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Discussion Starter · #1 · (Edited)
This is a modified version of a conversation I had on another forum about some fish finder images I had posted to a fishing report. I thought I would share it here in case it may help some one.

I am a firm believer in maximizing the use of a fish finder by understanding the transducer and utilizing multiple frequencies. Most fixed frequency machines offer a low frequency (LF) 50kHz and a high frequency (HF) 200kHz. Some Navico units (Lowrance, Simrad, Eagle) will run 83kHz for the low frequency instead of the 50kHz but the premise remains the same.

Lower frequencies tend to penetrate deeper into the water while higher frequencies tend to be more sensitive. Because of this most people typically have been told to use 200kHz for inshore (Chesapeake Bay) and 50kHz for offshore use. However I suggest to you if you stick to that general rule of thumb that you may miss things that can help you understand what is under the boat.

With most transducers the high frequency not only offers more sensitivity through the attributes of the higher sound waves but it does so because of the "cone" in which the signal is sent out. The high frequency of the majority of recreational transducers offer a relatively narrow cone angle vs that of the low frequency transducer elements. The low frequencies tend to offer a much wider cone.

What do I mean by "cone"? Let me give an example. The transducer I run is an Airmar p66 600w transducer (very common for inshore people and comes standard with many units). The "cone" of the signal with this transducer for 50kHz is very wide. It is 45 degrees. The cone for the 200kHz is narrow at 10 degrees. http://www.airmartechnology.com/uploads/brochures/p66.pdf

Here is an image that shows a narrow cone HF and a wide cone LF.



Each frequency and cone has their advantages:

The 200kHz narrow cone gives me these advantages:
  • narrower, more targeted view of the bottom since the signal is concentrated on a smaller area of the bottom. Because of this it more likely to pick up fish right on the bottom for bottom fishing
  • the narrower more sensitive cone shows bottom density changes (harder to softer bottom - hard bottom is a thinner line, soft bottom is a wider line)
  • the narrow beam is more likely to pick up water breaks like thermoclines. Sometimes i need to turn up the gain on that side to find them in the spring and fall. (increasing gain likely fills in targets for less discrimination though)

Here are the advantages of viewing the a wide cone low frequency:

  • I cover more water under the boat with the wider cone.
  • I get more of a defined "arch" for bigger fish than smaller fish and this allows me to better differentiate between game and bait. This makes it great for searching for suspended fish.

"Arches" are formed as a fish's swim bladder passes through the cone of the transducer frequency like this:

This is why you typically dont see as big of arch on the 200kHz side because the cone is either missing some fish and/or the fish is in the cone for less time.

Why hasn't the use of the low frequency recommended for shallower water? Before digital processing fish finders like today, you often got a lot of noise or clutter with low frequencies like the 50kHz in shallower waters. That is NOT the case today with digital fish finders since the processing filters out a lot of the noise/clutter. Some fish finders you need to still fiddle with the gain to balance noise and seeing marks clearly but I think it is a tool you shouldn't pass up on.

Here are some of my own screen shots to help you understand better:

Trolling in May with rockfish under menhaden
9059-albums2552-picture81660.jpg
Rockfish feeding on silversides this past Oct upper bay
9059-albums2552-picture82377.jpg
Rockfish on the bottom off PLO Fall 2014 (rougher day)
9059-albums2552-picture81661.jpg
Rockfish suspended trolling Spring 2015
9059-albums2552-picture81664.jpg
Drifting over rockfish upper bay fall 2015
9059-albums2575-picture82378.jpg
Drifting over rockfish chasing bait fall 2015
9059-albums2552-picture83645.jpg
Big solo rockfish preseason trolling 2015
9059-albums2552-picture81662.jpg

You can see the differences in readings of the wide cone on the left vs the narrow cone on the right to better understand the difference in readings.

To find the cone angles of your transducer, inquire with the manufacturer of your unit or check out http://www.airmartechnology.com/. Airmar makes many of the transducers on the market. If you have questions or comments, feel free to post here or email me at [email protected]
 

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Discussion Starter · #2 ·
I tried to search what the cone angles are on the Lowrance transducers. This is what I found on the Lowrance site: http://support.lowrance.com/system/...ZONE_OFFSET=&CMD=VIEW_ARTICLE&ARTICLE_ID=2969

We offer a variety of 200 kHz transducers with either a wide (20°) or narrow (12°) cone angle. The 50 kHz transducers come with a 35° cone angle. The dual-frequency transducers come with both a narrow (12°) 200 kHz and a wide (35°) 50 kHz cone angles. And the dual-search transducers come with both a narrow (12°) 200 kHz and a wide (35°) 83 kHz cone angles.
I also found this: http://www.chsmith.com.au/Products/Lowrance-Transducers.html
'Shallow' water HST-WSBL 106-72 transducer will operate on 2 frequencies on the HDS models: 200 (20°) & 83KHz (60°).

