Topic: 798 and EMI interference in VHF radios, anyone else have this problem?

[lolar3288]

I installed my 798 this spring.  When I turned it on both my vhf radios got static and could not be squelched clean.  I check the power lines and found the noise was being pickup by the antennas.

Playing around I wrapped a piece of aluminum foil about six inches long around the wires right at the 798’s bracket.  The EMI stopped!

Anyone else with this problem?

[Roddy]

Lolar; This is strange! The HB opn freq and the radio opn freq are so far apart,the units would need to be within a 1" to 2" of each other.
  Doe's the compass spin when the HB unit is turned on?
  Doe's the compass spin when the radio is keyed? Roddy

[lolar3288]

No the compass is fine (not that I use it with three plotters on board).  But the 798 effected both radios, with antennas on different sides of the boat, a good 12 feet apart.  Both radios are different years and makes.

Bring your hand near to press the view button and you will still cause interference.  No idea where it is radiating from?

[Humminbird_Greg]

It could be radiating from the power cable, the transducer, the GPS Receiver or even out of the display.  Best bet is to separate the cables of the 798 unit from all of the radio cables even to the point of powering the 798 unit off of a different battery that is not electrically connected to the battery that powers the radios (even through a charger).

[sonar2000]

Greg, is this a shielding issue for HB.  I dont see this on other brand sonar/gps units..

Chuck

[Roddy]

Lolar; If you can find a RF Field meter, power on one item at a time and check with the meter. That will tell where the interferance is coming from. Roddy

[lolar3288]

I'm traveling now (Bay of quinte as I type) so no RF meter is available to me.  The al seems to be doing the shielding.  I suspect it is a fault or something common to this unit as others would have had the problem.  Hard to say where to look?

Larry

[SC_Sonar_Kid]

I was out last week and noticed the interference on my regular radio, so I broke out my emergency VHF handheld and the noise was there too.  The noise was strong because I could not squelch it even at the highest setting.  I have a 25' Grady, so I tried to move the handheld to the furthest point but it was still getting jammed.  I was about 30 miles offshore, so this was a bit unnerving if I had to call for help and listen for responses.  I've surveyed the internet and one fellow said that he put aluminum foil around the base and that helped, while another fellow had to send his back into Humminbird.  My radio is mounted in the overhead electronics box, while the 798c is on the dash so none of the cables run together and there is almost 6' of separation.  I did wire them to the same power distribution panel, but that doesn't explain why its radiating over the air and effecting my handheld radio.  I assume the sonar is at audio frequencies less than 10KHz, so that is well off from the 156MHz of VHF marine band.  It may be powerful enough to create harmonics at the marine band, but that would be some sloppy filter design on Humminbird's part.  I hope Humminbird has a fix, because I really like this unit.  Let me know if anyone has a fix.