CATV tuner based Spectrum Analyzer Building Project,

CATV tuner based hb spectrum analyzers
Date: Wed, 11 Oct 2000 06:07:33 -0700
From: "Rein A. Smit" 

   Hello all,

   Looking for some answers on questions re CATV based spectrum
   analyzers in particular on the K2BLA design from QST Nov 1985.

   Looking forward for responses,

   73 Rein W6/PA0ZN

Subject: Re: CATV tuner based hb spectrum analyzers
Date:    Mon, 16 Oct 2000 20:32:58 -0700
From:    Brian 

    Hi Rein,

    I'm not sure if this is what you're looking for but here's a
    PDF from an Aug. 98 QST article on a spectrum analyser;
    and recent updates on it;

    There was an article on building a spectrum "monitor"
    in Sept./Oct. 89 issues of Radio Electronics, using a UHF CATV tuner,
    K7ITM was kind enough to scan & email me the first section of the
    article & I've scanned the second half. If you want them, please email
    me ( 2 x ~7Mb).
    Brian VE7IJQ

Re:   CATV tuner based hb spectrum analyzers
Date: Thu, 12 Oct 2000 00:35:25 -0700
From: "Rein A. Smit" 

   Hello Brian,

   Thanks for the info. I have the articles. I am actually looking for
   inputs on how to modify if any, of the cable tv boxes. Had problems
   understanding what is going on in those converters. But I believe I understand 
   now that it are in fact double conversion boxes with as 2d IF either channel 3 
   or 4 around 55, 60 Mhz Intend to build an hybrid design of the K2BLA and the 
   poor men's spectrum analyzer. With modifications in the log IF amplifier part. 
   The poor men's design appears to come with 3 tuners covering from 5 MHz
   all the way up to 1.7 Ghz. I have no idea about variations in sensitivity etc 
   if one sweeps through the freq range. I have lots of plans to start building 
   stuff and I think having some simple form of spectrum analyzer will be very
   helpful and building the spectrum analyzer will be a nice project just
   by it self.

   The latest aug 98 design is a very nice design but it overs only a
   limited input freq range. The performance and possible calibration
   beats all the others I think. I though am interested to be able to scan the 
   VHF/UHF and 1296 MHz and Radio Astronomy bands.

   Also intend to keep a sort for progress report on the construction 
   on the web and perhaps this will stimulate some more SA building. 

   73 es tnx again

   Rein W6/PA0ZN

   Something you might consider is buying an old Wavetek SAM
   CATV signal level meter off of ebay or wherever.  They go
   dirt cheap these days.  They have a fully functional
   spectrum analyzer built in.  IIRC, the range is 4-450 Mhz
   and its all tunable for width, res, etc.
   Bill Meacham
   Vieques, PR

CATV spectrum analyzers
Date:  Tue, 17 Oct 2000 19:13:11 -0600
From:  David Feldman 

   I had the "poor man's spectrum analyzer".

   It took me about 20 hours to build from a kit to get it barely working.


        1. Poor frequency linearity
        2. Poor amplitude linearity
        3. Changes to selectivity = big change in amplitude calibration
        4. etc etc etc


        I bought an old systron-donner 762 series analyzer - it cost
        me about $400 and did everything that the CATV product did and
        much much more. Of course I had minor repairs but basically
        it was easy to service and covered >10 GHz without external
        waveguide mixer (much better than CATV product <1 GHz.)

        I recommend not trying CATV based product - I think it is basically
        waste of time.

        73 Dave WB0GAZ

Re: CATV spectrum analyzers
Date: Wed, 18 Oct 2000 06:53:28 -0600
From: "David Feldman" 
To:   "Rein A. Smit" 

     On 12 Oct 2000, at 8:42, Rein A. Smit wrote:

>    Hello David,
>    Thanks for your input. I am afraid I have gone to far already.

     It is a good learning experience, and you can create some unique
     controls, particularly if you use a PC as the basic control element.

>    Did you have a scan or ramp board? The basic kit is using the
>    scope's timebase as ramping voltage I believe. I am planning

     Mine used a ramp generator board as part of the kit (called
     "poor man's spectrum analyzer" which I renamed "man's poor
     spectrum analyzer". 

     Anyway the scope had external X-axis input. Retrace was not
     solved (so there was a faint line visible during scope retrace.)

>    on using the K2BLA design as backend with improved log IF amplifier

     There are some great log amp/detector chips from ANALOG 
     DEVICES you may wish to look - you can get dynamic range about
     80 dB with these, maybe more - it is big improvement over my kit
     (about 40 dB dynamic range) and over my systron donner (about
     60 dB dynamic range.) In fact I am preparing design for replacement
     log amp/detector in my systron donner to use one of the analog
     devices chips.