'Deep' water HST-DFSBL 106-77 transducer will operate on 2 frequencies on the HDS models: 200KHz (12°) & 50KHz (35°). This compares to the Airmar P66 (ESA931) 200 (11°) & 50KHz (45°).
Looks like the shallow water 200/83 has a wide cone at both frequencies (probably not the best for bottom fishing since the cone is so wide at 200kHz) and the deep water 200/50 is closer to the p66 but only has a 35 degree cone at 50kHz.

Here is a discussion between the p66 and Lowrance transducers:http://www.thehulltruth.com/marine-...ar-p66-vs-lowrance-oem-skimmer-hds-5-a.html#b

Note that the p66 is a cheap Airmar transducer at less than $100. I think it is better for fishing the bay than the more expensive high power 1kw transducers because you get a very wide cone at 50kHz. My fish finder is a full 1kw capable unit and I would stick with the p66/b60 even if I was given a higher power 1kw transducer.

Here is a chart that shows how much area a given cone angle covers at a particular depth
 

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Very good post - gives insight to why you " see " fish on meter but they do not bite - might not be under the boat but off to one side , just out of reach.
 

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Good post and informative. What's the ping speed you have your unit set at? I have a garmin 840. It doesn't allow viewing dual frequencies at the same time. I've always been told and read numerous times that a higher ping speed, or screen scroll, the more likely you'll get the better fish arches on the high frequency setting. Have you found this to be true? I was a little disappointed when I realized I couldn't view dual frequencies but after paying the large chunk of change I'm not changing for a long time. This past summer I found my self switching back and forth numerous times because I was able to pick up different info from either setting.
 

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Discussion Starter · #7 ·
My unit has a fixed transmission rate and the pulse length is auto controlled through the range as part of the Furuno Digital Signal Processing. I can adjust the scroll but that just adjusts the time lapsed after a reading. I am not sure just getting an "arch" is what is helpful either. I believe it is the size of the cone that helps me differentiate between bait and game on the screen. If you just increase the scroll, you are just going to pass the return across the screen faster for faster updated info (I have an instant flasher all the way to the right on my screen for that info).

Your unit is a CHIRP capable unit. CHIRP essentially means it transmits a sweep of frequencies at once rather than two fixed frequencies in order to gain more detail/ target separation. It is a more advanced technology if you have a high quality CHIRP transducer. It still is the same premise though. Low CHIRP will offer wider cone angles and high CHIRP offer narrow cone angles.

I am not sure what transducer you have. On many units today the term CHIRP is over used and over hyped on lower end packages and dont include quality transducers that can take advantage of the technology. It is kind of like how everything got HD slapped on it for a while... For most part, to take full advantage of CHIRP, you need a very high end $1000+ transducer such as an Airmar B175H-W
( https://buy.garmin.com/en-US/US/sho...e-12-tilt-8-pin-airmar-b175hw/prod165270.html ). Sometimes you are better off with a a fixed frequency transducer and understanding how the unit works and what you are looking for. Lowrance and Simrad are guilty of this too. Furuno's CHIRP system is currently only available as and add-on sounder box for multi function displays and is a $2000 add on plus the expensive transducer(s). For fishing the bay, a true CHIRP system isnt worth the money IMHO. (buy a good pair of binoculars instead)

With all that said, if you have a unit that only allows you to view one frequency or frequency range at a time, you may want to consider the fishing you are doing. For trolling and looking for suspended fish, I rely much more on the LF to gain water coverage and helping differentiate between bait and game. (I sometimes will split my screen when trolling to view the top 40' of water on half my screen if I am in deep water and dont even view the HF) For bottom fishing, I rely heavily on the HF to pick up fish on the right under the boat and see bottom density changes (you can use the "white line" feature to help see the fish on the bottom or even bottom lock modes too). When running I look mostly at the HF because I get too much noise at speed with the LF and try to see bait pods with the HF.
 

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Can you offer any insight to the type of transducer you should be looking for fishing shallower waters.. reservoirs??

