FPC1500 Spectrum Analyzer - Review

Table of contents

RoadTest: FPC1500 Spectrum Analyzer

Author: DiligentMinds.com

Creation date: 1 Jul 2018

Evaluation Type: Test Equipment

Did you receive all parts the manufacturer stated would be included in the package?: True

What other parts do you consider comparable to this product?: There are no comparable instruments with all of the same features at the same price, in fact even the low-cost vendors can't compete with the price/performance ratio of this unit.

What were the biggest problems encountered?: The only way I could get the WiFi option to work was to use an old router that was configured as an 'open' access point (no passphrase).

Detailed Review:

The FPC1500 is an affordable VNA [Vector Network Analyzer], with a tracking generator that can be used in additional modes.  This is a review of this instrument.  As a disclosure, Element-14 and R&S supplied this instrument for this review, but it is not "free" for me, since I do have to pay income tax for the full retail amount of the instrument and options.  That said, I would not hold back any negative impressions of this instrument (and there are only a few-- hence my high rating).

The unit arrived in a surprisingly small box, but inside it was protected quite well with expanded polystyrene molded supports and open-cell foam padding-- and could probably take quite a bit of shipping abuse before the instrument would be damaged. My unit arrived without a scratch on the box or anything inside of it. I was particularly taken aback by the very light weight of the box before I opened it, and I was wondering if they forgot to pack the instrument inside!  But no, there it was-- this instrument is very light weight indeed. For spectrum analyzers, I am used to my old HP unit, which is basically a “boat anchor”-- and at about 100LBS it takes 2 people to safely move it around. I was quite shocked by such a light weight unit-- and that has a lot of advantages (and at least one disadvantage-- see below).

The FPC1500 is a 2-port vector network analyzer, that has a frequency range from 5MHz up to 3GHz. The unit supplied to me for this review was configured for a 3GHz maximum frequency.

The front panel is well laid out and very intuitive-- I found that I did not need to read the manual much at all, and only for the more esoteric features and tweaks. The buttons have a soft rubbery feel, but with a solid (and satisfying) tactile feel at the end of their travel-- very much reminiscent of the old HP calculators (HP-15C, et. al.). I found that I could do almost everything I needed to do, just by moving around in the menus and getting to know the instrument that way. This instrument is very much easier to use than my old analog HP spectrum analyzer. The screen is absolutely HUGE for what needs to be presented-- and you can directly view even the tiniest signal details without zooming in-- it is a real joy to work with, but you do need to be directly viewing it from the front-- there is not a great vertical or horizontal viewing range on this display. For classroom (or board room) use, an external display can be used with a computer connected to the instrument through the remote interface.

With a set of near-field probes and the 3GHz option, this instrument could be used for EMC pre-compliance testing. It is in fact well suited to this task due to the very low noise floor, and fantastic sensitivity.

This particular model has some unique characteristics-- the signal generation port can be a (more or less normal) tracking generator, but the frequency of the signal generator can also be controlled independently of the spectrum analyzer’s sweep frequency, as well as locked to center of span, which allows some additional tests over the normal (and expected) frequency response curve.

In addition to the special modes of the signal generator, there is also an internal VSWR bridge for additional measurement modes. This can be used to test cables (cable loss vs. frequency and “distance to fault”, much like a TDR), and will measure the frequency response (SWR) of an antenna over any frequency span in the range of the instrument. There are modes to correct for a different characteristic impedance (like 75-ohms)-- or a custom impedance. This came in handy for my TV antenna testing (below).

One thing to note though-- the signal generator puts out a square-wave-- not a sine-wave as most people would expect. This is not much of a problem for most measurements because of the super-high performance filters in the spectrum analyzer side of the instrument-- and this square wave will only become an issue in some very rare measurements, so the test engineer will have to be aware of this and take precautions (or use an external generator) if this will be an issue.

The only way I could get the WiFi option to work was to use an old router that was configured as an 'open' access point (no passphrase). All other attempts to get the WiFi connection to work with either a very modern access point (using WPA2-PSK-AES) to an older router (using WPA-TKIP) failed. The company took a while to respond, but they were very nice on the phone and promised to send the issue to the R&D group. It is entirely possible that my particular unit simply has a bad WiFi radio, or that radio needs a firmware update (but I don't see any way for me to check and/or update that).

