Agilent FieldFox RF Analyzer


Photo © Agilent Technologies 2009 All Rights Reserved

I am a bit of a test equipment junkie….it has something to do with working in the electronic measurement business for most of my career. There are many great pieces of test equipment out there but every once in a while, one comes along that really captures the imagination. Over the weekend, I got my hands on the new FieldFox RF Analyzer from Agilent Technologies. This analyzer is a combination 2-port network analyzer, cable tester and spectrum analyzer in one compact package. Add in an external sensor and it measures RF power, too. [Disclosure: I am employed by Agilent.]

With a base price of $7600, this instrument is probably out of the price range of most radio amateurs. However, the RF engineers and technicians out there in the electronics industry will appreciate its measurement capability and value.

The first thing I did was connect it up to my vertical antenna used for 2 Meters and 70 centimeters. I was able to check a few things on the antenna system and monitor some signals. Funny thing, when I tuned to the 2 Meter ham band, I didn’t see any transmitters on the air <sigh>.  So I switched over to the FM broadcast band and did a scan of 86 to 110 MHz. The spectral lines you see sticking up are the FM broadcast transmitters in my area.

Then I checked the VSWR of the antenna system (as seen looking through the end of the cable).  The sweep below shows the VSWR of the antenna system versus frequency. The center of screen is 146 MHz and the marker is set at 146.52 MHz. The VSWR doesn’t quite stay under 2.0 over the entire band.

Then I switched to the Cable Tester mode and displayed Distance to Fault (DTF). The DTF display shows the return loss of the cable as a function of the distance along the cable. (The FieldFox analyzer can correct for the propagation velocity but I did not have this feature turned on. So the distance shown is in error by that amount.)

The bump in the middle of the display is about 60 feet down the line, which corresponds to where an inline surge supressor is installed. Apparently, there is a small “impedance bump” in the line at that point. At the right hand side of the display, around 110 feet is an impedance change due to the antenna. If I had a good 50 ohm load on the end of the cable, we would not see this blip. The DTF measurement is a broadband measurement so anything that is not a good 50 ohms across all frequencyes (such as a high Q antenna) shows up as an impedance blip.

These results are not bad but I expected the impedance of the antenna system to be better than this. If I can hang onto the analyzer for a few more days, I’ll be sure to investigate the antenna system more carefully. Nothing like having the right test equipment to make useful and accurate measurements.

73, Bob K0NR

  1. #1 by Steve K9ZW on 2 February 2009 - 7:42 am

    Hi Bob K0NR

    Thank you for sharing your experience with this neat bit of kit!

    One cane dream about having access to such a neat instrument!

    Looking at your charts and how you used the FieldFox it looks to be also a VNA class of test gear?

    Been using a RiserBond TDR, Ex-US Army MegaOhmer and a TimeWave AntennaSmith in my shack, but this FieldFox really looks sweet.

    73

    Steve
    K9ZW

  2. #2 by Bob on 2 February 2009 - 9:23 am

    Steve,
    Yes, it is a Vector Network Analzyer (VNA) with one-port (S11) and two-port (S21) measurements. It has a flexible calibration system built in, in that you can use external loads / thru connections or just cal internally.

    73, Bob

  3. #3 by Richard McLean on 22 January 2010 - 8:39 pm

    Hi Bob,

    I am reasonably technically minded but not an electronics expert (I am a Medical Specialist) but I have an interest in Amateur Radio.

    I have the top level (Advanved) Amateur Radio License in my country (Australia), but little experience in antenna building – I got the license a couple of years ago largely as an academic exercise and have not really put it to much use so far.

    I am mainly interested in the HF bands.

    Can you tell me whether the FieldFox would be the answer to all my antenna construction needs…..

    In other words, with this instrument alone, would I be able to fine tune an antenna and feedline to the best they could be ?

    There seem to be many antenna analyzing tools out there, each claiming to be the perfect tool.

    Some are standalone, and some require a laptop, some are cheap and some costly (Fieldfox = ouch) – I would prefer standalone and one that is capable of measuring all the necessary parameters accurately and reliably. Price is important but secondary to the other requirements (capable standalone unit).

    It’s hard for a person like me to know which unit is best.

    Rather than experiment for hours/days/weeks with getting an antenna system right, I am the sort of person that would like to measure accurately, make the necessary corrections and re-measure until the system is at it’s optimal state.

    This is why such an instrument has some appeal, as it might take the guesswork out of antenna construction and be quite educational at the same time.

    While the FieldFox seems like a complex tool, I’m sure it would not be beyond me to learn how to use it, at least to do the basics of antenna and transmission line testing.

    Can you give me your thoughts on the applicability of this unit (or any similar units on the market) to my situation, given my brief description of my needs ?

    Regards

    Richard

  4. #4 by K0NR on 22 January 2010 - 9:02 pm

    Richard,
    The Fieldfox is an excellent tool for measuring antennas, so I am confident it would meet your needs. As you point it, it is expensive by ham radio standards (that is, compare it to an MFJ antenna analyzer at $250). It really is a professional grade tool and I have friends in the mobile radio business that think it is an outstanding value.

    The FieldFox covers frequencies up >4 GHz, which drives up the cost. For HF work, you might want to consider a much lower cost solution such as the miniVNA:
    http://www.ssbusa.com/minivna.html

    I have heard good things about the miniVNA but have not used one myself.

    73, Bob K0NR

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