I am currently looking at the Garmin Echo Map 73dv Chirp
The comment above with how lower priced units over use the word Chirp and not the technology and a giant eye opener..

Thanks!
 

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Discussion Starter · #9 · (Edited)
Call BOE Marine and find out what transducer would meet your goals. I would probably go with whatever one comes with it. www.boemarine.com

Being a DV unit, it will likely come with a combo transducer that includes the sounder and scanning in one. No sense buying/installing multiple transducers. Given that you are fishing shallow water, you dont need a high end CHIRP transducer to put a ton of energy in the water to find fish. Just try to find out the cone angles at different frequencies for frequency ranges so you can better interpret what you are looking at. Of course once you know them and fiddling with the settings on the water will be the best thing for your understanding of the unit. Note that most down view/structure scan units use a "fan" and not a "cone" when reading the bottom. Down view isnt the greatest for marking fish but it can be a useful tool in finding structure to fish around.

My thread wasnt necessarily about what is best but to help some understand that there are different attributes to different frequencies so you all can explore what equipment you are using in order to learn how to use them better. Most brands today will market CHIRP since it is the technology of the future. However if you get a good deal on a fixed frequency unit, it can be just as effective at the depths we fish if you understand how the sonar is getting its image. Most CHIRP untis will work with fixed frequency transducers too. For example, most Lowrance and Garmin units that are 50/200 capable can run the same transducer I have, which is an inexpensive unit at around $100. You will get the same 45 degree cone at 50kHz and a 10 degree cone at 200kHz as I referenced. If you get a different transducer, CHIRP or not, just try to find out what the cone angles are.
 

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iFishMD, so I did a little quick research this morning, as if I didn't do enough before I bought the unit last year, and found out that the transom transducer I got with the bundle is a Garmin GT30-TM. It works well enough but it doesn't have the traditional low frequency. I may step up to the GT40-TM which does have the traditional low frequency. This may enable me to view the low frequency and higher chirp frequencies as a dual screen view. I'm gonna contact Garmin to verify. It would be a simple swap for me but at a $250 +/- cost. Ouch!

Regarding the ping speed, on my current unit and my previous Echo unit, occasionally I could hear the transducer "clicking" in the water and it would definitely be faster with the scroll speed turned up. By hearing this "clicking" noise I just assumed that is the actual transducer doing its thing.

Regardless thanks for the informative post. I don't have the experience or the available time that a lot of people do that post on this site. Finding the fish is half the battle and I need all the help I can get. I'm sure many others are in the same boat, so to speak.
 

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Discussion Starter · #11 ·
While I had a Garmin system on my boat prior to going with all Furuno electronics, I am not the most familiar with making adjustments or the full capabilities of their new units. I have seen them on friends boats but I try not to fiddle with their electronics when I am on board. Give BOE Marine or Garmin a call to see if you can can view both frequency (ranges) at once. If not, try viewing in both modes in certain fishing situations as noted above rather than sticking with just the HF rule of the thumb that many have followed for years.

-
 

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Great discussion. Can you elabotate on ping speed versus scroll speed or combination of the two while trolling and or running at cruise speed? Thanks for your input...
 

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I have a Lawrence Hid I am confused about ping speed. Also does the down scan imagery with either a 400khz or 800khz setting act the same with regards to with and sensitivity of the cone?
Thanks
 

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Discussion Starter · #14 · (Edited)
Ping speed is basically how many times the transducer takes a picture of the bottom per minute. Scroll speed is the time elapsed across the screen. A higher ping speed will keep an image longer on the screen. A higher scroll speed will update the images on the screen faster.

I cannot adjust the ping speed on my Furuno. I can adjust the scroll rate. When running at higher speeds, it may be best to increase both if you can. I personally leave mine in the same fishing mode and just realize when I am running that bait balls get a lot slimmer due to the speed running over them and can show up a dense lines. I mostly monitor the 200kHz of my unit while running since it gives me a clearer picture with less noise.

