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thebugger
modified 9 years ago

100km RF FM Amplifier
22
60
702
07:59:15
Well 100km is very relative to say, but given a good line of sight I think 130W of RF power should be able to cover that distance. God I wanna try that. Too bad it's illegal and an appropriate power transistor will cost a few hundred bucks or so :/. Okay so basically the RF amp is comprised of two stages, the first can be viewed as a common base driver stage, and the second stage is the power amplifier. The efficiency is not very good, at around 40% but with the right transistor and heatsink it shouldn't matter. The input power required for the full 130W is 2W.
published 9 years ago
SigmaEOD
9 years ago
Why do you have like a thousand grounds? Like wouldn't it be easier just to have a few an connect them instead of placing all of them xD
thebugger
9 years ago
I just like to make my layout like so. It's basically the same thing, as having one ground rail.
SigmaEOD
9 years ago
I know that lol, but it seems like a lot of extra work to achieve the same thing
giomix
9 years ago
This layout is often used in old tubes radios & other layout. I like it.
Robert_Kidd
9 years ago
The important thing is the circuit. True a bad layout can be unsightly and sometimes makes it more difficult to understand BUT this isn't a bad layout.
thebugger
9 years ago
Yeah I just thought of something. It's usually good to use a lot of ground area for the grounds, and it's important for it to be continuous. That's why I use only the ground symbols and not a single rail, cuz a rail would imply that we use a single wire or something, and the ground may imply we use the chassis directly or a larger ground area
hurz
9 years ago
From 2m above the ground, if you are a tall guy, you have 5km line of sight! To bridge 100km you have to lift the transmitter to 800m! So not so many hidden places you can put your pirate transmitter. BTW, if you know you have to go to jail why do you care soooooo much about harmonics. Just remove that filter shit and call the police with your radio ;-)
thebugger
9 years ago
Not jail, at least not the first two times. We have different laws about that probably. I'll get a solid fine first :D P.S. 800m is very obtainable. We have a very good mountain view right next to our city, it's high enough to broadcast over 170km range, but FM tranamitters can't go that far anyway. P.S. This elevation factor can be slightly diminished because VHF waves slightly curve when propagating, but that will extend the range by no more than a few km. The bypass to this situation is to raise the antenna for instance up to 100m, so that you'll have a 35km range and use repeaters every 30km or so.
thebugger
9 years ago
P.S. I'm preparing for a zombie apocalypse, don't mind me :D
hurz
9 years ago
You have A very good mountain view, and they waiting there for you. Because they know this place is ideal/needed to bridge large distances. So, easy case for the police to get you. For 170km you need 2300m mountain! And again a unmodulated carrier FM or AM reach the same distance. Only the carrier frequency matters 100MHz and not the kind of modulation.
thebugger
9 years ago
Yes the mountain is 2.3km high, and is very afforested, so it's not gonna be as easy to find me as you think. Even more triangulation will be extremely hard due to the terrain. But that's irrelevant, I'm not gonna try it anyway. I can't afford the power transistor :D P.S. I know the frequency is what matters but what I meant is that due the refraction of the atmosphere, FM waves do not propagate in exactly a line of sight way. They usually curve slightly and can reach up to 15-20% the ideal radio horizon at which they're calculated. So for instance if it were possible to transmitt at 170km with an FM transmitter the actual height of the antenna won't be 2300m but around 2000m. For ground waves it's different. The range is directly proportional to the power of the transmitter, and is only slightly attenuated by the terrain.
thebugger
9 years ago
And P.S. the type of modulation is also important. With AM it's more important the distance between the transmitter and receiver, where at larger distances, more noise is added to the signal, making it at some point incoherent even with the most sensitive receiver, whereas in FM the received quality is more of a transmitter power/receiver sensitivity deal. For instance let's assume that both AM and FM can work perfectly fine at 1MHz. Which one will be received at further distance?
hurz
9 years ago
You say yes and no! “ I know the frequency is what matters but what I meant is that due the refraction of the atmosphere, ...........“ - sorry, again the atmoshere does NOT care about the type of modulation. Its only the carrier frequency that matters.
