My review of WITNESSES OF WORDS
A while back Norman G8ATO of Verulam ARC inspired me to make an expandable range voltmeter to monitor my 12 Volt battery. This would make it easier to read the critical readings from 11·5 Volts (safe minimum) to 14·5 Volts maximum (if on charge). But I had trouble with the idea of how I would present the meter scale in a professional manner. Then I realised an alternative. Take a 0 to 5 Volt voltmeter and rework the scale in your head from 0 to 10, the 1 to 11, the 2 to 12, and so on until 15. In other words you add a 1 prefix to each scale reading and label the meter as such. You may likely have to include a series resistor to accommodate the change. YMMV. The attached circuit diagram is from: http://www.thebackshed.com/windmill/articles/ExpandedScaleVoltMeter.asp
Here is a precis of the explanation:
"The Zener Diode ZD1 is chosen to suit the minimum meter voltage you want to display. I used Zener Diode 1N4740 to operate at 10V. Resistor R1 is chosen to supply a current of a couple milliamps through the Zener Diode to make sure it's regulating properly. The variable resistor VR1 is the meter scale current adjustment. I used a variable power supply set at 13 volts and adjusted VR1 so the meter was about mid scale."
So that's the theory.
Whilst not a radio website it does have some interesting articles all for free. If you have time then do explore from the Home page. If you don't have time then make time otherwise you'll be missing out.
For the benefit of those new to circuit diagrams here is a web page that explains the fundamentals: https://diyodemag.com/education/fundamentals_circuit_diagrams
Here is my latest battery monitor re photos below. The voltmeter is an expanded range meter as kindly suggested by Norman G8ATO of Verulam ARC. It makes it easier to ascertain crucial readings. The ammeter is non linear AC DC. It works regardless of series polarity connected. The cables and PowerPole connectors are rated at 30 Amps which I fuse at 15 Amps. The 12 V cig lighter auxiliary socket is wired across the supply and rated at 20 Amps which I fuse at 5 Amps made easier by the piggy back fuse holder. The voltmeter is wired in parallel across the supply and fused at 0.5 Amps. Dimensions: 12 cm x 10 cm x 7 cm. So I'm all set for 12V battery power QRP CW NFD. Now, was it: "You're 995 or 795 or... ?" crikey, you do the maths, there's so many combinations! HI.
Connecting your radio equipment to reverse polarity could have devastating consequences. The most likely risk is when you rearrange your shack or attend field day especially in the dark and/or in haste. The terminals of some rechargeable batteries may appear almost identical so the simple act of moving the battery through 180 degrees whilst tidying up then reconnecting... PowerPole connectors are ubiquitous so here is a method to establish correct polarity before connecting 12 Volts DC. The first photo shows how the positive (longest lead) of a 10mm bright light green LED is connected to the red +ve 15 Amp terminal. The shorter lead is connected to a 1k5 Ohm resistor and then to the -ve black 15 Amp terminal. The optional (keeps everything solid) black plastic splash protector boot is easier to attach over the completed item when softened in hot water. Connect the polarity checker to your power source. If there is no light from the diode the polarity may be reversed or no power present. If the diode glows green then the power is present and the polarity is correct. It is most unlikely that the device will go short-circuit but I still have fuses fitted to my power source. This device was inspired through Internet searching. Some people use small red & green diodes (red = reverse polarity using an additional resistor) but I prefer just one big bright green one (2nd photo) especially outside on a bright sunny day. Thank you to Norman G8ATO of Verulam ARC for technical advice.
