49X Series Comparison

This page is an attempt to compare the 49X, 275X, and 279X series spectrum analyzers that share many common hardware features. All data is for the base model without options. The 491 that number wise fits the 49X-series is an entirely different instrument and consequently not covered here.

Comparison Table

Model	492	492A	492BP	492PGM	494	494A	495	496	497P	2753P	2754	2755	2755AP	2756P	2792	2794	2795	2797	Notes
Frequency Range	50 kHz – 21 GHz	50 kHz – 21 GHz	10 kHz – 21 GHz	10 kHz – 21 GHz	10 kHz – 21 GHz	10 kHz – 21 GHz	100 Hz – 1.8 GHz	1 kHz – 1.8 GHz	100 Hz – 7.1 GHz	100 Hz – 1.8 GHz	50 kHz – 21 GHz	10 kHz – 21 GHz	10 kHz – 21 GHz	10 kHz – 21 GHz	10 kHz – 21 GHz	10 kHz – 21 GHz	100 Hz – 1.8 GHz	100 Hz – 7.1 GHz
Min. Span	100 kHz	200 Hz	1 kHz	2 kHz	500 Hz	100 Hz	100 Hz	500 Hz	1 kHz	10 Hz	200 Hz	200 Hz	100 Hz	10 Hz	2 kHz	100 Hz	100 Hz	100 Hz
Max. Span	5 GHz	10 GHz	100 GHz	10 GHz	5 GHz	100 GHz	1 GHz	1 GHz	5 GHz	100 MHz	1 GHz	10 GHz	10 GHz	10 GHz	12 GHz	150 GHz	1.7 GHz	4 GHz
Ext. Mix	Yes	Yes	Yes	No	Yes	Yes	No	No	No	No	No	Yes	Yes	Yes	Yes	Yes	No	No
Center Frequency Accuracy	±5 MHz	±30 kHz	±21 kHz	±30 kHz	Freq.Ref.	±20 kHz	±20 kHz	±5 MHz	±21 kHz	±20 kHz	±30kHz	±30kHz	±20 kHz	±20 kHz	±30kHz	±20 kHz	±20 kHz	±21 kHz	at 1 GHz, 100 kHz/div span
Frequency Reference Accuracy			1×10-6/year	1×10-5/year	1×10-7/year	1×10-7/year	1×10-7/year		1×10-6/year	1×10-7 /year	?	?	5×10-7 /year	1×10-7 /year	?	1×10-7/year	1×10-7/year	?
SSB Phase Noise		−105 dBc/Hz	−105 dBc/Hz	−103 dBc/Hz	−90 dBc/Hz	−105 dBc/Hz	−105 dBc/Hz		−105 dBc/Hz	-105 dBc/Hz	-103 dBc/Hz	-105 dBc/Hz	-105 dBc/Hz	-105 dBc/Hz	−103 dBc/Hz	−105 dBc/Hz	−105 dBc/Hz	−105 dBc/Hz	30kHz offset, N=1
Min. Resolution Bandwidth	1 kHz	100 Hz	100 Hz	1 kHz	30 Hz	10 Hz	10 Hz	30 Hz	10 Hz	10 Hz	1 kHz	100 Hz	100 Hz	10 Hz	1 kHz	10 Hz	10 Hz	10 Hz
Max. Resolution Bandwidth	1 MHz	1 MHz	3 MHz	3 MHz	1 MHz	3 MHz	3 MHz	1 MHz	3 MHz	3 MHz	1 MHz	1 MHz	3 MHz	3 MHz	3 MHz	3 MHz	3 MHz	3 MHz
Dynamic Range	80 dB	80 dB	90 dB	80 dB	80 dB	90 dB	80 dB	80 dB	90 dB	90 dB	80 dB	80 dB	90 dB	90 dB	90 dB	90 dB	90 dB	90 dB
GPIB	P model	P model	yes	yes	P model	P model	P model	P model	Yes	Yes	P model	P model	Yes	Yes	Yes	Yes	Yes	Yes
Marker	No	Yes	Yes	Yes	No	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Counter	No	No	Yes	No	Yes	Yes	Yes	No	Yes	Yes	No	No	Yes	Yes	Yes	Yes	Yes	Yes
Introduced	1980	1987	1989	1990	1985	1988	1987	1982	1990	1988	1987	1987	1989	1988	1993	1993	1993	1993

Common Features

The frequency conversion is identical for all models and based on two tunable local oscillators. The frequency coverage is split in several bands, where band 1 is selected with electromechanical switches. Therefore none of the members of the 49X, 275X, and 279X families allow for a span exceeding the band 1 limits, as this would require continuous electromechanical band-switching. As a new feature the 279X-family allows for a multiband sweep mode displaying a sweep over bands 2-5. For bands 4 and higher the mixer is operated as a harmonic mixer, which results in a degradation of the analyzers phase noise performance for frequencies exceeding 7.1 GHz. Bands 6-12 require external mixers of the WM490 family or WM780 family.

Band	Frequency Range (GHz)	1st IF	LO Range (MHz)	LO Multiplier
1	0 − 1.8	2072	2072 − 3872	1-
2	1.7 − 5.5	829	2529 − 6329	1-
3	3 − 7.1	829	2171 − 6276	1+
4	5.4 − 18	829	2076 − 6276	3-
5	15 - 21	2072	4309 − 6309	3+
6	18 - 27	2072	2655 − 4155	6+
7	26 - 40	2072	2393 − 3793	10+
8	33 - 60	2072	3093 − 5793	10+
9	50 - 90	2072	3195 − 5862	15+
10	75 - 140	2072	3171 − 5997	23+
11	110 - 220	2072	2917 − 5890	37+
12	170 - 325	2072	2999 − 5767	56+

Note:
A "-" sign after the LO multiplier indicates that the (multiplied) LO is above the received signal. f_if = N×f_LO - f_RF
A "+" sign after the LO multiplier indicates that the (multiplied) LO is below the received signal. f_if = f_RF - N×f_LO

Accessories

• TR503 dc − 1.8 GHz tracking generator
• 1405 sideband adapter
• WM490 external mixer
• WM780 external mixer (individually calibrated)

Links

• Comparison of 492 with 494 and 7L18
• 49x, 275X, and 279X Service notes @ John Miles KE5FX
• KE5FX GPIB toolkit
• ROM replacement
• Tek 492 DIY USB interface project
• YouTube: Tektronix 492 and 496 Portable Spectrum Analyzers