thebugger
9 years ago
The atmosphere doesn't care about the modulation type, but as far as a receiver is concerned, the atmosphere has a very different impact on the received signal, depending whether it's AM or FM. As I told you. If AM and FM were both capable of working at 1MHz, FM would be received at much greater distance than AM, despite that they both suffer the same path attenuation. With FM the distance through any medium is irrelevant as long as the receiver is sensitive enough to pick it up. With AM, you can be next to the transmitter and still unable to pick up anything in a thunderstorm for instance
hurz
9 years ago
But the question was how far you can get with 100MHz. Without a carrier there is nothing to demodulate. Doesn't matter if AM FM PSK QAM.... the modulation is of second priority and depends on what kind of signal/information you would like to transfer. You think to much about analoge audio signals and suround sound.... However, its nice to see that you learned AM is possible on any frequency and not only on far distance radio broadcast below 1MHz.
thebugger
9 years ago
Well duh :D The carrier doesn't decide the modulation type. It's the other way around. According to the requirements of the modulation type, you choose the carrier frequency. FM has a greater deviation than AM, so it's more suitable for higher frequencies. AM doesn't suck on so much EM resource, so it's more suitable for lower frequencies. P.S. 100MHz can get you to the moon and back with 3mW of power, so as I said, it's not about attenuation it's about receiver sensitivity. With AM it's mostly about noise.
emogenet
9 years ago
@SigmaEOD: I find explicit use of grounds *way* better than having a ground rail snake around in the circuit. It makes it much easier to understand how the circuit works intuitively, especially if it's a large one. Just like the convention to put supply nodes on top and ground nodes below whenever possible: it helps intuition. And @thebugger is also correct: for something that's gonna run at about 100Mhz you *really* dont want a ground rail on your real circuit, and the many grounds is clearly suggestive of the need of a ground plane. Ground rails are like goto's in code : grossly inelegant and make it impossible to understand how things work.
thebugger
9 years ago
Yes inelegant is probably the word. It just suits my eye more when it's with separate grounds. It's basically the same thing just looks better
thebugger
9 years ago
But yes with RF circuits it's pretty important to use a large ground area, and continuous too. The so called ground plane. This I learned the hard way
zorgrian
9 years ago
Sorry you are completely wrong! Amplitude modulation and its variants such as DSB SSB reduced carrier etc propagate over far greater distance than FM. Yes it is partly due to the way that FM is demodulated.
zorgrian
9 years ago
However, you are persistent in muddling FM with VHF. So half the time you mean to say VHF when saying FM and the other way around.
zorgrian
9 years ago
If you have two VHF FM transmitter systems of a watt at two ends of an open field. You will be able to walk in and out of each broadcast. The receiver will work to receive one or other signal. But not both. The fuzzy area will be a couple of meters at most. Were you to try the same with any type of amplitude modulation you would likely find a mix of both broadcast signals in most parts of the field save the closest proximity to one of the antenna
zorgrian
9 years ago
I suggest you look at better antenna than more power
thebugger
9 years ago
No man, you're wrong. The path attenuation has nothing to do with the modulation type. AM and all its forms like QAM and whatever all have lower noise immunity than FM no matter what. The signal is encoded in the AMPLITUDE of the carrier and as long as you have a strong RF source nearby, you're screwed. The scenarios you propose are mostly about interference, not path attenuation. Both AM and FM can be interfered with, in much the same way. Don't think for a second that in the open field scenario, you'll be able to demodulate anything coherent from the AM. On the other hand as long as you have a sensitive low noise receiver, you can always pick up FM, but no matter the sensitivity of your receiver you may not be able to pick up AM even if you're right next to the transmitter, if you have an EMI source somewhere in the vicinity. AM works at greater distances only because it works at the lower end of the EM spectrum, and even then it quickly becomes incoherent after some distance, despite the fact that the receiver is still locked good on its frequency. If FM were to work at the same end of the EM spectrum as AM, it could probably be received around the globe with the right receiver.
thebugger
9 years ago
When I say FM I mean FM, when I Say VHF I mean VHF, I haven't confused anything. It seems to me that you confuse modulation type with carrier frequency properties.
zorgrian
9 years ago
Okay, go do these experiments and then tell me what you think
zorgrian
9 years ago
Yes FM has a higher immunity to other signals than does AM. However AM and its derivatives are far better for long distance communication. The best of these is phase modulation such as psk31.