Whatever stage you're at in the hobby radio journey then you'll most likely need a multimeter. It will measure Voltages, Ohms & Amperes hence the title multi-meter. The most often use will be continuity to test switches, PCB tracks, fuses, aerial feeders & cables. This could be Ohms or an audio buzzer built into the device. The main multimeter differences will be either traditional 'analogue' meter display with a pointer (ideal for watching varying readings) or digital display ideal for watching stationary readings. The Hold (usually blue) button on a digital multimeter retains the reading until released. Expect to pay from £5 to £25 for hobby use and likely a battery extra. SparkFun have produced a print off PDF for use in a classroom (ideal for tutors & those studying the Foundation licence) that explains and tests your ability to learn via link '3' below. For even more explanation visit their following '4' link. Avoid parallax error when using an analogue meter by viewing straight at the needle (silver mirror strip on the dial helps) not from the side. The last link connects to an AVO (Amps Volts Ohms) multimeter information page where you will see the silver mirror scale. AVO multimeters were renowned for reliability. Whilst an apprentice the laboratory AVO was damaged and meter needle pointer broken. It was quite a serious matter but I was able to disassemble the device and glue it with (then not available to the public) what is now known as Super Glue. The senior technician was ecstatic that I had repaired it so well: "How did he do it?"
As much as I like the PowerPole connectors I have on two occasions encountered preassembled commercial leads of reverse polarity. The motto is when looking at the connectors from behind then tongue tip up red receptacle to the right. But on a field day (just a few months away) in the dark things like battery connections can go horribly wrong so I am in the process of building a PowerPole polarity checker. Using a conventional 15/30/45 Amp PowerPole two pole housing then a 1k or 1k5 Ohm resistor (depending on your Light Emitting Diode) is connected to the terminal that goes in the red housing. To this is soldered a green LED (longest +ve Anode lead) which is then bent round and the other lead (short -ve Cathode lead) connected to the terminal in the black housing. Then a PowerPole black splash proof boot is used to cover it along with some silicone sealant inside to keep it strong but can be gently peeled away if you want to recycle the components later. The LED is connected so that when the checker is inserted the green light indicates correct polarity. If the green light fails then wrong polarity or no voltage present. Thank you to Norman G8ATO for technical advice. On the Verulam ARC net Norman went on to suggest that a relay with a diode before the input to a 12 Volt DC radio would only allow current through if the polarity of the supply was correct as in the days of PYE Mobile Radios. If the polarity was wrong then the relay would not activate and all is well as you just connect correctly and the radio works with no damage. Norman: "That sort of precaution is seemingly absent these days." You could use a series diode or reverse diode that blows the fuse if the polarity is awry but the relay covers all eventualities with no need to replace fuse or affect the supply with voltage drop from series diode. Visit the link below for substantial information about LEDs.
Whether SWL or licensed then we're all mostly bearing the burden of mains borne interference to our radio reception so operation from a battery isolated from the mains could be an option to consider. Many radios are able to function from 12/13·8 Volts rechargeable battery but it must be a leisure battery e.g. two wheel hand golf cart gell cell NOT a car battery as that could be ruined from long term use. But it is generally agreed not to let the leisure gell cell battery go below 11·5 Volts for fear of permanent damage so...
Whatever stage you're at in the hobby radio journey or enthusiastic home handyman then you'll most likely need a multimeter to measure battery voltage. It will measure Voltages and also Ohms & Amperes hence the title multi-meter. The most often use will be continuity to test switches, PCB tracks, fuses, aerial feeders & cables. This could be Ohms or an audio buzzer built into the device. The main multimeter differences will be either traditional 'analogue' meter display with a pointer (ideal for watching varying readings) or digital display ideal for watching stationary readings. The Hold (usually blue) button on a digital multimeter retains the reading until released. Expect to pay from £5 to £25 for hobby use and likely a battery extra.
SparkFun have produced a print off PDF for use in a classroom (ideal for tutors & those studying the Foundation licence) that explains and tests your ability to learn via link 'suffix3' below. For even more explanation visit their following 'suffix4' link. Avoid parallax error when using an analogue meter by viewing straight at the needle (silver mirror strip on the dial helps) not from the side. The next link 'suffix5' connects to an AVO (Amps Volts Ohms) multimeter information page where you will see the silver mirror scale. AVO multimeters were renowned for reliability.
Whilst I was an apprentice the laboratory AVO (very expensive and vital for our work) was damaged and the meter needle pointer broken. It was quite a serious matter but I was able to disassemble the device and glue the pointer together with the new cyanocrylic glue (then not available to the public) what is seemingly now commonly known as Super Glue. The senior technician was ecstatic that I had repaired it so well: "How did he do it?" My good buddy at work did not take the warning seriously about fingers getting stuck together with the glue: "No, I don't believe it!" But he found out the hard way. Fortunately no permanent damage.
