As an introduction, I started building Vertical & Yagi Beam antennas in the early 1980s for CB radio. When the FCC dropped the ‘Morse Code’ requirement in 2007, many ‘tone deaf’ people like myself, transitioned to ham radio. My entire family are either General or Extra Class hams. Having this license and operating ability is an essential ‘Life Skill’, like the ability to read, write and speak the native language.
No tool is useful, in unskilled hands – unless you’re planning on selling/bartering it away, right? Our family and I have taught Technician, General, and Extra classes – but, none of us consider ourselves Super Duper hams nor engineers, just dedicated hams. Show us a radio, and any one of us can get on the air, make contacts, work a Contest, pass mail, and train others to do the same. That’s what hobbies are about, having fun, bringing in others, sharpening the skills, and in the case of ham radio, or Distance Exchange (DX), like Short Wave Listening (SWL) – you’ll need to train your ears and brain to effectively operate / communicate / carry on a conversation. CB radio is Grade School, ham radio is High School.
In layman’s language, everything has a Resonant Frequency. Like a Tuning Fork, when struck, emits a certain Frequency of Sound, we want to image that in the radio world, both transmitting and receiving.
If the Antenna is cut / tuned for the right Frequency, then two things happen:
- It will ‘HEAR’ that frequency better than anything else, as well as the associated Harmonics (don’t worry about Harmonics, yet.)
- It will NOT hear unwanted frequencies as well – or NULL those, like being Deaf to the unwanted Frequencies or Radio Signals. (This is very, very important!).
Our goal is to build something that ‘gathers’ the radio waves that we want, and ignore or reject the junk & interference. Interference can be the neighbor’s pole transformer, your dishwasher motor, computer monitor, another close by station, anything that seems to clutter up your listening frequency. Sometimes that interference is a Harmonic, electrical, sometimes it’s your Coax Cable leading to the antenna, sometimes it’s just poor grounding – there are ways to clean that up too.
Okay, I live in Virginia, but I want to listen to 700AM, WLW from Cincinnati, Ohio. There are Appalachian Mountains between us – absolutely not a line-of-sight route. Or, WLS 890AM in Chicago… 750AM WSB in Atlanta? How can we get those signals? Several ways, via the Internet, or via the signal bounce off the Ionosphere layer (up in the sky, under most conditions), – or – via the ground (yup, radio waves can reach you via the ground!). What we want to do is take advantage of Signal Propagation, under good and/or bad conditions. An EMP isn’t the end of communications as we know it (EOCAWKI?) Another curious thing, Radio Waves will be absorbed by some objects and bounce off of other objects, even though both objects are made out of the SAME material? Back to Resonant Frequency!
Our ears hear frequencies from 20Hz-20,000Hz, that’s quite a wide range! Our Broadcast AM frequency ranges from 535,000Hz to 1705,000Hz (also known as Medium Wave, your radio dial probably has it as 540-1600KHz). SW (Short Wave… Oh, it’s a shorter wavelength, just above AM Broadcast, but we like to refer to groups of frequency ranges as ‘bands’ in ‘Meters’, which is actually the length-of-the-radio-wave. WHY!? Trust me, to build any antenna for listening or transmitting, the conversion to the Length of the Radio Wave, determines the Length of the Antenna… to make it resonate, receive or transmit effectively. Somehow… we need to match the signal being ‘sent’ (Broadcast) to our Radio (Receiver / Transceiver… a Transceiver receives & transmits), we need a “System” of a Radio, Transmission Line, and an Antenna.<
Fortunately, we can make the antenna resonate across a rather wide frequency range, by adding ‘stuff’ to it, changing it’s shape or putting other things close to it (coupling, which works FOR and/or AGAINST us.)
Let’s start with WLW 700AM, or 700Kz or 700,000Hz… or we’ll use this: https://www.unitconverters.net/frequency-wavelength/kilohertz-to-wavelength-in-metres.htm [1] Oh, that’s about 428.27 meters, the length of the Radio Wave. If you convert that to FEET, 1405ft. My goodness, that’s a really LONG antenna! How come we hear stuff with much smaller / shorter antennas? What if the Antenna is 1/2 a wavelength (1/2wl) or 1/4wl or 1/8wl – sure, that’ll work, and it’ll also match up to other frequencies… but, at least it matches to a ‘portion’ of that wavelength. Ever notice how tall those AM Broadcast antennas are? The whole thing is one big antenna. FM Broadcast antennas are much shorter, because the wavelength is quite short by comparison 88mHz-106mHz, it’s also much higher in frequency. Our 1405ft antenna is impractical, way too long, 1/4wl of that is just 351.25ft – hey, we can build that easily!
