RAE & beyond...
My prime area of interest is to guide SWLs onto being qualified amateur licensees safely and/or learn Morse code. Although I qualified for my first class licence I was not really fully prepared to set up a HF station e.g. avoiding RF burns was a major concern to me as my uncle Des G3HSU SK had shown me his. It looked like just a tiny black dot but: "It's painful, goes deep and takes a long time to get better. You don't want it Robert".
Fortunately I was mentored by Frank G3JKS and Bob G3UJV of Verulam ARC with some useful tips not covered in the RAE. Then I was happy to proceed. Subsequently I have met other licensees who were in a similar predicament as mine. So I was thinking of presenting information that would help a newly licensed get on the air with confidence. Here it is:
Please be aware that the information I present is based on my opinions and experience consequently it may conflict with the text books which is why I advise maximum of 5 Watts TX no more than ten. That is because RF burns come in at 15 to 20 Watts. This means you will need a radio that can go low in power. When I first qualified that was a big issue for me as so many rigs were valve at 50 to 100 Watts only. Through the kindness of Verulam ARC I was guided to a secondhand low power transceiver using 12 Volts.
I recommend a similar rig but nowadays that shouldn't be difficult and an automatic ATU is often included. I stay away from valve equipment due to the high voltages and the skill needed to operate them safely.
I also prefer 12 Volt radios because they can be operated from a battery in an emergency or for outdoor activity. Never use a car battery for long periods of radio operation or you will quickly ruin it and may not even get home. You need a lesiure battery that can deliver power to your radio over a long time. Car batteries need to work hard by cranking the engine then being rapidly recharged by the alternator.
In my opinion mains powered equipment e.g. transformer in PSU are good for twenty, maybe twenty five but no more than thirty years. This is because the insulation on the windings of the transformer will degrade. The insulation is merely shellac similar to nail varnish. Therefore I like a 12 Volt radio that uses an exterior PSU which I can change at will for relatively little cost and keep my shack safe.
HF dipole aerial
There are three types of aerial. The one you used to have, the one you have now and the one you will have in the future.
Loudspeaker twin wire is 50 Ohms. Therefore it makes an excellent feeder and aerial combined. Separate the two insulated wires to required length: 143/Frequency in MHz gives the total length of a dipole and tie a knot. Remember to add a few inches to attach each leg of the dipole to support insulators. Connect the loudspeaker wire feeder to a PL259 plug inside the house/shack. This works excellently for the 40m band because there is usually always something on it 24/7. Not only that, because the only connection is indoors there is no weather or sealing issues. Ultraviolet light will break down the plastic insulation eventually but takes a few years. I prefer to insulate all my aerials in case it falls whilst I'm transmitting and someone is outside nearby. This also applies to aerials in the loft. I always use insulated wire. I realise that it my degrade the signal slightly and anyway from a technical point of view it's not necessary (point the ends down to prevent coupling into the wood of the attic). No, that's not the reason. If a workman enters the attic to attend to e.g. plumbing of the water tank he needs to know he's safe and bare copper wires will maybe result in: "Sorry Guv, not for me." I also keep everything neat & tidy up there.
This kind of aerial is quite stealthy so much so that my next door but one neighbour recently remarked: "What's that doing there... nobody uses shortwave these days?!" Actually Jeff, there's been an aerial there for thirty years. You just didn't notice. If you move into a property consider to install an aerial if you're not ready to use it. That way if TVI issues arise your neighbours won't necessarily blame you. Also, AVOID OVERHEAD HIGH VOLTAGE CABLES. Electricity is a harsh mistress so show some respect or she will bite you hard when you least expect it. Treat telephone cables with suspicion.
12 Volts or not 12 Volts?
Sometimes you will see instead of 12 Volts 13·8 Volts. This reflects that batteries when fully charged may exceed 12 Volts. André Skarzynski M0JEK of Verulam ARC Quote: "I've set all my power supplies to 13·5 Volts." At first I was outraged with... HERETIC! Surely the conventional wisdom is 13·8 Volts I mused but then it all made sense. I have noticed that my power supply voltage may vary ± a few tenths of a volt over protracted time so erring on the side of caution I too now set my PSU to 13·5 Volts. Comments appreciated to my E-mail via Home page link below.
Now comes the really tricky bit of drilling a hole through the house wall to accomodate the feeder from outside. WEAR OFFICIAL EYE PROECTION not just specatacles. Goggles or face visor are reasonalby priced at DIY stores. If the wall is solid then it may take sometime but you will get there. I'm not sure about modern cavity walls as I believe that they may have twisted metal ties. If you're lucky you won't touch one. Remember to include a J drip loop where the feeder enters the wall and a dab of silicone sealant and/or cable gland cap is good.