Norman G8ATO of Verulam ARC nets kindly advised me of the Expanded Range Voltmeter that makes the most of the scale by making the full scale deflection from e.g. 11 Volts to 15 Volts. This is all explained via the last link 'suffix6' below. There is also the option of using LEDs instead of a moving coil meter. Be mindful that all batteries (even the humble AA) can store a phenomenal amount of latent energy so fit fuses and wear eye protection when working on them.
I am making myself a simple battery voltage monitor with a DC 15 Volt meter connected parallel across the +V and -V and a few PowerPole sockets to double it up as a distribution board with internal fuses. Could be a while until it's finally constructed because to save on the cost I've opted for Ebay snail mail delivery of the components seemingly by donkey! HI.
Politics & Radio
I'm not a team player. I'm belligerent and at times selfish and myopic both metaphorically and literally but above all decidedly awkward with people. Consequently, when I studied for the RAE I knew that would be the easy part and dealing with neighbours the real challenge. Bob G3UJV of Verulam ARC gave me some useful advice for SWLs and licensed: "When you move into a new home put up an aerial even if you don't intend to use it yet. That way, if there is some local interference, your neighbours won't immediately blame you." Seemingly, if an aerial has been up for four years it can stay there permanently. Source: RSGB Yearbook 2018 page 68. I engineer my aerials to be discreet so as to avoid confrontation with residents and having to deal with the politics of the local council planning department. Besides, although I dream of a ninety foot lattice tower with rotator and three element beam on top the Station Manager... well... she still says: "No!" HI.
Politics & Radio History
Black Propaganda via Radio - the Nazis were masters of it. WWll saw the use of radio to undermine the morale of the enemy and uplift that of the home nation. He who wins the war gets to write the history but that isn't easy when so many relevant documents were destroyed on both sides for fear of recriminations. The link below attempts to reveal the disturbing facts as best they can be presented. You've heard of the VW Beetle as the German people's car along with the Autobahn motorway. Well there you will learn about the People's Radio... it was meant only to receive official German news frequencies MW AM. The German population would hand in their short wave radio set for destruction upon fear of imprisonment to hard labour if caught listening to alternative stations.
New radio book No.1
LORENZ first published 2017 - "Breaking Hitler's top secret code at Bletchley Park." We're all familiar now with the significance of The Enigma machine and Alan Turing regarding German U Boat submarine codes and elsewhere in their military but few of us, until recently, are aware of Lorenz. It was used by the German high command along with all ultimate major communications. Captain Jerry Roberts MBE explains how The Enigma had 3 to 4 rotors but Lorenz had 12 and then proceeds to recount how important to the war effort was the work to decrypt Lorenz messages. At £20 I personally would not recommend it because I rarely read a history book but the RSGB were offering it at members' 40% discount price of £11.99 so I snapped it up and I'm glad that I did.
New radio book No.2
International ANTENNAS first published 2017. Edited by Stephen Appleyard, G3PND. I like this book so much that I bought two of them. One for myself and one to make friends by lending it out. Over 50 articles along with photographs, diagrams and measurements of a good understandable size from VLF to 70cms. I would have appreciated a detailed index at the back but the Contents pages at the front will suffice. Brilliant value. I'm pleased to thoroughly recommend it 100% with 5 stars. Buy from RSGB £9.99. Conclusion: What this country needs is the 99 pence coin. HI
New radio book No.3
MORSE code for radio amateurs first published as 'Morse code for the Radio Amateur' 1947. Mine is the blue (not previous yellow) cover 12th edition reprinted 2017. This has substantial more information than the previous yellow cover issue. With permission of the author Roger Cooke, G3LDI I use the text for my GB2CW Morse tuition broadcasts. I bought several that I lend out to my students. But there is more, so much more. On the inside of the back cover is a CDROM with free software and practice files to help SWLs and licensed alike to learn the code. £8.99 from the Practical Wireless / Radio User book store
New radio book No.4
ELIMINATION of electrical noise by Don Pinnock, G3HVA - reprinted 2017. At first I was disappointed with this book because I was searching for solutions to my own specific situation. But then I realised I was being unreasonable because we all have our own specific situation. What this book does well is give an overview of the subject and then leaves us all to interpret as we see fit. It even advises on location for buying a new home. The information on rogue power supplies was most unsettling as we all seem vulnerable to 'grey' imports either in our premises or next door. Good diagrams and photographs all explained in a manner that does not require a knowledge of mathematics. No detailed index at the back. £5.94 from RSGB bookshop. At that price they're virtually giving it away.
