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Radio City inc,

1*400-426-2891 METRO: (612)786-4475 FAX: (612) 786-6513 2663 County Rd, I Mounds View, MN 55112

CÍRCLE 153 ON READER SERVICE CARD

73 Amateur Radio Today • September, 1993 43

Numoer on yoi

CaRR'S corner

Number 14 on your Feedback card

Joseph J. Carr K4IPV RO. Box 1Q99 Falls Church VA 22041

The Boyd Electronics RF Sweep Generator

Building and expenmenting with RF

circuits can be performed with a simple continuous wave (CW) signaJ generator, but the avid technician quickly learns that an RF sweep generator is a real assel on the bench, A sweep generator repeiitrvely tunes ¡trough its set range of frequencies, thereby allowing you to examine the frequency response ot the circuit under test on an oscilloscope Circuits that test better on a sweep generator compared to a CW signal generator include:

High-pass and low-pass filters Bandpass fillers L-C tuning circuits Antenna tuners

Crystal, ceramic or mechanical IF filters

RF amplifiers Video amplifiers IF amplifiers

Sweep generators are used by service technicians to test and align radio and TV equipment, and they are also used by engineers and technicians in laboratory sellings. Tne service grade sweep srgnai generators may be cheaper man laboratory models, but they usually dont cover all frequencies that amateurs need The lab models are in the mulli-kilobuck price range, so lhey are out of the game as far as most hams are concerned Perhaps the best alternative is to build your own sweep generator from a kit.

Last month, an advertisement by Boyd Electronics (1999 Southgate Way, Grants Pa&S OR; 503-476-9583) in 73 caught my eye.. They offer the Model RSG*30 RF sweep generator as a kit at a very attractive price. So. I contacted Jerry 8oyd, and he shipped an RSG-30 kit for review. (He also offers two assembled versions, but considering most hams would probably build the ktL J wanted to assemble this one myself Besides, building stuff is one of the fun parts of doing this column.)

RSG-30 Features

The Boyd RSG-30 offers sweep from 2 to 30 MHz, and has the stan dard 50 ohm load needed for RF circuit testing. The output level is approximately 100 mV RMS, and sweep width is variable from 5 kHz to 30 MHz. A negative 12 volt, 20 ms trigger pulse is provided so the oscilloscope can be triggered in step with the sweep (which makes the presentation coherent).

Three modes are offered in the Boyd RSG-30; CW, Video and Symmetrical. The CW mode outputs a continuous, non swept signal (Photo A) on

"The lab models are in the multhkilobuck price range, so they are out of the game as far as most hams are concerned. Perhaps the best alternative is to build your own sweep generator from a kit"

a single frequency set by the front panel FREQUENCY control. It can be used in the same manner as any RF signal generator The VIDEO mode is a swept mode m which the RF frequency is swept from 2 to 30 MHz, while the SYMMETRICAL mode is a swept mode in which the width of the sweep {min to max frequency) is set by a SWEEP WIDTH control on the front panel (5 kHz to 30 MHz). Photo B shows the waveform on my oscilloscope when the SYMMETRICAL mode was selected and the SWEEP WIDTH was set close to maximum (so it is sim-lar to the VIDEO mode).

RSG-30 Internal Circuitry

Figure 1 shows the block diagram of the Boyd RSG-30 circuitry, The RF signal is formed by mixing together two other signals: the output of a 50 MHz crystal oscillator, and a 52 to 80 MHz voltage tuned oscillator (VCO). A VCO is a circuit m which the RF frequency is set by a tuning voltage applied to a voltage variable capacitance diode (or *varicaprt). The output of me mixer is the 2 to 30 MHz difference between the crystal oscillator (XQ) and VCO signals. and I his signal is filtered in a low-pass filter (o remove the remaining components of the XO and VCO. The 2 to 30 MHz liitered signal is amplified by a Mini-Circuits MAR-i MMIC amplifier. These anpNlier iCs have a natural 50 ohm output.

The sweep and tuning voltage section contains a clock-driven saw-toothed generator as well as DC offset circuitry for setting the center Irequen-

Photo A. Sine wave CW output of the RSG-30.

Photo a Swepi RF output of the FtSG-30,

Photo A. Sine wave CW output of the RSG-30.

Photo a Swepi RF output of the FtSG-30,

Photo C. Output Of the circuit under test on oscilloscope screen.

Photo D. Output of detector on oscilloscope screen.

Photo C. Output Of the circuit under test on oscilloscope screen.

Photo D. Output of detector on oscilloscope screen.

SO MHz Crystal Ose

SO MHz Crystal Ose

Sawtooth

Sweap And Tuning VoltageCûntrot

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