Multiple transducers interference?

[potis]

I recently installed a new Garmin transducer for my new Garmin MFD (943xsv). I still have the older transducer in place from previous device, and it is mounter next to my new one, maybe 12” from it. Out of curiosity I connected a stand alone depth gauge (Raymarine i40) to the old transducer and powered up both units and they both seemed to work fine. I was under the impression that they would interfere with each other depending on frequency. My new Garmin is set for “auto” adjust for frequency and I have no idea what the old unit is running on as I don’t have the option to see that information. So here is my question: If both units appear to be giving accurate data is it OK to run them both at the same time or is this potentially causing some problem that I may not actually be seeing but will cause a detrimental issue down the road? Thanks

 

[ttmott]

I asked that same question to the installer on my boat. His answer was "it depends"..
First if the transducer is good quality it's receiver has a "tight" bandwidth to receive specifically the frequency it sends out so consequently it is less prone to interference to other close frequencies.
The receiver is expecting to see a reflection (bounce back) a specific time after it is transmitted; if another transducer is transmitting the same frequency obviously the reflection will be skewed and information not correct.
The answer is you need to know the operational frequencies of your devices to ensure they can work together.
And it gets more complicated when scanning transducers like CHIRP are installed.
The question is how do you know the information being received is accurate and not impacted by another device?
I have a scanning transducer and one time in the lock it was all wacked out, straight lined, but once out of the lock it recovered. As it ends up the boat tied behind me was also transmitting and messing up my signal. I knew that because him coming up on my aft further down the inlet it messed up again. I'm sure his was skewed also.

 

[Thornton69]

We run a couple different transducers with the same Lowrance Live unit. The unit came with the 3 in 1 which we use for sidescan to 200'. The second is a more powerful 2d transducer that will downscan and ping to 1000'. They will interfere with each other when multiple screens are selected. We just turn off the channel (transducer) we are not needing at the time.

 

[Skybolt]

The i40 default frequency is 200Khz, what transducer are you using with the 943?

Same frequency Transducers cannot be used when mounted close together. The issue can manifest itself in many ways, sometimes you cannot tell if there is an issue. Sometimes one xducer will read the signal from the other and get bad readings.

The real issue comes in when you are using different technologies like chirp from Raymaine and Chirp from Garmin. Almost the same frequency spectrum from both and these will misread or post bad data. It really is a "depends" type of answer. I have a chirp and a dual frequency (50K, 200K) transducer about 5' from one another on opposite sides of the keel and they work fine.

 

[potis]

SKybolt - I am using the Garmin GT 23M-TH transducer with the 943 xvs plotter.

 

[Skybolt]

SKybolt - I am using the Garmin GT 23M-TH transducer with the 943 xvs plotter.

The traditional side of the transducer, meaning just the depth reading, is 50/200Khz which overlaps with your i40. Can't say what exactly will happen but there will be some level of interference between the two. The sonar (not depth reading) side of the Garmin might display strangely at times. The depth reading between the two will be competing with each other, might display perfectly, might see signal rejection (wrong depth or depth blinking). You need 50K or more difference in frequencies to operate well.

https://www.garmin.com/en-US/p/537002/pn/010-01962-10#specs

Garmin's recommendations: https://support.garmin.com/en-US/?faq=cJQMIoKUtz7ze21oU68Id6

 

[potis]

The traditional side of the transducer, meaning just the depth reading, is 50/200Khz which overlaps with your i40. Can't say what exactly will happen but there will be some level of interference between the two. The sonar (not depth reading) side of the Garmin might display strangely at times. The depth reading between the two will be competing with each other, might display perfectly, might see signal rejection (wrong depth or depth blinking). You need 50K or more difference in frequencies to operate well.

https://www.garmin.com/en-US/p/537002/pn/010-01962-10#specs

Garmin's recommendations: https://support.garmin.com/en-US/?faq=cJQMIoKUtz7ze21oU68Id6

thank you this is great info. And what you predicted is exactly what I’ve seen happening so far. Good readings on both units 90% of the time and then suddenly the i40 will give a whacky reading for a short period, and then return to normal. I think if I cannot adjust the frequency to prevent interference, I will have to just have the i40 as a back up I can turn on if my other unit was to crap out.

 

[dtfeld]

Check you MFD/Fishfinder owners manual. Usually you can offset you frequencies by a good bit +/- from 50 or 200 Hz to avoid this.

I know this can be done on the Raymarine Axiom...I dont know Garmin/others well enough to tell you exactly, but I would think this is standard as lots of applications would have multiple transducers operating simultaneously.