Episode: 2403
Title: HPR2403: Amateur Radio Round Table #3
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr2403/hpr2403.mp3
Transcribed: 2025-10-19 02:24:36

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This is HPR episode 2,403 entitled amateur radio roundtable hash free and is part of the
series HAM radio QSK.
It is hosted by various hosts and is about 59 minutes long and can remain a explicit flag
in the summary.
Two guys try to answer Ken's questions about HAM radio.
This episode of HPR is brought to you by an honest host.com.
At 15% discount on all shared hosting with the offer code HPR15, that's HPR15.
Better web hosting that's honest and fair at An Honesthost.com.
Hello everyone, welcome to Hacker Public Radio and this is the amateur radio roundtable
number 3.
Today we have myself, Steve, Katie, zero IJP, we have Michael, DL4, MGM and we have our
very own Ken Fallon with us today, also on licensed.
Yeah, Ken's call is in zero, C-A-L-L, no call and we may also have Russ, K5-T-U-X joining
us here too after a little bit and maybe some others as well.
So welcome everybody.
Thanks guys for putting this on.
Hello everybody and I think Ken will qualify SSWL a short wave listener.
Alright, there you go.
Alright, so we did not really have any topics queued up for this episode.
So not exactly sure where to start, but then let me just jump right in there and ask you
a few questions.
Excellent, that's what you're here for, go ahead and go ahead and do so.
Random stuff.
Out of the top of my head in the US for, well from the point of view of Hacker Public Radio
we're assuming that people are getting that little bullfang radio and then we're going
to try and have the people do the entry level exam.
Here in the Netherlands you need to do a sort of technical piece of work.
In the US or in the UK you need to show proficiency on the soldering board.
What are the requirements for entry level in the US or where you guys are?
Alright well for the US I can probably speak to that.
Really, the only thing you have to do is you have to pass the test.
The test is, I guess the test questions are generated in conjunction with the FC
C, the Federal Communication Commission.
You have to pass that test and that test is just simply a multiple choice thing.
The entire pool of questions are available and they just take a subset of that pool and
give you the test.
And there's three levels of tests, we call them the Technician, the General Class and the
Extra Class.
That test is made up of questions related to some technical things like electronics.
It includes some operation stuff, some rules and just that basic stuff like that.
But once you've passed that test you get your call sign and you're ready to go.
There's no other requirements really whatsoever.
The only thing is with the beginning level, the Technician Class, you have a relatively
limited number of frequencies that you can transmit on.
If you want more privileges you have to get the higher level test, which again is just
another multiple choice test.
But there's no soldering proficiency.
We used to have a requirement for more code but that's no longer the case.
So it's pretty simple.
Someone else?
Yeah, the same here in Germany, you just have to do the paperwork and theory, know about
the electronic stuff and so on.
But no one is asking you to do some practical demonstration or a test.
You do not need to know where the hot end of the soldering iron is, so to speak.
Okay, very good.
If you're ever stuck for topics to discuss on this round table, good idea might be to
go over to the US test because I think most other countries are kind of based around
those.
It's been running the longest and take some sample questions and so people here would
get a feel for the level of technical proficiency in order to jump right in.
Because I think here the goal is if we can get anybody to get a novel's license or I think
was a technician license in the US?
Yeah, that's what the that's what the entry level is called now used to be called novice
but it's now called technician.
Yeah, so here it's the novice one.
So if we can get people to get the novice licenses, then you know, we can take it from
that up to the more advanced stuff and people can dip their toes in and they won't get
prosecuted for operating a radio as long as they operated within their bands that they're
allocated.
And then once they've been by the bug, then they can proceed on to get the more advanced
licenses and stuff.
Hey, related to that, can one time on some some show, I think you've mentioned that
where you're at, it's actually illegal to own an amateur radio until you have the licenses,
is that correct?
Well, they, I rechecked that and it is now not illegal to owners, it is illegal, you have
to keep the radio and battery in two separate places.
So you can't have an assembled unit if you're not licensed.
They have a special license if you're, if you're maintaining or repairing radios, I actually
I should get a case, one of the amateur radio enthusiasts to mark to explain this, but
I'll give you a taste for now.
He had, he used to repair radios and also outside his class and military grade, all
military World War II radios and stuff like that.
And he had a special license in order to be able to use those.
But now you can, or you can have it physically in your house, but you can't have a connective,
you can't turn it on.
And they do, they do listen and prosecute people who, who operate without a license.
Oh, but so you can't even listen in, even if you don't transmit.
That's from what I understand, that is correct.
You're not allowed, you can go and buy a shortwave radio all you want.
And you can listen to the, you know, a, online, there's a, there's a, there's a drent down
and drented.
There's a, a, a, best yard.
That's the bunny, yeah.
And you can listen to all those radio frequencies as long as your heart's content, but you're
not allowed to operate a radio that's capable of transmitting.
