A Matter of Frequency by Allan Tarvid (Sonar Scanning - Angle on Electronics)

Boats Product Reviews

 

Garmin steps up sonar scanning detail.

garmin sonar scanning

Garmin’s ultra-high-definition scanning puts higher frequencies to work to make a great feature even better.

About the time you think something is as good as it can get, somebody figures out how to make it even better.

This screen shot shows suspended fish detected by Garmin’s new UHD system. Both the bright fish reflections and the dark sonar shadows cast by them onto the bottom stand out well enough to be seen at a glance

Today’s side- and down-scanning sonar screen pictures reveal underwater structure like rocks, trees, and stumps as well as cover like weeds and brush piles with almost photographic clarity.

They accomplish this by scanning with fan-shaped side beams that are wide from top to bottom and vertical beams that are wide from left to right. Both beams are very thin from front to rear. Echoes from these consecutive slices of water are displayed as seamless composite pictures in a process somewhat like medical ultrasound.

High operating frequencies also play a big part in delivering photo-like detail.

'The basic principles of sonar haven’t changed since World War II and one of the constants says that higher frequencies deliver better detail but less depth reach while lower frequencies deliver less detail but more depth reach. Therefore, the higher a sonar system’s operating frequency, the better its potential for detail if you apply enough transmitting power to provide a useful amount of range.

This shot shows a reading from Garmin’s standard scanning frequency on the left and one from the company’s Ultra High-Definition scanning technology’s higher frequency on the right.

This shot shows a reading from Garmin’s standard scanning frequency on the left and one from the company’s Ultra High-Definition scanning technology’s higher frequency on the right.

We now have high-definition scanning systems with similar operating frequencies available from all the major manufacturers. They deliver such outstanding screen picture detail right now it’s hard to imagine anyone working to improve their performance and, if so, how they could do it. Garmin’s answer is to go for even better screen detail by stepping up its operating frequencies. The company just introduced a new black-box side- and down-scanning sonar unit and transducer with the highest operating frequencies I’ve seen in the recreational marketplace.

Two operating frequencies: 200 kHz and 50 kHz, became industry standards early in recreational sonar’s history.

200 kHz provided the best combination of target separation, interference resistance, and penetration to the most common fishing depths, and all at a wide range of boat speeds. 50 kHz delivered better depth penetration and became the top choice for deepwater use. Most dual-frequency transducers were built to accommodate this pair of frequencies.

Garmin’s UHD High-Definition scanning system is a black box unit compatible with many existing Garmin multifunction displays. (Images courtesy Garmin)

Garmin’s UHD High-Definition scanning system is a black box unit compatible with many existing Garmin multifunction displays. 

Other frequencies have become popular over the years.

50 kHz became notorious for losing the bottom at cruising speeds and it was discovered that 83 kHz performed almost as well in deep water but delivered better cruising-speed performance. 455 kHz appeared later in traditional down-looking applications and became the first choice when high-definition side- and down-scanning features with photo-like picture quality were developed. 800 kHz was quickly added to this scanning technology making 455 kHz its lower frequency. The lower versus higher frequency principles continued and owner’s manual specifications revealed that 455 kHz provided more reach and wider side beams that came closer to the surface on each side of the boat while 800 kHz offered less reach but provided an easy-to-see increase in screen image detail.

Garmin’s Ultra High-Definition Scanning sonar system once again raises the frequency bar.

It’s hard for me to call 800 kHz a “low” frequency but this system uses a lower CHIRP range of 760 to 880 kHz and a higher CHIRP range of 1,060 to 1,170 kHz.

CHIRP stands for Compressed High-Intensity Radiated Pulse and means this unit will cycle through each selected frequency range instead of transmitting and receiving just a single sonar frequency. Garmin literature also states the high and low frequencies as .8 and 1.2 MHz or as 800 and 1,200 kHz. The system’s 500 Watts (rms) of transmit power give it a range of 125 feet to each side of the boat for a total scan width of 250 feet.

The stated maximum depth reach for the down-scanning beam is 200 feet.

In comparison, Garmin’s standard side and down scanning system uses 455 kHz and 800 kHz with side beams reaching out to a maximum of 500 feet in each direction and a down-scanning beam reaching as deep as 750 feet. It does this with the same 500 Watts of transmit power.

This screen capture from a Lowrance HDS unit shows the difference between the views from its traditional 200 kHz beam (lower right window) and its 800 kHz down scanning beam (upper right window). 800 kHz was previously the highest common frequency used in most manufacturers’ high-definition down- and side-scanning systems. (Screen capture by Allan Tarvid)

This screen capture from a Lowrance HDS unit shows the difference between the views from its traditional 200 kHz beam (lower right window) and its 800 kHz down scanning beam (upper right window). 800 kHz was previously the highest common frequency used in most manufacturers’ high-definition down- and side-scanning systems. (Screen capture by Allan Tarvid)

This comparison shows that the new higher frequencies reduce reach as they increase screen detail. Is this a problem? In my opinion, absolutely not. This new system gives you the potential for the best screen detail currently being offered in a recreational system. As for the reduction in reach, how many times can you not get your boat within 125 feet of the desired target? How often do you really fish deeper than 200 feet?

Keep in mind this is a black box system compatible with all current Garmin GPSMAP and select ECHOMAP multifunction displays. If you have multiple networked displays on your boat, Ultra High-Definition system imagery can be seamlessly displayed across all of them. Using the included network expander on the GCV 20 sonar black box, Panoptix real-time sonar views can also be distributed across the network if you also have that system installed.

The higher a sonar unit’s operating frequency the better its potential for showing detail. This Garmin Striker unit’s screen capture shows the difference between 200 kHz on the left and 455 kHz on the right. The shape of the sonar beam used by the down scanning feature that made the screen picture on the right also helps. (Image courtesy Garmin)

The higher a sonar unit’s operating frequency the better its potential for showing detail. This Garmin Striker unit’s screen capture shows the difference between 200 kHz on the left and 455 kHz on the right. The shape of the sonar beam used by the down scanning feature that made the screen picture on the right also helps. (Image courtesy Garmin)

The system includes the networkable GVC 20 sonar black box and a GT34UHD transducer with both transom and trolling motor mounts. If you are a stickler for through-hull transducers Garmin offers either a single transducer or a pair of transducers. The pair is designed for use on deep-V hulls steep enough to block one side of a single transducer’s lateral reach.

The system is compatible with GPSMAP 8400/8600, 7400/7600, 10x2/12x2, 12x2/12x2xsv TOUCH, 7x2/9x2 chart plotters and 7- and 9-inch ECHOMAP Plus combo series units.

Visit www.garmin.com/newmarine for more information.

 

 



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