zorgrian
9 years ago
You can easily modulate a 7 MHz carrier and try this out. And no it won't go round the globe. But a skip of very large distance is possible. Although FM is great for hi-fi experience it is not, even in narrow band format, good for long distance communication. In the end no form of modulation is as good as a simple CW carrier using morse code. You can cover enormous distances with good conditions with just a few milliwatts. The human ear/ brain is better at distinguishing between signals and noise (QRM) than any analogue or digital modulation method. When the ear fails, you can achieve even greater selectivity by using your eyes.
zorgrian
9 years ago
http://www.qsl.net/m0ayf/Transmitting-QRSS.html
zorgrian
9 years ago
The people who are into this stuff use the 30 meter qrss sub band to cover huge distance using milliwatts
zorgrian
9 years ago
So yes FM has better noise immunity but at the expense of having a decent amount of carrier.
zorgrian
9 years ago
AM and FM and all other forms of modulation are indeed possible at 1 MHz. Please dont try this as its inside a broadcast band. But you could try it out at 1.8 MHz. Assuming that you have the space to make an antenna
thebugger
9 years ago
All analog AM techniques use the low end of the EM spectrum as the carrier, that's why they're able to propagate such distances. FM works at higher frequency because of the modulation requirements, and that's why it travels shorter distances, due to the line of sight restriction. Excluding carrier frequency restrictions all other FM parameters of FM are superior to AM.
thebugger
9 years ago
P.S. You're either giving me examples of LW AM transmissions of up to 30MHz, which is exactly why it travels greater distances or with digital AM, which has error correction to fix any noise problems. If you try analog AM and FM at VHF frequencies, you'll get further range from FM.
zorgrian
9 years ago
The 70 cm band is full of examples of propagation using SSB and CW amongst others including FM and DV. On the 70 cm band, (UHF), if you want to work long distances you will probably be using CW or SSB. This requires some form of horizontally polarised beam aerial. SO NO NOT ALL AM techniques use the LOW END of the EM spectrum... Shove that up your pipe!
zorgrian
9 years ago
Amazing that you carry on like this for years ad infinitum. You proclaim things that are not true repeatedly until eventually you discover enough combatant information. I advise that this is a rather puerile and totally inefficient method to learn a subject. Why dont you do more research in the first place or actually gain some experience by doing the things you say you have already done? OMG the answer is gonna be worse than the rest of your tripe... forget it!
hurz
9 years ago
@zorgrian, i couldn't say that better. 100% agree.
thebugger
9 years ago
You continue to give me bad examples, you tart. All commercial ANALOG AM techniques ARE at the lower end of the band. What you continue to give me as an example is DIGITAL modulation, which has got almost nothing to do with noise, there's error correction, fading considerations, doppler shift correction etc. With plain old ANALOG AM, WHICH IS FUCKING EXACTLY WHAT I'M TALKING ABOUT, the only reason it propagates further is due to the use of ground waves. Even then, after some distance, enough noise superimposes itself onto the carrier and the coherency is kaput. Put ANALOG AM and FM side by side at VHF and tell me which is gonna propagate further, and more coherent.
thebugger
9 years ago
Notice hom many times I've used ANALOG, since you've been avoiding analog AM transmissions at VHF
thebugger
9 years ago
Just you know what. Let's start with comparison of analog AM vs FM. You start.
zorgrian
9 years ago
he 70 cm band is full of examples of propagation using SSB and CW amongst others including FM and DV
zorgrian
9 years ago
433 MHz is UHF! Listen to that band. See how many DX operators are working the band with FM....
zorgrian
9 years ago
Why has digital modulation got nothing to do with noise? It has everything to do with making a reliable communication even with noise.
zorgrian
9 years ago
BTW. Noise does NOT superimpose itself onto a carrier wave. No!
zorgrian
9 years ago
BPSK31 does not employ error code correction PSK31 is created by software that generates an amplitude- and phase-modulated waveform that is converted to an audio frequency analogue signal by a sound card.
zorgrian
9 years ago
I will answer you question of putting AM and FM 'side by side at VHF' (here we must assume that we are talking about the next available 'channel' etc) OK, the answer as @Hurz explained a while back, is.... they will propagate exactly the same! So, your majesty, the subject is not about a battle between AM and FM. No! It is about the subject of radio. Additionally, I feel it is also about the way one chooses to learn....
