Episode: 756
Title: HPR0756: Basics of RF
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr0756/hpr0756.mp3
Transcribed: 2025-10-08 01:57:47

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Welcome to Hacker Public Radio. Today we're talking about the basics of our...
Hello and welcome to Hacker Public Radio. Today we're going to talk about radio
frequencies and radio. How does it work? My call signs W3 are AZ and I'm also
known as Gorkon from the Linux Link Tech Show. Can graciously has allowed
well a lot of us to actually put shows out on Hacker Public Radio feed and he
actually asked a question if I can cover it and I want to try and cover this to
the best of my abilities and that is what is RF exactly? What's radio
frequencies? How does it work? And some basics that you may need to understand if
you decide to go and take the Emature Radio exam. Now the next show I record I
will detail from the US aspect on what you need to do to get your
Emature Radio license. So first off what is radio frequencies or what is radio?
Well if you see a light bulb near you or a television or anything that
produces light you're actually looking at radio. Now what do I mean by that?
Well radio quite simply is an electromagnetic transmission that is
radiated from antenna. I'll get to more about some of that as we go further in.
So what happens is radio frequencies radio is essentially light. That's why
you know it is also guided by the speed of light. Your transmission is not
going to go any faster than C or the speed of light. Now getting a little bit
deeper into the physics than I wanted to but basically that's really what it is.
And how they ended up coming up with radio remember I talked about spark gap
transmitters and basically all they had to do was turn a sine wave on and turn a
sine wave off. That's really all they did and Morse code was decided by short
sine waves and long sine waves. So it's a combination of those that make up a
character. So it's really that simple. Now the way a phone or conventional radio
that most people are used to is how it works is you have like a microphone
which a microphone is essentially the same thing as a speaker. It's definitely
not exactly the same but it's essentially for all types of purposes is. There's a
diaphragm that vibrates as you talk and moves back and forth as your voice
comes out of your mouth and then translates that into a electrical signal. Now
in radio at least conventional one methods of radio that we're used to most radio
is analog. Now there is digital radio and I'm not gonna get too far into that
because I really don't have any of those but it operates in the same principle. How
it vibrates its diaphragm is different. So with radio what happens is that
signal that you're getting from a microphone will then do what we call
modulate a sine wave. Now most people have heard of what AM and FM. Those are both
forms of modulation. Modulation can occur in pretty much two different modes. First
one that was first invented was amplitude. So basically what happened is the
sine wave would be modulated in the amplitude of the signal. By amplitude I mean
that the louder your voice would be the bigger the sine wave the lower your
voice would be the smaller your sine wave. And the sine wave that you're
modulating is what's called a carrier. Now in the bandwidth terms when you look at
an AM signal it actually is very wide compared to the next one I went out
about which is single sideband. So an AM signal is essentially consists of
what they call two sidebands. And because radio spectrum is finite in most in
the basic sense of the term it's finite. There's only so much radio spectrum that's
usable. And I say usable because the spectrum actually is infinite but you can't
use for worldwide communication you cannot use high frequency like a
microwave frequency. It's not going to work on why that is I'll get to that later on in
the episode here. But sideband was invented because the AM signals took up
so much space. So they basically locked off a sideband either the upper or the
lower. And then that's how they were able to conserve bandwidth and let more
stations use the spectrum that was given. Now there's a lot of physics involved in
the circuitry and the superheterodine receivers and all that stuff. But I'm not
really getting into that. I'm talking very basics. If you want to get deeper into
this you're going to have to go do some of those sites I want to hopefully have
some sites to pop in the show notes. And you can go ahead and check those out.
So now the next mode is a mode that or the next kind of modulation is what most people
listen to now if they listen to radio especially if you're listening to music and
that's frequency modulation. So basically your voice then modulates the frequency of
the carrier. Now you actually have really I don't only think there is a upper sideband
lower sideband the probably is but we usually don't worry about that on that
sound because you're usually using where I use FM most commonly is on the VHF or very
high frequency band that's a two meters any amateur radio or UHF in that 70 centimeters.
So but that's the basics of both amp to the food and frequency modulation and a little
bit about sideband single sideband. So essentially in a voice mode that's your voice is modulating
that carrier. The carrier is cycling and they actually in the old days of my grandfather they
actually used to call that like a instead of a killer hurts or megahertz it's called a killer
cycle or a mega cycle. So then Heinrich I think it's Heinrich anyway. Mr. Hertz then discovered
some things and then they named it after him. That's why it's called megahertz. Anyway
so your carrier is cycling at the rate that you tune your your transceiver to. For example
if you're talking to a repeater that receives on and I'll get in the repeaters in a bit
if it receives on 147.24 or 147.24 megahertz that's your carrier. Now your voice is going to
actually go beyond that that's where what they're where the side bands come into play there.