Okay, well, over here in the US, I mean, you're obviously not allowed to transmit, but
I don't know of any rules that say that you can't have a radio and listen as much as
you want, as far as I know.
I'm not sure if the regulations have changed or if they're just hand, handling it, lose
more, more loosely these days, but in all days, you, we're not allowed to even activate
or operate a transmitter if you were not, we're not licensed and if you bought some surplus
equipment, it's some, some dealers, they would cut the, in a wiring harness unless you
prove them by sending in your amateur radio license that you are entitled to own these
equipment.
Yeah.
So it's, it's coming from that sort of, that sort of thing.
I'll get case on one time, I'll interview him on the, and since he promising himself
to show, but that would be interesting just to go over the licensing particularities of
the Netherlands here.
But I do have a question related to capacitors and capacitors and loop capacitors and coils
and doctors, and doctors, yeah.
So that's like the basis of all radios, capacitors and doctors, yeah, low pass, high pass filters.
Yeah, I mean, you know, if you're talking about the discrete component analog radio, if
you don't have capacitors and doctors, you're not going to have much of a radio.
Okay.
So what's, what's the purpose of this?
So how does radio work?
Very broad question, I guess.
Okay.
I'm going to let Michael take that one.
Okay.
Okay, let's, let's, let's try to figure this out.
So first, yeah, now I just write what, what, what, what I could not understand for the longest
time, I just can't be envisaged in my head the concept that in the, we're talking about
the electromagnetic spectrum here, yes.
So basically visible light, wow, visible in the, in the same spectrum that visible light
is in, yes, correct or not?
Yes, that is generally, generally considered the way it is sure.
Okay, that doesn't sound like yes, Ken, that's 100% correct there.
Well, I think it's 100% correct.
I mean, it is, it is kind of hard to visualize.
I'll agree with that when, when that electromagnetic spectrum gets to a certain frequency, it suddenly
becomes visible light is a, is a, I agree is kind of hard to fathom, but yes, that is
the case.
It is all one electromagnetic spectrum in the lower, lower frequencies of that.
We have RF stuff, you get higher, you get into infrared, you get into visible, and so
on.
Okay.
So the way I was now, I've been thinking about this for quite a while.
So we've got these two radio detectors in their heads, and most people's work, and
they're called eyes, correct me if I'm wrong, yeah.
So at any given time, does all this light infrared microwave, shortwave, longwave stuff broadcasting
in the ether, and it's all happening at the same time, correct?
I would say that is correct.
I mean, if you could actually visibly see the lower frequencies as well, like the, you
know, the radio waves, RF waves, I'm not sure what that would look like.
I think it would just be a blinding ball of light, if you can see all that.
Well, now then we get into the whole concept of color, especially RGBs, because in those
cases, the function of the eye, for those of us who can see, in those of us who can
see color, each of the three hozacornias are basically high and low pass filtering, filtering
out a particular bandwidth of that spectrum.
Would you agree with that?
I would agree.
That sounds right.
Yes.
So basically, we're all ham radio operators.
Exactly.
What do you want to be or not?
If there are ham bands in that visible spectrum, I do a license to use that.
Exactly.
Thank you very much.
Valid point.
So essentially, there's all this stuff going on, and it's all happening at the same time,
but it doesn't seem to interfere with the other things that's going on.
So that's kind of where I was.
That's where I am now in my journey of trying to get my head around this, the same way that
you can see red and green and blue at the same time.
You can have something on two meters, something on ten meters, et cetera, et cetera.
Yeah.
That's why you need front end filtering to filter out all the other stuff, which might overload
your receiver.
And to get to the signals you want to hear, to receive, and to convert them down to
something that we as humans can accept.
Okay.
So the analogy then of the whole audio wavelength and stuff, we use the same sort of terminology
correct.
But that's completely different.
That's a different medium entirely.
Yes, with audio, yeah, audio is really more about air compression and vibrations, air
vibrations affecting your eardrum.
So the confusing thing, I guess for me, was that if you have somebody talking on the
hand radio, they're actually sending a signal over the light spectrum, and then your radio
device converts that from the light spectrum to the audio, to the, you know, it compresses
the air wave so that you can hear.
If you exchange the light spectrum by electromagnetic spectrum, sorry, that's a very, yeah, electromagnetic,
sorry.
Thank you.
Well, don't you?
Yeah.
That's exactly right.
In fact, you know, there's been, I've heard this before, like at a, oh, like if you're
at a concert, for example, and you're sitting, you know, halfway back in the audience, and
right up next to the, to the stage, there is a microphone connected to a radio that's
going, you know, clear across the country, and somebody's listening to a receiver, and
they're setting next to that receiver.
They're actually hearing the sound before you do, even though there are thousands of miles
away because of the speed difference between sound and electromagnetic.
Okay.
I want to confuse that debate now with the buffering on impact packets and stuff, so, but
yes, back in the day, I guess.
Sure.
Assuming analog transmission.
Exactly.
Exactly.
Okay.