Just 351.25 feet of wire, hanging out the window, with “favor” or resonate at 700kHz best for our radio! Tie a short rope on each end, so it’s not touching a tree or house (gotta insulate, for lightning and a wet tree can become part of the antenna, even if the wire is insulated!). On one end of the 351ft wire, we attach the center of the Coax, the braid or shield that surrounds the coax, attaches to the ground. This is a long wire antenna. The antenna’s direction will vary with height, any angle, composition of the ground (rock is generally less conductive than clay or dirt). One thing to note, the wire between the coax and ground, does add to the overall length, which can be quite handy for shortening the antenna, to raise its Resonant Frequency.
The other end of the coax, attaches to the radio. Without getting too technical, the length of the Coax also has an effect on how well your Radio, rather your Transmitter will ‘Match’ or like the Antenna wire. Ham and CB Radios are built for a 50 ohm Antenna. A bedside clock radio, with the 2 screws on the back, likes to see a 300 ohm load / Antenna. Those little black things with 2 wires on one end, and an “F connector” (screws onto Coax), converts the Impedance from 75 Ohms to 300 Ohms. It’ll work without it, but it’ll work much better with it – besides, they’re cheap!
Now, 700AM will typically be the loudest signal on the AM band. We’re receive other stations, not quite as loud. If there’s a nearby station that’s overwhelming the radio, disconnect the ground wire. In my location, nearly 20 miles from any radio tower, we got a station around 530kHz, which is line-of-sight, and broadside to the Antenna wire… Yeah, it’s really strong. My options are limited by the Trees available to hang the wire, if I turned it, I’m sacrificing some of the intended signal, nuts! Several options besides reorientation, like narrowing the bandwidth of the antenna, sort of ‘sharpening’ the frequency it hears by increasing the NULL, deadening frequencies we don’t want to hear.
Okay, that’s an antenna suspended in the air, is there another way?
Well, a Vertical antenna, follows the same idea, 1/4 wavelength being a good place to start. At this point, you’ve probably realized the antennas ‘hear’ broadside, or off the sides best, but not so good off the ENDs. Bingo, that END is also the ‘deepest NULL’ where the wire antenna is nearly deaf. Then the antenna is capturing electrical energy out of the air, from the Broadcast source. The greater exposure to that Broadcast source, the stronger the signal – or the move voltage (power) is induced or picked up by the wire. We’re trying to capture Micro-volts of energy, which the radio receiver will amplify, decode and convert to Audio energy you can hear. The NULL for a Vertical antenna is also off the end, the tip, which points upward. The vertical hears best to the side, but NULL straight up… this is important to keep in mind with any Antenna. Like turning a Rabbit Ear TV antenna to get a station, or spinning a Table top Radio, we’re trying to orient the most amount of wire, pipe, structure broadside to the Transmission source.
Voltage, that’s what makes an Antenna work, give the receiver enough voltage, it has something to amplify, stick a bunch of ‘resistance’ between or into the Antenna and the Receiver has *less* voltage to work with. Naturally, you want a good electrical conductor, Silver begin the best, is expensive. Copper and Aluminum are pretty much equal, Steel and Iron suck, Stainless Steel, Chrome – horrible. Gold which is commonly used for “electrical contacts”, is not a good conductor, but, it doesn’t oxidize, like copper, aluminum, and silver. Why do those Telescopic, chrome-plated, antennas work? They’re so short, there isn’t a whole lot of accumulated resistance – and when compared to the antennas we described, there’s no comparison at all.
Litz Wire and Starlink and Repeater antennas, what do they have in common? All of them are multiple receive Antennas, with matching coax / spaced to a single point. Litz wire, commonly used on Tube TVs (the Yoke around the tube), and Older radios (looks like cloth, wrapped over a whole bunch of very skinny wires), increase the signal strength by folding the signal of each wire on top of each other, into a single point, the end which then connects to the receiver. 60 insulated wires, combined increases overall voltage. Starlink uses a similar technique, instead of a curved Dish, the flat antenna has hundreds or thousands of tiny antennas, all connected together to give a big signal from a very weak satellite (Dang! That Musk is smart!).
A Repeater antenna usually has 4-5-6 small loop antennas, and a special harness, every wire equal length so the signal from each antenna reaches the focal point at exactly the same time, producing a much stronger signal. You didn’t think that 5 watt Baofeng Handi-Talkie (walkie-talkie), really cranked out serious power, did you…? Why can you ‘hit and open’ a repeater 30-50 miles away, but can’t seem to talk to your hunting buddy 5 miles away…? It’s the antenna. Put your “Bad-fang” on one of those repeater antennas (with lots of loops), and it’ll make your buddy’s 5 watt signal like +100 watts. We’re collecting voltage, all we need to do is synchronize all the signals to a single point. This is important, because if the single point is getting signals out-of-phase, then the signal is cancelled.
Cancelled…? Okay, we set up 3 or 4 vertical antennas, identical lengths, and just randomly hook them up with Tee connectors, eventually back to the radio. Signals will come from all different directions, as normal, but because the vertical antennas are spread apart, one antenna is collecting a positive pulse, while the other might be collecting a negative pulse – add in the random Coax lengths, probably got some Cancellation.
(To be continued tomorrow, in Part 2.)