The Tektronix SG503 is a 250 MHz leveled sinewave generator plug-in for the TM500 system. It was primarily intended to be used as an oscilloscope calibration device for measuring bandwidths up to 250 MHz. Unlike later instruments like the SG504, it does not use a leveling head but was designed and calibrated with high quality coaxial cable (P/N 012-0482-00) to operate as a closely matched system when terminated into a 50 Ω load.
Nine overlapping ranges cover the frequency band from 250 kHz to 250 MHz, with an additional range reserved for a 50 kHz reference frequency.
The SG503 shows the selected frequency on a 3-digit LED counter.
|Frequency||50 kHz, 250 kHz to 250 MHz in nine ranges|
|Frequency accuracy||Within ±0.7% of one count of the least significant displayed digit for the indicated frequency|
|Amplitude||5 mVp-p to 5.5 Vp-p in three decade ranges (terminated into a 50 Ω load)|
|Harmonics||2nd harmonic ≥35 dB down from fundamental, 3rd and higher harmonics ≥40 dB down|
The sine output, remote amplitude control input, and a 12-bit BCD version of the counter value are available via the rear connector.
The SG503 uses two LC Hartley oscillators, one for 100 MHz and above with an air-core inductor, the other for the lower ranges using switched ferrite-core inductors. Tuning is via a traditional three-section variable capacitor. After filtering, a regulated power amplifier stage (caution: beryllium oxide in transistor cases!) is followed by a peak-to-peak detector for the amplitude control loop, and switchable output attenuators.
The frequency counter is built from a 10131 ECL prescaler followed by 7490 TTL BCD counters and 7-segment decoders (display not multiplexed).