ELEC 432

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Background

Although Part 15 allows unlicensed operation at almost any frequency in the spectrum, in most cases the allowed power is so small that the maximum range is only a few meters. An exception to this is to be found in the set of frequencies called the Industrial, Scientific, and Medical (ISM) Bands. In these bands powers ranging from 10s of miliwatts to several watts are allowed. If you have an interesting application that you want to investigate, one of these bands is an obvious place to try it out.

Economical test equipment is available for HF and VHF frequencies, but the ISM bands in this range are fairly narrow. More interesting are the higher ISM frequencies, e.g. the 900 MHz, 2.4 GHz, and 5 GHz bands. Unfortunately, commercial equipment for these frequencies is extremely expensive. However, the popularity of these bands for commercial applications has brought about the availability of a variety of high frequency integrated circuits at very low prices. These could be used to build instruments which, although not as accurate as expensive laboratory equipment, nevertheless provides useful functionality at a much lower price.

Description

Although there are many different types of RF instruments available (e.g. signal generators, power meters, spectrum analyzers, frequency counters, network analyzers, antenna analyzers, etc.), most can be assembled from various combinations of controlled sources and calibrated receivers. In fact, one possibility would be to realze this system as an application of the Modular SDR project. However because of the need for calibrated measurements and close coordination between transmitter and receiver, the hardware requirements are somewhat more stringent.

Specifications

Almost any level of functionality has some utility, but the more accuracy, sensitivity, range, etc. that your instrument has, the more useful it is. And of course the more expensive. Choose a balance of cost and performance that will achieve a satisfactory market for your product. Here are some example specifications:

Functionality

Your instrument should provide as many of the following functions as is economically possible:

Signal Generation

Produce a sinusoidal output signal which is tunable over the supported frequency range (see below). Output power should be adjustable over a range of at least -60 dBm to +10 dBm. Spectral purity and accuracy of indicated frequency and amplitude should be appropriate for the intended use of this instrument. The ability to apply simple modulation to the signal (e.g. AM and FM tone modulation) is a desirable feature.

Frequency Measurement

Measure the frequency of a sinusoidal input signal.

Power Measurement

Measure the delivered by an input signal to a 50Ω load.

Signal/Spectrum Analyzer

Display the power spectrum of an input signal. This module could be used to implement the frequency and power measurement functions.

Transfer Function

Combine the generation and measurement functions to automatically plot the transfer function of a network being tested.

Impedance

Measure the (complex) impedance at a port of a network (e.g. filter, antenna, etc.) being tested.

Frequency Range.

Obviously must include at least one ISM band. 49 Mhz and below are already well addressed by existing products, although significantly lower price or increased functionality in a single package could produce a viable product. (A 15 kHz to 150 MHz combination signal generator, spectrum analyzer, and network analyzer for under $1000 would be a really hot item.) There are no US ISM bands between 49 and 900 MHz, although there are several amateur radio bands in this range.

Also, there are no US ISM bands between 5 GHz and 24 GHz. 24 GHz is more of a challenge than we are equipped to take on. In fact 5 GHz is probably on the boundary of what we should attempt.

So, at least the 900 and 2.4 ISM bands should be supported. This should include the ability to measure harmonics, at least of 900 signals. Although power limitations for continuous operation in non-ISM bands are severe, allowed power for intermittent and periodic operation is significantly higher across most of the spectrum. Since the ISM bands are becoming increasingly crowded while many other parts of the spectrum are nearly empty, additional or full frequency coverage would support development of applications which could utilize this niche.

Input and Output Impedance.

Each RF input and output should have an impedance of 50Ω.

Cost.

A system providing the first four functions listed above should cost less than $1000, exclusive of the PC.