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Spectrum analyzer vs scope for radio experimentation

Discussion in 'Electronic Design' started by M. Hamed, Apr 21, 2013.

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  1. M. Hamed

    M. Hamed Guest

    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 lowfrequency 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.
     
  2. Phil Allison

    Phil Allison Guest

    "M. Hamed"

    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.



    .... Phil
     
  3. M. Hamed

    M. Hamed Guest

    Honestly, I never fully understood the concept behind a frequency counter. If I have multiple spurs at different frequencies, does it automatically display 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!
    Interesting!
     
  4. Phil Allison

    Phil Allison Guest

    "John Larkin = Asshole"
    ( snip crapology )


    ** No idiotic context shift is beyond fuckheads & arseholes like Larkin.




    .... Phil
     
  5. Phil Allison

    Phil Allison Guest

    "M. Hamed"
    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!
     
  6. M. Hamed

    M. Hamed Guest

    Sorry. I don't see where I misread you.
     
  7. Guest



    Yeah you can get by without a SA, but the fact is that the SA and NA are the
    the primary lab tool tools of the RF eng..

    Get your self a good stable tracking gen along with your SA and now you have 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.
     
  8. Phil Allison

    Phil Allison Guest

    "M. Hamed"

    ** I was giving you general advice.

    Not answering your question re spurs.


    .... Phil
     
  9. Phil Allison

    Phil Allison Guest

    <>


    If you are serious about RF work you won't be sorry investing in a SA.


    ** But the OP clearly is not "serious" - he is a hobbyist hoping to become
    a radio ham.


    If you just want to "piddle" around stick with a scope.


    ** You are one smug prick - aren't you.




    ..... Phil
     
  10. M. Hamed

    M. Hamed Guest

    I appreciate all the help and answers. Aside from quoting you, I tried thistime not to address you directly as to make my follow up questions directed to the group. Can't say I'm experienced with USENET but I see question/follow up to the question a standard practice here. I did not expect you would have to answer my followup question in any way, I was merely expressing need for further explanation. I do not know how I would have done it differently. In any case, the group here has a number of very helpful people and very knowledgeable and I do not wish to alienate anyone. My apologies.
     
  11. M. Hamed

    M. Hamed Guest

    True. I come from a digital background (Software, HDL, FPGA, Microcontrollers) but Analog/Radio was a long time obsession for me despite lacking proper 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) 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.
     
  12. M. Hamed

    M. Hamed Guest

    On Saturday, April 20, 2013 10:20:43 PM UTC-7, Jeff Liebermann wrote:

    First of all, thanks for the very thorough answer.
    My intention is to design a receiver from modules. At this point I will notbe able to design say an oscillator from scratch, but I would like to experiment 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 somepunctuations in about 10 hours last weekend just for fun. I'm still very slow 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 mostly lack practical experience so most of this knowledge is paper knowledgeand unconnected dots.
    Thanks for this. I will give it a look. I'm almost sure I have it on my hard 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: http://www.amazon.com/Retailstore-Frequency-Generator-Equipment-Shipping/dp/B009I7DR7E
    Thanks. All other points were very useful.
     
  13. Tim Williams

    Tim Williams Guest

    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

    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.
     
  14. Tim Williams

    Tim Williams Guest

  15. Phil Allison

    Phil Allison Guest

    "M. Hamed"
    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.



    ..... Phil
     
  16. mike

    mike Guest

    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.
     
  17. miso

    miso Guest

    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.
     
  18. Phil Allison

    Phil Allison Guest

    "Bruce Varley"

    ** The topic is " ham radio" - Bruce.

    What I said was that hams are not using HF like they once used did - the
    tiny bits they own are barely used.

    Get a communications receiver and you will see what sort of garbage the band
    is really full of - mainly data transmissions that sound like buzz saws.


    .... Phil
     
  19. Glenn

    Glenn Guest

    On 21/04/13 10.38, Jan Panteltje wrote:
    ....
    then use...
    ....

