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Review: Rohde & Schwarz FPH spectrum analyser

Review: Rohde & Schwarz FPH spectrum analyser

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By eeNews Europe



General

While termed "handheld", the unit is more than a handful (Figure 1). While it matches the form factor of many of its competitors, such as Keysight and Anritsu, it still weighs in at a hefty 5.5 pounds. The hand strap on the side does help steady it using a single hand, but I’d not want to carry it one-handed for very long. R&S does provide an optional neck strap and carry case that will support it at a usable angle. The side handle is also convenient for carrying. There’s also a handy rear foldout support that’s a bit finicky to unsnap as there’s little to grasp, but once deployed, props up the unit safely. Underneath the support leg, you’ll find the replaceable lithum-ion battery and micro SD card slot for storing data and screen shots. The plastic enclosure is covered with a rubberised protective boot. There are no vents or fans and all ports are covered with rubberised plugs, so the instrument is rated to MIL-PRF-28800F class 2 and against dust and drip water (rain, typically) to the IP51 spec. Boot-up time is about 17 seconds. For more information on specifications, click on the link in the References section.

The colour touch screen is impressively clear and sharp and is easily readable in direct sunlight. It includes gesture control, so the frequency, span, reference level and markers may all be controlled by finger control (either scrolling or two-finger pinching, etc.).

Figure 1 – The Rohde & Schwarz model FPH handheld spectrum analyser with collapsible stand deployed.

 

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Controls

The primary controls: Frequency, Bandwidth, Sweep, Trace, and Measure, and Marker are located above the numeric keypad, with Span and Amplitude going down the left side. Above that are the system keys: Preset, Setup, Mode, Lines, Save/Recall, and Screen Capture – which I love, by the way. You can configure the file name text in Settings, and then each press of the Screen Capture button auto-increments the count. Files are saved in JPEG or PNG format.

Figure 2 – Front panel showing the major controls.

Setting the frequency limits is easy. You can either set Centre/Span or Upper/Lower limits. For communications purposes, there’s a way to enter the channel uplink or downlink. The Frequency Offset control allows shifting of the displayed spectrum in 1 Hz increments. The Bandwidth button allows control of a manual or auto BW setting. RBWs (resolution bandwidths) can be set from 3 Hz to 3 MHz in a 1/3/10 sequence. In like manner, sweep time may be set manually or set to auto. Setting can run from 20 msec to 1000 seconds. The Scroll wheel has a centre push button that serves as an “Enter” control.

Figure 3 – The top panel showing the various ports; Input, Trigger/Ref In, Headphones, and two USB.

The top panel (Figure 3) includes the Input port, External Trigger/External Reference Input, headphone jack, and a couple USB ports. The left side panel includes the battery charger connector and a security slot. The right side panel includes an Ethernet and USB port. The instrument may be controlled remotely using either the Ethernet or USB ports through standard SCPI or VISA control. All ports include rubberised covers for weather protection.

Figure 4 – The Rohde & Schwarz model FPH handheld spectrum analyser probing an embedded controller board using a Rohde & Schwarz RS H 50-1 near field probe.

The Trace control allows setting of Clear/Write, Max Hold, Min Hold, and Average. It also controls the detector modes: Auto Peak, Max Peak, Min Peak, Sample, and RMS. This is also where you would enable the second trace and save to memory 1 or 2. There are also some trace math functions.

Figure 5 – A plot showing the harmonic content from a ST Microelectronic STM32f4 Discovery embedded processor from Figure 1. Note the marker located at the peak clock frequency of 269 MHz. The display was placed into Max Hold and we’re looking from 30 to 1000 MHz.

The Marker control allows finding the peak signal (New Marker), which is immediately connected to the scroll wheel. There are six markers available with associated delta frequency and amplitude readouts in the upper display. In addition, setting a marker on a specific signal and then pressing Marker Function, reveals demodulation settings for AM and FM. I love the fact the marker label (“M1”) is located off the trace. There is an oddity, though. I suppose in order to preserve display real estate, R&S has chosen to use the entire left-hand portion of the screen to display the trace. The issue is that the trace obscures the vertical scale. My preference would be to sacrifice part of the screen and go with the convention other analysers use, by keeping the vertical scale information clear of trace data.

Span allows setting of manual, full, zero, or last span. The Amplitude control will set the reference level, range/reference position, vertical units (dBm, dBmV, dBµV, or W. With the appropriate transducer, additional units of dBµV/m, dBµA/m, V/m, and W/m² are available. The Att/Amp/Imp soft key allows setting of RF attenuation (0 to 40 dB), input impedance (50 or 75 Ohms).

