- BONGHITZ
- Jan 1, 1970
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in this thread we discuss everything involving those wonderful ways in which humanity hurls epithets at each other via the invisible magic of RADIO WAVES
you've got questions? we've got really wordy answers typed by a guy that probably likes radio stuff a little too much
focus on ham/scanning/shortwave but we cover all the waves in all the spectrums
"the spectrum?"
yep. the spectrum. 
Electromagnetic waves (we'll call them radio waves) all have a period of oscillation which is inversely proportional to their frequency. They travel pretty much at the speed of light in a vacuum or air, so we often refer to a particular frequency range based on how long one wavelength is at nominal c.
300 Mhz is one meter. 50 Mhz is six meters. 440 Mhz is 70cm, you get the idea.
"what's this 'shortwave' stuff?"
The terms 'shortwave' and 'HF' or 'high frequency' are interchangeable.
reframe your context to like 1920 or so. everybody's starting to mess with radio, but the tech sucks so bad that they can only operate on a few hundred kilohertz. Wavelength here is long, on the order of miles sometimes. Then they got better equipment and could transmit on higher frequencies. Thus, 'shortwave'.
The shortwave band is the band that is most strongly affected by YE OLDE IONOSPHERE. These frequencies have wavelengths that treat the ionized layers of the ionosphere as a mirror, more or less. If you are on Earth, and send a signal to the horizon, it'll eventually bounce off that ionosphere and head back towards the Earth, pretty far away.
The ionosphere is almost 100% affected by our friendly little yellow nuclear fusion reaction in the sky. Specifically, sunspots. Basically, as the sun comes up over an area, lower layers of the ionosphere are 'activated' by solar energy, which basically brings your mirror closer to Earth, shortening propagation. As the sun sets, these layers dissipate and your mirror rises again. You can once again talk to Europe from the US!
The higher the number of sunspots, the stronger propagation gets. These ebb and flow on a roughly 22 year cycle. Right now we are right around the peak of a somewhat-lackluster solar cycle, but conditions are still pretty good. Around 2018, my shortwave radios will probably go into storage for five years during the solar minimum.
The main appeal of shortwave is: the ionosphere. You can bounce poo poo over the horizon, and if you're lucky it will bounce again off the earth and back up into the ionosphere. You can get allll the way around the world with this (and matter of fact, if conditions are right, you can briefly transmit and hear your echo about 90 mS later after its gone all the way around the world.)
The main disadvantage of these bands are that antennas are large, and propagation is inconsistent. Monday might be gangbusters, then the sun sneezes and the next day you can't hear a god drat thing.
Now, as you go up in frequency, the waves stop bouncing off the ionosphere. however, they start to become better and better at point to point transmission in free air. This goes allll the way up to visible light and beyond (yep, light is this same energy, just at really high frequencies. You got antennas in your head) Also, shorter wavelengths are attenuated less by obstructions, to an extent.
So, if you don't need the range boosts from shortwave propagation, or if you can't fit a big antenna, and you just need local coverage, you go up in frequency. 100 Mhz is your FM radio. 150-ish used to be the primary law enforcement band. Then for a while the cops moved to systems around 460 MHz, and now the most common systems run around 850 MHz or so.
Engineering challenges go up as your frequency does. It's really easy to build a 1 MHz transmitter - it's really hard to build a 1 Ghz transmitter. Tolerances are low, precision must be high.
"what the hell is an antenna, anyways"
A piece of metal. that's it. As radio waves pass through an antenna, they induce an alternating current between the 'halves' of the antenna. This voltage is transmitted by your feedline, which can take many forms, into your radio receiver. The exact opposite happens on transmission - your radio produces a voltage, it is presented to the antenna, and the antenna takes that energy and converts it into radio waves - the better tuned the antenna, the better it does its job.
If the piece of metal has dimensions such that it is 'resonant' at the frequency of the waves, its properties will reinforce and enhance the voltage presented at the feedline, giving you a stronger signal. If it's not a resonant length, it becomes more complex and could possibly work well, or possibly be awful.
"you talked about two halves. But my car antenna only has one piece!"
Not quite. Your car antenna uses the vehicle as a 'ground' reference. It's not actually connected to the earth, but it is a big enough piece of metal that it will also pick up the radio waves and be the 'other half' of the antenna. This concept is called a 'counterpoise'.
This translates to fixed antennas, too. Those big AM broadcast antennas use the earth as a counterpoise. In order to effectively do this, you usually lay down a network of ground wires, directly on or in the earth, and use that as your counterpoise. There is a LOT of copper in a broadcast antenna's field.
"What's HAM radio?"
First of all, not an acronym. it's just ham radio.
I will take a US-centric view, as I am a US amateur operator. Just to get this out of the way, I was first licensed 23 years ago at age 11, and held a Technician class license with limited HF privileges until 2007 until I upgraded to Extra, the terminal license class. These are on a ten-year renewal and do not require retests, so i will be an Extra until I die.
In the early 20th century, the vast majority of technical advances in the new radio field were by non-professional experimenters playing with spark gaps and big coils in their garages. The government realized that the 'amateurs' were contributing a lot of help to the new tech, and allocated them specific frequency ranges in which they could talk to each other. To preserve the economic appeal of official licensing and regulation, all commercial traffic was banned. This provided basically a safe area free of high-power commercial broadcasters where guys who just liked to tinker with radios could put them on the air and talk to other tinkerers.
Over the past 100 years, hams have provided a lot of technical advancements to the radio art, and this continues to this day. Hams brought the world single-sideband transmission (greatly enhances long distance shortwave), moonbounce (literally bounce a signal off of the moon), various digital modes of transmitting information, and so on. The trend continues, with a lot of software-defined-radio development being done in the ham radio world today.
