PVC-encased Vertical Antennas for 2m

These PVC-encased 2m vertical antennas were built years ago.

PVC-encased TV Ribbon J-Pole & Slim Jim Antennas

One is a J-Pole, housed in a thick-walled  ¾” PVC pipe, with a SO-239 connector. The other is a Slim Jim, in a thin-walled PVC pipe, with a BNC.

Both were homebrewed, using 300 Ω TV Ribbon, with good results (SWR < 1.5:1). The ends were sealed against water ingress using 'M-Seal' (epoxy sealant in dual component lump form).  

     

TV Ribbon

Thanks are due to W0IPL - OM Pat & N4UWJ - OM Don, for construction details of the J-Pole & Slim Jim respectively.

Related post: Sleeve Dipole Antenna for 2m

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Audio Signal Injector

This decades-old audio signal injector was wired on a piece of perfboard.  All components were sourced from the junk box.

Audio Signal Injector

The enclosure was fashioned from an empty tapered spool of industrial sewing thread, a cosmetic tube cap and a film canister cap on which the push button switch was fixed.

A machine screw, filed to a point and fixed to the cosmetic tube cap, served as the prod.

Audio Signal Injector - Schematic

Over the years, this unit has helped service the audio stages of several ham rigs.

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Quartz Crystal Tester

This unit was built years ago when there was a need to test surplus crystals. It also came in handy as a signal generator for receiver alignment.

It's basically a Pierce Oscillator Circuit which works even with low-activity crystals.

Quartz Crystal Tester

'Octal' and '807' valve bases were wired for vintage crystals in addition to crystal holders suitable for HC-6/U, HC-18/U & HC-25/U crystals.

Quartz Crystal Tester - Schematic

The indicator is a 6V 0.06A dial lamp. Tuning / Loading is done using the PVC-2J 500+500 pf variable. The 2000 pf is switched in parallel for very low frequencies.

Quartz Crystal Tester - Inside view

This tester works in the range 455kHz to 20Mhz, with overtone crystals oscillating at their fundamental frequency.

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Salvaged RF Ammeter

Years ago, a 0.75A 'thermocouple heating element' was salvaged from a meterless BC-442 Antenna Relay Unit. Only recently was it taken out, to build an RF Ammeter for low-power rigs.

Salvaged RF Ammeter

A junk-box 50Ω, 1mA FSD  moving coil meter, with a bakelite housing, was also put to good use. It has graduations only upto 50% of its scale.

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

The unit was tested after completion of assembly and wiring.

Thermocouple RF Ammeter - Schematic

Salvaged RF Ammeter - Inside view

A homebrew CW rig was loaded to get a reading of 0.75A on a Weston 1.5A RF Ammeter. The Weston was then replaced by the unit to be tested.

The meter pointer stood at exactly 50% of full scale, indicating that the graduated portion of the scale covered the full range of the thermocouple. Notwithstanding the non-linear output of the thermocouple and the unmarked meter scale, staying within the graduated portion of the scale would avoid damage to the element!

Related post: Adjustable RF Ammeter
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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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