That, I think, has cleared it up for me.
So now we have all this stuff floating around in the, and it all seems to coexist and nothing
seems to interfere with nothing else for the most part.
Are there interferences where wavelengths are multiples of each other, does that cause
interference?
Say, two measures, four measures, whatever.
You depend.
It depends.
It's not like what the harmonics are about.
Yes.
So some of the amateur radio shortwave bands are located at harmonic relations.
So say 80 meters, 3.5 megahertz, 40 meters is seven megahertz, and so on.
I think this was on purpose to have most of the harmonics of the amateur radio transmissions
within our own bands.
And so can you explain very quickly what harmonics is for us?
Just people might not know.
And why they deliberately do that, why it's a, why we will be keeping the crud in amateur
radio bands.
Yeah.
Okay.
So harmonics are just basically multiples of your transmit frequency.
Say you're transmitting a carrier wave at 3.5 megahertz.
And if you have an ideal transmitter, it will transmit this one carrier wave and nothing
else.
But real transmitters produce a certain amount of harmonics.
So you will have some energy at seven megahertz at 10.5 megahertz and so on.
Of course there are regulations saying that your harmonic content has to be a certain level
below your transmitter output and so on.
But every real transmitter has some sort of some amount of those, those emissions too.
And you thought what causes the harmonic in the first place at non-linearities in components.
So at every non-linear characteristic of some component in the, in the signal path, you
will create harmonics or mix signals and so on.
Okay.
So what does non-linear mean in this case?
Yeah.
For example, if you increase the input signal in an amplifier or something else, and
you, by a certain amplification, you increase the output signal.
And it's all, all the same relation.
There's no, no change.
For example, if you overdrive an amplifier, you increase the input signal.
But the output signal can't go any higher because it will reach the limit of the amplifier,
or at least the amplification factor is going down.
So you will have some sort of compression of the output signal.
And this is a non-linearity.
And that's why you hear, also in audio.
You will hear harmonics in an audio signal if you overdrive an audio amplifier,
like a microphone amplifier, or what are those, those disorders called compressors of them.
Yeah, yeah, not compressors, but those effects, generators where you deliberately overdrive
an amplifier to get, so it can sound effects on electric guitars.
And that's where you use these effects to get an audio modification.
And if you do this with an audio amplifier, it will produce lots of harmonic energy.
And that's normally not what you want to be output to your antenna.
And a lot of this is happening in the, I mean, one of the stages in radio modulation involves mixers.
You're doing a lot of mixing of different frequencies.
And it's just sort of a side effect of that.
Like you say, due to non-linearity and probably some other things, I'm not an expert in this,
but it's just sort of a side effect of the electronic manipulations that are going on with the signal.
But you can put it to good use.
For example, in frequency multipliers, where you produce deliberately those harmonics
and then use a filter to select the higher harmonic you want to use.
And voila, you have multiple idea of frequency by that factor in between.
OK, a more in-depth show on that would be called for, I think, because...
But also where I think that's more advanced.
So these things happen, these...
What do we call them? Harmonics happen at a particular space that's predictable.
That's just a feature of the music.
Yes, yes.
And then they've divided the ham radio bands up so that those on the lower bands
will appear on the higher ham radio bands and not squashing somebody else's ham radio band.
Well, I mean, the ideal thing is that if you have a well-made radio,
there's going to be some filtering involved, such that the energy outside of what you're
really trying to transmit gets taken down to basically a negligible amount.
I think, though, there's a recognition that an amateur radio part of the whole DNA of amateur radio
is experimentation.
And so people that are going to build their own equipment or whatever might not do a very good job of that.
And so, you know, if you have that spurious emissions also landing on amateur bands,
it's not going to cause as much interference with other things that are maybe more important.
But that's exactly the reason why we need those tests and that you are aware of those regulations,
what you have to fulfill, that you know the technical background to construct
or to build a correct, correctly working transmitter.
And that's why we are given this privilege to build to transmit on our own,
because we are the only radio service that is allowed to have their own equipment
without certification by some government organization or so.
Okay. But then when you say that, that's great. I guess it.
But somebody's thinking, well, if I'm going to be allowed to build,
if somebody in my license is allowed to build a radio,
then it's going to be an awful lot of, that's going to be a really tough exam to do.
So are there restrictions on the types of radios that an novice can do?
Or not? Not in Germany.
Yeah, no, not explicitly.
I mean, you're correct.
You are being able to pass the test.
Does not, in any way, mean that you know enough to, you know,
really build a radio from scratch and have it work properly.
I mean, that's just, there's way more to it than that.
It, the idea, I think, is that if you pass that test,
you understand the general issues.
And so hopefully you are maybe a little more careful.
If you, you go into doing your own construction and that kind of thing,
and I mean, building a, building a radio from scratch is a pretty big deal.
Not that many people actually do that.
There's, it's more a matter of, you know, kits, there's kits available and various things.
And in a lot of times, they're pretty low power on purpose because of this issue.