So I just wanted you to understand that even though you are tuning at 147.24 you're not actually
only passing your information on that frequency you actually expand past that. So
you know that's why a single side band was invented just because like I said it allowed more
people to use the given frequencies. So now one little sidebar here I'm actually recording this
for the handheld recorder as I walk along to the bus stop this morning and I just wanted to give
you a reason why why I'm doing that. As emergency communications is part of amateur radio
we often have to work in conditions that are not ideal. We often work you know on the side of road
or out in a rain in a camp whatever you know excuse me anyway that's why I decided to record
this episode with the handheld mic and why I will record some future episodes. I try not to do too
many of them because I know that the noise can be a little distracting but one thing I do want
you to know is why emergency communications is at the forefront of having an amateur radio license
and it should be one not the only reason you get your license you should have fun doing it too
but it should be a big reason you know I want to have a good way that you you as a hacker or a geek
and serve the community amateur radio is the perfect hobby to serve the community.
A lot of times people won't understand what us hackers worked on but they do understand you
being able to hook up a desperate person who's lost their relatives
Satan, Joplin, and Zuri with Tuscaloosa, Alabama they can
the amateur radio operators can hook you up for those and get this important status messages
in and out of the area so cybar over so back to the basics of radio frequency.
So talk to a little bit about MFM what in our single is so let's talk about what you need to
actually transmit one and detect one now most most people now instead of buying just a receiver
just a transmitter will buy a transceiver transceiver does exactly what you would think
it's a combination of transmitter and receiver so that's why they call it a transceiver because it
can do both now each aspect of a radio is different receiving aspect is definitely a little bit
different than the transmitting aspect but in the basic sense of the term this is actually not all
that different so for for a receiver you need far less attention to some things that you do
a transmitter now a critical piece is the antenna now for receive antenna you don't really
need to have an antenna that is tuned to the receiving frequency it helps but it's not really
needed you can attach your radio your receiver to a piece of metal and that will act as an antenna
and absorb the radio frequency and convert that to audio and essentially the opposite method
of you converting your voice to an RF wave so a receiver basically will use that antenna
to absorb and pick up the received frequency produces it audio it's a very basics a very simple
receiver is if you if you ever if you're my age I don't know if they do this anymore but if you're
my age one of the things you might have done in science class was build build a crystal radio
the crystal radio is a very simple receiver it consists of mainly of three parts a earphone
a coil and actually four parts a earphone a coil a diode and an antenna the main circuit
in question here is the diode well it's not really a circuit so much as it's a component
but the diode is at the very central eight when you combine it with the coil which is an
is an inductor special inductor it has to be you have to have access to the coils because that's
how you're going to tune the radio okay and without those other parts that diode can't do its job
but you don't even need a battery with a crystal radio because basically what happens is
the antenna picks up the RF and then the diode converts that to an electrical signal
that then vibrates the earphone so if you want some like a fun project that you can do a very
simple project that you can do with your kids look up how to build a crystal radio now I can see
if I can put a link in the show notes but yeah crystal radio is a very crude receiver
and it doesn't have the what they call selectivity of a modern transceiver selectivity means
you are only concerned with the signal that's modulating around the carrier that you're tuned to
and you want to reject anything else so more selective radio is the more sensitive it is to
picking up weak signals so what is needed for a transmitter well basically the reverse of a receiver
you need a microphone a method to modulate the carrier and then antenna and an antenna in a
transmitter is far more critical than it is in the in the receiver the antenna in a transmitter
has to be tuned to be able to resonate at the frequencies that you want to resonate at
now usually most basic antenna's amateurs start out with is a quarter wave antenna
now it can be a whip it can be a dipole and a dipole what a whip is or a vertical whip or vertical is
a essentially it's a wire it's cut to a certain length for example quarter wave length
two meter antenna it's probably going to be around 19 inches long give or take
now the further away it is from a resonant from resonance
it means you get something what they call a standing wave
a standing wave will actually work to reduce the amount of signal that your antenna is radiating
now what we call the standing wave ratio is a ratio that's measured with a special
piece of equipment in the SRW meter or SWR meter I'm sorry anyway a good standing wave ratio is
two to one okay you put out one what like a good example is you put out one it's this is
greatly simplified but you put out one one for every two that you put in perfect as in 100%
100% of that two watts would be one to one
anything higher than two you're really starting to lose a lot of your transmission
