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Jonny 290
May 5, 2005

[A]sk me about OS/2 WARP


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.

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PuTTY riot
Nov 16, 2002


i read the whole thing and ur the best jonny

X-BUM-RAIDER-X
May 7, 2008


nobody wants to use 2.4ghz cos of water attenuation, not cos its wifi. wifi is just literally the only thing that can use 2.4ghz band w/o being terrible.

Silver Alicorn
Mar 30, 2008

I'll get to it eventually.


what's the deal with those needles they shot up into the ionosphere way back when

Phoning It In
Oct 17, 2010


i got a baypac from a yard sale hooked it up to a scanner & a dos palmtop & saw PACKETS just whizzing by i tell you it was something else

French Canadian
Feb 23, 2004

Quick Robin, to the Fatmobile!

every time i'm on a road trip and someone breaks out a handheld cb radio i never hear any interesting trucker chat. it sucks and totally ruins my illusions of trucker chat on the wide open road. what gives?

Jonny 290
May 5, 2005

[A]sk me about OS/2 WARP


I WANNA LISTEN TO THE COPS

You can probably still do this! But now that we have COMPUTERS, maybe not.

See, cops hate it when people listen to what they're up to. So, the past 20 years has been a long push for digital radio and encryption, accelerating greatly after 9/11. Digital radio is generally monitorable if it's not encrypted. If it's encrypted DONT EVEN WORRY ABOUT IT BECAUSE YOU WILL NEVER DECRYPT IT.

A good rule of thumb is that the more a police department humps encryption, the shadier they are. See, the 'if you've got nothing to hide you've got nothing to fear' works both ways. Encryption is not scrambling. Scramblers are easily defeatable and are a good indication that your local PD is both cheap and secretive.

Law enforcement and public services are on VHF, or increasingly UHF bands. It's all line of sight, local stuff. They use repeaters and linked networks just like hams to extend their range.

Your first step is to go look up your jurisdiction on http://www.radioreference.com/apps/db/

If the organizations that you want to listen to are using a "P25" system, that's the most common digital voice modulation these days. Generally monitorable.

"MotoTRBO" is a proprietary digital voice network that does not have commercial receivers out yet. You have to hook a laptop to a radio and do some hacking. Pain in the rear end, but doable.

Generally all other transmissions are going to be able to be listened to, with a few exceptions.

You will also see references to 'trunked' and 'conventional' systems. Trunking radio systems basically add a layer of abstraction between the user and radio network, so that each radio has logical channels, or 'talkgroups' on it. These do NOT correspond to actual frequencies, and radios may hop frequencies between transmissions or even in the middle of one depending on how it operates. However, the radios and base stations are all communicating digitally to keep the talkgroups straight, so that if your radio is only set to police dispatches, your radio won't pick up the fire department. Conventional systems use the old school method - Police Dispatch is on 460.025, Police Tac is on 462.225, whatever. You tune the radio to talk to the people you want.

Almost every scanner can decode and follow trunked analog systems. Trunked P25 systems require a scanner thats a couple hundred more (99% of the price difference goes to IP licensing royalties for the voice decoder chip - the actual tech is trivial).

My main scanner is a Uniden BCD396t, decodes P25, PC programmable, built like a brick shithouse. I bought it november 06 and it has been rocking every day since, and I'm not exaggerating that - probably on my 12th set of NiMH AA's. I have a couple Radio Shack shitscanners too that I use just for particular systems, and the VHF/UHF ham rig in my car tunes in the public service bands too, so I can do limited monitoring on that as well.

MALE SHOEGAZE
Oct 1, 2002

Centered for your health.



i dont know anything about radio but i come from a radio family. my grandfather was a big dj back in the 40s/50s/60s/70s and he'd entertain all kinds of celebrities when they came to california (including jonny cash. i guess my mom brought him some 'brown paper bag' full of 'things' to his hotel when she was like 9. also her name is sue)

anyhow he also had a brother who was broadcasting from the top of the honolulu tower (or some poo poo) during perl harbor!! wow. he's not the guy on the most famous broadcast

i dont know where all those social skills went because i certainly didnt get them

Phoning It In
Oct 17, 2010


prob going to take the ham nerd test so i can send PACKETS of my own

is aprs for serious location/weather data only or can i have a beacon that just says "sup text me"? this 200lx only has one com port soooooo

MALE SHOEGAZE
Oct 1, 2002

Centered for your health.