Online publications via link below.
The Max-Planck-Institute for Radio Astronomy in Bonn and the 100-m radio
telescope in Effelsberg. Fifty years of the Stockert Radio Telescope and what came afterwards in the 1950s is something I stumbled upon whilst surfing the Internet. It's the first PDF link below but if you back track to http://onlinelibrary.wiley.comand search for 'radio' you will be rewarded with 352922 results. Some you have to pay for but there's plenty of free content such as: 'Community Radio' focusing on youngsters by Catherine Wilkinson, The University of Liverpool, via second PDF link below.
BTW we all use www.ebay.co.uk to access components here in UK but there is an even greater range by accessing the American and Australian / New Zealand markets. There may be higher postage and possibly import charges but for that hard to find item then maybe useful to know. Google: 'currency converter' to compare prices. In some instances Ebay will do that for you. In the small print below 'Add to basket' you can access to double check the postage by choosing 'see details' then select United Kingdom from the drop down menu and clicking on 'GET RATES'. You may be pleasantly surprised with possibly Free postage. Also, the most popular time for people to buy from Ebay is seemingly Sunday evening so you may want to take that into consideration when listing your goods. Source: Tony 2E0WAP of Verulam ARC his club night lecture.
PM Gordon Brown's Government guidelines were that we should all have a two week supply of food, water & medication for the event of a national disaster. When I was studying A Level Physics at college as a teenager we were taken into a darkened room to watch a film. "Why do we need this I thought to myself." Well, it was related to physics in that it was a documentary about the aftermath of a nuclear strike on our country. First there's a blinding flash of light and after that you have just a few seconds to find shelter for when the wind blows. Those more than twenty five miles from the blast centre would probably survive but conditions would be dire. The authorities may well be able to provide relief within the two weeks but conventional communications e.g. cell 'phones would be down. In the meantime that's where hobby radio comes in. Whether SWL or licensed always keep your batteries in good condition ready for any eventuality either for monitoring public service broadcasts (probably MW AM) or RAYNET (Radio Amateur Emergency Network) activity. If using 12 Volt gell cell leisure batteries (NOT A CAR BATTERY which will be quickly ruined for this application) then it is good to monitor the voltage not to go below 11·5 Volts to prevent over discharge damage. A simple voltmeter wired in parallel across the battery terminals will suffice for temporary use but fit fuses if this is going to be a long term activity. Wear eye protection when working on batteries. Those of you who just want a bargain price used meter to monitor your battery then visit link below. You can even pick up an Aircraft Jet Temperature Indicator Gauge there.
Key Pad consternation. In the early 1970s the father of my girl friend was delighted to show of his new bright shiny red telephone with a number pad instead of a clockwork dial. Seemingly it was not standardised to common practice with adding machines. Consequently we are now in the situation where telephone number pad starts at the top left with 1, 2, 3 and PC & calculator number pads start top left with 7, 8, 9. The middle row 4, 5, 6 applies to both but telephone key pad bottom left is 7, 8, 9 whereas the (yes, you've guessed it) PC & calculator number pads start bottom left with 1, 2, 3. Maybe we should all talk to each other more often I muse.