Next you must install a screw threaded eye to attach the leg of the aerial nearest to the house probaly with a carabiner or dog lead clip preferably stainless steel but there are two types of stainless steel. The cheaper one will corrode eventually outdoors. Good idea to use some form of insulator too. This will probably be just a few feet down from the gutter. For safety of the wall I recommend no less than five bricks down from the soffit for no other reason that I saw it on a website some years ago. You'll need a ladder and a ladder stay is only £25 so get one. Remember the 1 in 4 rule with ladders. For every unit the ladder comes away from the wall then use four units up to enhance stability. If you don't understand what I'm talking about then pay a professional to do it for you. Then you'll need a support at the other end of the dipole. Hopefully a tree with rope and another insulator or install a pole or tie off from a fence. It's different for everybody.
The rope I use is 3mm para cord black from www.kombatuk.com It's very strong. There are overhanging trees here so if a branch falls the paracord will likely survive but the loudspeaker wire will fail. That is what I want to happen. Therefore my supports are protected and the loudspeaker aerial wire is relatively cheap and easy to replace.
With regard to drilling into and through walls be sure to avoid nearby windows that may fail due to intense hammer drill vibration. The station manager won't be pleased if she has to order replacement units.
Going discreet with a HF Random Wire Antenna and 9:1 unun. UNUN = unbalanced (LW) to unbalanced (RG58C/U).
(When winding the toroid wear safety spectacles as the wire could easily flick into your eyes.)
You live in a place where there are neighbours. You have space available to place some kit, but not that much. Even if you decided to use that space, you wouldn't want your neighbours to imagine what all that stuff is about. If your neighbours found out chances are that one day you would end up having a discussion with one of them, not because you disturb TVs and they hear you talking in their toaster, but because they don't like what they don't know.
If all of the above sounds somewhat familiar, welcome to the SOC - the Stealth Operators' Club. We are people who, for one reason or another, have to go discreet - or even stealthy.
An ideal choice is the magnetic LW UNUN. With this simple piece of equipment you can use 20m of antenna wire across all HF bands using the inbuilt ATU of your TX/RX. You may also need an unun several turns (usually six to ten turns but you may need to experiment for your unique situation) of RG58C/U would on a troid as shown below to deal wiht common mode currents.
My effort for an end fed long wire antenna using alternative components. End fed LW antenna most convenient but often requires its high impedance, typically 450 Ohm, to be matched to common 50 Ohm TX/RX. Maintaining the trifilar winding spacing helps to minimise common mode currents IMHO. With the use of an antenna tuning unit this project works well on all HF 160 to 10 metres TX amateur radio bands. Also likely useful on its own for SWL broadcast bands RX. If you require to connect an earth or counterpoise use the chocolate block where the RG58C/U terminates or a coupler on the coax PL259 with shield/earth terminal. YMMV. As shown not suitable for long term external use.
Caution: It is possible to exceed the power rating of a core and the performance of the UNUN may be degraded during high SWR causing heating of the core. If the core is over heated its magnetic properties will most likely change and your UNUN will not work efficiently and may even damage your radio or ATU. The highest power I've used so far is 15 Watts.
I use a FT240-31 toroid which is generally regarded useful for HF, cost about £10.
MKll version below using enamelled copper wire 8SWG 1.250mm Maplin YN81:
Source: Phil VK5SRP, John M0UKD & M0ZZM.
QRP output indicator for LW end-fed antennas.
TX tuning without a visual reference is like winking at a pretty girl in the dark. You're full of good intentions but it's a wasted effort. G8ATO/Norman: "WWII radio spy sets used car/domestic/pygmy light bulbs wired in series with the LW antenna to aid tuning. Tuned up with peak of brightness in the light. No specialised knowledge required."
K7HKL inspired project for QRP TX with basic LC tuner to LW antenna. Insulated LW antenna wire is passed through a ferrite ring (typically 35 mm diameter Fair-Rite 43 material from Radio Society of Great Britain £2·25) upon which several turns of insulated wire are wound and connected to LED - polarity not relevant. Mine: 5 mm red extreme brightness LED (easier to see on a sunny day) Maplin stock code N69AJ £1·39.
Key the TX & observe the LED as you adjust your tuner. It glows maximum brightness at optimum tuning. This basic simple method (not component critical) is ideal for setting up a QRP station outdoors. New take on an old idea. < fiver. Text and picture in the public domain so feel free to copy & distribute. You can tune a radio but you can't tuna fish! MTMBWY.
TX Transmitter | LW Long Wire | QRP Low Power
LC Inductor Capacitor | LED Light Emitting Diode
VHF & UHF aerials
So that's HF dealt with. Next you may like to contruct a 2m dipole aerial for the loft. I use white (not grey or black that may impede the signal) 16mm x 16mm electrical trunking. This gives the 2m dipole rigidity and means you can just lean it upwards in the attic rather than climbing a ladder to install support. I use a pigtail lead to ease the strain on my handie when I connect the 2m via RG58C/U see below. If you can, board the attic, to prevent accidents like falling through the ceiling like I did. I lost my concentration for just one second... With regard to 70cm my handie seems quite happy using the 2m dipole but I wouldn't recommend it. Also, if there is an old metal water tank in the loft maybe turn it on it's side and attach a 2m/70cm mag mount vertial antenna. (See below for more information.) I've yet to try it. Homebrew alternaties below
In these days of postage stamp gardens mounting a detachable slim vertical aerial on your car seems to be attractive at a cost of about £40 without drilling holes in the bodywork. When mounted on a steel car roof, the steel under the magnetic mount of an antenna is the ground plane. If you remove the antenna from your car and use it in the house or camping, etc, you WILL have to mount it on a piece of conductive metal e.g. a redundant metal water tank in the loft or make a counterpoise from wires. Your piece of metal should be at least 17 inches in radius (34 inches in diameter) as kindly advised by Norman G8ATO of Verulam ARC. It can be round or square. The shape really does not matter in the real world as long as you have at least 17 inches of metal in all directions.
