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Portable Spectrum Analyzer

The FSH-3 is a small portable fully-featured professional spectrum analyzer, developed by Rohde & Schwarz in Germany [1] around 2005. It can be used for fault finding, field maintenance, e.g. on mobile radio stations, and monitoring of the radio spectrum. Furthermore, the FSH-3 can be used for location of (intermittent) interferences and even for locating hidden transmitters (bugs).
The FSH-3 covers a frequency range from 100 kHz to 3 GHz and has a resolution bandwith of 100 Hz to 1 MHz. It can be powered by an external mains adapter or by the built-in rechargable batteries. With the built-in tracking generator, the FSH-3 can be used to measure the properties of filter networks and amplifiers.

All controls are at the front panel, directly below the full-colour display. The connectors for RF in, RF out (tracking generator) and optional Power Sensor are all at the rear, just above the grip. At the left, hidden in the grip is a 3.5 mm jack socket for connecting a pair of headphones.
FSH-3 with HE-100 (20-200 MHZ)

Rohde & Schwarz was among the first manufacturers to introduce portable spectrum analyzers and the FSH-3 belongs to their earliest developments. Other members of the the family are the FSH-6 (no longer available) and the FSH-18. The latter has a frequency range of 10 MHz to 18 GHz and a resolution bandwidth of 100 Hz to 1 MHz. The FSH-3 and FSH-18 were succeeded by the FSH-range of spectrum analyzers and related products like the PR-100 Portable Receiver.
Packaging FSH-3 in original packaging FSH-3 portable spectrum analyzer Front panel of the FSH-3 Operating the FSH-3 FSH-3 seen from the rear Carrying the FSH-3 Connections at the rear

All controls of the FSH-3 are nicely arranged on the clear uncluttered front panel. The top half of the front panel hold the large colour LCD screen, with 5 function keys (F1-F5) at the bottom. The lower half is taken van the keyboard, which has a row of grey MODE selectors at the top.

The rest of the keyboard consists of a full numerical key pad, buttons for selecting the required measurement units, and navigation keys. At the right is a large rotary dial that allows easy adjustement of parameters. At the bottom left is the (orange) ON/OFF button.
All connections to the FSH-3 are at the rear (just above the display) and at the sides. All HF connections are at the rear. A signal source or an antenna is connected to the first connector (at the left, seen from the front of the unit). The rightmost socket is the output of the built-in tracking generator. The remaining sockets are for an external trigger signal and a power sensor.

Two small sockets, one for the mains adapter and one for a pair of headphones, are hidden in the lower part of the blue carrying grip. The headphones can be used to listed directly to the demondulated signal. Furthermore, an optical serial port is available at the right side of the FSH-3. It can be connected to any PC, by means of the supplied serial interface or the USB interface.
Rear view of the FSH-3 Audio output Power adapter socket (charger) View from the right Optical port connected to the USB adapter FSH-3 and USB cable connector to the optical port Optical interface Optical USB interface

Bug tracing
The FSH-3 is a very convenient tool for locating HF eavesdropping devices, also known as 'bugs'. Such bugs are generally very low power transmitters that operate on a fixed frequency in the VHF, UHF or SHF band. Finding bugs is commonly known as bug tracing, bug fixing or sweeping.
Over the years, a wide variety of tools to perform a sweep have been developed by manufacturers all over the world. Such tools are often described as Technical Surveillance and Counter Measures (TSCM) and the FSH-3 falls into that category.

When searching for an unwanted radio signal, it is important to investigate only a small portion of the frequency spectrum, e.g. 100 - 200 MHz. If the frequency span is chosen too wide, it will not be possible to see any small signals. It is also important to known which signals (stations) normally resided in that part of the spectrum.
The FSH-3 with an FM radio bug at 203 MHz and a span of 200 MHz

Strong local radio stations will generally appear as a high peak and can easily mask the weak signals of a radio bug. For example: when scanning the spectrum between 100 MHz and 300 MHz, the center frequency should be set to 200 MHz and the frequency span to 200 MHz.
The image above shows the FSH-3 with a center frequency of 200 MHz and a span of 200 MHz. This means that the display shows all signals between 100 and 300 MHz. By using a special directional antenna, such as the HE-100, the effect of external signals can be minimised. The image above shows our test-bug at 203 MHz being detected (at the center) by the FSH-3.