There has already been a tear-down and review on “The Signal Path” YouTube channel, and on that channel the presenter provides a great deal of information on the functionality of the instrument. I particularly like that he discovered that there is a lot of space inside (in the back of the unit), and the unit runs on a 12V supply. This opens up the possibility that a battery can be installed for use in locations that have no AC power-- (like the top of a tower, etc.-- a lot like a “Field Fox”). It is certainly light enough for this-- in fact so light that I have to hold onto it with my other hand to push the front panel buttons when the unit is sitting on a slippery lab bench. The “fix” for this is to put a rubber pad underneath the unit when on your bench.

As far as the spectrum analyzer function goes-- this unit has one of the lowest DANL specs I have seen-- even compared to my ancient HP spectrum analyzer that uses “old school” YIG filters and oscillators. In fact, in one of my tests, I set the RBW and VBW to 1Hz, and the number of sweep (trace) averages to 100, and was able to achieve a noise floor of -195dBm (with the LN preamp turned on). The small "blip" at the center of span appears to be an artifact of the signal chain-- and it appears no matter the span or center frequency.  This setting takes a ridiculously long time to take a measurement, but I did it as an exercise to see just how low we can go.

The spectrum analyzer also has an AM/FM/ASK/FSK demodulator option, that I was unable to test at this time (but will post back later in the forum as I use these obscure functions)-- this feature would be very handy if you need it.

Of particular interest, is the ability to connect a filter in the traditional tracking-generator/spectrum-analyzer (insertion loss) mode (S₂₁), and then the response of the filter can be monitored as the filter is tuned. If you are doing this kind of work, there is no better tool to help you with this task. You can also use this mode to get a fairly good idea of the frequency response for a cable.

In the single-port (return loss) mode (S₁₁), there are some additional tests that can be done to test a cable-- even when you don’t have access to the other end of the cable (though it’s better when you do). This mode is also magnificent in determining the frequency response of an antenna. After reading some scientific papers on wide-band disc antennas from MIT, I made a UHF TV antenna out of (2) 12-inch pizza pans (88 cents each at Walmart) and a standard 4:1 balun. I mounted this antenna right on the wall-- very crude! Since I’m only 17 miles from the major TV broadcast stations, I was able to pull in all of the prime channels, with the exception of the one channel that is broadcasting on physical channel 2 (low end of the VHF TV spectrum-- 54MHz..60MHz)-- the pizza-pan dipole was just too small to get a good signal and so this channel is very marginal. It was interesting to see the frequency response and SWR curve of this “weird” antenna. It has an SWR of below 4.0 over the entire upper VHF and lower UHF TV bands-- which would probably be a lot lower if I could find a 1:1 balun to test it with-- (the characteristic impedance is closer to 75-ohms than 300-ohms).

Enhancements I would like to see:

1. I would like a way to see the version information of the WiFi radio firmware and be able to update it in the same way the instrument can be updated through the USB port (by using a thumb drive). Additionally, it would be nice to be able to TEST this radio (somehow)-- and to know if it is set to USA standards or some other standard (which is usually just a setting in the radio’s configuration memory).
2. There was little support for a keyboard-- when plugged in, it only replicated the front panel buttons, making signal labeling (and entering a WiFi passphrase) tedious. It should be easy to add HID support to the application-- since the hardware seems to support this, it most likely would be a firmware-only upgrade.
3. As the 5.8GHz (ISM) band is becoming increasingly important-- it would be nice to see a version of this instrument with a 6GHz bandwidth option.

Conclusions:

The size, weight, and price of this instrument, along with it’s “Swiss Army Knife” feature set, makes this a “must have” instrument for anyone engaged in even very rudimentary RF work. Even someone that only manufactures (or installs or aligns) antennas could use one of these, and would save countless hours of fussing around with lesser instruments. Designing, and adjusting filters is made much easier with this instrument-- it would easily pay for itself rapidly if you make a living doing these things. If you already have a high-end oscilloscope in your lab, this should be the next instrument you buy if you are doing any work that needs RF testing or EMC pre-compliance testing (embedded systems, etc.). The price from R&S is very reasonable for the performance and features offered-- and is an even better bargain than some of the lower cost alternatives out there (like company ‘R’ for example).