"Operating on satellites is relatively straightforward, but over the years many tips, tricks, and secrets have been discovered which make operating more efficient and pleasant. Here we are collecting information of use to both the new and experienced operator:"
We all like to view where our radio contacts come from but a map that is cluttered up with too much information is about as much use as a chocolate teapot. Fear not because Tim Makins EI8IC has come to our rescue with his GOM - Global Overlay Mapping. Quote: "GOM is an important new tool for all aspects of Amateur Radio throughout the world. More than just a static map, GOM combines the 12 different overlays with an easy-to-use navigation system that can select and load a map from a single click. In addition, every map has Real-Time Mouse Tracking, that displays continuous Positional and Grid-Locator information on the Status Bar, plus instant Beam Headings and Distance Display, customised to your Home location. Also, every IOTA entity is mapped and searchable - its the only Ham Radio Mapper to do so!... Shareware for $15." Not only that his website features more free maps. Well worth a visit at:
Monitoring the stability of our UK mains electricity supply. Monitoring the Voltage is relatively easy. I use a Martindale SB13 'safebeak' adapter with 4mm shrouded sockets. Then a fully shrouded test lead is connected to a multimeter (again with fully shrouded 4mm sockets) to read the Voltages. 1997 the European Union 'harmonised' our mains supply at (230 V +10% -6%). 230V + 10% = 252 Volts maximum. 230 Volts -6% = 216·2 Volts minimum. So that's 252 V max & 216·2 min. Photo attached above shows my meter at 242 Volts along with the Martindale, shrouded leads and four safety end blank caps. In case you're wondering the meter is on Hold. I'm not too fussed about the Amperage because most appliances have the Amps or Watts marked. Watts ÷ V = Amps but 50Hz frequency stability is interesting. (Some meters have Hz function.) For most practical uses the 50Hz is stable but only over time. In order to accommodate synchronous clocks, that rely on the 50Hz to maintain accuracy, the supply company will balance out any 50Hz deviations over the course of a day. I've not noticed any problems, high or low, with the Voltage of my supply or the 50Hz and from studying data on the Internet all other issues are addressed. The people who may have concerns are those living in remote rural areas where regulation of all aspects of the supply could prove troublesome. For those who wish to pursue this subject further then visit the link below. p.s. 240 Volts can cripple/kill you. Treat it with respect, carefully consider the procedure you use and always employ fully shrouded leads. BTW the meter in the attached photo is many years old. I decided to calibrate the DC Volts range by comparing it to a PSU with a meter already installed. The only problem I had was to identify the appropriate preset potentiometer for adjustment. It was labelled CD V. I was expecting DC V for direct current voltage. I took a chance and go it right first time. So, CD could mean current direct? It's a common budget meter so that information may be useful to some.
Ralph G1BSZ of Verulam ARC: "What can we do to get youngsters involved with amateur radio?" After considerable thought I don't think we can. But we could introduce junior school age children to the wonder of ELECTRICKERY! A good place to start is the fresh potato/fruit cell. One electrode -VE (zinc) is a clean galvanised nail. The other is copper +VE. A bright clean copper penny will work but that's defacing coin of the realm so I use a copper nail. An analogue meter may not read so well as a digital meter. This may be due to the digital meter being powered by a PP3 battery that does not load the circuit nearly so much as an analogue meter. Alternative to fresh potato is vinegar or a fresh juicy lemon (yummy) as via link below. Insert the electrodes into the potato close but not touching i.e. one centimetre apart. Clip leads to connect electrodes to the multimeter. Usually it will read 1 Volt to 1.5 Volts. Connect three in series to light an LED. In 1800 Alessandro Volta invented the first battery. Two centuries later a project as above could fire a young child's imagination to greater things... Make/break the connection and you're into Morse code. CQ? p.s. Citrus juice vapour is detrimental to delicate printed circuit boards. Using a moving coil analogue meter the three cells together indicated 2 Volts. The DMM indicated 2.79 Volts. Varying the spacing of copper and galvanised nails on individual lemons produced little change in voltage readings nor did using small or large fruit.
My try at this experiment:
Cut the 3 lemons in half to create 6 cells. Wired in series = 5 Volts and the LED glows even brighter:
Lemons printer friendly.
