Tests for power on a 2m antenna

Caution! To avoid dangerous RF exposure, these tests are to be carried out using a maximum power of 5W only. A 2m HT is quite safe for the purpose.

The ability of a neon lamp to glow in the presence of an electromagnetic field made it a handy RF indicator of yesteryear. Many a handie talkie (HT) was tested by just holding a NE-2 near its whip antenna.

Curiosity led to a search of the junk box for a NE-2 but a different type, having plate electrodes, was found (see inset).

Power was applied and the antenna probed with the neon lamp. A static-charged plastic bag, placed in between , helped trigger the neon lamp.The ensuing red glow was sustained by the RF energy. The plastic bag may not be required when dry weather and synthetic clothes make it more conducive for the test.
Neon Lamp Test on J-Pole Antenna
At high voltage points the neon continued to glow even when moved away from the antenna.

Neon Lamp Test on Rubber Ducky
A more reliable method is to use a dipole as a pickup and a 6.3V-150mA dial lamp as the indicator.

My version of the pickup has two 21" telescopic whips fixed on a wooden strip, with the dial lamp soldered in between. It's quite convenient to push the telescopics in and fold them for storage.

Dipole-lamp pick-up - folded
With only 3.5W from my HT, and the dipole length adjusted to ½λ, the lamp glowed to more than full brilliance at a good distance from the antenna.

Dipole-lamp test on J-Pole antenna 
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'Wire Slim Jim' for 2m

This is a 'Wire Outside PVC' Slim Jim for 2m. It was made using enamelled copper wire and a vacuum cleaner nozzzle!

2m Wire Slim Jim
The wire ends and the BNC connector were fixed with self-tapping screws. The feed points were

connected to the BNC using the same wire. Water ingress points were sealed off with 'Araldite'.

An SWR of 1.5:1 was realized.

Related post: 2m J-Poles and a Slim Jim
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2m J-Poles and a Slim Jim

Last summer an attempt was made to homebrew a couple of 2m antennas, using parts salvaged from a disused VHF TV Yagi Beam.

The radiating element (folded dipole) provided the stub portion for two J-Poles. Bakelite pieces were used to ensure rigidity and also to locate the BNC connector.

2m J-poles and a Slim Jim
The moulded plastic box was used for the second version of the J-Pole. For the stub portion, the 2 elements were shorted inside the box. A BNC connector was located at the lower end of the box. A length of PVC pipe was fastened to the box to facilitate mounting of the antenna.

Close-up of the J-poles
'M-Seal’(epoxy sealant in dual component lump form) was used at the joints and to waterproof the connections.

The dimensions were arrived at using 'K4ABT's J-Pole Calculator'.

Absolutely no trials / adjustments were required to get the SWR very close to 1:1!

With the remaining material a Slim Jim came into being.

Construction was on similar lines and with good results.

Related post: Homebrew ¼ λ Magmount for 2m
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UHF on a VHF Rig

This circuit enables fair copy of strong 444 MHz signals, off a local repeater, using a 2m rig and an indoor 70cm ¼λ ground plane antenna.

UHF Converter 
The 300 MHz 5th harmonic of the local oscillator, mixing with the incoming signal, delivers output on 144 MHz.

UHF Converter - Schematic
The enclosure is a plastic trinket box reworked to fit two BNC sockets plus one RCA for the DC supply and also to screw the cover in place.

UHF Converter - inside view
The converse (VHF on a UHF Rig) is also possible by just changing over to a 2m antenna and a 70cm rig.
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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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Low-cost ½ λ Dipole for HF QRP rigs

Here’s an economical dipole for simple QRP HF homebrew rigs. It’s a one-piece radiator/feeder arrangement made of surplus insulated telephone drop wire with twin copper-clad steel cores.

Low Cost ½ λ Dipole
The cores are separated to get the λ/2 radiating length and then tied together with string to arrest further separation.

Telephone Drop Wire
The string could be done away with, and the λ/2 length yet maintained, using the reliable 'Underwriters Knot'.

Underwriter's Knot
The end insulators are scrap bakelite pieces, drilled to take the wire and string. Banana plugs are used at the rig-end.

Works real good when strung high up between two trees or other supports.
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Improved 7 MHz QRP CW Rig

This QRP CW transmitter's output is of the order of 5W.

Improved 7 MHz QRP CW Rig
Fairly comfortable QSOs are possible with the higher power level. The driver and the final transistors require heat sinks. The aluminium enclosure serves as the heat sink for the final.

