BUYER BEWARE when buying 'as is' Spectrum Analyzers!

    We here at Electronics Revisited, LLC specialize in the repair and refurbishment of electronic test equipment.  I am writing this particular review to warn potential buyers of spectrum analyzers 'as is' sales with no return policy.

  Some models of spectrum analyzers are sensitive to DC inputs or any input beyond the manufacturer's recommended maximum input levels. So sensitive in fact that the input circuitry can be burned-out (fried) and the unit may not function at all or may appear to function but in fact be only partially functional or completely unusable.


    Here are two scenarios that can occur either alone or together (we've seen them both.)   It is possible that one of the first circuit paths taken by the RF input signal is an attenuator device.  The attenuator ( step attenuator ) is generally an unbalanced resistive device which operates into the GHz bands of spectrum analyzer in use.  Exceeding the inputs will damage the step attenuator but the device may still appear operational when an input signal is supplied. Appear operational that is until that particular attenuator pad is selected by the front panel control, at which point the signal will drop to zero or be completely uncalibrated.  An Ebay listing picture may show a nice signal on the front of the spectrum analyzer but unless the seller warrants that the signal is present for all combinations of input attenuation, the buyer may get burned.   All is not lost.  If you end up getting stuck with such a failure, you could purchase an external attenuator and operate at some reduced functionality.

    The second failure mode is one of the internal mixer diodes gets fried.  This is a no-win situation with no solution for you. The Ebay picture may show what appears to be a working spectrum analyzer and the seller may show a screen shot of what appears to be a normal noise pattern, but no signal.  Be especially wary of such a device.  The noise pattern does not mean that the device is operational ( it might be but it might not.)  Ask the seller if he/she is willing to show a picture of some type of input on the screen, either from the device's own calibration output (if so equipped) or from an external source.


    We are not implying that people selling these are dishonest, it just may be that they do not know how to properly test this equipment past the power on stage.

   Spectrum Analyzers are expensive pieces of equipment and it is, in our opinion, always better to purchase from a dealer who has good feedback, has fully tested the device for all functional modes ( or otherwise discloses any deficiencies) and offers some type or return policy.