This gold leaf electroscope actually uses the ultra thin aluminium foil from a traditional (not chunky) Kit-Kat chocolate bar. Rub a lambswool garment on to a vinyl (not metalised) inflated balloon. Then approach the balloon to the top plate of the electroscope and observe how the charged foil separates. (Like charges repel.) I used a spiral of copper wire for the top plate with a blob of solder at the end to prevent sharp point, from using side cutters, rupturing the balloon. A piece of copper circuit board would do also. The jar previously held coffee. I cleaned it and the lid scrupulously. The top plate is connected to the downwards copper wire in the jar with a hook for the foil again with a blob of solder to avoid cuts or scratches to the operator especially if children which is to whom this project is primarily for. In addition to the static electricity from the balloon Norman G8ATO of Verulam ARC kindly advised me that with just 20m of LW aerial connected to the top plate distant thunderstorms could be detected. It therefore becomes a VLF radio receiver of sorts but I've yet to try it. Best not to do it with local storms methinks. Photos as best as I could do attached. Not easy for me to photograph through glass of curved jar. p.s. When demonstrated to one of my teenage YL guitar students: "Cool!"
I admire the PowerPole range of connectors for their unique qualities but I find the nine pin Molex power cable attachment, with side clips, is superior for security as used by Icom, Kenwood & Yaesu radios. The rear of my radio is a rats' nest of cables so the PowerPole connector, mounted on the back panel, is vulnerable to partial / full disconnect when I change Morse key or aerial configuration... until now. I take a small cable tie and use it to secure the main power lead to auxiliary power lead via a Switchcraft phono plug. I like the Switchcraft because it is all metal that can be lightly squeezed to be good and tight. I've applied Tippex to the tail of the cable tie to aid identification when viewing the photos attached below. Any convenient lead e.g. data, aerial, Morse key, earth strap will likely suffice.
A while back the band I was in was late for a gig. It was all hands on deck connecting up but just before I turned my 100 Watt amp on... it's full output was connected directly to my wah wah pedal. Yikes! From then on I determined to blank off unused sockets with tape to reduce connection errors. But now there are 'jack caps' to the rescue. Both 6·35 mm jack plug socket and XLR dust plug protection sizes available. Although I have years of experience singing into a microphone I am quite microphone shy talking on the radio. I mostly use Morse code with straight key where I can chat away happily for hours. This means my HF radio microphone & electronic key sockets are rarely used. I don't like them sitting there vulnerable especially the eight connector pins exposed so I shroud them with a black jack cap XLR dust cover and yellow 6·35 mm socket plug as shown by attached photos. Although primarily a TX issue it occurs to me that SWLs using a TX/RX may find this useful if only receiving with no microphone connected. Search eBay: 'JACKCAP 6.3mm ¼ in XLR' or use the link below. BTW don't mix & match your microphones. Just because they have 8 pins doesn't mean they may be compatible. Damage may occur to the radio if you get it wrong.
Digi-Key offer free online conversion calculators for most electrickery needs methinks:
In response to Harry Leeming G3LLL PW page 24 December 2019 I have made myself a mains voltage monitor that doubles as a handy extension lead photos below. It features a detachable mains lead, a 13 Amp mains socket along with a useful USB socket to run my shack clock and an internal fuse mounted on the end panel. Harry is correct in that yes the mains voltage may exceed our somewhat naive expectations.
Harry Leeming G3LLL of Practical Wireless December 2019 offered most valuable advice to use fuses on the 12 Volt accessory socket of a transceiver. Mine's a RCA phono socket difficult to access from inside the radio and I only need a few milliamps so I chose two 6mm x 32mm 250 milliamp fuses as a compromise to fitting the fuse in the radio itself. These are mounted in an inline mains connector secured with silicone sealant but not on metal parts that the sealant may corrode. Photos 1 & 2 attached. This is not the most ideal situation because if a fuse blows there is some work to replace it but that is not likely I muse. Be prepared that the fuses will have an internal resistance. Norman G8ATO of Verulam ARC: "There will likely be a voltage drop across fuses. You can measure it with your meter." Attached photo 3 shows fuse resistance of 3 Ohms.
