Homebrew equipment

If you are a radio operator, amateur or not, part of the fun is to make your own equipment, this will be added to over time, to make some of the equipment below you will need to be confident with a soldering iron, and others you will need some equipment to help set up, for example with building antennas you will need at the very least a SWR meter for the band you are working with, a multimeter is also helpful in these instances.

Do note however that if you build your own transmitter, you would not legally be allowed to operate it unless it was for the Amateur bands and you held an appropriate Amateur radio licence, in the UK this is the Intermediate and Full licences, all other bands can only be operated on legally with commercial mass-produced transmitters that meet the type approval for that band.

DeviceEquipment category
11 meter band dipolesAntenna
Dipole antenna for PMR446Antenna
Saltwater dummy load for HFTest equipment
A converter to use stereo headphones on your rigAudio connecting equipment
A 12v power lead for taking portablePower connecting leads
Dipole antenna for the 2-meter bandAntenna

Dipole antennas for the 11-Meter band (CB radio)

A dipole is an antenna with two parts fed from the center, and one of the most simplest antennas to make, it can be made out of wire, copper pipe, or the coaxial cable itself, but before we begin we need to know about wavelengths.

All radio waves have a length, in the case of the CB channels the radio waves are about 11 meters long. To have an 11 meter antenna would be very impractical, so, manufacturers tend to make base antennas 1/2 wave or 5/8 wave, in the case of our dipole this will be 1/2 wave, which is 5.5 meters, still large but more practical.

The dipole is made of two elements, both of which are 1/4 wave, the element pointing up connects to the center core of your antenna cable, the element pointing down connects to the braid
To make this antenna you will need two pieces of wire or pipe (or strip a quarter wave length of a piece of RG58 and seperate the centre dielectric and braid), 5.5/2=2.75, but to allow for trimming and adjustment make them 3 meters.

Although this is out of tune, you will be cutting it down later to tune it, in the case of a wire dipole connection can be made using terminal blocks but solder would make a better connection, copper pipes would require the wires being soldered directly into them.

You will also need a piece of plastic pipe of 4.25″ diameter, this is to make what is known as an ugly balun, or the cable becomes part of the antenna.

You also need feed line, low loss RG213 is recommended for the feed line but difficult to wind the balun with, RG58 is a better choice for the short run between the antenna’s elements, the choke itself, and a small tail to a PL259. Use an SO239 coupler to connect the antenna to the feed line.

For a wire dipole, which can also be made into an inverted-v, proceed as follows

  1. Insert your two lengths of wire into two terminal blocks (or strip a quarter-wave lenght of insulation off a piece of RG58 and seperate the dielectric and braid), set these aside for the moment if using seperate wires
  2. Wind your ugly balun, 5 turns of RG58 on a 4.25″ diameter former, do NOT allow the first and last turns to contact each other. Add any connectors to your ugly balun at this point
  3. choose a mounting point for your antenna and waterproof the connections if you are planning to use it outside (which is likely), connect the ends of the coaxial cable from the ugly balun at this point (if using seperate pieces of wire), again waterproofing the connections if you are going to use it outside
  4. Mount the antenna, either vertically or in an inverted-v shape if used in the attic, run the feedline from the ugly balun to the radio, and connect the cable to a SWR meter
  5. Power on your radio, when you transmit you will find the SWR is high across the band, as the antenna is 6 meters long uncut, a 1/2 wave for 12 meters cut both halves of the antenna until the SWR reaches acceptable levels on all channels, under 2 is ok, but aim for 1.5 and under, it’s unlikely you’ll ever reach the elusive 1:1, take care not to cut off too much or you’ll have to replace both halves of the antenna
  6. When your antenna is tuned correctly, remove the SWR meter and work the world, at time of writing the conditions should be improving

The above is also applicable to antennas made of copper pipe, though care has to be taken to not only waterproof the solder joins but also electrically insulate the two elements, or you will have a short in your antenna system and risk damage to your radio, you could use the ugly balun as a center insulator for this kind of dipole, just ensure the coils don’t contact a conductor, copper pipe antennas are also less versatile as they can only be mounted vertically or horizontally, and can’t easily be made into inverted v antennas, you can also buy dipole centres used for amateur radio use that have an SO239 socket on them and the antenna parts attach using ring terminals, or a centre that accepts 2 mobile whips (I have one of these)

PMR446 dipole antenna

This antenna can be built in a similar way to the 11m band antenna above, however it only needs to be around 32cm total height, as PMR446 operates in the UHF portion of the radio spectrum and thus has a significantly shorter wavelength, to get this right you will need a SWR meter that covers between 420 and 480MHz, a CB SWR meter won’t give you a correct reading and you could risk damage to your equipment.

