Dual Sonar usage

[Satisfaxion_Gauranteed]

Background info:

I'm currently setup with a Lowrance X51 sonar unit(with speed and temp if it makes a difference) that is a 1500watt peak to peak at 200kHz transmission. I love the unit and it performs the function I need adequately. I use it as a second sonar and it is located in a position that anybody onboard could see it, not just the driver. In conjunction with my older gps, it works well for users who aren't driving the boat.

Some time ago, I upgraded my gps system to a Garmin 498c. This is a combination gps/sonar unit and I really like it, too. This unit is positioned to be in direct viewing/control of my driver/navigator. The sonar transmitts at 4000watts peak to peak at dual frequencies of 50kHz and 200kHz.

Question:

Do the two sonars tell me the story accurately? I was told by somebody they would interfere and give me false readings.

I talked to guy at a local(Kzoo) area boat dealer and he told the two would NOT cancel information or provide false information and that he has a similiar system on his boat.

I called Garmin tech service, and he said that here is about a 50/50 chance they would interfere with one another given the cone angle/geometry of the sonar transmitting into deeper waters.

I called Lowrance tech service and they said it would not be an issue.

I talked to another boat dealer who told me they would deffinately interfere!

I've use the two together, and they seem to work, but how would I know if what I'm seeing on the graph is true?!?!?!?

I'm a mechanical engineer, so I have a good understanding how the units work, which makes me think the 200kHz signals will deffinately be read in combination by each sending unit. I.E. the X51 unit will read it's 200kHz and the 200kHz of the 498 and vice versa. But, would that falsify the signal return and what is displayed to me on the graphs?

If anybody has experience or expertise with this, please help to educate me:D

[huntingfool43]

I know we tried to run a Bottom Line on the back of the boat and a Hummingbird at the driver's seat and were picking up false info on both units. This was several years ago so maybe the problem has been fixed.I don't remember what the out put was on the units but there was a problem with interference between the two.

[BlueIceCPA]

Unfortunatly they could all be right on , but only one with your electronic's with you boat.

Test by Turning one off , do you see the same prior to shutting down the other unit ? Do the Same with the other.

I run a Lowrance LCX18, LCX25, LCX110, Fish Hawk 840, Humminbird 997.

For most times I get great readings with minimal interference.

I have the Lowrance on the Left Side of the Transom and the Humminbird & Fish Hawk on the Right Side, Both units can also be on the Bow trolling motor.

[DKuiper]

I have a LCX15MT with gps mounted for the driver/navigator and a Garmin 250 mounted in the rear for the crew running the lines. With both units on I definitely get interference on the Garmin, but not on the LCX. Lowrance has a help site that indicates because of the overlapping of the cone angles it would cause interference. Sure wanted to use both units but nothing has seemed to cure the problem. I have the transducers mounted 6' apart and the power cables on opposite sides of the boat and still get interference. Also was told that possibly running both power cables from the same battery might cause this. Have not tried bringing another battery on board to try this so I don't know if this would help or not. Good luck, and if you get the problem solved, if you determine you really have one, please post your solution. Thanks.

[Satisfaxion_Gauranteed]

Thanks for the post. I've been meaning to get back to this and post what I found out from the Garmin tech support(which is very good and extremely helpful).

Here's how it works:

Sonar is vibration, so no matter how you cut it, you're vibrating the water column with an amplitude(power) at a time rate(frequency).

My boat with cone angles the way they are will experience interference from the 200khz units when I have both operating at 200khz at depths greater than ~35fow.

However, two things can help/fix the issue. First, sonar won't interfere at all if you're frequency is 50khz or more away from one another. Second, the ping speed of the units can be adjusted so that the interference can be minimized greatly. Ussually, it will amount to being very faint verticle lines on the graph of the unit being interfered with and is ussually liveable for the user.

On my setup, my Garmin is dual frequency and runs at 50 and 200khz while my Lowrance only runs at 200khz, so I never experience an issue because I just use the 50khz frequency on the Garmin and the 200khz on the Lowrance. The 50khz frequence covers much more water, but the 200khz gives you more visualization right below and covers bottom detail extremely well. My Garmin at 50khz marks the depth at the bottom very well, but bounces at +/- about 2'. It will show me fish/bait that the Lowrance will not operating at 200khz because of the greater water coverage of the 50khz. However, the Lowrance running at 200khz marks the bottom depth extremely accurately with great detail, but does not cover as much water horizontally(parallel to the bottom).

So, to make a long story short, you CAN indeed run dual transducers on a single boat, but you need to ensure your operating frequencies are 50khz or more different. They sell a variety of units that operate at different frequencies for just this type of application. 50 and 200khz is the standard, but 130 and 270khz units are both available.