I get this, yeah.
But, you know, the other thing to mention is you've mentioned the Balfang radio earlier.
And, you know, the Balfang radio is a cheap Chinese radio.
And it gets knocked quite a bit by a lot of people because they don't do a very good job of filtering either.
And there's a lot of people that are really against those cheap Chinese radios
because they do produce emissions that are outside of what is really legally allowed.
And so it's one thing just to kind of be aware of if you do buy those cheap radios,
they're not the best radios.
No, that's fair enough for 75 bucks.
I wasn't expecting, I wasn't expecting a lot.
But what it will do is allow me to listen on a, if necessary,
and if the country suddenly decides to flood,
then I can put the battery in and contact somebody.
Guys, remember me?
Yeah, sure.
But, you know, as we're talking about this issue,
the whole issue of filtering and stuff is important on both ends of both on the transmitter side and on the receiver side.
On the transmitter side, it's important so that you're not sending out a bunch of spurious energy that you don't intend to.
But on the receiving side, it's equally important to have good filtering
so that you are eliminating external signals that might interfere.
And if you have a strong signal coming in, it could overwhelm the signal that you're trying to listen to.
And so filtering is a huge deal on both ends of the radio.
Yeah, and as we already explained,
at non-linearities, not only harmonics can be generated,
but also multiple incoming signals can be mixed.
And then you get multiples of the difference of some signals or different frequencies if you subtract or add up signals.
And if you have multiple signals, this can be quite a mess.
OK, if I can leave that one there for a minute and then go back to some basic fundamentals again.
If in our hypothetical analog radio back in the day,
when there's nobody, no regulations or whatever, we're building that,
the basic principle of a radio is this whole concept of resonant frequency.
Yeah.
Now, can you talk to me about that?
Because I have an analogy, I think, that may or may not work.
And I want to hit you with it.
But the whole concept of resonant frequency, as far as I understand it,
is core to every radio, correct or not.
Yeah, sure.
If you take a resonant circuit, for example, a parallel resonant circuit with the capacitor and the coil,
and you have an electromagnetic wave, not the wave, but energy,
from the coil going to the capacitor and the endrovers.
So, for example, you charge up the capacitor, then you have a potential voltage across this capacitor.
This voltage across the coil, which is basically just wire, causes a current to flow,
which will build up a magnetic field around the coil.
Yeah.
And the capacitor will discharge until the point where you have the maximum current flow,
and then the voltage will go down, and the magnetic field will collapse.
Inducing a voltage into the coil itself, which will charge up the capacitor,
so the energy will travel from the capacitor to the coil, from the coil to the capacitor and so on.
Until it filters out.
Yes, yes.
Because you have losses in the circuit, it will be reduced in amplitude,
and someone suddenly tap it down and vanish.
It's a bit like a seesaw, I guess.
Where one side is a vacuum pump, and the other side is a spring.
So, you sit on the spring, it pulls up a vacuum, you know, a pump, bicycle pump, for instance.
And then that gets strong enough, the vacuum sucks the back down,
creating energy in the spring, and vice versa, flip-flop, over and back, over and back.
Yeah, I mean, I think that's not a great analogy.
Well, it's not about analogy,
but when you start talking about resonance, the issue is that by adjusting the values of, say,
the capacitor and the inductor, or in your case, the, you know, adjusting the values that represent
the, you know, the physical characteristics of the spring and the vacuum and so on,
when you, there's a certain frequency at which, if you, if this back and forth is happening
at a frequency that is tuned to the values of those devices,
the, this action has a tendency to go on much longer.
And even to a certain extent amplify itself, because they're, they're working together
at exactly the right frequency, the right rate to, to tend to propel this action on.
And that's really what resonance is about.
Okay, now I always remember when I was in the reserve, when you walk across a bridge,
you were told to break marching, so that you wouldn't cause resonance frequency in the bridge.
And when, if you ever walk across a rope bridge and you're walking at a particular pace,
you feel that in your foot coming back up, is that from a mechanical engineering point of view,
that's resonant frequency, is that the same sort of concept?
Sure, that's exactly right.
Okay, now, take into the next level.
I have a trampoline in my back garden and I grab one of my children and I have them bounce on the trampoline.
And they're bouncing up and down at a, at a frequency of, say, one bounce per second.
Yep.
And they're getting maybe, I don't know, half their height up.
Are they getting, you know, quarter of their height up, every bounce?
However, if I hold their hands and bounce them up so that when the bottom of the trampoline is down
and they hit it just at the right point, they go higher and higher and higher.
Is that like amplification of the, is that the resonant?
Right, that is, I mean, that's exactly right.
What you're doing is you're adjusting the frequency of their jump to match the resonant frequency of the trampoline.
And so when you hit that resonance, you get a much bigger effect.
So that is the wavelength is coming in or in the, what do we call it, the electromagnetic spectrum.
And because you're hitting the resonant frequency of this component that you built,
you're amplifying it and therefore it will detect it.