Normally PMR446 radios do not have an antenna socket on them as the antenna is soldered to the board, some others just have it glued down or held in with a screw, in which case the connector is an SMA type connector. Use of N type connectors is recommended for best performance (SO239 and PL259, despite being also known as UHF connectors, do not work well in the UHF region), so you would most likely need an SMA to BNC adaptor and a BNC to N adaptor, if you are connecting a modified Intek DRS-5070 then it is most likely that you would have fitted a BNC socket so a BNC to N adaptor is all you will need. BNC plugs do not fit on the end of RG213, and I recommend this for UHF use where possible due to it’s low loss properties, but still keep the run as short as you can possibly get away with.

Again, as this is a dipole, a means to prevent the coax becoming part of the antenna is needed, this is different from the 11-meter antenna above and can be made from the coax, I have yet to try this myself as the last dipole I built for this band was a receive-only one and is connected to an RTLSDR stick. Suitable chokes can be found on the Internet, look for one suited to 70cm that isn’t too narrow-band.

Place up high and you should get a lot of activity on PMR446, and be able to transmit further, though take into consideration that the entire antenna system must stay within the PMR446 specification to remain in Ofcom’s good books, a transmission dipole should exhibit no gain as it is a general reference antenna along with the theoretical isotropic antenna

You should follow the same instructions above to ensure the SWR is safe before transmission, though running a 500mW transmitter it shouldn’t be a major issue, if you plan to use it for the unofficial UHF CB system on the PMR446 system run the SWR measurements at 4 watts at your own risk.

Saltwater dummy load for HF

I don’t take credit for this as I found the design elsewhere, though for a novice CB operator the instructions would probably go over their head, so I am going to make this a little simpler

To make this all you need is an SO239 socket like you would find on the back of a CB radio, you can get these from Maplin Electronics or any good electronics or radio supplier, silicone sealant from a DIY store, some copper wire, the “earth” part of twin and earth works for this, water from your kitchen tap, salt (doesn’t matter if it’s iodised, it is what I had in my cupboard and it appears to work), and an empty peanut butter jar.

First of all, cut or carefully drill a hole in the lid of the jar that the SO239 will fit through, then fix it in place with suitable mounting hardware, after this you can then cut the copper wire into two pieces, soldering one to the centre and using one of the mounting screws to hold the other in place, seal this up with silicone sealant and leave overnight.

You then need to space the two pieces of wire as far apart as you can and trim them so they are both equal length and about half an inch off the bottom of the jar.

Fill the jar with water, screw on the lid, connect a radio and SWR meter, tune it to channel 40 on the UK band (or your highest used HF frequency), and perform the usual SWR measurement, it should measure very high (I got somewhere close to infinite), once you’ve let go of the key, unscrew the lid, and add a small amount of salt, stir it up, and repeat, the SWR should have dropped considerably, keep repeating until you get to 1:1, if you add too much salt, it will start increasing again, remove some of the water and add more from the tap if this happens, you may find yourself doing this a few times. Once you have the SWR down to 1:1, you’re done and you can disconnect it from the radio. The 4 watts from a CB did not appear to heat up the water when I built this, however I expect a linear amplifier to heat it up, the limits depend on the jar, I’d advise using caution if connecting this to a linear amplifier

A converter to allow you to use stereo headphones directly with your rig

As you will know, the extension speaker output found on your rig is a mono output, plugging a pair of off-the-shelf headphones into it results in one side not working, so to get around this you have to somehow connect the left and right to the mono output of the rig at the same time, and here is how to do it

You just need a couple of resistors, I tried with 10k and found I had to turn every rig I tested it on all the way up, so these were replaced with 1k, I could use lower value ones but 1k is sufficient for now, you also need a cable with a 3.5mm mono connector plug on it, a small piece of veroboard, and a 3.5mm stereo socket and short pieces of wire to connect it to the resistors on the board.

