This unit is designed to address a common problem in wireless voice communications today:  To maintain quality speech content and control the deviation levels at all times.  Once easily calibrated to your radio transmitter, the DSL-300 will provide +/-12 dB of gain to your transmitted audio levels while ensuring low distortion and no clipping of the audio signal.

Ideal for HF, VHF, UHF and link transmitter applications, all users operating on your radio system will be driving the transmitter with the same audio levels. Users with low deviation levels will sound just as good as the user with the highest level of deviation.  The device does not enable "Hot" users to drive the transmitter into hard limiting (clipping) thereby reducing the quality of their transmission.

When used for telemetry purposes, the DSL-300 provides nominal deviation with both weak and strong signals.  This is an important key feature for linked voice or other telemetry / mixed signal systems.  For example, a user with an average frequency deviation of 2.5 kHz will now be re-transmitting with a typical deviation of 3.0 kHz or whatever you have the DSL-300 calibrated for.   

DSL-300 Specifications

Parameter	Symbol	Min.	Max.	Units
Operating Voltage   (12 VDC  Typical)	VSUP	11	28	VDC
DC Current Draw	ISUP	25	40	mA
Input Impedance  Balanced *	ZIN	600	600	Ohms
Input Impedance Un-Balanced **	ZIN	10,000	10,000	Ohms
Output Impedance	ZOUT	600	600	Ohms
- 3 dB Frequency Bandwidth	FBW	300	3,400	Hz
Total Harmonic Distortion Below Limiting	THDBL	-	.01	%
Total Harmonic Distortion Above Limiting	THDAL	-	2.0	%
Input Limiting Range (Balanced)	-	-30	+3	dBm
Input Limiting Range (Un-Balanced)	-	.03	4.0	Volts P-P
Limiting Dynamic Range	-		40	dB
Output Limiting Range (Balanced)	-	-30	+3	dB
Output Limiting Range (Un-Balanced)	-	.03	4.0	Volts P-P
Attack Time @ 1 KHz	TA	-	500	µS
Decay Time	TD	-	20	mS

Absolute Maximum Ratings

Ambient Operating Temperature	0º to 50º C
Maximum Supply Voltage (diode protection)	28 VDC
Power Dissipation @ 12 VDC	360 mW

Mechanical Specifications

*    The DSL-300 can be configured with different impedances.  Contact us for options.
**  Special Order un-balanced unit
 

Price $195.95
 

      Link to Installation Instructions

AGC circuits vs. the Dynamic Speech Limiter

The AGC audio processor designs have many limitations which limit their use in critical audio transmitter applications.   The DSL-300 uses a custom designed chip which limits modulation peaks to specified levels set by the user.  Figure 1, graphically illustrates the methodology of Dynamic Limiters.

Figure 1;   Compression Characteristics of a Limiter

In this example illustration, curve OA is the curve of a linear amplifier.  Curve OTD is that of an "ideal" limiter with point T set as the threshold of limiting.  Note that the output of the "ideal" limiter does not rise above the set level of 12 dB, no matter how great the input level becomes.  Curve OTB is that of a practical limiter, the curve TB indicating by its slope a compression ratio of 10 to 1 dB.  The compression in dB at any point is as indicated by the arrows. 

Curve OC is that of a limiter having "over control" which does not exceed 100% modulation (line TD) until the compression reaches 12 dB.  AGC processors have a comparatively slow "attack" time, that is the time taken for the processor to operate on a sudden increase in input level.  Their design is limited to attack times exceeding many milliseconds.  A slow attack time results in overmodulation and overdeviation of a signal and distortion for short intervals following each transient.  Outlined below, is a summary of the limitations of AGC audio processors:

1. An AGC has a very slow response (attack/decay) time. Typically 1 to 3 seconds vs. the Dynamic Speech Limiter with an attack time of 500 microseconds and a decay time of 20 ms. This is well aligned with normal speech syllables AGC circuits also suffer from "Breathing" (slow attack and decay times).
2. An AGC will not ensure your transmitter will not limit and clip the "Hot" audio.
3. The Dynamic Speech Limiter tracks the audio source and not noise levels so the noise component is minimized.
4. An AGC does not sample the entire speech envelope (Peak to Peak). As such it will not accurately track speech patterns. This results in Asymmetrical limiting in the transmitter. The DSL tracks the full speech envelope and provides fully symmetrical limiting in the transmitter.
5. The AGC processor has significantly poorer audio frequency response than dynamic limiters.
6. AGC will not accurately track DTMF or other forms of telemetry accurately, resulting in dynamic distortion. The DSL will track the DTMF envelopes and not allow distortion to occur.