I am getting ready to start working on my first radio receiver (not countin g the crystal radio). I plan to start my experimentation first on the AM an d FM broadcast bands and then move to the amateur bands once I get my licen se, so I initially won't go much higher than about 100 MHz.
Can I get by without a spectrum analyzer? I have a 100 MHz scope at home, a nd intermittent access to a 1 GHz scope at work. Would that be enough for c ircuit verification?
If not what would be the max frequency I should be looking for in my spectr um analyzer (presumably from ebay)? I had read somewhere that even with low frequency stuff my oscillators or mixers could be giving out spurious osci llations at several GHz that I should be aware of.
I have also searched the group and found some leads to signal hound analyze rs and I wonder if those would be adequate for this kind of experimenting.
Aside from crystal radios and a few low frequency oscillators that I built, I have very little experience with radio and so I expect there could be pl enty of things going wrong spectrum-wise.
I am getting ready to start working on my first radio receiver (not counting the crystal radio). I plan to start my experimentation first on the AM and FM broadcast bands and then move to the amateur bands once I get my license, so I initially won't go much higher than about 100 MHz.
Can I get by without a spectrum analyzer?
** Get yourself a radio scanner and a frequency counter first.
Both a quite cheap and scanners are very sensitive and accurate detectors of RF energy - no coupling to the circuit is ever required.
I had read somewhere that even with low frequency stuff my oscillators or mixers could be giving out spurious oscillations at several GHz that I should be aware of.
** Pricks who own expensive spectrum analysers ALWAYS use that bogey man to impress others.
Honestly, I never fully understood the concept behind a frequency counter. If I have multiple spurs at different frequencies, does it automatically di splay the highest frequency component? My 100 MHz home scope (Kikusui 7101A ) has a frequency counter display, would that count (no pun)?
Thanks for the radio scanner info, I'll be hunting for one!
That's the spectrum of a Linear Tech switching regulator that was FM modulated by a sawtooth to make it spread-spectrum. That takes the emission peak down about 20 dB. It didn't seem to affect the DC output.
You sound like a guy who can't afford a spectrum analyzer.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
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Honestly, I never fully understood the concept behind a frequency counter.
** Essentially, it will count the number of zero crossings in a wave per second.
You have MISREAD me again.
It is an essential piece of kit for RF experimentation.
If I have multiple spurs at different frequencies,
** Usually they will be simple harmonics, so having found the fundamental frequency - you can set the scanner to each multiple and see if there is a strong signal there.
Also, a portable analogue TV will allow you to see if significant RF interference is being generated across the VHF and UHF bands and at approximately what frequency. Then you can zoom in using a scanner.
.... Phil
Thanks for the radio scanner info, I'll be hunting for one!
ing the crystal radio). I plan to start my experimentation first on the AM and FM broadcast bands and then move to the amateur bands once I get my lic ense, so I initially won't go much higher than about 100 MHz.
and intermittent access to a 1 GHz scope at work. Would that be enough for circuit verification?
trum analyzer (presumably from ebay)? I had read somewhere that even with l ow frequency stuff my oscillators or mixers could be giving out spurious os cillations at several GHz that I should be aware of.
zers and I wonder if those would be adequate for this kind of experimenting .
t, I have very little experience with radio and so I expect there could be plenty of things going wrong spectrum-wise.
Yeah you can get by without a SA, but the fact is that the SA and NA are th e the primary lab tool tools of the RF eng..
Get your self a good stable tracking gen along with your SA and now you hav e a scaler NA.
Scopes typically have limited dynamic range rendering the FFT stuff usless for serious RF work.
If you are serious about RF work you won't be sorry investing in a SA.
If you just want to "piddle" around stick with a scope.
Does "working on" mean designing a receiver from scratch, building a kit, or building one from instructions found on the internet? It makes a big difference as to the equipment required. With a kit, you can get away with a soldering iron and your 100MHz scope. Designing something from scratch is going to take a signal generator, sweep or tracking generator, oscilloscope, distortion analyzer, frequency counter, junk parts collection, LRC meter, DVM, etc.
If you had a low capacitance, high impedance broadband amplifier for the scope, you could probably get away with a 100Mhz scope. The idea is to not load the circuit that you're probing. Still, a spectrum analyzer would be better to tune the various filters required and to get accurate filter loss measurements.