To ensure we have the ability to be proficient in many styles of communication, hams are allocated a wide variety of allowed bands of operation across the spectrum. Here's a real quick breakdown of what each major band is really like:
- 160 meters (1.8-2.0 MHz) - HUGE antennas. A quarter wave antenna here is 131 feet tall. Only the finest gentlemen operate here, there is a high standard of conduct and the circles are tight-knit. Many old guys use converted decommissioned AM broadcast transmitters. Referred to as 'Top Band', again a nod to when we measured things in wavelength instead of Hertz.
- 75 and 80 meters (3.5-4.0 MHz) - Used to be two bands, now is one big one. Atmospheric noise is high but medium-range (500-2000 mi) propagation is great at night. PACKED TO THE BRIM WITH RACIST GRANDPAS. Antennas are still big here, so the biggest signals you hear are the retired engineers who could afford to buy 200 acres of Kansas farmland and put huge towers on it. They have the expected political views. Seriously, this is the new CB radio. Stay off 75 meters. It's a cesspool.
- 40 meters (7-7.3 MHz) - Propagation is farther but less consistent than 75/80 meters. The main problem here is that there is a major shortwave broadcast band that co-exists at the top end of this range, and Radio Moscow can wreck like 20-30 KHz of spectrum when it's coming in strong. This is also used for local communications to a certain extent.
- 30 meters (10-10.15 MHz) - My favorite shortwave band. Why? YOU CAN'T TALK ON IT. 30 meters is a digital-only band, across the world. You won't hear anything but beeps, boops, squawks and squeals on here. It's guys chatting! Hook your radio up to your soundcard and watch the conversations fill your screen.
- 20 meters (14-14.35 MHz) - This is a cool band, as atmospheric noise is lower and propagation actually develops during the morning and through the early afternoon. Antennas are starting to come down to a reasonable size, and you can get some good signal out. However, there are small slices of this that host some absolutely legendary abusive operators, and you can tune in to hear them scream about communism and Obama. Still, most operators are good guys, and 20 meters is worth getting set up for.
- 17, 15 and 12 meters (around 18.1 Mhz, 21 MHz and 25 MHz) - these are lesser-used these days but in times of solar maximums can give you both good local propagation and some good ionospheric 'skip'.
- 10 meters (28-29.7 MHz) - Pretty popular - it's right next door to CB so they share a lot of propagation aspects. Lots of local, lots of worldwide at solar maximums. Tons of spectrum, so it's easy to spread out - or easy to miss somebody transmitting.
- 6 meters (50-54 MHz) - the first "VHF" band. Has properties of both line-of-sight bands and the higher HF bands. Not really popular except among guys that specifically like 6 meters.
- 2 meters (144-148 MHz) the most popular amateur band of all time. Antenna is about 19" for a quarter wave. Used radio is 30 bucks. Here is where you start to see 'repeaters' which are just strategically located relay stations that listen on one frequency , and retransmit whatever they hear on another. Your radio listens to the repeater's transmit freq, and transmits on its listening freq. Some guys network repeaters using telephone lines or (more commonly now) VoIP links, enabling you to talk up to a couple hundred miles on your little handy-talkie (we don't call them walkie-talkies).
- 70cm (420-450 MHz) - Becoming more and more popular every day. We can make better radios now, and these bands have decent penetration in semi-urban areas, leading to less fading and dropouts. Repeaters here are heavily networked due to slightly shorter range, and 2 meter repeater networks often use 70cm backhauls to connect their machines.
Above here is still kind of experimental.
- 33cm (902-928) - kind of dead except in super urban areas like Boston. Nobody makes ham rigs for this band so everybody hacks up surplus 860 MHz cop radios. hacker poo poo.
- 23cm(1296 MHz) - Another urban band, more popular than 33cm but the issues of short wavelength start to rear their head here. You gotta keep your connections short and solid. Often used for satellite work.
- 13cm (2.4 Ghz) - yeah bitch, we got spectrum right below the Wifi band. Except we can use up to 1500 watts of power. Just can't transmit Goatse or Bitcoin.
there are a bunch of microwave bands, and last I checked, amateurs were actually given exclusive use of all frequencies above 300 GHz. Anybody using the 902 mhz bands or higher is a GUARANTEED NERD and is likely a much better RF engineer than you or I.
"You mentioned CB, how's that doing?"
Weirdly. it's kind of fun to hear truckers and such, but everybody runs illegal power now through dirty transmitters, so the band is full of distorted shouting rednecks hitting sound-effects boxes and trying to make their neighbor's TVs blow up. It's basically the fyad of radio. We'll get more into CB on some later posts.
OP is getting big and fat, so I will wrap this one up with a quick list of what I have done with radio so far:
-Been the fourth youngest licensed amateur in North Carolina at the time of my licensing
-Won an award for being a coordinator for a ham-radio based score reporting network at a national soccer tournament
-Talked to the bass player from .38 special and Ronnie Milsap (both famous hams) as they toured through my area
-Said hi to astronauts on the ISS and cosmonauts on Mir
-On a camping trip, hooked a laptop to a battery powered HF radio, threw a wire in a tree and basically IRC'ed with South Africans and Europeans
-Used VHF and UHF bands to speak to hams in Vancouver, California and Michigan - by using low-earth-orbit satellites
The last item is my current obsession, and we will be talking more about satellite communications soon.
this weekend i'll try to get a good camera setup and maybe we'll have a youtube or two of what you can listen to, who you can talk to and what it's all about. We'll also cover scanners, commercial shortwave and other common ways you can snoop on invisble energies to figure out what they're ordering at the nearest drive-thru.
lotta words here
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Feb 25, 2014 09:23