That's right.
And that, I mean, that's what we're really talking about in the radio spectrum is,
we're talking about antennas quite frankly because the, when you send out a signal on a certain frequency to an antenna,
if that antenna is resonant on that frequency, you're going to get the, the radiation of that energy at a much more efficient level.
If it's not resonant, then a lot of that energy is sent to the antenna is actually going to bounce right back to the radio
and, and it's not going to propagate like you want.
So resonance becomes a huge issue when you start talking about antennas.
And that's just for transmission, but is the same true for reception.
The same is true for reception.
If, if your antenna is resonant on the, on the frequency you're trying to hear, you will get a much better reception.
It's not as critical though in reception as far as like damaging the radio.
When you're transmitting, if you're transmitting to an antenna that is not properly tuned,
you will get energy that comes back and it'll be strong enough that it could damage the radio.
That's not going to happen for receiving, but yes, receiving it is important in terms of being able to hear a good signal.
Okay, so you're bouncing, bouncing, bouncing this child up and then all of a sudden it goes completely wonky and the child goes smashing back into you.
I guess would be a bad analogy, but fine, I get your point, which is why you need tuned antennas and all the rest, I guess.
Yep, that's, that's basically it.
Do you agree with what I'm saying, Mike?
Yeah, yeah, basically.
Sorry, all these questions may seem very, very strange to you guys, but these are the ones that have been blocking me for
in my whole understanding of what the hell is going on here because it's not enough for me personally.
Everybody else may be different, but I need to kind of visualize what's going on in my head to get the concept itself.
That's fine, that's why we're here.
Okay, now I've got a garden, right?
And I've got a length of holes.
And if I, if I have that holes and I wiggle that holes up and down, up and down one of the kids and I make one wave that goes two measures, that's a two meter wavelength.
That is essentially the actual physical wavelength of this thing that's coming into the radio.
Is that correct?
If the length of the hole is your propagation medium and then the wavelengths across this, this medium, yes.
So if I had a two meter piece of wire, then the wavelength that's coming in is, has to be two meters.
Or is it not the two meters or where is it?
Is it the transversing of the, of the sine wave or is it the, does it all hit at the one time?
Like this is something else I don't understand.
No, so if you have a two meter wavelength in air or vacuum or something and you have a two meter wire, then you have a full wavelength antenna radio, whatever you want to call it.
So you, you can, can use this if you couple the signal correctly to this, to this two meter wire, can use this as a transmit or a receive antenna, but you can also use half wave antennas, quarter wave antennas.
Okay, no, no, no, you can be complicated now, getting too complicated to talk about.
On the two meter band, we're building a simple radio, a theoretical radio with no tuning around thing.
It's just going to be tuned to one frequency, frequency is two meters.
So the wavelength coming in, if I've got a two meter piece of wire and I have my kids wobble at a pipe and that the wavelength of the pipe is two meters, then once I stand over that wire,
at some point, there's only one piece of the wavelength hitting that wire at any one time.
So how is this possible?
Do you get what I mean?
Wavelength is a piece of wire that's a vertical thing, that's two meters long, yeah?
But a wave is not, is not actually a physical object, it describes the movement of a thing.
So just like the waves on the sea, you draw them as a kid, which is very confusing because they're not,
it's actually the surface of the water that you're drawing, and you're drawing the way the surface of that water moves.
So there's no such physical object, you cannot touch a wave because it's a movement, correct or not?
I think you're correct there.
Yeah, I mean visualizing electromagnetic waves is tough, we draw them as a sine wave or whatever on a piece of paper.
But that really doesn't depict how they work quite, what all that's doing is it's graphing the change in voltage over time or something,
but in terms of a physical rendering of it, it's really quite different.
But you will have some current and voltage distribution along these two meter wires.
Let's say you have an electromagnetic field with the correct wave length, which is in resonance with the two meters of the wire,
and you will get a current flowing in the wire.
At the end of the wire that cannot be any current flow, so therefore you will only have a high voltage at the ends.
And because of this sinusoidal shape, you will also have high voltage in the middle.
And about quarter of the wave from each end, you will have points where you have a high current in the wire,
because the wave resonates in this two meter wires like in a resonant circuit.
Okay, so in the center and on the ends, that's like where the kids are holding the host pipe as it goes up and down.
I don't know if you...
Yeah, yeah.
Yeah, okay.
So therefore there's nothing happening there.
What did you say was detectable voltage?
Yeah, there you have the high voltage, and where you have the host going up and down is the points where you have the high current.
Okay, now I'm confused, because I'm thinking of VI over R and stuff like that.
Tonkip silence probably won't do justice to the way that I'm going silent here thinking about this concept.
So the amp...
So they...
Okay, they center a bit between the...
So three quarters of the way up and quarter way up.
That's where the highest amplitude is.
The highest current in the wire.
Sorry, highest current.
And the lowest voltage.