When investigating the signal, it is advised to center the display at the signal's frequency (203.170 MHz) and decrease the span to, say, 10 MHz as is shown in the image on the right.
The FSH-3 with an FM radio bug at 203 MHz and a span of 10 MHz

If the span is further decreased, it should now be possible to see if the signal carries any modulation. In this case it is an Frequency Modulated signal (FM), but some bugs have their audio signal modulated on a so-called subcarrier. These are the so-called silent bugs or SC-bugs.
The bug in the example above is just a test bug that is often used by TSCM personnel to verify the operation of their sweep-equipment. Real-life professional bugs are often much smaller. An example of such a professional radio bug is the ATET S35 shown in the image on the right.

When the option FSH-K3 is installed, the FSH-3 can also be used as a receiver and can directly demodulate the intercepted signal. An external headphone can then be used to listen to the signal. Another R&S device that is very suitable for bug fixing is the PR-100 digital receiver.

 More about radio bugs
 Other TSCM tools
ATET 135 MHz radio bug

The FSH-3 with an FM radio bug at 203 MHz and a span of 200 MHz The FSH-3 with an FM radio bug at 203 MHz and a span of 10 MHz FSH-3, HE-100 antenna and a ATET radio bug at 135 MHz ATET 135 MHz radio bug FSH-3 showing a signal at 135.2 MHz Radio bug detected at 135.2 MHz FSH-3, HE-100 antenna and a ATET radio bug at 135 MHz

Serial (RS232) adapter Serial USB optical interface, can be used on PCs with no serial port USB FSH-Z22 parallel adapter Parallel A pair of Sennheiser headphones for listening to demodulated signals Phones Mains power adapter and charger Charger Quick Reference User manual Manual CD with software CD HE-100 directional antennas (optional) HE-100

Serial RS232 port
The easiest and most reliable way to interface a computer with the FSH-3 is via an RS232 interface. A suitable cable, that converts the optical port into a bi-directional serial RS232 port, is supplied with the device.

The serial port can be used to transfer data from the FSH-3 to the PC but also to remote control the FSH-3 from the PC.
Serial adapter

USB interface
As most modern desktop computers and laptops are no longer supplied with a serial RS232 port, an suitable USB converter is available as well. It basically contains a built-in converter from RS232 to USB and makes the device appear as a COM-port on the PC.

A suitable driver for this interface should be installed on the PC, and is supplied on the enclosed CD-ROM.
USB adapter

Parallel interface
In order to print images (screen dumps) directly from the FSH-3, an external parallel converter is available. It converts the optical port into a Centronics-compatible printer port.

A parallel printer can be connected to the 25-way D-type connector on the interface.
FSH-Z22 parallel adapter

A thin light-weight pair of Sennheiser PX-30 headphones is included with the FSH-3. It should be connected to the Phones socket at the left side of the carrying grip and can be used to listed to the demodulated audio of an intercepted RF signal.   

Power adapter/charger
The FSH-3 can be powered for approx. 4 hours by the internal rechargable NiMH batteries, but also by the included mains adapter. When the FSH-3 is connected to the mains, the internal batteries are automatically recharged.

The main adapter is suitable for virtually any mains wall socket in the world. Suitable wall socket pins are included with the adapter and by we swapped in seconds.
Mains adapter (charger)

A quick reference manual is supplied with the FSH-3. It is small enough to be stored with the device and describes the most common functions of the analyzer.

A more comprehensive Operator's Manual can be found on the supplied CD-ROM.
User Manual

The FSH-3 comes with a CD-ROM that contains the full Operator's Manual, as well as the FSH View software that can be run on a Windows PC. Furthermore it contains information about related products.   

Directional Antenna
The FSH-3 can be used as an effective tool for locating hidden transmitters (bugs) in a room, by using the active HE-100 directional antenna set, also developed by R&S. This antenna set was originally designed for the EB-100 surveillance receiver (Miniport), also from Rohde & Schwarz.
The HE-100 set consists of three pluggable antenna's and a pre-amplifier in the shape of a pistol grip, with a field-strength meter at the back. Depending on the required frequency range, one of the three antennas is attached to the front of the pre-amplifier, and is enabled by pressing the trigger-button on the pistol grip.