zorgrian
9 years ago
On a positive note, I concur with your choice to use multiple earth symbols, which especially in EC is more practical than if one were to connect a diagram with a negative rail. I am not too sure that this would imply the use of a ground plane instead of bus bar wire but if you specifically state this in your accompanying circuit description then, yes it seems very reasonable.
thebugger
9 years ago
Let's just moce the carrier frequency out of the equation and discuss the properties of analog amplitude modulation and freqency modulation, not the wave propagation. That's a whole other topic.
thebugger
9 years ago
Let me start. AM and FM obviously encode the signal in two different aspects of the carrier wave (the amplitude and the frequency). The implications of this is that AM has less requirements for bandwidth, while FM has 3-4 greater requirements. A point goes to AM. AM systems are usually simpler, both modulation and demodulation. You can receive AM without external power supply e.g. the crystal radio. Another point goes to AM. Interference - Both AM and FM are affected by interference, but FM has superior noise immunity. Yes both can be overshadowed by a strong RF source nearby, but only AM increases its S/N ratio in the presence of a strong RF field. FM will either be overshadowed or reception will remain the same. A point for FM. This leads us to our next implication. If you neglect the carrier frequency of AM and FM (again speaking analog, and standardized) FM will be received at much greater distance than AM, because the ability to receive it is mostly restricted by the receiver's sensitivity, where with AM it's also about noise. Another point goes to FM. Okay so far they both got two points. I say we leave it at that and call it a day, okay?
hurz
9 years ago
Have you ever heared about noise to phase and frequency conversion in FM receiver. Are you aware of the fact that FM can and is mostly “overmodulated“ which mean 80kHz for radio broadcast can not be made with AM and 15kHz audio. But to compare both, the resources have to be equal, right? Same carrier freq and equal bandwidth use. And after line of sight both methodes wont work at 100MHz. And YES FM does have a little modulation gain 12dB but this drops quickly shortly before line of sight and will get even ugly because of noise to phase transformation which is quite hard to listen while AM signal can be still decoded by humans. My point wasn't to talk about modulation. It was just a question of 100MHz and line of sight were the signal drops into thermal noise and disapears. If we want to go into modulation and its robustnes, we would need much better start definitions. And please accept at least there is on all avaiable frequencies AM present as zorgrian told you as active radio amateure, i guess.
thebugger
9 years ago
Yes I accept that AM is used throughout the spectrum, but mostly digitally. Analog AM resides in the low end. Also yes the resource requirements for FM are greater, but that's only because it's used to transmitt high resolution sound. If you compress the sound to the human speach range (300-3400Hz), the deviation requirement will fall. Anyway that's irrelevant, to answer your question, yes VHF is mostly restricted to line of sight propagation, but as long as you have a strong sensitive enough receiver, you'll always get it. Recently I was reading about Earth-Moon-Earth Communication and it turns out NASA managed to transmitt, bounce and receive a UHF signal, with only 3mW, where the path attenuation is extreme at -300dB. So as I said as long as you got a sensitive enough receiver you'll get even the faintest signals demodulated, but travelling 600000km will impose too much noise and it probably won't work with AM. There was no mention of the modulation type
hurz
9 years ago
But they are in line of sight!!!! If you are of line of sight there is nothing to amplify then noise!! Noise amplified by 100000000dB is still noise.
thebugger
9 years ago
Yes exactly. I just find it unimaginable, to have 3mW attenuated at -310dB. I can't even calculate the power at the receiver
do7prm
9 years ago
Just become an amateur radio operator and it is no longer illegal. There are hams in every country and courses for the exam.
hurz
9 years ago
Congrats do7prm ! Grüße aus Bayern.
do7prm
9 years ago
Ofcourse tx in the radioband is still illegal.
do7prm
9 years ago
See bfra.bg for a start
thebugger
9 years ago
I know I know, I wanted to get a certificate for a ham operator, but that still doesn't give me the right to transmitt in this range, also I live in a flat, and I haven't got the place to put an antenna for lower frequency bands
do7prm
9 years ago
We have the 2m band 144 Mhz, which ahould be similar. One can get 600km with a portabel antenna (ex. Hb9cv) and 10watt power.
thebugger
9 years ago
Yeah 144MHz is the freeware band so to speak, I think in Bulgaria we don't have limitations on that band, as long as there's no interference, but not too many receivers can capture the transmission, only special ones. I wanna transmit in the FM range

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