And the voltage will increase to the ends and to the middle.
Okay, but then when somebody else is transmitting
and that signal comes along through the ether that induces a varying current quarter way up and three quarters of the way up.
Would that be correct?
Yes, yes.
Yes, I agree.
And does that affect then the voltage as well at the ends?
Yeah, the strength of the signal will influence the amplitude you see at those points.
So therefore if you...
Because you plug into this as...
So you're measuring the voltage difference.
Is that correct?
Are you measuring the amplitude?
Because we need to convert it.
So now something is changing.
The voltage and current along that antenna or piece of wire is changing.
So therefore if you're able to detect that,
you're able to detect the signal.
Yeah, and that's why you have to pay attention.
What, how you feed or a couple of your feed line, your cable to the antenna.
For example, at the low impedance point where you have the current,
you can have a low user coaxial cable and then some connection point.
And if you have a high impedance cable, which can be connected at the end where you have high voltage and low current.
And I can't really explain it right now.
Yeah, no, and that's okay.
That I think is too complicated for the basic concept that I'm trying to guess,
which is just understanding there's a signal.
It induces a changing current and a change in voltage.
And which one do you check for?
Do you check for the voltage or do you check for the current or voltage in a radio, in a receiver?
I'm not exactly sure how to answer that.
Yeah, because now we've got a piece of wire outside.
And in that wire it's two meters.
And you've just told me that that's in the middle of that two meters.
There's a voltage induced detectable, which varies with the strength of the incoming signal.
And three quarters of the way up and a quarter way up, there's a variation in current.
So therefore, okay, that's lovely.
Now how do I take that in and then run the through amplifiers and then run it into a speaker
and hear something coming out in the old classic crystal radio type thing?
This is the last time I get invited to the round table.
No, no, no.
Okay, so let's assume we have a parallel tune circuit with the coil and the capacitor
at the correct frequency.
And a parallel tune circuit is high impedance at the resonance point.
What does that mean?
Not the time, it means.
Yeah, so it has a high voltage or a high resistance at the point where it's resonant
the circuit.
If you use a series resonant circuit where you have the coil and the capacitor
in series, in a signal path, it's low impedance.
So it conducts at that frequency of resonance.
At the best, so if you want to filter a signal,
if you put a series resistance in line with your signal,
you will get the best signal throughput at the resonance frequency of the tune circuit.
And if you put a parallel circuit between signal and ground, let's say,
you get the lowest signal attenuation at the resonance point where this
tune circuit is high impedance and will not contact and will not short circuit the signal.
So, okay, let's assume we have this high impedance circuit.
And we can take the upper point of the tune circuit and connect a wire,
half-wave length wire, which we learned is high impedance at the end because we have the high voltage
there, which perfectly matches the high impedance of the parallel tune circuit.
Okay, then we can use, for example, a tap where we make a connection at some point
of the tune circuit of the coil where we take out our voltage, which builds across the coil,
and then we put it into some rectifying diode crystal detector, which will then
just produce an output voltage depending on the amplitude of the radio frequency that's still
received from the antenna and filled by the tune circuit.
Okay, I'm with you. So, this radio wave that's been come into the wire, it has come in
and you filter it out. So, you're then having something else detect a voltage,
or not a voltage change, produce a voltage change proportional to what it is detected on the antenna.
Yes, so, proportional to the strength of the incoming signal, you get this voltage across
some point of the full tune circuit. So, in as an example of the kids, they have a big
two-meter hose pipe that they're wobbling up and down, and now inside you've got a two-centimeter
piece of string that you're wobbling up and down, but if you look at it, you can still see the same
shapes appearing on both both hose pipe and a piece of string, I guess. Yes, yeah, I think if we
say the tune circuit is the form factor reduction with the small string, then this could match
as an analog machine. Okay, so, if they're going like one, two, three, one, two, three, you will see
one, two, three, one, two, three on the process side, I guess. Okay, so you carry in the signal through
as all I'm saying. Probably everybody's hitting their head against the desk going, why isn't he
getting this? Yes. Okay. Yeah, or about my explanations. So, please join in next time. Yeah, exactly.
Exactly. Hey, you're doing a better job than I do on this, but the other thing I suppose we
talk about here at some point is this signal that we're receiving is probably not just a carrier wave.
It's a carrier wave that has been modulated with some form of information. And so,
you know, going through that diode, like you talked about after the tune circuit, you go through
that diode, what you really want to get out of that is you want to get rid of the carrier
frequency and get a voltage fluctuation that matches what the original information signal was
that was modulated on that. And I think that's where that's where the diode comes into
in place is part of the demodulation of that. Am I correct? Yeah, exactly. So, if assume the
amplitude of the incoming RF signal varies slowly, in quotes slowly as in audio frequency timing.
And then you can rectify the RF, the radio frequency signal. And after the rectification,
you get a jumping voltage with the changes in amplitude similar to in accordance with the
changes of the amplitude of the radio frequency signal. And if you put a capacitor there that
will charge up and discharge slowly in the gaps where you have the wave going down,
you can recreate your modulating audio signal assuming amplitude modulation.