and therefore your range the more power you transmit the closer you are to that one-to-one ratio
the more power you're going to transmit the further your signal will go
so in order to have an antenna you're going to want to look at quarter waves half waves
and very very rarely full wave antenna now full wave antenna is essentially exactly the
it's the same basically this has the same bandwidth as the same width as your signal
all right so if a 144 megahertz antenna is 19 inches at a quarter imagine how learned that the antenna
will be at a full wave that's why you're not using full wave antennas mostly so
and then we actually can get for even further into it take a dipole antenna dipole is essentially
two pieces of wire one going on each side of the feed point and each of those wires
well I'm trying to remember how it's been a while since I built a dipole a base basically your
dipole is cut to certain bandwidth to a certain wave and one antenna that is an improvement
upon a dipole design is called a yagi antenna which was invented by I'm trying to remember the
last name of him was yagi and that was a Japanese name yagi uda and basically two amateurs in Japan
and what they do is they take different lengths of wire metal
and they put one behind the the dipole so for example inadvertently polarize antenna
you're all your connectors are going to go up and down in a horizontally polarized you're going
to be going they're going to be basically flat against the earth not against the earth you know
it'll be up on a pole but so in a vertically polarized it's perpendicular to the earth
that that might be a little bit easier to understand I think
anyway they put two connectors on either side of that dipole
one connector is larger than the dipole the other connector is smaller than the dipole
and there's a whole lot of math involved with this fortunately a lot of that has been figured out
for us by some companies that you know see interest and and money making opportunities in making
these antennas so you can generally buy one for I'm trying to think I probably paid about forty
fifty dollars for my antenna my yagi antenna but what does that do what do those things do with
that antenna well the the element behind that goes what I would say behind the larger element
is what they call the reflector and the one on the other side of the antenna is called the
director all right and essentially the reflector reflects signal in one direction and the director
helps direct that same signal in the direction that basically antenna is pointing so basically a
yagi antenna is a way to give your radio signal some direction and it's basically after vertical
in a dipole antenna it's probably the next one that a lot of people look at
they can get far more complicated than that but they're the basics of antenna
manufacturing and making your own antenna is very very very same very much
all right so card a little bit about AMFM sideband radio frequency what is it how do you receive it
how do you transmit now what do you do with it well you communicate and there are many modes you know
with a lot of modes that we already covered talked about there's AMFM sideband and those are
both all what they call phone modes because I think back in the day they actually use something
you look like a phone oh and one one important thing I forgot is back in early times of radio
you didn't buy a transceiver you bought a receiver and you bought a transmitter so you had to buy both
so you essentially back then probably had to have two antennas unfortunately now with a transceiver
you only have to have one antenna so that's a good thing but so as radios themselves got a little
bit more complicated some of the other things got a little more simple so what like I said what
can we do with this stuff well you have a conversation with your friends talked to very many people
over the years 2013 will be my 20th year as an amateur radio operator and I've just had a good
time just chatting that that's my favorite mode right now it is what they call an analog mode
digital voice modes very similar to voiceover IP technology like asterisk
they exist however the downside to those modes right now is very few there's not really
a standard I guess is what I want to say the standards are mostly manufactured different the standards of
those modes right now for example Icom which is a Japanese amateur radio company they have something
called D star and then I'm trying to think if Kenwood has their own standard or Kenwood is and
actually I want to say I thought Kenwood was an American company but I think they're now
Jeff Japanese as well most of the companies are Japanese or Chinese companies we're out of Taiwan
like Yezi I think Yezi is Chinese they're Japanese also but I mean that digital modes for voice
they're a little rare most voice communication on the amateur man are still happening over analog
frequencies TV may have gave it up but radio has not they have not given up the the analog stuff so
now the one unique thing with amateur radio is there still are digital modes that are different
than phone or voiceover you know digital voice modes like D stars for example there are on the
two meter and VHF UHF frequencies or something called it's called packet radio packet radio
we'll take a digital packet and it uses the ones and zeros to modulate that signal in a certain way
and then transmits it on the handbands then on the receiver side they pick the same signal up
is using same concepts and then it converts a back to the digital bytes so that you can read it on
your computer screen that's greatly simplified but if you want to look at an idea of what packet
radio is like go back to the old days of your modem essentially that's what a terminal no