My two units work GREAT together. I love having them. I can zoom in each graph to see different things. About 80% of the time, both graphs are telling me the exact same thing. This gives me the flexability to zoom the Lowrance in on bait clusters or certain portions of the water column to see great detail while leaving the Garmin focused on the whole water column. There are occaisons that the Lowrance will pick up a fish right at the bottom that the Garmin misses or the Garmin picks up fish that the Lowrance misses.

Again, I love having both units and have found the added investment well worth it.

Hope this helps anyone looking to have a similiar setup.

[GLF]

Thanks for taking the time and sharing your findings.

There are occaisons that the Lowrance will pick up a fish right at the bottom that the Garmin misses or the Garmin picks up fish that the Lowrance misses.

Do you know what degree cone the Garmin and Lowrance have? This may be why one is picking up fish and the other is not. I have a 50/200khz transducer on my Lowrance. I pick up more fish when I have it set to 50khz.

50 kHz transducers typically have wider coverage angles than 192 or 200 kHz transducers. This characteristic makes them useful in tracking multiple downriggers. Thus, even when these downriggers are in relatively shallow depths, 50 kHz is preferred by many fishermen.

Lowrance has a great support document on how sonar and the different cones work located here.

[Satisfaxion_Gauranteed]

My Garmin, being dual frequency, is 35 degree cone angle for the 50khz and 12 degree for the 200khz. My Lowrance has a 20 degree cone angle. You can use geometry to figure the depth at which you'll get interference.

I'm not 100% sure how the Lowrance units work, but I know with my Garmin I do not notice any difference in fish marking when using the dual frequency option. I do know the 525c Lowrance with dual frequency has the ability to show you two sonar graphs simutaneously, one graph per frequency.

My Garmin has the same functionality. However, with my Garmin, if I have the gps/sonar split screen enabled(which is the normal for me), AND I have the dual frequency sonar enabled, then the graph will show me both sonar returns on one sonar graph. I'm not sure if the Lowrance units do that or if they automatically choose which sonar to use based on depth or some other value.

My Lowrance works great for big lake fishing! I would use 200khz system over just a 50khz by itself. It will mark thermoclines and provides a more detailed picture of what is happening right around the boat than a 50khz system does.

Most 50khz units are dual frequency. Having a dual frequency is awesome for deep water fishing on the great lakes. I'm not aware of any units that run strictly on 50khz that also don't have the option to run at a second higher frequency. The reason being that 50khz sonars will miss fish around structures.

The main advantage 50khz has is the ability to cover more water. A good rule of thumb is that a 50khz sonar will cover 2/3 the depth horizonatlly. So, if you're in 30fow, it'll cover 20 feet horizontally at 30' down.

For the 200khz frequency, the ratio is closer to 1/3. So, if you're in 30fow, it'll cover approximately 10 feet horizontally at the bottom.

Having the knowledge of how the cone angle and frequency works gives me added knowledge. For example, under normal circumstances, I set my Garmin to run at 50khz and my Lowrance runs at 200khz. I know that the 50 covers more water, so if I get a fish on my Garmin and don't get it on my Lowrance, I shouldn't expect that fish to take anything right around my boat because it's likely to be far to the side of my boat. If I'm getting a lot of bait fish in a certain portion of the water column, I'll use my Lowrance to zoom in on those regions and leave my Garmin covering the whole water column.

[DKuiper]

About ping speed? Can find nothing in either manual for the Garmin or Lowrance for adjusting this function. Would like to try that before buying a dual frequency transducer for one of the units. Not sure which unit I should buy the df transducer for either. The Garmin is the one having the interference problem, so maybe that is the one that needs a different operating mhz transducer? Any thougths on this, anyone? Thanks for any opinions or ideas.

[Satisfaxion_Gauranteed]

About ping speed? Can find nothing in either manual for the Garmin or Lowrance for adjusting this function. Would like to try that before buying a dual frequency transducer for one of the units. Not sure which unit I should buy the df transducer for either. The Garmin is the one having the interference problem, so maybe that is the one that needs a different operating mhz transducer? Any thougths on this, anyone? Thanks for any opinions or ideas.

Not all units have adjustable ping speed. If it's not in your manual, then I suspect niether unit is adjustable.

Double check your manual for dual frequency capability. Not all units have dual frequency capability. Some units require the settings to be changed to match whatever transducer you have. My Garmin can run various single frequencies or the dual frequency transducer I have on it while my Lowrance is locked and cannot operate without a 200kHz transducer.