Okay, so, but in my example of the kids just throwing the hose pipe or skipping rope, I guess,
would be better. Let's call it a skipping rope. They're skipping rope where it will be
that would be more CW, the old spark gap type stuff where... Yeah, it will be a constant signal
constant carrier. And then there's nothing. The fact is that it is just a... You have a signal,
then you have no signal, there's no carrier wave or anything. The carrier wave, sorry,
go on. Yeah, that's correct. I mean, when you're talking about CW Morse code type stuff,
you have a carrier for a bit and then you don't have a carrier, then you have a carrier for a bit
and then you don't. And there's no, very simple, it's either there, you detect it or you don't
and you just count in the equivalent to ones and zeros going down the wire at that point.
Yeah, I mean, it's dots and dashes. You have a short amount of carrier and then nothing,
then maybe a longer amount of carrier to represent a dash and then nothing and so on. And it's
the combination of the dots and dashes that carry the information. So then on top of that, as a
neat way to transmit the signal, you have this carrier wave concept where you send out a strong
signal that goes up and down and up and down at a known frequency or amplitude or both.
If you modulate amplitude modulate an audio tone or something for a Morse code,
you just turn on and off the carrier and you will not hear a tone by just...
Yeah, yeah, demodulating this carrier. But I'm talking about, say, the AM type,
yes, then exactly. You need one signal all the time broadcast and then on top of that little
signal, you have Wiggles, forgive my technical description here, you have a big signal that goes,
and inside that signal you've got...
Am I correct here? Yes, absolutely. I'm so embarrassed that I've done that.
No, that's exactly what it is. The first is the much higher frequency and the little
Wiggles are the lower frequency and then that's exactly how amplitude modulation works.
So the little ones are the lower frequency? I thought they would be higher because they happen
more often. Yeah, that's what I was wondering too. If you've got the big and little backwards
there, I mean, basically your carrier frequency is going to be the high frequency and then that's
going to change at a lower or audio frequency. And so to a certain extent, to a certain extent,
the little Wiggles, all right, if you want to say it, is your carrier frequency and then that
carrier is going to modulate or change over some lower audio frequency?
Okay, so basically we've started. The original thing was more schooled, you turn something
on, you turn it off. That wasn't very useful. So then they came up with you turn it on for a
little bit, you turn it on for a little bit more and then you've got a dash and a dot. And then
you have to look up tables, but that wasn't very useful, I guess, when people wanted to talk.
So then all these other, it's a hell of a lot useful. No, no, I get that. Don't attack me. Yes,
I get it. For people wanted speech to be able to transmit, to be able to transmit speech. Yes.
Yeah, right. Sure. So whatever system you come up with on one side, whatever hacking come up with
to carry the information, you need to, on your receiver, dehackify it. So if you use frequency
modulation on one side, you need to use frequency modulation on the other side. Yep, that's right.
And then if you do, if you decide, well, I'm only going to do a single sideband, then you need to
be aware of that on the receive side. So every trick that you do, you need to be aware of what the
trick is that's happening. Okay. So if people understand the concept of turning it on, turning it off,
what will be the next step will be amplitude modulation, I think is probably the easiest, is it?
Yeah, I think that was probably developed first. I'm just going to go to the wiki page for this,
actually. Yeah, the point is demodulation for amplitude modulation is as simple as just rectifying
it with some one one diet or a crystal detector. And I think that's why the system was used first.
Okay, so I'm looking at the, there's a very good animated give for something on the wiki
article. If you go to amplitude modulation. And what it's got at the top is basically a signal
that goes up and down, up and down. Then underneath that, you have the same shape only for the
down bitch, you're wiggling a little bit. So you have the shape there, but there are lots of,
I wonder could I put this to convert this to some sort of audio?
Is the main signal? I'm so embarrassed at doing this, but okay.
Yeah, I hear what you're trying to do there. That's sort of right. That's sort of right, yeah.
Right. But it really sounds more like a frequency modulation.
Well, the frequency modulation is, yeah, actually, both. Yes, it seems that's frequency modulation.
But the idea is you're carrying the same signal in a different way. So if you want to get
the original signal back, you need to undo whatever it is you've done. Actually, actually,
if you really wanted to, using your little audio thing there for amplitude modulation,
which you shouldn't be necessarily changing pitch, you should be changing volume.
So as your, so your, your carrier frequency is getting louder and softer basically. Whereas
changing and changing and yeah, changing and pitch is more of an FM.
Someone should do a show about amplitude modulation using using a 1 kilohertz carrier and
two hertz modulation signal. Yeah, somebody could do this. This could be audio.
That would be a nice description on the audio. But essentially, so I
say, now understand what you mean about the amplitude. You have a higher signal.
Because the main signal is actually slower. The amplitude of the smaller signal
varies. But there and the frequency of it is a lot faster as well. But seems to be constant though.