You can attenuate the signal to a suitable level either manually or automatically. In the "automatic attenuation" mode, the level of attenuation at the RF input depends on the current reference level. The R&S Spectrum Rider provides two ways of automatic attenuation. For the highest possible sensitivity, it provides the "Auto Low Noise" attenuation mode.

For the lowest possible intermodulation, it provides the "Auto Low Distortion" mode. The main difference between the two modes is that the attenuation level is 5 to 10 dB higher in case of "Auto Low Distortion" than it is for "Auto Low Noise". In the default state, "Auto Low Distortion" is active.

The Transducer soft key will bring up a variety of R&S antennas and power sensors. This automatically adds the transducer factors, which is pretty cool. For example, you can enter the antenna factors for a given antenna and the display will read out directly in dBµV/m. Up to 1000 data points may be entered and stored. These data sets may only be created or edited using the supplied R&S Instrument View software.

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Measurements

One of the features I love and use a lot is the “display line” – something found on the Rigol and Keysight analysers. I use this for quick “A-B” testing where the line is positioned at the top of the harmonic “before” condition. It’s then easy as you make changes to the circuitry by watching whether the harmonic amplitude increases above or decreases below the reference line. You can tell at a glance whether you’re making progress. While the FPH does not appear to have a dedicated display line, it’s possible to use the Lines > Upper Limit > Set Threshold and then adjust the vertical position with the scroll wheel. The threshold level is displayed to the nearest dB in the bottom right corner of the screen (see Figure 6).

Figure 6 – A spectral plot of the 2.4 GHz ISM band showing a couple Wi-Fi channels, along with several Bluetooth frequency hops. The analyser was placed in Max Hold in order to capture the BT channels and Wi-Fi envelope. Note the Threshold Line (red) at -62 dBm being used as a substitute for a “display line”.

Figure 7 – The commercial FM broadcast band displayed from 88 to 108 MHz as received just west of Colorado Springs. Three markers were activated, indicating the three largest signals. Despite the wide span, the marker frequencies were quite accurate.

One very handy feature for broadcast communications professionals is the ease by which AM or FM modulated signals may be demodulated. Placing the marker at the peak of the modulated signal and then use Marker > Marker Function > AM/FM will demodulate the signal and feed it to the built in speaker. Audio is interrupted periodically by the sweep time, but station identification may be confirmed easily.

I also checked for internal spurious signals by terminating the input port with a 50-Ohm load and searching over the entire frequency range with a narrow 30 kHz resolution bandwidth. The trace was placed in Max Hold and allowed to sweep (22 seconds each) several times. The trace was free of spurs, with the exception of a very small one near 3.555 GHz. That’s considered pretty “clean”.

Figure 8 – The model FPH is very clean as far as spurious signals.

Summary

The Rohde & Schwarz model FPH “Spectrum Rider” is a high quality affordable portable general-purpose spectrum analyser that may be used in the lab or field. The basic frequency range is 5 kHz to 2 GHz, but can be user-upgraded to 3 or 4 GHz as budgets dictate. I wish the upper frequency limit went to at least 6 GHz so the 5 GHz Wi-Fi (ISM) band could be viewed. The built-in functionality is amasing and nearly matches most lab-quality bench top analysers, which is saying something considering the size. Speaking of size, the analyser should be able to fit in most briefcases. However, I would suggest purchasing the optional soft carrying case to protect the display.

This would be the perfect spectrum analyser for the field technician. Battery life appears to be close to the advertised 8 hours. The display is easily read in full sunlight. The controls are familiar and laid out neatly. The e-manual is excellent and the index and contents are linked, which is a nice touch. The base price starts at $5,220 and upper frequency upgrades are $870 each (2 to 3 and 3 to 4 GHz). The built-in broadband preamplifier, which I recommend, is an additional $440. Highly recommended.

Things I like:

Rugged and weatherproof

Versatile touch screen control

One button screen captures

Markers automatically find the highest peaks

Fast demodulation of AM and FM

Ability to enter transducer factors

Things I’d like to see improved:

The upper frequency range should optionally go to 6 GHz

Add dedicated display line

Displayed trace should not cover the vertical scale

References

R&S FPH abbreviated product brochure
R&S FPH comprehensive product brochure
R&S FPH specifications
R&S FPH Getting Started manual
R&S full User Manual

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