USSMICHELLEBACHMAN posted:

i dont know anything about radio but i come from a radio family. my grandfather was a big dj back in the 40s/50s/60s/70s and he'd entertain all kinds of celebrities when they came to california (including jonny cash. i guess my mom brought him some 'brown paper bag' full of 'things' to his hotel when she was like 9. also her name is sue)

anyhow he also had a brother who was broadcasting from the top of the honolulu tower (or some poo poo) during perl harbor!! wow. he's not the guy on the most famous broadcast

i dont know where all those social skills went because i certainly didnt get them

another funny story about my grandfather: he got cancer and died before i was born

MALE SHOEGAZE fucked around with this message at Feb 21, 2014 around 19:57

Stereotype
Apr 24, 2010









Ground floor.

I actually know about radio stuff too and like reading about it.

Jonny 290
May 5, 2005

[A]sk me about OS/2 WARP


French Canadian posted:

every time i'm on a road trip and someone breaks out a handheld cb radio i never hear any interesting trucker chat. it sucks and totally ruins my illusions of trucker chat on the wide open road. what gives?

It's a piece of poo poo! Specifically, the antenna. Radio's as fine as any other CB in that price range.

Wavelength at CB is 11 meters (actually "11 meters" used to be a ham band, and hams still refer to CB as 11) so a quarter wavelength is just over 2.5 meters - this is the reason for the big rear end 102 inch CB whips. As your antenna size goes down, so does performance, and it becomes more finicky about tuning. Those rubber duck antennas on the handheld CBs are basically just resistors - barely antennas at all.

I have one of those handhelds in my car (Cobra HH 38) and it works fine when I hook it up to a proper antenna. Right now I don't have a dedicated antenna for it, but that's going on in the next couple of weeks (if I ever get sick of CB I can retune the antenna to use it on the 10 meter ham band).

Stereotype
Apr 24, 2010









I actually have that EM spectrum poster hanging in my office, so does my adviser. It is great for figuring out what exactly the source of the pickup is on our super sensitive instruments.

MALE SHOEGAZE
Oct 1, 2002

Centered for your health.



(and sorry for making GBS threads up your thread jonny i'm done now)

Stereotype
Apr 24, 2010









Here is a fun list of cooler antennas than dipoles and quarter-wave stuff.

http://www.antenna-theory.com/antennas/main.php

We just started using something like a log-periodic spiral antenna and it looks like it is from the future

Jonny 290
May 5, 2005

[A]sk me about OS/2 WARP


Phoning It In posted:

prob going to take the ham nerd test so i can send PACKETS of my own

is aprs for serious location/weather data only or can i have a beacon that just says "sup text me"? this 200lx only has one com port soooooo

Nah guys use it for other random stuff too. It's not really two-way chatsville, but they won't hunt you down if you put a "email to blah@gmail.com" type thing in there. Now that I have a spare 2m radio, i'm going to set up an APRS node with a raspberry pi, i think.



---

DID YOU KNOW? The most hated, reviled troll on the 20 meter amateur band.....is a canadian?

meet karol madera, VE7KFM

http://www.youtube.com/watch?v=BGwwIJ6sQao

Stereotype
Apr 24, 2010









I just bought this too:

http://www.amazon.com/gp/product/B0...0?ie=UTF8&psc=1

Gonna see if I can use it as an SDR

Stereotype
Apr 24, 2010









Sorry for posting so much in your thread Jonny I am just so excited. You are great and cool etc.

Jonny 290
May 5, 2005

[A]sk me about OS/2 WARP


Nope, spam away. im trying to find good youtubes and getting some drafts cleaned up

im sure it'll pick up after a bit

Werthog 95
Nov 21, 2006

windows 8 is fine


dear pagancow, if your drat cat5 thread is worth a sticky, so is this

5d and subscribed

Jonny 290
May 5, 2005

[A]sk me about OS/2 WARP


i'll try to do some little sub-focus things

QRP

QRP is the international code for "reduce power". Hams in the US are allowed to transmit on most bands with up to 1500 watts of radiated RF power, with no limits on antenna gain. however, the technical wording of the law is that we are allowed to use "the minimum power necessary to communicate, with a hard limit of 1500 watts power". This isn't a strictly enforced law, more of an agreement to keep excess unneeded RF off the bands. However, some hams take this as a technical challenge, and practice QRP operations - turning the power as low as they possibly can, and using operator skill, efficient modes and good antennas to make up the power difference. The brag number is just distance divided by power output, miles per watt. If you're transmitting more than 10 watts, you are not QRP.

here's a video of a guy on the 40 meter band making some single-sideband (voice) contacts with just a few watts of power.

http://www.youtube.com/watch?v=GvBVbZBHPX4

"QRPp" specifically refers to the hardest core of the weak signals. You can't claim QRPp unless you are putting out less than one watt.

