Dynamic range expansion system for radio frequency /RF/ signal detection equipment consists of RF amplifiers, RF amplitude modulated detectors, and operational amplifier. The analog output gives maximum resolution over fixed voltage range, without switching. Two minor drawbacks of this circuit are cited

Watterson, R. F.

English

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_ R 
Threshold Schmitt Trigger 
Level 
Setting
0 V Positive Slope 
0 to 30 dB; 
5 V Negative Slope 
30 to 60 dB.
Final 
Output (Curve A) 
Range 
F lag 
One 
August 1971	 Brief 71-10279 
NASA TECH BRIEF 
Goddard Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the. Tech Brief program may 
be directed to the Technology Utilization Off ice, NASA, Code KT, Washington, D.. 20546. 
Isosceles Detector Provides Maximum Resolution in Expanded Range 
A dynamic range expansion system for radio fre-
quency (rf) signal detection equipment contains a 
range expander which consists of a unique combina-
tion of standard electronic circuitry; i.e., rf amplifiers, 
rf amplitude modulated detectors, and an operational
In a system containing a receiver with 60 dB of

dynamic range, the analog output, which uses a

standard AM diode detector, can be modified to pro- 
vide more resolution within the 0 to 5 Vdc range.

Incorporating the isosceles detector into this 
Instrumentation with 60 dB Dynamic Range 
El
Positive 
A 30 dB 
>T-D3^O	 LR 
Detector 
0 to —1 Vdc	 Summing, 
Amp 
Negative	
+5 Vdc Detector
Figure 1. 
(summing) amplifier. The analog detector is com- 
prised of a trigger circuit, dual amplitude detectors, 
and an analog summation circuit. 
The device is called an isosceles detector because 
its output waveform (curve A, Figure 2) resembles 
an isosceles triangle. The analog output gives maxi- 
mum resolution over a fixed voltage range, without 
switching. 
The heart of the detector is the summing amplifier 
(see Fig. 1), which combines the negative and 
positive detector outputs and introduces a fixed 
gain as a scaling factor to determine the output volt- 
age range. A Schmitt trigger circuit senses when 
the negative detector overcomes its threshold. When 
the negative detector reaches —20 mV over back- 
ground, the Schmitt trigger fires, giving a range flag 
output. This indicates that the analog voltage being 
sampled on curve A is on the negative slope.
When a 0 dB signal level is present at the input to 
the string of amplifiers, the positive detector output 
is at 0 Vdc. Note that the negative detector input 
is down 30 dB from the positive one, and is at 
0 Vdc until the amplifier input level is above 30 dB. 
As the input level is increased from 0 to 30 dB, 
the positive detector output follows the input to 
(continued overleaf) 
Now
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5 
0
max 
0v 
provide a 0 to I Vdc output level. The summed out-
put of both detectors is amplified by the summing 
amplifier to provide the positive slope of curve 
A. Therefore, a 0 to 5 Vdc output curve is detected 
for the 0 to 30 dB input levels. Up to this point, 
which corresponds to the peak of curve A, the range
Only 60 dB of range has been shown in the block 
diagram. However, the basic technique used in the 
single isosceles detector may be expanded to cover 
larger dynan7ic ranges, while keeping the same 
resolution. This is accomplished by cascading two 
or more isosceles detectors, in which case the analog 
Note: Range Flag on for .30 to 60 dB Range 
(30 to 120 dB)	 (60 to 120 dB)
	 (90 to 120 dB) 
Range Flag One ON
	 Range Flag Two ON
	
Range Flag Three ON 
0	 30	 60
	
0	 30	 60	 90	 120	 150	 180 
Range dB
	
Range dB 
Curve A
	
	
Curve B 
Figure 2. 
flag output is at 0 Vdc. The positive detector goes 
into saturation at an input level of 30 dB. This is 
also the level at which the negative detector comes 
out of the background noise level. Over the next 
30 to 60 dB, the negative detector goes from 0 to - 
Vdc. Meanwhile, the positive detector output sits 
at +1 Vdc. The negative detector output then 
subtracts from the positive detector and provides 
the negative slope of curve A from 5 to 0 Vdc for 
input levels from 30 to 60 dB. The range flag fires 
when the negative detector output reaches —20 mV. 
This flag gives a 5 Vdc level indicating that the 
negative slope of curve A is being used. Therefore, 
60 dB of dynamic range is expanded over a 10 V 
curve (two 5 V ranges). 
Two minor drawbacks of the circuit are: (1) the 
final output's symmetry depends upon how well the 
detectors and/or summing network are balanced; 
and (2) the range flag output must interpret the 
output voltage.
output and range flags shown in curve B would 
result. Different output voltages are possible; i.e., 
final analog output may be a positive or a negative 
voltage from 0 to —15 Vdc and range flags cati be 
positive or negative, using conventional integrated 
circuitry. 
Note: 
No additional documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Goddard Space Flight Center 
Greenbelt, Maryland 20771 
Reference: B71-10279 
Patent status: 
No patent action is contemplated by NASA. 
Source: R. F. Watterson of

Sanders Associates, Inc.

under contract to

Goddard Space Flight Center

(GSC- 10932) 
Brief 71-10279	 Category 01


Isosceles detector provides maximum resolution in expanded range

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