Ham radio licenses no longer require Morse code, have a minimum of theory, and are mostly rules and regulations intended mostly to prevent you from becoming a source of RF interference. Get your license first and then build things. The very basic theory you need to learn in order to get the license will certainly help with any design or construction project.
Yes, if you know what you're doing and have other equipment that might serve the purpose of measuring frequency response and signal levels.
The problem with electronics is that we can't see electrons. We're effectively blind and need to rely on test equipment to "see" what's happening. The better the test equipment, the easier it is to "see" the circuit in action. RF is even worse, because it often doesn't even have the decency to remain on the wires and likes to hop around landing in unexpected places.
I found a copy of the 1963 version of the Tektronix "Funadmentals of Spectrum Analysis", which should offer a clue as to what can be done with a spectrum analyzer. Perhaps it would be best if you decided what you're going to be doing with one before buying:
No. You're lacking a proper signal source. Actually, you'll need two or possibly three signal generators to do intermodulation measurements.
For a receiver, just the highest frequency that you expect to be looking at. Since many receivers use high side injection, that would probably be your maximum frequency. However, you will not be able to see harmonics of the various oscillators or spurious oscillations at much higher frequencies. If these are of interest, 1GHz would be a good maximum frequency.
Yeah, sorta. Amplifiers and oscillators like spew odd frequencies that need to be suppressed. About the only way you're going to see these is with a spectrum analyzer. You'll never see these with a scope.
Most of those are CATV receiver front ends programmed to act as a spectrum analyzer. Personally, I would prefer older used boat anchor name brand test equipment, over a CATV receiver, but if money is a problem, it might suffice. The few that I've tried were marginal and could be used for most everything except making accurate measurements.
If you start from scratch, you're going to learn proper construction techniques and RF bypassing in a hurry. I'm not sure where you should start. Probably building something that's beyond your current abilities, but which you know for sure will work in the end. You'll pickup theory and how it works as you progress through the usual mistakes. Perhaps dissecting a working radio, making measurements as you go along, annotating the schematic with voltages and waveforms, and looking for possible improvements might be a better start. At least you'll see how a proper receiver works before you embark on doing your own. Don't be afraid to make changes and tweak things. You'll see the effects of those changes with your measurements.
Good luck.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
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I appreciate all the help and answers. Aside from quoting you, I tried this time not to address you directly as to make my follow up questions directe d to the group. Can't say I'm experienced with USENET but I see question/fo llow up to the question a standard practice here. I did not expect you woul d have to answer my followup question in any way, I was merely expressing n eed for further explanation. I do not know how I would have done it differe ntly. In any case, the group here has a number of very helpful people and v ery knowledgeable and I do not wish to alienate anyone. My apologies.
True. I come from a digital background (Software, HDL, FPGA, Microcontrolle rs) but Analog/Radio was a long time obsession for me despite lacking prope r education, mentorship and not being very good at it. I will not become a serious RF engineer (being in my mid-thirties, too late for that I think) n or will I change careers. I would like to be a bit more advanced though tha n a ham radio operator. I would like to gain proper understanding of the ci rcuits I'm working with.
First of all, thanks for the very thorough answer.
My intention is to design a receiver from modules. At this point I will not be able to design say an oscillator from scratch, but I would like to expe riment with different oscillator topologies from text books and tweak them until I get a good understanding of what works and what doesn't.
After being impressed a coworker, I learned the alphabet, numbers, and some punctuations in about 10 hours last weekend just for fun. I'm still very s low though (3-5 WPM max listening).
Working on those slowly. Morse was more fun.
Not even broadcast receivers?
I think my school education and extensive reading covers me well here. I mo stly lack practical experience so most of this knowledge is paper knowledge and unconnected dots.
Thanks for this. I will give it a look. I'm almost sure I have it on my har d drive somewhere.
I was thinking of constructing my own oscillators for this purpose as part of the learning process. I also thought of buying modules like this:
Can you get by without? Certainly. Part of the original purpose of a spec is that it can be easier to observe signals in the frequency domain. Back in the day, no one succeeded in building a CRT with many GHz of bandwidth, but a sufficiently high frequency oscillator can sweep through all those frequencies like it's nothing; add a dumb detector and you've got the essence of a spec. So back in the days of inventing radar, they didn't have scopes that could observe carrier frequencies, but it wasn't a big deal, either.