And here's a guy using a 450 mW transmitter communicating between SC and NY, giving over 1300 miles per watt of power.

http://www.youtube.com/watch?v=-SxxKCN6oXY

PuTTY riot
Nov 16, 2002


kinda unrelated but if i want to be able to charge my radio/phone/whatever in an extended outage is a 12v deep cycle marine battery in the garage plugged up to a battery tender gonna suit my needs? do i need more than alligator clips to connect to my inverter or is there a better (and safe enough for an ihpone) way to do DC charging w/o involving inverters?

Jonny 290
May 5, 2005

[A]sk me about OS/2 WARP


If your radio can eat 12 volts (automotive systems generally run on 13.8 volts peak but we refer to it as 12v nominal), you can just hook up directly. For low current stuff, just clips or clamps to the battery post is fine. If you need 5 volts or 6 or something like that to the radio, you can get a little converter board. Marine battery has about 100 amp-hours of storage (it's a product, higher amps mean less time and vice versa) so if you radio draws about 2/3 of an amp at 12 volts, it'll run for a week straight more or less.

Phoning It In
Oct 17, 2010


some rechargeable stuff like power tools don't play well with cheapo auto shop inverters but most laptops and home appliances have enough circuitry or whatever between the inverter and the battery to handle it safely

Mr. Nice!
Oct 13, 2005

I'd fuck on the first date but truckers usually just want their salads tossed

Also



this thread loving owns

EMILY BLUNTS
Jan 1, 2005



Who started calling the little stubby antennas "rubber duck" anyway?

weede catte
Dec 23, 2010




Jonny dis thread is rad but what about yosbbs?

Bloody
Mar 3, 2013



software defined radio is really cool but gnuradio is a steaming heap of poo poo (obvious from the "gnu" in the name, but)

thats my radio contribution, cya

Jonny 290
May 5, 2005

[A]sk me about OS/2 WARP




Say hi to OSCAR. This Orbiting Satellite Carrying Amateur Radio was launched in 1961 and simply transmitted "HI" in Morse code (easy cause it's only dits, no dahs) in the 10 meter band. Over the next 22 days (until it deorbited), thousands of hams worldwide excitedly tuned in to provide reception reports of the very first amateur radio satellite.

Over the next 53 years, we launched over 130 satellites with various transponders, repeaters, and beacons. During the 80s and 90s, a great deal of energy was put into the satellite program, and this is generally considered the Golden Age. In the late 80s through mid-90s, we had several satellites in orbit, giving virtually complete earth coverage, including a few High Earth Orbit satellites that had a very elliptical orbit. At apogee, these satellites would hang out on end of orbit for hours at a time, giving line of sight coverage to almost 40% of the earth and staying in a relatively fixed location in the sky. I never got enough equipment ready fast enough to operate these birds, but the stories abound about long extended chats between opposite sides of the Earth.

Sadly, funding and interest has dropped significantly. we no longer have any high-orbit satellites, and only a handful of birds active, all in relatively low polar orbits. However, it is still an exciting specialization, and teaches a lot about astronomy, physics, and engineering. Doppler Shift becomes a very real concept once you learn that you have to tune two radios at the same time in opposite directions!

Low earth orbit ("leo sats") have rapid polar orbits, basically letting the earth rotate under them as they orbit north-south-north over the poles. Their altitude at 600-800 miles means that each spot on earth generally gets about two to three usable orbits (passes) during a session. Each pass gives about 16-20 minutes of usable communication. Basically, if it's over the horizon for two people, they can talk on the satellite. Contacts are fast and general "hello, here's your signal report, ok signing off" to avoid hogging the bird.

Low earth orbit birds are easy to hit with a simple antenna and radio; you can get started with a handheld, even. Believe it or not, you can get full scale signals from a solar powered satellite on VHF/UHF with a handheld antenna, quite simply because it's line of sight! People (like me) often do build higher-performance stations, with directional antennas that can not only be turned horizontally (azimuth) but have elevation rotators to aim them above the horizon. Then you wire up some computer control interfaces to your rotators, fire up your satellite tracking program, and let your software tune the radios and point your antennas. it's pretty bad rear end.

