Power Supply Dummy Load

A 13.8V 25A DC Linear Regulated Power Supply was in need of testing after its defective main rectifier was replaced. It had protective circuits for under-voltage, over-voltage, short-circuit and over-current.

The filaments of a couple of 12V 55/60W automobile headlight bulbs were connected in parallel and used as a dummy load, but their very low cold resistance caused instant tripping.

A length of galvanised curtain wire (~ 1.5m long), connected in series, saved the day. The power supply did not trip and the bulbs emitted a feeble glow.

Power Supply Dummy Load - Schematic

The connecting wire was then slid along the curtain wire. The illumination progressively increased and so did the load current. When the curtain wire went out of circuit, the bulbs were fully illuminated and drawing 23A from the power supply.
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Simple ¼ λ Ground Plane for 2m

This simple ¼ λ ground plane antenna is based on G3OGR - OM F.G. Rayer's design for a 2m vertical antenna.

 ¼ λ Ground Plane for 2m - details

It's built-in at the top end of a 25 foot long, 2-piece telescopic aluminium pipe mast with the elements made of 3/8" aluminium tube.

A view of the ¼ λ Ground Plane for 2m

The elements are flattened at the ends to facilitate sealing/mounting/coax connection and the joints are made water-tight/corrosion-resistant with epoxy sealant.

This antenna has been up for more than 10 years and still going strong.

Related post: Moxon Antenna for 2m
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Coax Collinear for 70cm

This 70cm Coax Collinear Antenna was homebrewed one evening in the year 2008.

The job was made simple, thanks to N1HFX - OM Mike Martell and his detailed article 'Build A 9 dB, 70cm, Collinear Antenna From Coax'.

A view of the Coax Collinear for 70cm

All instructions were strictly followed.

A brass sleeve was soldered to the braid at the feedpoint and a SO-239 connector was used.

Both the ends of the antenna were waterproofed with epoxy.

SWR was close to 1.5:1 when checked at a power level of 50mW.

Signal strength with this antenna was 2-3 'S' points higher compared to that using a ¼ λ Ground Plane Antenna at the same height.

Related post: Direction-finding Yagi Beam for 70 cm
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J-Pole Collinear for 2m

A makeshift, phasing-coil variant of a 2m J-Pole Collinear was recently homebrewed.

J-Pole Collinear for 2m - details

It was fabricated with a single length of 20SWG copper wire and taped to a bamboo pole for rigidity.

The coil section was 64 turns close-wound on a 10mm mandrel and then stretched to a length of 300mm.

SWR measured close to 1.5:1 across the 2m band.

Antenna performance exceeded that of a normal J-Pole at the same height.

A 16SWG rugged version, encased in a PVC pipe, is in the works.

Related post: PVC-encased Vertical Antennas for 2m
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Noise cancellation on 2m using 2 antennas

A while ago, static-type QRM was encountered right across the 2m band.

It proved to be a nuisance while receiving weak signals using either of the shack antennas - a 1/4λ Ground Plane at a height of 15m and a Slim Jim at a height of 10m, located 5m apart.

The noise was presumed to be of commercial origin as it was not present at nights and on weekends.

Then, on an impulse, both the antennas were connected to the rig through a BNC-T connector. Surprisingly, the QRM disappeared and the audio level went up considerably.

The offending noise had been phased out just like that!

The antenna feeder lengths were then changed one at a time. The QRM promptly returned, confirming that it was indeed phase cancellation at work.

SWR was 3:1 with both the antennas connected. Inspite of that, it was now possible to comfortably work through a distant repeater.
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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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