A salvaged RF Ammeter

Years ago, I had salvaged a 0.75A 'thermocouple heating element' from a meterless BC-442 Antenna Relay Unit. Only recently did I take it out of cold storage, to build an RF Ammeter for use with low power rigs.

A junk-box 1mA FSD 50Ω moving coil meter, with a bakelite housing, could also be put to good use. It had graduations only to 50% of full scale.

An aluminium baking tray was reworked to accept a couple of SO-239 sockets and the meter.

On completion of assembly and wiring, the unit had to be tested.

My homebrew CW rig's antenna current was set to 0.75A, using a Weston 1.5A RF Ammeter for measurement. The Weston was then replaced by the unit to be tested.

As luck would have it, the meter pointer stood at exactly 50% of full scale. Inspite of  the non-linear output of the thermocouple and the uncalibrated meter scale, at least staying within the graduated portion of the scale would avoid damage to the element!
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Yet 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.


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.
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A 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.


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.
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An open-stub J-Pole for 70cm

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


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.


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

SWR at 435MHz is less than 1.5:1.
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A 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 'Bierdosenantenne' or '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 1" diameter plastic bushes 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.

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

SWR at 435MHz is around 1.5:1.
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A 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).


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".


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.
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A 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.


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.
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