As far as downscan imagery goes, that is another ball of wax. I was hoping to stick to the traditional sounders in this thread but I will touch on it. This technoligy typically uses VERY high frequencies to give the bottom/structure definition. I think my fathers unit uses 455kHz and 800kHz. It doesnt do a great job at marking fish but shows structure well. It is almost better for looking for fish shadows since the fish returns are typically so small. It is not great for very deep waters (not a concern on the Chesapeake) and uses a wide "fan" instead of a circular "cone". I would need to look up the coverage areas to see the angle in which the fan is spread. I think the fan is the same for each frequency but I could be wrong. I believe structure scan basically follows the same premise as a regular sounder unit though. 800kHz will give you greater detail but not penetrate as deep, while the 455kHz will penetrate deeper but give less bottom detail but will likely pick up fish better. I have all Furuno equipment on my boat and do not have structure scan. I have used on both friends and my fathers boat though. It is not high on my priority list like it is for my father, who wreck fishes a lot, since I am satisfied with how my fish finder shows bottom density changes and marks fish well. If I have extra money in the future, it is something I may look to add since more toys are always fun.

**edit** from what I found with quick search before running into a meeting, the structure scan fan is 60 degrees. I will try to confirm later.
 

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Greg thank you for sharing your knowledge and starting this thread. Sorry for chiming in so late.

Most of the thread has been about Standard Sonar. With this equipment 1 single frequency is sent at a time.


The new sonar technology on the market today is called CHIRP or Compressed High-Intensity Radiated Pulse. CHIRP sends a continuous sweep of frequencies ranging from low to high CHIRP sonar then interprets frequencies individually upon return. A much wider range of information is gathered allowing CHIRP sonar to create a much clearer and higher resolution image.


I will be teaching this subject as part of my 2016 - 2 Part Lecture Series at CCBC in Essex on Apr 9th & 16th. You will learn about the CHIRP sonar technology before purchasing a new unit...you will not be sorry.

 

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Tom, much better explanation that lowrances! thanks i am very happy with my new ff with chirp. I could see my lure below me as i was jigging in 25' of water.
 

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Discussion Starter · #18 · (Edited)
Greg thank you for sharing your knowledge and starting this thread. Sorry for chiming in so late.

Most of the thread has been about Standard Sonar. With this equipment 1 single frequency is sent at a time.

The new sonar technology on the market today is called CHIRP or Compressed High-Intensity Radiated Pulse. CHIRP sends a continuous sweep of frequencies ranging from low to high CHIRP sonar then interprets frequencies individually upon return. A much wider range of information is gathered allowing CHIRP sonar to create a much clearer and higher resolution image.

I will be teaching this subject as part of my 2016 - 2 Part Lecture Series at CCBC in Essex on Apr 9th & 16th. You will learn about the CHIRP sonar technology before purchasing a new unit...you will not be sorry.
Thanks for chiming in Tom. Best wishes on your seminar series. That is a great opportunity for fishermen to gain some knowledge in the off-season. Hopefully plenty of people will take advantage of your offering!

CHIRP is where it gets more complicated, mostly due to transducers, but the premises are the same..

I did want to clarify that while CHIRP does sweep a range of frequencies that it doesnt sweep from Low to High all at once. You have different transducers and settings where the same premise still applies. There typically is high frequency and low frequency CHIRP just like a fixed pulse sounder. Here are the typical frequency sweeps with a CHIRP unit

  • Low - 28 kHz to 75 kHz
  • Medium - 80 kHz to 135 kHz
  • High - 130 kHz to 210 kHz
The same premise applies to CHIRP as it does fixed frequency sonars too. Typically the low CHIRP is good for deeper water and offers a wider cone. The high CHIRP typically offers a narrower beam (than low or medium CHIRP) but gives greater definition but wont travel as deep. With that said, it gets a little more complicated with CHIRP because there are "wide cone" high chirp transducers. You give up bottom detail if you are bottom fisherman with the wider cone but you gain water coverage. The "wide cone" high CHIRP transducers typically do not still offer as wide as many low frequency CHIRP transducers. Anglers will need to decide the type of fishing they do to decide what CHIRP transducer works best for the fishing they do. I think I would lean towards a high chirp wide beam frequency since bottom detail is not as important to fishing for striped bass as it is for say coastal flounder fishing.

Now this is going to be my personal opinion: I personally still think a fixed tone burst fish finder that allows you to view both high and low frequency is a better tool for fishing the shallower waters of the Chesapeake Bay than a CHIRP unit that limits you to one range of frequencies. I say this because you can still get the best of both worlds, wide beam coverage and narrow beam sensitivity over being limited to one range and one cone angle. CHIRP technology does allow for greater target separation by sweeping multiple frequencies but you are not likely to mark fish that wouldnt with a fixed tone sounder. Typically with the less expensive units are stuck with a more limiting transducer unless you want to spend ~$1200 on the transducer alone or multiple transducers. To me CHIRP really gains advantage in deeper waters when you spend the money on a high end transducer(s) to utilize the power and ranges of frequencies to pick up targets. At depths less than 60' like we fish in the bay, I do not believe it is worth spending that kind of coin. If I spend the money on getting a new fish finder this year, I will likely personally stick with a fixed frequency sonar. I actually find it easier to distinguish bait from game better with my current Furuno vs the CHIRP units I have used. Again, this is just my personal opinion.