         Re: CATV spectrum analyzers
         18 Oct 2000 08:51:25 -0700

>    My thanks again. Yes I found an AD8307, they are very difficult to
>    get, seems.

     I did not try to source them - there are some evaluation kits available,
     and another part (I believe AD8309?) has somewhat different specs;
     you might want to look across their product line. These IC type
     log detectors seem ideally suited to homebrew spectrum analyzer.

     I believe I can get things under control except if
>    there are big problems with the tuner tuning voltages. Returning
>    to this K2BLA design ( Nov 85 QST ) they show a spectrum with
>    harmonics of a 10 Mhz xtal and the freq scale looks quite lineair??

     I haven't looked at that article - actually there is a hole in my QST
     collection from 1980 thru 1990 so I may never have seen it.

>    I have been looking for a spectrum analyzer for some time but 
>    really never found anything in the right price range. I also
>    see the project as an interesting exercise to get it going.

     Try - he often has systron donner 762 for sale and
     is a good vendor to work with if you want to try the surplus route.

>    Anyway I like to stay in touch with you as you have experiences
>    with this sort of approach. You might also have seen the articles

     It would be good to continue the dialog - I was interested in the homebrew
     approach too but have been more interested in modifying the systron
     donner (main thing now is new log detector and replace the sweep osc
     with a D/A converter to interface to a PC.)

>    in more recent QST's by W7ZOI on a 100 Mhz wide spectrum analyzer,
>    I will use this design as well to modify the "man's poor spectrum
>    analyzer." 
>    BTW the K2BLA design has a blanking provission on the display. If
>    you are interested in that paper I can send you a copy. Have not seen
>    much on the net about that paper. 

     I would be grateful for that,. if you can!

Subject: Home made Spectrumanalyzer.
Date:    Tue, 24 Oct 2000 11:24:44 +0200

     Some info can be found at .
     I have made a 200 MHz SA from scratch, with homebrew VCO and
     filters etc. I have studied the circuits used by HP, 30-years ago.
     Regards  Stein LA7MI in Bergen  Norway

Subject: Home made Spectrumanalyzer.
Date:    Thu, 2 Nov 2000 10:25:16 +0100
To:      "Rein A. Smit" 

     Hi Rein.
     Tnx fer mail.
     Back in 1988 Al Helfrick described a simple spectrumanalyzer
     in RF-Design. Later an improved version was described in Radcom in
     England.   (up to 90 MHz)
     I made a 200 MHz SA in 1988 based on circuits used by HP in their
     HP141T system.
     Some time ago I obtained some RF plug-in modules used in the HP141T
     system, with handbooks.Dont know their condition .
     In my design I found the VCO the most difficult part to design.
     The POS VCOs from Mini-Circuit have been used in a design from Germany.
     Another complex unit was the filter assy (3MHz) with eight  BW`s
     from 100 Hz to 300 kHz. Jitter in the VCO made the 100Hz and 300 Hz BW 
     I wish you good luck with your project.

     73 de  Stein LA7MI in Bergen,  Norway.

Subject: Re: Spektrum Analysator.
Date:    Sun, 12 Nov 2000 17:15:39 +0100
From:    "Prof. Dr.-Ing. Wolf-Henning Rech" 
To:      "Rein A. Smit" 

     Hello Rein,

     this was in 1990, and the circuit and PCB is published in the proceedings of 
     the Gigahertz meeting in Dorsten 1990. A republication by someone else has 
     been made in one of the AGAF journals (TV-Amateur) in the past years.

     Technology has moved quite a bit since then, so I do not longer recommend 
     (and support) such old projects. Nothing is available electronically. Sorry.

     Yours / 73

     Henning  DF9IC  N1EOW

Re: SV: W7ZOI's spectrum analyzer
Date:   Sat, 18 Nov 2000 11:57:46 -0800
From:  "Rein A. Smit" 
To:     J M Noeding 
References: 1

    Hi Jan-Martin

    Thanks for list. I have tried some of the Germans but very little success.
    I believe a lot of what is presented on those Tagungs never gets saved. It
    is the same in this country here. I am getting my stuff slowly together.
    And once it is running I can try to improve things in my own way.

    It are those tuners that I like to use that are causing the problems as
    very lilttle info is available. Did run via the net into a friend in Holland
    who deems to knpow about a few of these things.
    The main reason I want something is to be able to build LO's for th higher 
    Have strated an info page for the subject and will expand it as soon as
    more info is available.