Yes. So that signal, the signal itself that I'm seeing going past and if you're looking at
the Wikipedia page in red, there's a signal that goes, if you ever saw the,
tacky, or the seismographs that goes over and back and then when there's a north quick,
it's scrolling across a piece of paper and it's very much like that. The wave goes over and back
and then goes a little less and then over and back a lot and a little less and over and back
a lot and a little less. But the moving of the hand is constant between the, so what am I seeing
here actually? Which is the carrier wave? So the carrier wave is the red one and the distance
between zero crossings, if you think about the zero line in the middle. The frequency will
stay constant. The distance between crossing the zero line, independent of the amplitude,
but the frequency of this carrier wave will be constant. So it always crosses the center line
at exactly the same time. So it's always going out at the same. So is it just the power?
Is it then to carry the other signal? Yes. Okay, so it's a bit like the, you said, with the volume.
It's quiet. It's loud. It's loud. Okay, I get that. That is actually more difficult to understand
than the frequency modulation, although you wouldn't think so. Okay, guys, I'm totally, I'm
totally impressed. And then all the other modes and everything else are just basically more
efficient variations on this. Why send a carrier down when we don't have to? Why only send,
that's only send half of it when we can get away with that. Yeah, and then when you get into
actually sending data as opposed to like digital data and as opposed to audio,
you get into some really interesting modulations that they figured out ways to send digital
information and as opposed to just audio too. Yeah, at Kwam and all the rest and 256, 256 Kwam,
we use quite a lot of work. Obviously, it's a work cable company. So Kwam, so it's quadrotour
amplitude modulation, where you change the amplitude and the interface of a signal
irreference to some of the signal. And there is no way I'm going to be able to explain that with
sound effects to be honest. But the constipation diagram does like to hear that. Yeah, exactly.
But if somebody could actually, somebody who, that's a show right there, if somebody can take
the amplitude modulation GIF or whatever it is, animated GIF there and convert that into some sort
of signal, I would just like to hear that. Okay, anything else? I don't know if we've been going
for as the question. I've been recording for about an hour, but I started before we really started,
so I don't know. I think I have enough to be thinking about at least for the coming period of time.
I would probably want to look at some of the books and stuff. What I've been trying to do actually
has been get in touch with some people who produce a book and there's a guy in Ireland for the
Irish exam, which is very similar to English one. And he has produced a book that's free for
non-pinging use, but I have been able to get in touch with him to see if he'd released it under
the Creative Commons CC by, say, NC even. And then we could all work off that.
Okay, the other thing is you mentioned earlier the question pool for the US tests. Those are
public domain and so that's a good idea. Next time we could maybe pick out a dozen or two dozen
of those questions and just kind of get a feel for what they are and what kind of things you have to
know. They're all in different sections. In the Netherlands you're asked, there's always a question
on resistor codes and stuff. Yeah, that's the same way here. The questions are divided into
categories and a given test will contain, say, one or two questions from this section, one or
two questions from that section and so on. Okay, yeah. If somebody wanted to do the resistor
color codes while they're there, what a resistor is basically and why it goes from black to white
and the difference in mnemonics to remember them, that will be awesome. So cool. You have homework.
All right. Well, hey, thank you Ken for joining this discussion. It definitely expands our
expansion for noobs. Well, it expands our mind here a little bit because some of the stuff we
take for granted and having to try to explain it is a little bit tricky at times, but it's good
to be reminded of that. I noticed that K5 TUX is unmuted and still on here. Do you have anything
you want to add to the discussion at this point? There was. Well, unfortunately, I came in a bit late,
so I'm not sure I can contribute a whole lot. I think my UTC calculation was off by an hour.
All right. Well, hey, it's good to have you in there at least and as we say in a net, we'll put
you in there for the count and maybe next time it'll work out better for you to participate in
the discussion too. Anything else anybody else wants to say before we wrap this up? Yeah, sure,
I want to congratulate you today's show. It's fantastic. I fear I embarrass myself publicly.
Hey, I do it so you don't have to. No, I was talking about Steve's what's in my ham shake episode,
which was aired today. Oh, yes. Well, thank you. Thank you. No, I haven't listened to it yet,
because I listened to it in the following morning. Yeah, kind of interesting timing there. So,
yeah, see what you think about that. If there's any other ham radio operators listening that
would like to do a show on that series, I think that'd be pretty cool too. Yeah, thanks very
much for that Steve. Thanks very much for everybody for coming up and doing these shows.
Yeah, and we could use any number of participants. Please just join and correct us and help us
with explaining stuff to Ken and the others. And the next recording is at least planned for
15th November, about the same time, 80, 18 UTC, or if someone needs another time, we can wiggle this
a little bit. All right, well, that sounds good. I guess we'll go ahead and wrap this up then. So,
thanks everybody for listening and tune in tomorrow for another exciting episode of Hacker Public Radio.
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