Affordable Spectrum Analyser ?

Discussion in 'General Electronics Chat' started by monster_catfish, Apr 19, 2014.

  1. monster_catfish

    Thread Starter Active Member

    Mar 17, 2011
    For more precise trouble-shooting of the RF components that will need to be assembled during my ongoing RC aircraft hobbyist tinkering, I have been toying with the idea of acquiring a spectrum analyzer, BUT, the prices of such gear are out of this world, way up in the tens of thousands of dollars range.

    Anyway, after much dejected online price-shopping, I finally stumbled across a spectrum analyzer that costs a hair under the one thousand dollar mark, so I thought I would post its PDF spec sheet here, to see if any of you more experienced circuitry practitioners might have some pointers to offer regarding whether or not this model of spectrum analyzer will be worth its sticker price, which I can just about afford if I restrict myself to a diet of dog-biscuits for the next couple of years.

    The RF and video signals I will be looking at will range from 72MHz to 1.3GHz. I sure would appreciate any advice regarding whether or not the spectrum analyzer model in the below link would be a worthwhile addition to my modest collection of bench-test equipment.

    Thanks in advance for any insights that can be offered.
    Last edited: Apr 19, 2014
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    It depends on what you intend for the instrument to do for you. It is a trainer, and the specs read like something that will demonstrate concepts rather than give any kind of precision answers. Still, it can do things a scope can only dream of.

    Do you have an idea of the performance level you need? For example, the amplitude accuracy is only +/- 3 dB in its sweet spot range, and +/- 6 dB outside of that. The noise floor is barely 100 dB, 30 dB worse than those dream machines. But if that is 10 dB better than your test environment, your good.

    Overall I like it. It reads lke the right tool for someone who isn't designing the space shuttle. It should be fine for transmitter work, and anything in a receiver avter the first RF preamp. And you might find it for less without the signal source bundle.

  3. monster_catfish

    Thread Starter Active Member

    Mar 17, 2011
    Thanks for the response, AnalogKid. As an example of a project where I thought that a spectrum analyzer could eventually pay for itself, the video transmitter to be installed aboard my Bixler2 FPV glider is sold by ReadyMade RC at the following link.

    It operates over a frequency band between 1.08GGHz and 1.258GHz, sending out a 400mW signal to its matching receiver around which my FPV ground station is being constructed.

    My RC control signal sent from the ground station will be 72MHz, and not 27MHz as I wrote in error in my first post above. The frequency which most RC fliers looking for longer range select is currently 488MHz, but I decided to stay with an-old fashioned 72MHz RC control signal, because of its reputation for more reliable transmission through foliage.

    My understanding of RF electronics is very limited, which is why I decided to try and find an affordable spectrum analyzer that would help me better identify possible sources of noise and RF interference in my setup, and also enable me to study the effects of any filters or chokes that I may need to add to wiring as a fix.

    The only other spectrum analyzer that was comparable in price to the one in the first link I posted above is a refurbished unit selling at $1,400, shown in the below link. It costs fair bit more than I was hoping to spend on this gear that will be used mainly for hobby electronics testing, but it is a tempting buy for sure.

    I must confess that I haven't done enough reading on the subject to really have a grasp on the specific dB noise tolerances to expect with the RF and video transmitting modules that I am assembling for this project, so I decided that an affordable spectrum analyzer could perhaps save me money in lost RC airplanes over the coming years, since I am in this hobby for the long run, unless of course I bankrupt myself first ha ha.

    Additional comments or observations on both of the above models of spectrum analyzers would be much appreciated, since thus far in my RC electronics career I often feel a bit like a carpenter determined to try his hand at brain surgery, in defiance of common sense.
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
    why not check out the specs on the "fun cube dongle"? a tv tuner based reciever from .150 mHz to 2 gHz controlled brom the usp port? at around a hundred dollars US.
    I built a spectrum analyzer from several articles in ham radio magazines using a cable tv tuner and a uhf tv tuner that sweeps from around 1 to 1000 mhz, loosley based on the science workshop spectrum analyzer. works fine for me, even pretty good calibration in db and fair nose level.
  5. gootee

    Senior Member

    Apr 24, 2007
    There are some decent-looking used HP/Agilent (and other) spectrum analyzers on ebay, for well under $1000.
  6. monster_catfish

    Thread Starter Active Member

    Mar 17, 2011
    Alfacliff I thank you much for this very useful pointer on how to obtain a spectrum analyzer at a fraction of what I thought was the least expensive option on the market. I am about to do a Google search on the Fun Cube Dongle, and this new option may well be the way to go, since the price is so attractive.

    Gootee your input is appreciated as well. Generally speaking I have always been a bit skeptical of the quality of test equipment sold on Ebay, but there is no harm in taking a look at what is on offer currently.

    Much obliged fellas. I have some more homework to do on this subject for sure.
  7. ian field

    Distinguished Member

    Oct 27, 2012
    72MHz is a tad lower than a switchable band TV tuner and it doesn't quite go up to the top end you want.

    But years ago one of the UK consumer servicing mags published an article outlining how to convert a TV into a VHF/UHF spectrum analyser.

    The original idea had a level converter translating the vertical sweep waveform to 0 - 32V to sweep the varicap tuning. The agc was fed to a comparator with the horizontal sawtooth and used to switch the electron gun on/off, this gave horizontal lines whose length corresponded to amplitude at that frequency, the height of the line up the screen indicates frequency.

    The original design was for a CRT TV, which was bulky then and hard to find now, you could do the same with a VGA input LCD screen but you'd have to build the sawtooth generators that sweep frequency and drive the trace comparator, they'd also have to provide the sync signals for VGA. Also you'd have to search around for the bits to build your own tuner board - band IV/V tuners are fairly common, but the ones with band I/III and sat IF are a bit harder to find.
  8. alfacliff

    Well-Known Member

    Dec 13, 2013
    one hazzard to watch for on older test equipment is like the hp141 display, they used an epoxy inside the crt to hold thngs together that slowly outgasses and makes the display bad. the only replacements are made the same way and about the same time, so will probably have fuzzy displays.
  9. nsaspook

    AAC Fanatic!

    Aug 27, 2009
    I build one with the Linux SDR gqrx software using this cheap device.

    I also have the upconverter (older 100mhz version) to cover the full MF and HF band frequency range.

    There are several Spectrum Analyzer programs like this one.
    It won't give you an HP class instrument but it's pretty good for the price.