    Thanks again for your help.

    73 Rein 

Subject: W7ZOI's spectrum analyzer
Date:    Sat, 18 Nov 2000 22:10:09 +0100
From:    "J M Noeding" 
To:      "Rein A. Smit" 

     DJ8ES Wolfgang used to be a reliable part, but not certain if his email is 
     He describes several new circuits every year in the Weinheim VHF meeting 
     book (Weinheim UKW-Tagung Scriptum der Vortrge until 1995), some later 
     appear in VHF communications, I enclose a file, although not updated, you 
     will see who has been active, and W means weinheim, UHF Unterlage is 
     translated to English and believe it is UHF Compendium by DJ9HO


Subject: Homebrew Spectrumanalyzer.
Date:    Mon, 20 Nov 2000 08:23:53 +0100

     Hello Rein.

     I have received copy of your mails to LA8AK. I have also received
     mail from you some time ago.
     The Al Helfrick story was in Rf-Design January 1988.  So far the
     best design I have seen was in Rf-Communication 11-12 years ago.
     If you are unable to get this magazine, I can send you a photo-copy
     of the introductory part of the story via snail-mail.
     I need your home address to do so (no charge ,HI).
     I told you  I made a 200 MHz SA based on the HP141T system back
     in 1988.
     Later I have made a 1 GHz SA based on a 1300-2300 MHz VCO from
     Z-Comm. I bought the VCO in San Jose, CA,in 1992 for $33. -.
     After  four conversions the final IF is 9 MHz. The log-detector
     is an AD606 from Analog Devices . The filter assy has eight  BWs from
     300 Hz to 1 MHz. To build an instrument like this you need knowledge and
     access to a networkanalyzer to tune the IF-filters.


     Stein LA7MI in Bergen  Norway.

Subject: Homebrew Spectrumanalyzer.
Date:    Mon, 20 Nov 2000 13:52:56 +0100

    Hello Rein.

    I did a mistake in my mail. The best design of a SA was in 
    VHF-Communication 11-12 years ago, not RF-Communication. Sorry.

    73 de LA7MI

Subject:  Re: Homebrew Spectrumanalyzer.
Date:     Mon, 20 Nov 2000 10:31:02 -0800
From:     "Rein A. Smit" 

    Hello Stein and Jan-Martin,

    Thanks for info again, and I am certainly interested in the UKW 
    Berichten article of 10 -11 yrs ago.

    As far as the my plans are concerned I will go ahead with the tuner
    so far. The backend is were I like to see the other info for.
    I have an AD606 here and will run down to 10.7 Mhz at the end.
    Use ceramic filters and will not try real narrow filter bandwiths.
    The spectrum analyzer oroject might take over everything else in the end!
    For now though, I want to have something I can tune LO's with and
    do some other work, like figuring out how much RFI there is at this
    time, before I start a new dish and other antennas.

    It has been and is frustrating how difficult it is to get info on this
    subject for whatever reason. I believe there must be quite a few 
    people that have tried or built SA's with more or less success.

    Just to do something about that I have started a project page and
    intend to report on progress etc etc. If the 2 of you do not
    object, I will list our emails.

    My main concern is still how to get a good tuner with specs.
    It appaers there is a wide variety of them, and believe it they
    are also hrd to find. Was Saturday here at a major fleamarket
    and there was nothing there, even not old VCR's.

    I will also get you copies on the K2BLA article.


Subject:  Re: 433 MHZ radio
Date:     Mon, 20 Nov 2000 15:53:36 -0500
From:     Charles S Osborne 
To:       Patrick Wood ,
          Society of Amateur Radio Astronomers 

     Just food for thought..

     Years ago TV tuners were used by some among us as downconverters for radio
     astronomy and Amateur TV. The Mitsumi tuners were cheap and plentiful.
     Recent cable ready tuners cover even more frequencies. filling in virtually
     all frequencies from 54 MHz to 900 MHz with a hopscotch numbering system
     implemented in phase locked loops and microprocessor logic.

     Has anyone tried using a VCR as a downconverter? Do the detection at channel
     3 ( 60-66 MHz). The catch, as usual, is that the automatic gain control has
     to be disabled. You may have to disable a few other video related chips
     before getting pure noise out.

     VCRs that munch or won't play tapes without ejecting at random times are $5
     items at lots of garage sales. Even a mediocre one usually has a pretty good
     SAW (surface acoustic wave) filter to reject adjacent channels and images.
     The electronic portions including the tuners seldom go out before the
     mechanical end of things begins to need frequenct attention. Of course
     lightning is another story. The tuner is the first "fuse" in that picture.