By the way, get really good at understanding and seeing the Fourier transform. Long time is small frequency and vice versa.
What the scope is good at showing is features within a cycle: distortion, harmonics, glitches, edges, that sort of thing. Or features among several cycles, like pulse trains. The frequencies corresponding to these features are spread well apart, on harmonics of the fundamental. But a radio circuit is probably tuned to the fundamental only, so most of the time, those harmonics will be attenuated and you won't be seeing much on the scope. The scope is good at short time differences, which means big frequency differences -- harmonics.
The other valuable feature of the spec is dynamic range. Looking at a visually pure sine wave, you might guess it's less than 2% distortion, but with an amplitude about 10 times less than the main waveform, you can't tell how much is left. A transmitter's harmonics should be 60dB down, a factor of a thousand (by voltage) -- you have no chance of proving this with a scope!
The interesting stuff in radio happens over many cycles, the modulation. Looking at an AM radio signal on the scope, cycle to cycle, you'll see only a blur, it won't mean anything. But zoom in on that signal with a spec and you'll see the complementary sidebands (which, if you could zoom in further, maybe you'd see familiar patterns again, like the harmonics of musical notes, or, the grating drone of talk radio..), characteristic of AM. This narrow difference in frequency (a few kHz out of a MHz+ signal) is impossible to resolve on some scopes -- actually, some of the better digital scopes might intentionally antialias high frequency signals, like the carrier, preventing one from seeing the modulation at all (this isn't so much a problem with the scope as it is a matter of setup, however).
Radio, holistically, is all of these things at once, so you're looking for the distortion of the modulation, and of the carrier, and even though you're filtering it, harmonics are like exhaust noise from an engine; it's always nice to have it smoother before you muffle it down, since all those filters get tedious to build otherwise. With mixers, multipliers and dividers, all sorts of frequencies can get into your signal path (or out from it): image signals, spurs, noise, overloading, etc. In a receiver, it's a matter of how nice it sounds, how easy it is to operate; in a transmitter, it's a legal requirement to operate with a sufficiently pure output.
Tim
--
Deep Friar: a very philosophical monk.
Website: http://seventransistorlabs.com
"M. Hamed" wrote in message
news:6797245f-48c6-4f58-a17b-68477e11a79f@googlegroups.com...
I am getting ready to start working on my first radio receiver (not
counting the crystal radio). I plan to start my experimentation first on
the AM and FM broadcast bands and then move to the amateur bands once I
get my license, so I initially won't go much higher than about 100 MHz.
Can I get by without a spectrum analyzer? I have a 100 MHz scope at home,
and intermittent access to a 1 GHz scope at work. Would that be enough for
circuit verification?
If not what would be the max frequency I should be looking for in my
spectrum analyzer (presumably from ebay)? I had read somewhere that even
with low frequency stuff my oscillators or mixers could be giving out
spurious oscillations at several GHz that I should be aware of.
I have also searched the group and found some leads to signal hound
analyzers and I wonder if those would be adequate for this kind of
experimenting.
Aside from crystal radios and a few low frequency oscillators that I
built, I have very little experience with radio and so I expect there
could be plenty of things going wrong spectrum-wise.
True. I come from a digital background (Software, HDL, FPGA, Microcontrollers)
** That explains a lot.
but Analog/Radio was a long time obsession for me despite lacking proper education, mentorship and not being very good at it.
** Stereotypical hobbyist.
I will not become a serious RF engineer (being in my mid-thirties, too late for that I think) nor will I change careers. I would like to be a bit more advanced though than a ham radio operator. I would like to gain proper understanding of the circuits I'm working with.
** You do realise that 99% of radio hams for the last 30+ years have simply bought commercial ham radio equipment.
The HF bands have been abandoned and VHF is too hard to roll you own for all but engineers with well equipped workshops.
the crystal radio). I plan to start my experimentation first on the AM and FM broadcast bands and then move to the amateur bands once I get my license, so I initially won't go much higher than about 100 MHz.
intermittent access to a 1 GHz scope at work. Would that be enough for circuit verification?
analyzer (presumably from ebay)? I had read somewhere that even with low frequency stuff my oscillators or mixers could be giving out spurious oscillations at several GHz that I should be aware of.
and I wonder if those would be adequate for this kind of experimenting.
have very little experience with radio and so I expect there could be plenty of things going wrong spectrum-wise.
