A 10 MHz to 1 GHz Spectrum Analyzer Adapter

Protek Inc.
Northvale, NJ

The explosive growth in wireless instruments has made spectrum analyzers an indispensable tool for testing and troubleshooting wireless equipment and systems. Realizing the need for a moderately priced, fully functional spectrum analyzer, the model 7700 10 MHz to 1 GHz digitally synthesized spectrum analyzer adapter has been developed. This unique device connects to a dual-channel oscilloscope and converts it into a 1 GHz spectrum analyzer with all of the features and functions needed to make precise frequency and power measurements.

The model 7700 spectrum analyzer adapter is the front end of a spectrum analyzer, which includes the mixers, local oscillators, log amplifiers and synchronizing circuits. The user’s oscilloscope provides the display and sweep circuits. This design results in a compact package that is easily transportable from site to site in a toolbox or under the user’s arm. It also provides lower power consumption than most spectrum analyzers. The actual power consumption is less than 1 A.

The spectrum analyzer adapter has many applications and uses in the communication and service industries. It is also a valuable tool in technical school laboratories for demonstrating the principles of spectrum analysis by connecting a complex electrical signal to the RF input and displaying on an oscilloscope the resultant harmonic frequency components and their mathematical relationships. The solutions to Fourier transform problems also may be verified in the same manner. The unit can be put to use in a multitude of industrial applications, including checking and troubleshooting IF and RF circuitry in wireless products such as two-way radios, PCS and cellular telephones in addition to cable TV systems, wireless remotes, wireless microphones and video equipment.

All spectrum parameters, such as center frequency, resolution bandwidth and reference level, are accessed via menus displayed on a back-lit liquid crystal display. All menu items are selected from front-panel keys and their values can be entered or changed by numeric or up/down arrow keys, thus making set-ups fast and easy. In addition, two frequency markers can be selected from the menu. These markers may be moved to any position on the waveform via the front-panel keys to display the frequency and amplitude values.

Fig. 1 The display of a 100 MHz carrier modulated with a 20 kHz tone. The model 7700 offers features and functions critical to the needs of the wireless industry. These capabilities include zero span for monitoring the amplitude of a carrier signal in the time domain. This mode will display any variations in the carrier amplitude over a period of time. Thus, long-term trends and carrier irregularities may be observed and noted. The instrument also provides frequency spans from 2 kHz/div to 100 MHz/div. These spans are sufficient to cover most wireless applications in the industry today. The 2 kHz/div span is narrow enough for viewing small frequency deviations, closely spaced adjacent carrier signals and sidebands. It is also useful for testing RF output-type sensors where a change in the sensor input value produces a proportional change in RF carrier deviation. Figure 1 shows the instrument’s display of a 100 MHz carrier frequency modulated with a 20 kHz tone. The spectrum analyzer adapter’s settings for this display are a 100 MHz center frequency with a 20 kHz frequency span and a -30 dBm reference level.

An average noise level of -140 dBm/Hz provides a noise floor as low as -105 dBm. This low noise level with a wide 120 dB input measuring range is critical for detecting and measuring weak fringe area interference signals as well as a receiver’s basic sensitivity. Table 1 lists the spectrum analyzer’s key performance specifications. The unit operates from a 12 V DC (1.5 A) power adapter. A type N female connector is used for the RF input while the video output is via a BNC connector to the channel 1 oscilloscope input and a trigger output BNC to the channel 2 input. Accessories include an AC/DC adapter. A tracking generator and extended frequency range to 2.6 GHz are available as options.

Table 1
Key Performance Specifications

Frequency range

10 MHz to 1 GHz

Frequency resolution (kHz)


Frequency stability (ppm)


Frequency spans

0 span, 2 kHz/div to 100 MHz/div

Resolution bandwidth

3 kHz, 30 kHz, 220 kHz and 4 MHz

Input range (dBm)

-100 to +20

Display range (dB)


Reference level range (dBm)

-30 to +20

Accuracy (dB)

±1.5 to 80 MHz

Linearity (dB)

±1.5 over 70 dB range

Flatness (dB)

±1.5 (10 MHz/div)

Average noise level (typ) (dBm/Hz)


Phase noise (typ) (dBc/Hz)

-87 at 10 kHz offset

Input attenuation selections (dB)

0, 10, 20, 30, 40 and 50

Maximum input level (dBm)


In addition, the company intends to release software that will allow the user to control the 7700 from a PC via an RS-232 interface or modem. The software also will download the spectrum and its settings (span, center frequency) and display them on the PC monitor.

The model 7700 spectrum analyzer adapter retails for $1600. Complete details and specifications are available upon request. Additional information can be obtained at the company’s Web site: www.hcprotek.com or via e-mail: hcprotek@hcprotek.com.

Protek Inc., Northvale, NJ (201) 767-7242.