Κόλπα και tips

This month's column is a selection of hints and tips that I trust will be found useful around the shack and workshop.

Vertical dipoles from coax cable

With a Stanley knife make a cut around the coaxial feedline approximately one quarter wavelength from the end of the cable (length in metres = 71.5/frequency).   Then slit the cable to remove the outer jacket from the cut to the end of the cable.  With a small screwdriver make a hole in the braid near the start of the outer jacket.    With the screwdriver, lever the inner conductor out through the hole.  Solder an eye terminal or washer to the end of the inner conductor to provide a support for hanging from a tree branch or curtain rail.

Uses for scrap circuit board material

These include small boxes, dividers where shielding is important, small nameplates (if etched) and square pads for 'paddyboard' construction.  For the latter, tin snips or multipurpose shears will cut the material nicely.

Soldering two wires together without an iron

Wrap join with solder.  Then wrap with aluminium foil.  Hold a lighted match to joint until solder melts.  Remove foil when solder sets.

Illuminated dummy load

A 12-volt 300mA light globe soldered into a PL259 plug makes a useful dummy load for HF QRP equipment running up to a few watts.

Cutting ferrite rods to size

Saw groove around rod with hacksaw.  Hold rod in two hands and apply force.

The rod should snap cleanly.

Determining loss of coil formers for antenna traps, etc

Place material in microwave oven with glass of water.   High loss material will get very hot or melt.  Material that stays cold or warms only slightly is suitable for use.  Remember to remove all metal traces (eg wire or mounting screws) before doing the test!

Portable antenna mast

An eight or nine metre giant squid pole forms an excellent mast for portable operation.  These lightweight poles (also called roach poles or telescopic poles) are available from fishing shops and collapse down to about 1.1 metres.  Squid poles can support lightweight wire antennas for HF and VHF/UHF groundplanes.    The poles will not support coaxial feedline unless it is supported by taping it to the pole.

 

Handheld antennas

Antennas that a quarter wavelength or less on handheld transceivers often benefit from the addition of a counterpoise.  Clip a quarter wavelength of wire onto the earth connection of the radio's antenna socket.

Holding nuts in tight places

1. Blu-tac or small dab of glue on end of screwdriver

2. Rubber band across handles of long-nose pliers

Easy connectors

Terminal blocks cut up into strips make handy barrel connectors.

Insulators for wire antennas

For temporary portable antennas, use toothbrush handles.  Otherwise use sections of plastic conduit.

Pedestrian mobile HF station

 

A case to hold a transceiver, gel battery and antenna can be made from pieces of 10mm-thick chipboard.   Thread old coaxial cable through holes in the box to make carry handles.  To prevent rubbing against the operator if the station is used whilst walking, glue carpet to the side of the box closest to the operator.  For the transceiver, use a converted CB for 10 metres or Yaesu FT-817 for HF/VHF/UHF coverage.

 

Spreaders for open wire feedlines

If you have a few more toothbrush handles, you can use them as spreaders in home-made open wire feedline.   Alternatives include hair curlers, or my favourite, plastic irrigation tube about 6mm in diameter as sold by garden suppliers.

Doing well in contests

If you use a good antenna from a good location and consider yourself to be a 'strong station', spend most of your time calling CQ – others will find and work you.  If your signal is weaker than others, spend most time tuning the band and calling other stations.  Once all stations heard have been worked, find a clear frequency and call CQ for a while.

 

Cheap VHF/UHF signal generator

An HF rig fed into a dummy load makes a crude signal generator for doing tests on VHF/UHF receivers or as a BFO for receiving SSB on an AM receiver.  Set the transceiver to just above 28.8 MHz for harmonics in the 144 and 432 MHz bands.

Projecting sound forward from top-mounted speakers

Transceivers with top-mounted speakers can benefit from a yoghurt container (with a forward facing cutout) placed over the speaker grille.  The container projects the sound forward towards the operator.

 

Improving access to station equipment

When you next renovate the shack, consider placing the operating desk about a metre from the wall.  This will make it easier to access power and antenna connections and add new equipment.

Labelling leads

 

Cables should be labelled to minimise the risk of equipment damage, for example when transmitted power is applied to the antenna socket of a receiver.  A good way is to write (with a ballpoint pen) labels onto strips of paper 5mm wide and as long as the label requires. Clear adhesive tape is placed over the front of the label and around the cable. The tape is then continued so that it sticks to the back of the paper and around to the front of the label, where it is cut with scissors. The result is a descriptive 'flag' at the end of the cable near the connector. A refinement could be to write on both sides of the paper strip instead of one.