    Hi Jan

    It is because you need a digital dip meter. Analog display fiddling
    sucks. (just joking!) ;-)

    I think he has found a smart way by simply exchanging the whole
    oscillator to change bands. He simply "route" higher bands signals to
    the prescaler - and bypass the prescaler, when measuring the lower bands.

    Digital Dip Meter:
    http://elm-chan.org/works/ddm/report_e.html
    Quote: "...
    The microcontroller performs as simple frequency counter and level
    indicator but there is no user input.
    ....
    The oscillation frequency is measured by an AVR and displayed to the LCD
    ...."

    Schematic:
    http://elm-chan.org/works/ddm/sch1.png

    The above is a very crude and cheap digital spectrum analyzer with
    builtin frequency counter.

    MB501 ought to exchanged with what you can get cheaper. Maybe some
    source code need to be changed:
    http://elm-chan.org/works/ddm/ddm.zip

    -

    Other analog dip meters:


    A Dip Meter Using the Lambda Negative Resistance Circuit:
    http://users.tpg.com.au/ldbutler/NegResDipMeter.htm
    http://web.archive.org/web/20090412013051/web.telia.com/~u43200663/blocks/lambda_diode.htm

    German:
    FET-Dip-Meter Mk2 (2*dual gate MOSFET):
    http://www.mydarc.de/dk3wi/html/fet-dip-meter_mk2.html

    Glenn
     
  20. Glenn

    Glenn Guest

    (Answer is send to sci.electronics.design )

    ....

    Hi Bruce

    They have not been abandoned. They just have heavy competition from
    PCs... The competition also happened to model railway, football, and
    other indoor and outdoor activities.

    -

    The bands are stil used - especially 80 and 40 meters - but it also
    depends on the time of day and the sun spot cycle:
    http://en.wikipedia.org/wiki/Amateu...ocations#Table_of_Amateur_MF_and_HF_Bandplans

    Listen for yourself. Press "View: all bands". Move the/click filter
    cursor to the frequency you wan't to listen to. Drag the skirts to get a
    wider/narrower filter. The waterfall tells tell the band story ;-) This
    is point and click receiving!:

    Uses Java and Javascript:

    WebSDR de W4AX:
    http://w4ax.com/

    WebSDR at K7UEB Walla Walla University Club Station:
    http://outside.wallawalla.edu:8901

    Can use HTML5 instead of Java:
    Wide-band WebSDR:
    http://websdr.ewi.utwente.nl:8901/

    (found via http://da.wikipedia.org/wiki/Internet-fjernstyret_radiomodtager )

    -

    Maybe Phil just want the bands for himself ;-) (just joking).

    The public longwave, middlewave and shortwave stations have declined
    heavily the last - let say 10..15 years - because of radio by the
    internet I think.

    The station as a function of time, can be found here for free:

    ilgradio.com: This is the International Listening Guide:
    http://www.ilgradio.com/

    -

    There has been a movement toward digital (including stereo) public
    longwave, middlewave and shortwave stations instead of AM, but the
    receivers that support DRM are hard to find - there are only a few DRM
    stations (case of chicken and egg problem?):
    http://www.ilgradio.com/language-data/drm-broadcasts/index.html

    But you can use your PC and its soundcard to demodulate DRM (SDR!) - on
    Windows, Mac OS X and Linux. You simply mixes the 455KHz IF down to two
    signals spanning approx. 0..12KHz called I(for inband signal; real part)
    and optionally Q(for quadrature signal; imaginary part):
    http://www.spetzler.dk/bjarke/Projects/DRM/DRM.htm#A complete computer based DRM receiver system
    Universal DRM- miniature mixer unit:
    http://www.eham.net/reviews/detail/5919

    http://sourceforge.net/apps/mediawiki/drm/index.php?title=Main_Page

    DRM - Digital Radio Mondiale:
    http://en.wikipedia.org/wiki/Digital_Radio_Mondiale

    Glenn
     
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