A ¼ λ Ground Plane for 70 cm

It is easy to homebrew this ¼ λ ground plane antenna for 70cm. All one needs is a TNC connector (see inset), 1.6mm brass brazing rod and a pack of ‘M-Seal’(epoxy sealant in dual component lump form).

¼ λ Ground Plane for 70 cm
Radiating element length in inches is 2808/f MHz minus the projecting length of the TNC hot end.

Radial length in inches is 2950/f MHz plus a little for soldering on to the TNC connector flange.

The soldered points are sealed against water ingress using M-Seal.

Related post: Coax Collinear for 70 cm
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Fox Hunt Attenuator

Here's the circuit of my homebrew fox hunt attenuator.

Offset Attenuator - Schematic
It's a simple offset attenuator with a low part count.

The potentiometer is used to vary the signal strength of the attenuated signal, available at +1MHz, +2MHz, -1MHz, -2MHz of the fox frequency.

This attenuator was successsfully employed at a couple of fox hunts in Bangalore.
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Coupling a commercial VHF handheld to an external antenna

Some good commercial VHF handhelds have only one drawback - no external antenna connector.

Modification is also a problem as the rubber ducky is either integral or screwed on to a threaded stud, with no access to ground.

The result is a frustrated, repeater-bound ham. When a fellow ham in such a predicament set me pondering, realisation dawned that another rubber ducky could be used to couple the rig to an external antenna.

My own rig (which has a BNC connector!) was used to check it out. The coupling rubber ducky was mounted on the input of a homebrew SWR meter, with a dial lamp loading the output.

Rubber ducky coupling to a dial lamp

The glow of the dial lamp indicated a coupling efficiency of about 20% (2.5W to 0.5W).

A 2m external antenna was then connected instead of the dial lamp.

Rubber ducky coupling to an external antenna

On-the-air tests were successful. Comfortable simplex QSOs, not possible with the rubber ducky alone, were now possible.

Related post: SWR Meter - Easymatch
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Handy 1 kW HF Dummy Load

Years ago, after replacing the tubes of a Heathkit SB-200 Linear Amplifier, I was on the lookout for a dummy load to test it.

It then struck me that a 230V ~ 1kW electric hot plate, with its heating element resistance close to 50Ω, would do.

Handy 1 kW HF Dummy Load
The mains plug of the hot plate was replaced with a PL-259 before connecting it to the output of the linear amplifier.

The amplifier was successfully tested, with its Pi tank circuit providing a proper match to the dummy load.

At a later date, the same exercise was repeated with a Dentron GLA-1000.
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SWR Meter - Easymatch

The 'Easymatch' has a length of solid copper wire as its transmission line. The diode leads,

 Easymatch
running parallel to the transmission line, double as sensing lines.

A salvaged 100µA meter is used as the indicator, along with a 47KΩ potentiometer for sensitivity adjustment.

Easymatch Schematic
There is no indication till a load is connected.

Related post: SWR Meter - Pencil Box
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SWR Meter - Pencil Box

This SWR Meter is housed in a pencil box. The transmission line is a length of TV hardline. Sensing

Pencil Box
lines are hook-up wires, run close to the centre conductor through longitudinal holes made in the foam dielectric.
Pencil Box Schematic
A tuning indicator (salvaged from an old Philips transistor radio) is used as the indicator, along with a 47KΩ potentiometer for sensitivity adjustment.

Related post: SWR Meter - Minimatch
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SWR Meter - Minimatch

The 'Minimatch' differs from the 'Monimatch' with respect to its transmission line (RG-58/U
used instead of stripline-on-PCB).

 Minimatch
Two lengths of hook-up wire, running in parallel inside the braid, are the sensing lines.

Minimatch Schematic
A tuning indicator (salvaged from an old Philips transistor radio) is used as the indicator, along with a 47KΩ potentiometer for sensitivity adjustment.

Related post: SWR Meter - Monimatch
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SWR Meter - Monimatch

This SWR Meter is identical to the 'Monimatch', published in ARRL's 'Understanding
Amateur Radio'.

Monimatch
It was not difficult to follow the 'stripline-on-PCB' design.

Monimatch Schematic
A 100µA meter reads 'forward' or 'reverse', based on the toggle switch position.

A 47KΩ potentiometer is used for sensitivity adjustment.

Related post: SWR Meter - Easymatch
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