What you need to do is solder the wire from the tip of the mono plug to the veroboard, then the wire from the sleeve to another track on the veroboard, then solder on both resistors, both must go in to the same track the wire from the tip of mono plug is soldered to, the other leg on each must be placed into their own seperate tracks, and then soldered

You must then wire up the stereo socket, the pin for left should go into one of the tracks meeting the free end of one of the resistors, the right should go into the free end of the other resistor, and the ground should just connect to the sleeve of the mono plug, you may need to test the pinout first, using an old severed stereo plug or 3.5mm TRS to phono lead would work for this, solder the wires at both ends

Now connect the mono plug to your rig and plug your headphones into the socket, you should hear sound through both earpieces, if you cannot hear anything turn up the radio’s volume until you do, if you are finding you have to turn it up all the way, try some lower value resistors, if the volume levels are acceptable, you’re done and can use any off-the-shelf headphones with your rig in comfort

A power lead for hilltop DXing

Warning! As you are dealing with electricity it is important to make sure that there is a suitable fuse in the plug rated for whatever you are connecting, use of the wrong fuse may cause a fire risk if rated too high or persistent blowing if too low, do not use this lead for anything over 10A, cigarette lighter sockets are not rated for more than this. Your rig will also have an inline fuse in it’s own power lead on the positive line, if you’re unsure, seek proper advice

As many radio operators go hilltop DXing, one thing they need is power to their rig, if you’re in a car you can simply either hard wire the rig to the battery as normal or fit a cigarette lighter plug to the rig’s power supply, but what if you’re hilltop DXing away from the car.

One method of powering your radio is using a portable power supply, similar to the type used to jump start cars as these are often fitted with a 12v cigarette lighter socket, though not designed for the lighter element itself, however you may not want to attach a permanent cigarette lighter plug to your radio’s power lead which is where this cable comes in.

What you need is a cigarette lighter plug, if there is a cable with bare ends fitted to it then that’s half the job done, if not you have a little extra work to do, you also need a terminal block (sometimes known as “chock blocks” or similar) these are the blocks with two screws in, and are sold in strips, preferably aim for one 10A or higher, though current should not exceed 10A anyway, a ring terminal, a bolt that fits through the ring terminal, and at least two nuts for the bolt, more than one nut may sound silly but there is a reason for this.

Here is what you need to do

  1. If you have no wires on your cigarette lighter plug, now is a good time to fit the wires to the plug and it’s done, centre is positive
  2. Strip the ends of the two wires for the terminals, tin these with solder
  3. Fit the ring terminal to the negative wire using a crimp tool (you can optionally heatshrink this, I didn’t in my first lead)
  4. Put the bolt through the ring terminal and screw on one of the nuts, another nut can be used for the ring terminal on the negative cable of your CB radio, don’t worry about insulating this side.
  5. attach the terminal block to the positive side, you may need to trim the wire so it will fit into the terminal block, tighten up the screw
  6. Finally check for continuity and you’re done

Now you have a cable that will only take a matter of moments to connect to your rig and should work with most CB radios on the market, the vast majority of them come with a bare ended positive wire and a ring terminal, or similar, on the ground wire, this will allow you to power your radio without having to fit a permanent cigarette lighter cable

This can also be done similarly with Anderson Powerpole connectors, which if installed correctly are polarised, I’m slowly migrating over to this type of connector

Dipole for 2-meters

As the CB and 446 dipoles above except this is cut for the 2-meter band and has a different choke, however when I built one I found I needed to place the choke as close to the antenna’s elements as possible
To make this you can simply follow the instructions above for CB and PMR446 dipoles except change the measurements to suit this, I also found that if you solder the elements to the coax rather than use terminal blocks it makes for a better connection, if you do this you need to not only insulate the two parts of the antenna where they are soldered but you also need to waterproof the coax at this point, Sugru can work for this whole job as its electrically insulating and can waterproof joins like this, but take note that it takes about a day to cure.
A feedline of RG213 is recommended, RG58 as used for CB is more lossy at 2 meters, the dipole elements should be cut a little over 50cm each, make sure that they are longer than what you need then you can cut it down, it is recommended to tune it on an analyser but if you don’t have this luxury like myself, use a free simplex frequency but not the calling frequency, and remember to check the frequency is clear, and identify and make a point that your transmissions are tests, when you’re happy clear the frequency and put your new antenna to use (also check the SWR on 70cm as it might work there too)