THE TECHNOLOGY BEHIND ACTIVE TRANSDUCERS
Presently, commercial transducer manufacturers have developed a variety of transducers for the commercial fishing industry that are based upon analog (Passive) technology. Meaning, that the transducers were designed to send a signal at a given frequency and then receive the echo's from that frequency. A second device, or piece of equipment, was then needed to decipher this information and then display it. Analog technology has some built in inherent problems that are difficult to overcome and in many cases result in poor transducer performance.
With the advent of the Micro Processor, many of yesterday's technologies are being updated with amazing results. RADARSONICS INC. has brought this space age technology to a family of its commercial line of transducers and are eliminating many of the inherent problems that the analog transducers may experience.
The RADARSONICS "Active Transducer" has an embedded transceiver that incorporates digital signal processing. The "Active Transducer" has an RMS power output range of 1.3 to 320 watts RMS, depending on transducer element impedance and depth. The Effective Processed Power is about 20 times the RMS power output due to the Digit Signal Processor (DSP). The term Effective Processed Power (EPP) is a new term but best explains what actually occurs.
One of the major Inherent problems of analog transducers is the fine balance between display resolution and deep water response. Utilizing analog technology there are only a few options to improve deep water response of a depth sounder:
1. Increase Power - The brute force approach. This works, but requires the use of a physically larger transducer and transducer elements to keep the sound pressure below the water cavitation level. It's not that you would damage the transducer if you increased the power too high, but start to form air bubbles under the transducer, just like a boat propeller cavitates the water if it is spun too fast, the air bubbles will prevent the proper operation of the transducer.
2. Use Lower Frequencies - The lower frequencies are attenuated less and penetrate deeper. This technique also works but suffers from loss of resolution. Higher frequencies will produce returns from smaller targets but don't penetrate as deep. For example, at 200kHz a target as small as 1/4 inch in diameter will generate an echo, whereas at 15kHz, targets must be at least 2 inches in diameter to produce a detectable echo. Lower frequency elements are also physically larger and typically more expensive.
3. Improve Sensitivity - In analog hardware, narrow band filters are used to filter the return signal to reduce the noise. Narrow band filters are difficult and expensive to manufacture and require an Automatic Gain Control (AGC) and careful tuning and adjustment, all with high cost associated with them. In fact, if high quality (high cost) filters are not used, the transducer will have poor performance due to filter drift induced by vibration and temperature changes.
Superior sensitivity is essentially what is accomplished using DSP without the associated high cost of filters. The RADARSONICS "Active transducer" does very little filtering, mostly amplification that goes straight into the micro processor as a series of 1's and 0's. The narrow band filtering is performed in software which does not require an AGC or expensive components. In addition, the DSP transducer will not drift due to temperature or vibration and requires no factory or operator adjustments.
The RADARSONICS INC. family of "Active Transducer" performs extremely well at high speed because it is unaffected by ringing due to transducer slap & buffeting. This occurs because the "Active Transducer" does not transmit at the transducers natural ringing frequency and the Active Transducer only responds to signals at the transmitted frequency.
An additional benefit of the "Active Transducer" is, once it is locked onto the bottom, the DSP sounder is unaffected by other nearby depth sounders (even at the same frequency) for the same reasons as stated above. In addition, the DSP depth sounder uses less power, thus, has less effect on other nearby depth sounders which can be a benefit. At depths to about 300 feet the DSP depth sounder only uses about 1.3 watts, which is why you can't hear the "click".
The RADARSONICS Inc. "Active Transducer" is just the next step into the future. Don't get left behind.