Note that some of less expensive Garmin "CHIRP" units only sweep multiple frequencies with the Down Vu and are fixed frequencies on the sonar too. The down vu is much like the Lowrance structure scan and not as good for finding fish as traditional sonar.
 

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Discussion Starter · #19 · (Edited)
iFishMD, so I did a little quick research this morning, as if I didn't do enough before I bought the unit last year, and found out that the transom transducer I got with the bundle is a Garmin GT30-TM. It works well enough but it doesn't have the traditional low frequency. I may step up to the GT40-TM which does have the traditional low frequency. This may enable me to view the low frequency and higher chirp frequencies as a dual screen view. I'm gonna contact Garmin to verify. It would be a simple swap for me but at a $250 +/- cost. Ouch!

Regarding the ping speed, on my current unit and my previous Echo unit, occasionally I could hear the transducer "clicking" in the water and it would definitely be faster with the scroll speed turned up. By hearing this "clicking" noise I just assumed that is the actual transducer doing its thing.

Regardless thanks for the informative post. I don't have the experience or the available time that a lot of people do that post on this site. Finding the fish is half the battle and I need all the help I can get. I'm sure many others are in the same boat, so to speak.
I spent some time looking at Garmin Transducers. The transducers you are looking at do not off "CHIRP" sonar. They are only CHIRP (sweeping multiple frequencies) on the down vu. http://www8.garmin.com/transducers/d/transducer-selection-guide-2015.pdf

Personally, if I had your unit and had to have CHIRP sonar for the bay, I would likely go with the GT52HW-TM (same one as listed on Capt Tom's Garmin Screen shot above). It is low on power at only 250w but you dont need as much power with CHIRP since you are putting energy in at multiple frequencies and we are fishing mostly at less than 60' and no more than 120'. It is a High CHIRP Wide on the sonar. It only gives you up to a 25 degree cone for coverage but that is better than 10 degrees.

If you can live without CHIRP on the sonar portion, look at the GT21-TM. This would be my first choice personally if you can view 50/200 separately. It gives a 40 degree cone at 50kHz and 10 degree cone at 200kHz. Of course this is looking at the transducers on paper too. I switched from a Garmin unit a few years ago (GSD22 with 3010c) and found the 50kHz unusable due to the amount of noise on the returns. However Garmin fish finders have come a long way since then. I would call BOE marine with this info and ask their recommendations. Capt Tom's Seminar may be good to attend too.

If you can afford it, get the Airmar B175HW.. Full 25 degree cone across all frequencies.. It is only a grand: http://www.boemarine.com/garmin-bro...cer-w-depth-temp-20-tilt-8-pin-airmar-b175hw/
 

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They are only CHIRP (sweeping multiple frequencies) on the down vu http://www8.garmin.com/transducers/d...guide-2015.pdf
Thanks for posting this Greg it's an excellent guide to read.

Most of the new units on the market do not need to be set up anymore…and that's a good thing. If the unit needs to be set up or not my trip on Guidance and Understanding Your Electronics is still popular with anglers. I'm in the process of updating this page.

If you're looking at the Garmin echoMAP CHIRP Sonar/CHIRP DownVu/CHIRP SideVu two things should be considered:
1) Transducer - GT52HW is the one to get if you fish the majority of time in 150' saltwater or less.
2) Chart - purchase the BlueChart g2 Vision. This is the best chart Garmin makes and it will allow you to use the Enhanced Auto Guidance feature on one of the units below. The echoMAP CHIRP units all have the QuickDraw mapping feature preloaded. That allows you to make custom maps of the bottom in 1 ' contours.
The echoMAP CHIRP 72sv and echoMAP CHIRP 92sv come with the GT52HW-TM transducer.

Understanding the technical information on line can be difficult. You have to read and re-read this information and normally ask questions from the manufacturer's technical department before making an intelligent purchase. But in the end it's well worth it.

However Garmin fish finders have come a long way since...
And then some.

Please let me help you understand CHIRP....2 Part Lecture Series, CCBC, Essex, MD
 
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