2m Folded Dipole - a loft-mounted vertical folded dipole for the 144-146MHz band. Theory: Vertical antenna most appropriate for 2m. A fat dipole (therefore wide band) will have a lower feed impedance at resonance than a thin dipole so 50Ω feeder cable e.g. RG58C/U may be used. It's an economy, lossy cable (best to keep the length less than 10 metres) for low power use and has a stranded centre conductor so less likely to break if the cable is bent. The conductors are tinned so easy to solder.
Making it: The dipole is made from 2∙5mm2 × 90cm long power cable: strip off the outer insulation then use the two insulated cables to make the two elements of the dipole. Use a twisted pair of 1mm2 lighting cable cores 63cm long to make the balun. There is no direct connection from the coax screen to the dipole. The return current gets back across the capacitance of the balun. This is all assembled using a chocolate block connector. Coil up the balun to save space. The match to 50Ω cable is good.
Source: Dave Kimber G8HQP http://myweb.tiscali.co.uk/g8hqp/
I did write about this aerial in RadCom but people are asking about it so here it is above with Dave Kimber's pictures.
1/4 wave ground plane antenna.
This relatively easy project is ideal for SWLs and licensed.
John M0UKD has blessed us with a most useful hobby radio website via ground plane antenna picture link below.
My favourite offering is his 1/4 wave ground plane antenna calculator. Enter the frequency you require and the element lengths are displayed along with construction details.
I've made one and it works fine for me on the GB3VH repeater. My element lengths are: Driven element A = 16.5 cm ground plane elements = 17.5 cm. Feeder RG58C/U.
The radiating element is a quarter wave and the radials are 12 per cent longer. There are usually four radials.
These antennas can easily be built for UHF or above by using a chassis mount N-Type (or SO-239) connector, some solid wire and solder. For VHF and below, as the elements get bigger, some more structured design is needed.
A quarter wave monopole mounted against a perfect ground will have an impedance of around 36 degrees but by bending the radials down at an angle of 45 degrees, we increase this to around 50 Ohm whilst at the same time lowering the radiation angle more towards the horizon. (42 degrees is the theoretical perfect angle.)
RG58C/U and you... & me too!
Much has been said about the performance of different coaxial cables but here I consider the positives of RG58C/U. 1) 5·5mm diameter so fits through hole drilled in house wall by common 6mm hammer drill bit and fits common sized PL259 plugs. 2) The conductors are tinned therefore easy to solder. 3) With the absence of easily damaged foam (but solid dielectric) may be bent at relatively tight angles and easily wound on a toroid to impede common mode currents. 4) Possibly the most abundant and cheapest cable available. However, I accept that exceptionally long VHF/UHF runs may degrade the signal significantly but for most applications the humble RG58/CU is optimal. p.s. If you do run the cable through house wall and then route up consider to create a J drip loop to impede rain water ingress.
Where ever your journey in radio takes you the time will likely come when you want to match a high output line audio to high sensitivity input. In my case it was the 2 Volt output of a CD player to the 250 mV input of a guitar amplifier for my teenage student. I use L pad attenuator to balance things out and minimise overload distortion. It also seemingly improves the timbre. Two 10k Ohm resistors one in series the other parallel. Graphic attached. I install the pad in the shell of a wide body jack plug (to accommodate the thick CD phono leads photo attached) where the two channels are joined for mono. Thank you to Norman G8ATO of Verulam ARC for introducing me to L pads. BTW radio enthusiasts have always been the friend of electric guitarists e.g. the legendary (Leo) Fender Radio Service:
p.s. Subsequently I replaced series resisitor with 22k Ohm. This brings it inline (no pun intended) with commercial products and attenuation of -10dB to -12dB expected so the audio will sound half as loud.
Visit my Home page via link below to access my GB2CW Verulam ARC CW training web site. If you can't RX my broadcasts then you may listen to audio files of previous lessons kindly hosted by Peter G0OIK.
Alternative vintage sound for a dynamic microphone as used for stage performance e.g. SHURE SM57 is to solder a 680 Ohm resistor across pins 2 & 3 on a short patch lead that can be passed around the group / studio to experiment. Picture below illustrates. Does it work? Well, I don't have a SM57 but using a general purpose microphone it reduces the output and smooths the high end of the frequency response so yes it seemingly does work.
So those are my thoughts. I will be adding more over time so please check back once in a while. Terms & Conditions? There are none. If you do copy/paste into your own e.g. website or magazine/newsletter then please link back, thanks.
73 Bob Houlston G4PVB MA3053SWL 21st November 2017
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