I really hope that in the next few years we have a resurgence in interest in satellite in general - it appears that we are getting a steady volume of the low earth orbit birds up - but I'd really like to see us get high orbit satellites up there again. I've specialized my radio purchases towards units that have good performance on the best satellite bands,and can use the special modes and features that are required for the high orbit birds. My vintage Icoms will be ready.

Jonny 290 fucked around with this message at Feb 22, 2014 around 00:26

Fax Sender
Aug 11, 2013

kiss my ass


I have a cobra 45wx. it is a handheld cb. can I and should I hook it up to a real antenna?

Jonny 290
May 5, 2005

[A]sk me about OS/2 WARP


Oh, I forgot the funniest ham satellite


http://en.wikipedia.org/wiki/SuitSat

HEY
WE GOT AN OLD SPACE SUIT FROM RUSSIA

WHAT SHOULD WE DO WITH IT?

LETS PUT A RADIO ON IT AND JUST PUNT THAT MOTHERFUCKER OUT THE AIRLOCK



it only worked for a couple months, but you could receive transmissions from a space suit. cmon.


Fax Sender posted:

I have a cobra 45wx. it is a handheld cb. can I and should I hook it up to a real antenna?

Possibly! Do you want to run it in the car or check it out at the house? i have antenna recommendations for both situations. also advise if you'd be willing to diy/solder as it means your first experimentation can be sooooper cheap

ANIME MONSTROSITY
Jun 1, 2012
Probation
Can't post for 4 days!


i bet u r on the spectrum

Fax Sender
Aug 11, 2013

kiss my ass


i love to diy, and idk, i'd probably use it more often at home than on the road. i take it on trips only, not every day driving

julian assflange
Jul 29, 2010


I note that the ham radios in Fallout 3 rarely work, if at all.

PuTTY riot
Nov 16, 2002


Mr. Nice! posted:

this thread loving owns

julian assflange
Jul 29, 2010


In all seriousness I wish I was as in to something as much as 290 is into radio and soldering

Pewdiepie
Oct 31, 2010



julian assflange posted:

In all seriousness I wish I was as in to something as much as 290 is into radio and soldering

Solder your rear end into your rear end.

Jonny 290
May 5, 2005

[A]sk me about OS/2 WARP


Fax Sender posted:

i love to diy, and idk, i'd probably use it more often at home than on the road. i take it on trips only, not every day driving


alright, to get any sort of usable signal into that thing, you're going to need an external antenna. For now let's set something up at your home QTH (location) and see what we can pick up!

So, the very simplest real antenna is the dipole. Two metallic thin elements a quarter wavelength each in length, pointed 180 degrees away from each other and fed from the center. This antenna has 75 ohms free-air impedance which provides a reasonable match to the 50 ohms that most radios expect. Just look at the numbers for now, dont worry about what impedance actually is- we'll hit that poo poo way later. Closer numbers = better for now.

Now, what you can do is take one element, and instead of having the mirror element, feed it against a counterpoise as I mentioned in the OP. This can be the earth itself, a resonant ground plane (star or cone shaped array of 1/4 wave metallic elements), a car body, basically anything RF conductive and big. Tin roof? Holy poo poo what a ground plane. Long metal gutter? Not bad. You now have a monopole antenna.

CB largely operates with vertically polarized antennas - elements pointing up and down. So, what it comes down to is that you're going to need about 17 feet of vertical antenna, OR about 8.5 feet of vertical antenna right above some sort of ground plane. However, antennas like to be higher up off the ground if possible, so it's not really helpful to put up an 8.5 footer mounted at ground level. Much better is to mount it up in a tree or on your roof, up as high as possible, and use some counterpoise wires maybe stretched across the roof or even just hanging down from the tree limb.

From the center of the antenna, you're going to need to run a coax cable feedline into the house to the radio. Length is not SUPER important at CB frequencies, but you still want to keep the run as short as possible. Lower-loss coax is WAY pricey and like a half inch around, so you want to try to keep the run to less than maybe 50 feet or so.

In that context, do you have some sort of tree that you could throw a rope over, or a roof that you're comfortable with climbing on? If we can get a 1/4 or 1/2 wave antenna like 15 feet off the ground or so, you are virtually bound to hear anything going on in a few mile radius, and you might be a lot luckier than that.

Jonny 290 fucked around with this message at Feb 22, 2014 around 01:01

Pewdiepie
Oct 31, 2010



My favorite things about the radio are Macklemore, Jayson DeRulo, Ke$ha, and Pitbull.

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theadder
Dec 29, 2011




PuTTY riot posted:

i read the whole thing and ur the best jonny

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