m
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Moxon Antenna for 2m

3/8 " aluminium tubular elements, left over from a cannibalised VHF TV Yagi beam, were used to fabricate this 2m Moxon Antenna.

2m Moxon Antenna

Screw joints became a necessity since the elements were not long enough. The ends were flattened and drilled for the purpose.

A scrap plastic handle came in handy for the spacers. It was easy to cut it, drill the fixing holes and make a recess for the BNC socket.

Dimensions were obtained using the 'MoxGen - MOXON Rectangle Generator'.

For vertical polarisation, this antenna is directly mounted on a PVC pipe mast with a screw through each spacer.

Preliminary checks showed that this antenna is as good as, if not better than, my 'simple 2 element array'. Both, being 50Ω antennas, are capable of outperforming even a 3 element array with its associated matching problems.

Related post: Simple 2-element Array for 2m
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Simple 2-element array for 2m

This array was homebrewed using four 18" long telescopic whips and a length of ¾" diameter thick-walled CPVC water pipe.

Data for the 2-element array was obtained from an old ARRL Handbook.

Dimensions in inches: Driven Element - 5540/f MHz, Director - 5263/f MHz, Spacing - 2750/f MHz.

The spacing close to 0.25λ would result in a good match for 50Ω coaxial cable.

Maximum gain would be possible with a director at 0.1λ or a reflector at 0.15λ. However matching issues related to the very low radiation resistance would then have to be tackled (F.C.Judd G2BCX in '2 meter Antenna Handbook').

2m 2-element array

The shorter length of the telescopics was made up with spacers which also served as mounts for the elements. The spacers were made using scrap bakelite strips. Self-tapping screws were used to fasten the elements to the CPVC pipe. A BNC socket was mounted at the feed point and wired to the elements.

2m 2-element array - close-up (element folded)

The array is easy to carry as the elements can be 'telescoped in' and folded. Hence it lends itself to portable operation or direction finding.

Theoretical gain for this array is 3dB.

Preliminary on-the-air checks for gain, front-to-back ratio and null, were encouraging.

Related post: J-Pole Collinear for 2m
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