Solder dispenser

Pierce hole in 35 mm film container.  Wrap solder around pipe or tube to form coil.  Thread one end of solder through hole, and place coil inside container.    Replace cap.

Antenna accessories at fishing shops

Apart from squid poles (see previously) several other items useful to the amateur can be procured at fishing shops.  Fishing reels are ideal for storing wire antennas.  Depending on the length and thickness of the antenna wire, diameters between 10 and 25 centimetres are suitable.  Sinkers and fishing line are also useful for raising antenna wires over tree branches.

Uses for octal valve bases and film containers

Octal valve bases screwed to 35 mm film containers form useful plug-in coils for receivers, dip oscillators and antenna coupling units covering the low HF bands.  Octal plugs and bases are still stocked by major parts outlets.  For coverage of higher frequencies, use 5-pin DIN plugs and formers approximately 12mm in diameter, such as conduit.

Use for old coax

Lossy or water-damaged coax can still be used for ground radials. The braid can also be used for earth connections.

Calling on repeaters

When putting out a call, press the PTT button, wait 5 seconds and then call. This gives time for people's scanning transceivers to stop on your frequency, for your call to be heard and increases the chance of getting a response.

On indicator

To add an on indicator for projects that operate from 12 volts, wire an LED in series with a 560 ohm resistor.

Polarity protected projects

 

Simply wire the positive and negative power leads to the positive and negative connections of a diode bridge rectifier.  The polarity applied to the two AC inputs is not critical.  This technique is only recommended for low-powered projects with plastic or non-earthed metal cases and in situations where the voltage drop across the bridge will not impair operation.

Learning about Spread Spectrum

An excellent web page about spread spectrum communication can be found at  http://sss-mag.com/    The site includes an amateur section.

BFO for SSB

Cheap one or two band shortwave receivers seldom have a beat frequency oscillator required for amateur SSB reception.  A portable AM broadcast radio placed near the receiver can be used as a BFO, with no connections required.  Setting the radio near 1.3 MHz should cause a carrier to be heard near 3.5 MHz or 7 MHz.  To use, tune for maximum 'duck talk', and carefully adjust the broadcast receiver until the signal becomes intelligible.  Move the receivers closer together for strong signals and further apart for weak signals.   It's fiddly, but it works!

Estimating thickness of enamelled wire

Wind 10 turns onto a pencil, measure in millimetres with a ruler and divide result by ten.

Tuning indicator for base loaded HF antennas

Attach one side of a neon bulb to the top of the loading coil.  Leave the other side of the bulb floating.  Use 5-10 watts and aim for maximum brightness.

Use for computer power supplies

Many articles have described how two disused computer power supplies can be made into a high-current 13.8 volt supply for transceivers, etc.  Not all constructors have found this project straightforward, and only competent builders should attempt it.  However if you are willing to accept a reduced voltage (11.5 to 12 volts) and reduced current (up to a few amps), the 12-volt output from a single, unmodified supply will adequately power CB and low power amateur equipment.

 

Using small bits in large drill chucks

Wrap a few turns of solder around the bit, insert in chuck and tighten.  The technique can also be used to salvage drill bits that have been broken.

Preventing components being lost

When assembling kits or constructional projects, place the parts in a shallow dish to prevent them rolling off the table or bench.

SO239 antenna mount

A square-type SO239 chassis mount socket makes a handy base for quarter wave ground plane antennas for two metres or seventy centimetres.  The feedline can be fed up a tube (with an inside diameter larger than the PL259 diameter) or taped to a squid pole for a quick home station antenna.

Emergency supply of solder

Wrap solder around cord of soldering iron to form emergency supply of solder to use when your reel runs out.

Quick six metre antenna

It's worth a reminder that a 5/8 wavelength whip for two metres will operate effectively on six metres as a ¼ wavelength whip.

Cases from component stereo systems

1970s stereo equipment is now available cheaply from garage sales and car boot sales.  The boxes from amplifiers, tape decks, graphic equalisers make fine enclosures for large projects, such as homebrew transceivers, antenna couplers and power supplies.  Use printed circuit board scraps to cover holes if necessary.