 More information
FSH-3 with one of the HE-100 antennas

The HE-100 antenna was later superceeded by the HE-300 active directional antenna, which has an extended frequency range from 20 MHz to 7.5 GHz. At the lower end, the frequency range can be further extended down to 9 kHz by adding the optional HE-300-HF module.
20-200 MHz antenna 200 - 500 MHz antenne 500 - 1000 MHz FSH-3 with HE-100 antanna Using the HE-100 with the FSH-3 FSH-3 with one of the HE-100 antennas FSH-3 with HE-100 (20-200 MHZ) HE-100 connected to the FSH-3

Software options
  • FSH-B1 - Distance-to-Fault Measurement
  • FSH-K1 - Remote Control via RS-232
  • FSH-K2 - Vector Transmission and Reflection Measurements
  • FSH-K3 - Receiver Mode
  • FSH-K4 - 3GPP FDD Code Domain Power BTS/Node Measurement
Optional accessories
  • FSH-Z1 - Power Sensor (10 MHz - 8 GHz)
  • FSH-Z2 - VSWR Bridge and Power Divider (10 MHz - 3 GHz)
  • FSH-Z3 - VSWR Bridge with DC Bias and Bypass Switch
  • FSH-Z14 - Direional Power Sensor (300 mW - 300 W, 25 MHz - 1 GHz)
  • FSH-Z18 - Power Sensor (10 MHz - 18 GHz)
  • FSH-Z44 - Directional Power Sensor (200 MHz - 4 GHz)
  • FSH-3
    This is the basic model that has a built-in pre-amplifier and covers a frequency range from 100 kHz to 3 GHz. This is the model that is featured on this page.

  • FSH-18
    This model can be regarded the 'big brother' of the FSH-3. At the upper end, the range has been extended to 18 GHz, but at the lower end the range is limited to 10 MHz. For frequencies below 10 MHz, the FSH-3 is required, or any of the later FSH models (below).

  • FSH-4/8/13/20
    The FSH-range is the successor of the FSH-3 and FSH-18 models. The range consists of 4 models, each with a different upper frequency limit. At the lower end of the spectrum, these models can measure as low as 9 kHz. The upper limits are 3.6, 8, 13.6 and 20 GHz respectively.

PR-100 Receiver
The FSH-3 is part of a large family of portable measurement devices from Rohde & Schwarz. The FSH-3/18 range is now superceeded by the newer FSH-4/8/13/20 range that is housed in a similar but sligtly modified case, with more function keys and additional navigation buttons.

The range comprises various spectrum analyzers, radio direction finders and digital receivers, many of which were developed with feedback from FSH-3 users in mind.

 More information

Several years ago, around 2005, Crypto Museum received an FSH-3 as a gift during a large HAM Radio fair in Germany. We used the device for several years to demonstrate it in combination with the HE-100 directional antenna for locating hidden transmitters (bugs). Although the device had some quirks, it worked fine until mid-2013, when it suddenly refused to switch on.

After consulting Rohde & Schwarz, it became obvious that our device was an engineering sample which was not intended for real use. So, was that the end of our FSH-3? No, it wasn't. When the kind people at Rohde & Schwarz learned that it was for the Crypto Museum, they decided to donate us a brand new one, for which we are very grateful. We are now able once more to demonstrate this beautiful and versatile instrument and show its wide range of applications. We are indebted to Ben Maarleveld and Alfons Verpoorten of Rohde & Schwarz Belenelux [1]. Thanks!
  1. Rohde & Schwarz Benelux, FSH3 Handheld Spectrum Analyzer - THANKS !
    Device featured on this page kindly donated by Rohde & Schwarz. January 2014.
    R&S Order No: 1145.5850.13.

  2. Rohde & Schwarz, R&S FSH Handheld Spectrum Analyzer
    FSH-3 brochure PD 0758.1593.32, version 04.00. March 2007.

  3. US Patent 2247743, Broadband Uni-directional Shortwave Antenna
    Harold H. Beverage. Filed 10 December 1938.

  4. DARC Verlag, Rothammels Antennenbuch
    ISBN: 3-88692-033-X. 2nd print 2002. p. 269-270.

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