Improved 7 MHz QRP CW Rig - Schematic
The variable capacitors, coil cores and 100Ω potentiometer are adjusted for maximum clean output.

Related post: Standard 7 MHz QRP CW Rig
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Standard 7 MHz QRP CW Rig

This rig works well even with low-activity crystals.

Standard 7 MHz QRP CW Rig
Heat sinks are required for the buffer and final transistors. The variable capacitors and coil cores are adjusted for maximum clean output.

Standard 7 MHz QRP CW Rig - Schematic
The enclosure is homebrew.

Related post: Basic 7 MHz QRP CW Rig
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Basic 7 MHz QRP CW Rig

This is the second version of my solid-state 7 MHz QRP CW transmitter. A heatsink is required for the transistor.

Basic 7 MHz QRP CW Rig - schematic
The base variable capacitor is adjusted for a chirpless signal and the collector variable for maximum output (minimum collector current).

Related post: Simple 7 MHz QRP CW Rig
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Simple 7 MHz QRP CW Rig

This is the schematic of my very first solid-state 7 MHz QRP CW transmitter. A heatsink is required for the transistor.

Simple 7 MHz QRP CW Rig - schematic
The part count is less than 10. The 1000 pF variable is adjusted for maximum brilliance of the lamp.

DX on this rig was ~1000km (VU2SL - OM Dalvir in Valsad).

Related post: Improved 7 MHz QRP CW Rig
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Simple CW Keyer

This is a homebrew IC keyer using a 7400, a 7473 and two 555s. Here's a schematic similar to the one used for this project.

Simple CW Keyer
The difference is that I used two 555s instead of one 7413 for the clock and tone generator functions.

Simple CW Keyer - inside view
The paddle is made of spring strip, silver contacts, nuts, screws and bakelite pieces. The enclosure is also homebrewed.
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A Homebrew 100W (DC Input) Class 'C' Amplifier

This 7/14 MHz amplifier was built as a companion to my Homebrew HF Transmitter.

It is based on an article 'A 150-Watt Amplifier', published by ARRL in their book 'Understanding Amateur Radio'.

100W Class 'C' Amplifier
It has two 807 tubes in parallel. The 'clamp tube' was done away with by using negative-bias-grid-block keying. Hence the unused tube-socket cutout.

100W Class 'C' Amplifier - inside top 
I attempted using a 'receiver-type' variable capacitor for Pi tank tuning, but heavy arcing between the plates put an end to that.

The project was on hold for about six months, till I succeeded in laying my hands on the wide-spaced variable seen.

The 'receiver-type' variable for Pi tank loading, mounted under the plate/grid current meter, is not visible.

100W Class 'C' Amplifier - inside bottom
The chassis is an aluminium baking tray picked up from the neighbourhood 'pots & pans' trader!

The cutouts were made by drilling/filing with hand tools and the cover homebrewed by cutting/bending aluminium sheet.

A few coats of enamel paint, baked on the kitchen stove, gave a fairly acceptable finish to the enclosure.

Here are the design manuscripts:

Class 'C' Amplifier Schematic
Power Supply Schematic
Class 'C' Amplifier 
Class 'C' Amplifier - Instructions
This amplifier fetched me a lot of DX contacts on 7 and 14 MHz using only simple dipole antennas.


Related post: My first Homebrew HF Transmitter
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My first Homebrew HF Transmitter

It's a 15W CW/10W AM transmitter for the 40m / 20m bands, based on G3OGR -  OM F.G. Rayer's  
article 'QRP Transmitter for the LF Bands' published in the August 1971 issue of 'Practical Wireless' 
magazine.

15W CW/10W AM Transmitter for 7/14 MHz
The transmitter stages are as follows:

 ECC81 - VFO on 3.5 MHz
EF89 - Buffer
EF89 - Multiplier to 7 MHz
EF89 - Multiplier to 14 Mhz
EL86 - Final with Pi tank

15W CW / 10W AM Transmitter for 7/14 MHz - top inside

It has a companion power supply cum modulator.


The modulator stages are as follows:

 ECC83 - Speeech Amplifier
EL84 - Modulator

Here are the design manuscripts:

Transmitter 
Transmitter Schematic
Power Supply cum Modulator
Power Supply Schematic
Modulator Schematic
Transmitter - Instructions
Using this transmitter, a number of CW DX stations (including a 'W' on 40m) were worked in the late 1970s. AM DX contacts were also made with 4S7 and YB0 stations.


Only simple dipole antennas were used.

Related post: A Homebrew 100W (DC Input) Class 'C' Amplifier
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