     Set it to "cable" and channel 53 is probably in the 403-409 MHz area, though
     I haven't checked the charts on that. A good preamp ahead of it and you've
     got a tunable front end. So if interference presents itself at one channel,
     hunt around a bit till you find less troublesome RFI. Similarly this
     appraoch would allow one to do 608 MHz or the high 300MHz range, dodging
     military satellites and garage door openers.

     Internal spurs may provide some challenges in a few VCRs. And certainly the
     temperature stability was not a concern when they were designed. But for the
     flexibility and price, its worthy of a look.

     For a more bulletproof aproach there's Carl Lyster's 408 downconverter
     available via Jeff Lichtman. Lots of filtering and attention to temperature
     / gain effects make that one quite a bit better than the VCR approach ever
     will be.

     The SARA 408 project kit by Jim Carroll is another excellent downconverter
     design with extensive temperature control and filtering. But its by no means
     a beginner's project. Chuck Forster had the parts for those kits, but he may
     be out.

     Charles Osborne
     SARA VP

Subject: Re: 433 MHZ radio using VCR
Date:    Mon, 20 Nov 2000 16:37:50 -0500
From:    Charles S Osborne 
To:      Patrick Wood ,
         Society of Amateur Radio Astronomers 

     I realized one will have to dig a little deeper into a VCR than it sounds at
     first from my previous message. The chan3 output is a remodulated output. So
     they take the signal all the way down to video/audio before modulating it
     back as channel 3.

     That means the signal would have to be intercepted for detection at some
     point in the circuitry prior to the video filtering at baseband.. getting
     deeper into uncharted or unschematic'd territory I'm afraid for most.

     Charles Osborne, K4CSO
     SARA VP

Subject  406 MHZ radioastronomy via a VCR
Date:    Mon, 20 Nov 2000 17:43:57 -0500
From:    Charles S Osborne 
To:      Patrick Wood ,
         Society of Amateur Radio Astronomers 

     Patrick, others,

     Here's a handful of good comments from Robert Rolf who has some experience
     with  the tuner ideas. The TV PC cards are a particularly good idea he
     mentions. For $50 they provide a built in TV tuner under PC control. The
     penalty is potential for noise from the PC's various clocks getting onto the
     signal as spurious signals.

     Charles Osborne


     Most older VCR tuners have a coax output at 45Mhz for the IF amp.
     Also, the AGC is usually on a pin on the case, and can be ID'd with
     a voltmeter or scope. Just apply strong signal, then none, and you'll
     see a couple of volts change. Make sure it's not the AFC (auto freq ctl)
     line. The old units typically have a Vcc, and Gnd, tuning (1-35V),
     AGC (0-2V), and several 0-5V digital pins for band selection (Lo, mid,
     hi, UHF).

     The really old voltage tuned units make great
     spectrum analysers. You just sweep the tuning voltage with a simple
     555 ramp generator (use a current source instead of a pullup R)
     and dual op amp to vary the gain/DC offset) and buffer the sweep to
     to the 30 odd volts required.

     Many machine schematics are available at your public library in
     the 'Sams Photofact' collection or 'RCS' reference manuals.

     Newer tuners put out baseband Video and Audio so they're harder to
     hack, and they are digitally tuned (which makes for great
     If you know a bit of PIC programming to bit bang the I2C
     control bus [which can also be done via the PC parallel port} you can
     also sweep them with great precision.

     I've used an old voltage controlled satellite tuner (950-1450) as a
     cheap SA. I'm looking at using one of the 'TV tuner' PC cards as a
     modern SA
     since it is digitally controlled. One has to hack on a narrow band
     filter prior to the video detector, but that's not too hard (except
     that the stuff is now all surface mount). A modern cable convertor
     is also an option for HF-UHF work.

     With the great penetration of DTH satellites, the old C band stuff
     is readily available for cheap, and it's tuner could be hacked to
     directly work H line (1420Mhz is within the normal downconversion

     The downfall of all these approaches is that the tuners are not
     particularly sensitive (they don't have to be with cable), so a preamp
     with front end filter is a good idea.

     IMO the most important first investment for a RA entheusiast is
     a good oscilloscope. You can't fix/tune/adjust what you can't see.
     A good RF probe will let a 10Mhz scope work out to Ghz.

     And you can always use a TV radio (54-88Mhz) to tune the 70Mhz
     IF out on many satellite receivers to do 1420 spectum work.