RF INTERFERENCE CURED
We must all ensure that our own environment is RFI clean first before despair. I say this because I was plagued with interference on 2m to the point that I gave up ever thinking it could be resolved. Then quite by chance I turned off the overhead dimmable LED light bulb in the shack whilst the Rx was on. The interference ceased immediately. So now I know to source a different light bulb possibly not dimmable and that is presently an Osram LED Star Classic A 100 11.0W = 100W Warm White. Problem solved. It's tiresome but we must check all our appliances for RF interference before proceeding off our premises.
Aerials in the loft.
If it's not possible to put your aerials outside, for optimum performance, then using the loft space may be better than nothing.
However you need to consider the construction of the loft. Grey slate tiles and especially aluminium backed roofing felt will likely diminish your RF signal to almost unusable.
In my experience clay tiles will only impede the RF from aerial in the loft space a little. Great for 6m, 2m, & 70cm. HF aerial works too but lack of space inhibits use of the lower bands. Also, protection from weather enhances maintenance free lifetime of the aerials. So there is a good side to all of this.
Magnetic loop antenna may be worth investigating but I've never used one. Beware of high intensity RF fields.
The only thing that I can think of that may ruin all your efforts is snow on the roof... maybe?
All should be considered before renting or purchasing your dwelling.
Then there is the most important point of how much power you can safely use in the loft especially if you have neighbours close by.
Here's a useful online calculator:
Free RF Safety Calculator by Stacey E. Mills W4SM that you can download to your Windows PC. I've used it on XP only. Written a while ago but adequate to give us an idea of where we're at. Scroll down the page for plenty of other useful information and software:
Although not strictly required by the laws of physics I use relatively thick white easily seen insulated wire (to avoid severe abrasion damage) for all my loft space aerials. I avoid blue, brown, black, red green, green & yellow wires that could be mistaken for mains electricity conductors. That way if a workman is needed he's less likely to say: "Sorry Guv, all those dodgy and bare wires... not for me." Not only that I keep my power to QRP.
Big headphones & fluffy microphones.
Roger Daltrey of the WHO rock band knew exactly what he was doing when he rolled up his jacket on the floor and rested a PA Public Address speaker on it at 45 degrees angled up to him. Now at last he could hear himself at a live gig. It's called side-tone. If the vocalists can't hear themselves they start to shout and that may ruin the performance. Even a traditional telephone has side-tone. You'll see artistes in radio and music studios with substantial headphones providing side-tone.
Ever noticed early Bee Gees footage with at least one of them holding their hand to their ear? That's an attempt at DIY side-tone. Early PA systems were just that. Equipment borrowed from a political party rally or football stadium. You can still see the 'finger in the ear' performer at traditional folk club gatherings. You place your finger tightly onto your ear and place the palm of your hand tight across your cheek as you speak. That way you will hear your voice in a most effective manner even if the surroundings are noisy. In a studio the vocalist may wear large headphones to use as a monitor.
As for the microphones they will usually be low impedance typically 200 Ohm dynamic moving coil for live stage use and condenser 48 Volts for studio use. THIS IS VERY IMPORTANT: Do not unplug or in plug or switch on or off power supply for 48 Volts condenser microphones whilst the rest of the equipment is operating as to do so will likely cause a loud crack noise that my damage your sound system or even the hearing of the vocalist wearing headphones.
If you've heard radio, TV or CDs in the last fifty years then you will most likely have been served at sometime by a Neumann U87 condenser microphone at 48 Volts. But why 48 Volts I muse. Decades ago Neumann were invited to install some condenser microphones in a Norwegian radio station. They needed a voltage to power the microphones. The in-house fire alarm was running at 48 Volts... so that was chosen and 48 Volts is still in use to this day but other manufacturers are now adopting 12 to15 Volts.
The Neumann U87 style of microphones will usually be supported in a spider mount to impede low frequency vibration noises and the grill of the microphone may have a spoffle (fluffy microphone cover) attached.
The other type of microphone that you may find on an amateur radio transceiver is a fist held crystal microphone. This cheap and cheerful equipment is ideal for general conversation on SSB or narrow band FM.