Executive Summary: The secret to a happy life is managed (LOW) expectations.
In a newsgroup like this, you'll find some very smart people, a lot of "mine is bigger than yours" and some very disagreeable people. Problem is that you can't tell which advice is good.
Having a ham license is good, but you don't need one to join a ham club, go to swapmeets to buy equipment and get advice from practical people.
By all means, if you can afford a spectrum analyzer, buy one. But find someone experienced to help you decide. Demand far exceeds supply. Basic rule of thumb is that if a spectrum analyzer is affordable, it's seriously busted and the parts to fix it are unavailable. It's tempting to assume that, just because it shows a green line on the screen, and the seller is smiling, it's working. Resist that temptation.
A spectrum analyzer is very delicate, so most people won't lend you theirs, but many people will help you if you take your gizmo to them. Most anybody in the cable tv or cellphone business has access to a service monitor.
But you already have all you need to build a receiver for the broadcast (or most any) band. People built receivers and transmitters for decades without spectrum analyzers. There's a reason the ham bands are harmonically related.
Start with copying other's designs and go from there. Realistically, you won't be able to do any better for a long time. People here can tell you how to get the last microdb of noise figure, but it won't make any difference to you if you're not trying to do mars bounce.
Take it slow, hang out with some hams, read some books and do what is fun.
People like the signal hounds. That is a good sign because just about every device has detractors. One thing to keep in mind is you always want Linux compatibility in any USB device. Computers OSs change as time goes on and new drivers do not get written for windows.
Your scope is pretty low in bandwidth, so it would probably only be useful in designing HF gear, but your first ham license will be VHF. There is a device called the RF Detector Probe. Lots of companies make them. It is just a probe with an envelope detector. Not really a great device, but it lets you see energy beyond the bandwidth of your scope.
Regarding buying old gear on ebay, I buy less used gear and more Chinese stuff. I hate to admit it, but since the major instrumentation companies like Agilent and Tek have gone to Chinese OEMs (maybe ODM), you can cut out the middle man. A sampling scope can do crude spectral analysis.
All this said, you might want to consider googling rtlsdr and just go software defined radio if you want to hack. One of those dvb-t dongles on ebay and a mcx to some friendlier connector puts you in the radio biz, at least as far as receiving goes.
I'm not a big SDR fan, though I am hacking with the stuff now that the price of entry is less than an ATM unit ($20). They are good for decoding digital signals, and that is the trend these days.
The old HP gear is good, but they are getting long in the tooth. Expect repairs. If you don't live in a high tech area, you will probably end up junking the gear. Professional repairs often cost more than what you pay for the item on ebay. In Silicon Valley, there are retired people that used to work on the gear and can fix HP stuff. Same goes for the Portland area.
On a sunny day (Sat, 20 Apr 2013 20:28:54 -0700 (PDT)) it happened "M. Hamed" wrote in :
Absurd. All I ever learned about 'radio frequency' circuits (say up to a few hundred MHz) I learned with only a 5 MHz scope that I build myself BTW, and some radios. And that includes analog TV. And of course I did read Elector... Wireless World, Radio Electronica, Radio Bulletin, Dr Blan, ARRL, Veron magazine, or whatever I could get my hands on...
Did you ever get that ARRL (or whatever) handbook, and build some stuff?
So, now, !!%#&^!@#&^%!#* build something, and if you worry about THz or even light radiation of your oscillators: DONT.
OH NO , DARKEN THE ROOM, SEE YOU ANY LIGHT EMANATING FROM YOUR CIRCUIT? BAD BAD BAD H A R M O N I C S.
LOL
You read too much and build too little, or read the wrong things. WTF do you care if you interfere with quantum communication of the planet Zork... (with your 100MHz Ft cutoff transistor).
Yes but unless you build something nothing will ever be wrong.
And beware of LEDs, those shine at very much higher frequencies..
Old school: If you were lucky you had a grid-dip meter to test LC circuits, I once tried building one, it worked in some range, but was more work then use...
And it ALSO helps to have some idea of what you actually want to use the things for you are building.
Interesting comment. Is the abandonment because of spectrum overload, or some other reason? I would have thought that a lot of the historical occupants of HF - propaganda radio (Radio Hanoi etc) as well as marine would long ago have transitioned to more modern methods, such as local microstations on higher frequencies, or satellite. What's HF used for mainly these days?
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