controller is that's what you use to hook up that's basically what you hook up to your radio in
order to use packet radio now they're the old ones used to use a purely a serial cable because it
is a serial mode and new ones there are devices that basically let you use your sound card and
software as a TNC now it's more efficient to use a kind of cool to use a regular terminal
no controller because a terminal no controller in many ways is the computer it usually has a
processor on it it has some memory for storage and basically if you want to leave your
transceiver on all day because the terminal no controller has your call sign plugged into it
that makes it legal so you can leave that on all day you would know you're you're not necessarily
at the control point you're still within the legal mounts as long as you can get to that receiver
or that a station and turn off that radio you're still in control anyway you can leave that terminal
no controller in the radio on all day and people can actually send messages that would arrive on
your terminal no controller and there will be a little message like the lights up and you log into a
like a like a terminal program you'd hit the serial port and talk to the terminal no controller
and then get your packet email and there is even the ability with packet radio to send an email to
somebody all the way other other other side of the United States and I was doing this before the
internet really came into play so that's one one way amateur radio continues to just kind of
move on and do things and a lot of times it seems a little bit archaic but you got to remember in
some of these cases amateur radio operators themselves invented the mode and came up with it
like for example the APRS or automatic position reporting system which is another use of packet
radio that was invented by WA4 APR Bob Bruninga and the original APRS program was written on DOS
there is of course windows APRS programs there's a Linux one called Exaster
and then there's also a Mac one called Mac APRS I think that Mac APRS still exists and then there's
also a Java based APRS program called Java APRS you can also view APRS maps on the internet so in fact
I've got a program on my phone well I can get a program for my phone called APRS Joy
and basically I can get my phone out and I can look at the APRS map I think it will even actually
somehow I don't know exactly how but digit peak my position with my cellular
now cellular phones there really is no analogy in amateur radio to cellular phones there's no
cellular phone that I know of that operates on the amateur radio bands now that I mentioned cellular
phones there one important thing that you need to remember and I actually had somebody right
after my first show ask about this but he asked if there was a way that he could receive hold on
in it this is what I call talking about non-ideal situations anyway um he asked me if he could
actually receive the internet using an amateur radio well technically it's very possible
but because we're limited in bandwidth right now the maximum packet bandwidth that we can use is
9600 that's slower than your old 144 modal slower than your 288 modal right so it's not
going to be very usable for a modern day internet not like your phone is there's also a different
aspect of that because there is a there's this thing that we'll get into a little bit when we
talk about the licensing call the pecuniary interest basically you cannot make money using I
mean you can make money selling things for amateur radio but you cannot make money
as a result of your amateur radio license i.e. if you want to transmit a message for somebody
to a disaster area you can't take money for it if there's an amateur radio operator that
works anywhere in the company there's these things we'll talk a little bit later I might
do this I think I'll probably do a special show on repeaters be a little bit shorter than this one
but uh there's this thing called an auto patch basically it's a way that you can make a phone call
via amateur radio now in a disaster situation you can't call pizza place or pizza
for the people at your location okay but only in a disaster situation for example if I'm on my
home I whip out my radio to order a pizza because there might be a person that works for
dinados or for whoever I'm ordering pizza hum that may have an amateur radio license that would be
any legal transmission same thing goes for the internet you know because there's a chance
that somebody who is an amateur radio operator could be making money as a result of your transmission
on the internet over amateur radio then you basically cannot do it plus you're also
not allowed to use potty mouth on amateur radio bands because kids listen to it kids can go
I think the youngest kid I've heard of when the amateur radio license was set okay the cover
today was a lot of technical information some of it should be correct a lot of it should be correct
and if I made any mistakes let me know you email me at gorken at gmail.com or you can also
email me at gorken at tllts.org thank you for listening I'm actually recording this live at the
booth the links link tech show booth at southeast linux fest uh by the time this comes out you missed
the show uh hopefully I might well just listen to tllts and uh we'll definitely have a show or two
out that we record down here so I want to thank you listening to hacker public radio got a lot of good
comments in the last show keep listening to hacker public radio I want to have some more
information I have an amateur radio and uh limits and whatever else I decide to record thanks for
listening thank you for listening to hacker public radio for more information on the show
and how to contribute your own shows visit hacker public radio dot org
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