So whether licensed or SWL you will likely encounter microphones and may be tempted to buy a radio microphone. WATCH OUT: The law for the frequencies used by radio microphones changed a while back. This means that there are still some radio microphones available second hand that if you buy unwittingly will cause you problems with the authorities.
Nowadays most microphones for stage or studio use 3 way cable. Two insulated inners and a screen connected to XLR eXtra Low Resistance plugs & sockets originally for use by laboratory technicians for their reliability.
Then there's the fluffy cover placed over the microphone in a studio or outdoor interviewing. This is called a Dougal after The Magic Roundabout childrens' TV series for outdoor use to suppress wind noise and a spoffle for indoor studio use to suppress 'plosives from the vocalist. They both diffuses outdoor wind and indoor 'pop' noise from the vocalist.
If you watch BREXITCAST BBC1 now called NEWSCAST you will see the big headphones and fluffy microphones' spoffle.
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: https://tinyurl.com/leoradio
p.s. Subsequently I replaced series resistor 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.
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.
Whilst on the subject of the Shure SM57 USA microphone it was the almost always used for several decades for presidential use. Usually two mounted side by side. One for the room and the other for the press. The microphones were angled up to the president at 45 degrees. The 'plosive wind noise was sent over the microphone and the required vocal down into the microphone. It only changed when President Trump came to power and he now uses only one large microphone (straight at him) covered in a large grey foam pop protector which he actually touches which is something other presidents never did. Source: Various Internet blog pages.
Now we come to something really unsettling... counterfeits. Not always easy to spot especially if you are a newcomer to microphones also known as a transducer:
The most often counterfeited microphones are all
SHURE: SM57, SM58, BETA 58A & BETA 87A:
So those are my thoughts. Terms & Conditions? There are none. If you do copy/paste into your own e.g. website or magazine/newsletter then please link back:
Many HF communication receivers have a tiny speaker facing upwards. It's okay for brief listening periods but with my hearing in decline (tinnitus) I wanted something a bit more upmarket. At first I contemplated an extension speaker but they are either small and tinny looking or simply enormous fit for matching visually to extra large transceivers e.g. Kenwood, Icom & Yaesu.
So a sideways approach using my old music centre boom box as a stand alone amplifier with tone adjustment and plenty of relatively distortion free audio. The line output from the HF radio using shielded cable via 3.5 mm mono plug connects to the boom box via 3.5 mm stereo plug line input socket.
Attached photo shows the mono & stereo plugs. Clip on ferrites for good measure to protect from possible interference. The yellow tape I use to colour code my cables. Now we can listen to HF in reasonable quality audio. It has certainly enhanced my enjoyment of hobby radio international broadcast stations listening.
p.s. There are various cables and adapters on eBay but I found it easier to make my own connecting lead. I use an elastic band wrapped over the handle of a pair of pliers to act as a mini vice whilst soldering. So that's the basic minimalist version.
However, some line outs can be at a surprisingly high level and/or you might want to connect your receiver to a PC to use its speakers. To compensate for this consider to use an interface. From the receiver line out a 1:1 600 Ohm isolating audio transformer (about £3 off eBay). From there a 2.2uF (preferred value) capacitor and 22k Ohm resistor in series and 10k Ohm resistor in parallel all to protect your devices from unexpected transient voltages. Circuit diagram attached. The L pad resistance circuit will impose -10dB to - 12dB so the signal will sound half as loud. Component values are non critical.
If no line out then headphone out may suffice... be sure to keep levels LOW to start with.
The 2.2 uF capacitor stops DC flowing in the transformer especially useful if using lap top PC where DC is applied to the ring connection of the audio in socket. That voltage is there to power electrect microphone if needed. Connecting your receiver to a PC opens up a whole world of opportunities such as receiving weather broadcast images on HF and using 145.800 MHz (if you have a converter) slow scan television pictures from the International Space Station. Thank you to Norman G8ATO of Verulam ARC.
73 Bob Houlston G4PVB MA3053SWL
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