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-   -   VHF transmit interference (http://www.trawlerforum.com/forums/s4/vhf-transmit-interference-34335.html)

olegreg 08-25-2017 06:25 AM

VHF transmit interference
 
My VFH radios transmit a AC hum which makes it hard to hear me. I have 2 sets with their own antennas. Even my handheld. Tracked it down the house charger/inverter. It is a Xantrex modified sine and I have been told this is my issue. I have Link 2000 R and a Pathmaker with 2 alternators on one engine. It all works very well. I would rather not replace it with a pure sine unit.
Anybody have any success with attenuation of the hum? I want to do it at the source.

meridian 08-25-2017 06:42 AM

I would check to see if the Xantrex is grounded properly.

psneeld 08-25-2017 06:53 AM

The radios too.

Often they sre not an issue, but cant hurt as it is recommended Often not done at install.

There are filters available, took one off my boat that was there for the old LORAN unit.

Guess the alternator interfered with it.

olegreg 08-25-2017 07:44 AM

Grounds good,
Thanks

diver dave 08-26-2017 07:49 AM

HIghly unlikely 3 radios are transmitting hum on the signal, especially the HH. Please describe the test condition.
I do believe the non-sine invertor is a noisy device, electronically speaking, however.

"Non-sine" or "Modified sine" means there are many frequencies being generated beyond 60Hz, which is not an advantage to any comm device.

olegreg 08-26-2017 08:32 AM

Dave,
The hum was first reported to me from a dock master when we requesting berth assignment. Other guys just said I was hard to hear. He described is as an AC hum. So, later I started tracking it down by shutting down systems and devices. When it got to the inverter/charger, it went away on the main radio and it's remote. The dock master stood on the dock and reported what he heard. We repeated this with the main, remote and back up set. I had my HH listening too. Just for kicks I transmitted on HH and he heard the hum also, but a lot fainter.
Happened to discuss this with a marine systems guy, and he mentioned that the Xantrex modified sine unit with its squared waves and harmoncs is well known for this. Xantrex now offers a pure sine unit that will be a drop in. I can keep the Link 2000 and network including the Pathmaker.
Expensive solution. For now through the rest of our cruise in BC inside passage, I will shut down the charger before I transmit.
BR,
Greg

High Wire 08-26-2017 08:57 AM

Long shot but check your battery electrolyte levels. Twice I've found this to solve the problem when there was no problem then was with no other system changes.

olegreg 08-26-2017 09:40 AM

Just added water several days ago.
Thanks

olegreg 08-26-2017 09:45 AM

BTW,
The chopped up wave fried my new Keuric, had a fan smoke on another boat. Inductive loads do not like square wave.

koliver 08-26-2017 11:00 AM

Is yours the Xantrex MS2000?
I use that unit. I have never had any radio interference. I use only one radio, a Standard Horizon mounted at the lower helm, with a Remote Mike (RAM) mounted up top. More likely it is your radios fighting each other.

diver dave 08-26-2017 12:15 PM

Quote:

Originally Posted by olegreg (Post 587140)
Dave,
When it got to the inverter/charger, it went away on the main radio and it's remote. The dock master stood on the dock and reported what he heard. We repeated this with the main, remote and back up set. I had my HH listening too. Just for kicks I transmitted on HH and he heard the hum also, but a lot fainter.
Happened to discuss this with a marine systems guy, and he mentioned that the Xantrex modified sine unit with its squared waves and harmoncs is well known for this. Xantrex now offers a pure sine unit that will be a drop in. I can keep the Link 2000 and network including the Pathmaker.
Expensive solution. For now through the rest of our cruise in BC inside passage, I will shut down the charger before I transmit.
BR,
Greg

Wow; this is one evil charger. If you were closer, I'd like to investigate this one. I do EMC stuff at work and have a pretty extensive radio background.
As a general rule, if you can listen to your transmit audio on another radio, and the mic is quiet, you should not hear anything. (transmit hum and noise spec).

Is the Xantrex in invertor mode or charger mode?

olegreg 08-28-2017 07:49 AM

Keith,
MS2000 is a true wave, mine is the Freedom modified wave.
I use only one radio, Raymarine Ray/70 with a remote Ray Mic . The Standard Horizon is a backup unit sharing it's antenna with the AIS transponder through an A/B switch.

olegreg 08-28-2017 07:51 AM

Dave,
Charger mode.

diver dave 08-28-2017 07:57 AM

CHarger hum. It might be possible for you to measure this offensive signal on your DC bus with a DMM in AC mode. THis is why a previous posted mentioned adding water to his house battery. If the plates were not covered, and then you added water, it would lower the impedance of the battery and tend to reduce this noise voltage.
Even better to use what I have, a self powered digital oscilloscope. :)

rwidman 08-28-2017 08:31 AM

If the interference is when the unit is operating as a charger (connected to shore power), we can forget about all the "modified sine wave stuff".

Battery chargers are notorious for creating RF interference but it's rare to transmit on a VHF radio when plugged into shore power and charging the batteries.

RF Interference can be transmitted two ways, through the air like a small radio station or through the AC or DC power system. If it's being transmitted through the air, it might interfere with receiving devices like your VHF reception or AN/FM reception but your VHF won't retransmit it.

So - if everything you have posted is accurate, the interference is being carried on your DC power circuit and is entering the VHF through the power leads and is being retransmitted by the VHF.

So - You need to filter the DC leads as close to the charger as possible. You need to keep everything but DC voltage off the leads. A capacitor across the leads is a pretty basic filter and will short the interference from one lead to the other. This may solve your problem or you may need a more sophisticated filter with one or more capacitors and an inductor.

I suggest going to a place that installs high end car stereos and talking to them about filters. Keep in mind that this filter must pass 40 amps or more of DC current so a small, cheap filter may burn out.

BTW: One of the best ways for someone who doesn't want to buy expensive equipment to trace RF interference is to buy an "old time" hand held transistor radio. Tune it between stations and move it around until the static increases dramatically. That's where the RF is coming from.

psneeld 08-28-2017 08:46 AM

1 Attachment(s)
Might try one of these...they come in different amp capacities...what I took off between my alternator and batteries years ago.

https://powerwerx.com/newmar-150a-alternator-line-noise-filter?gclid=Cj0KCQjw_o7NBRDgARIsAKvAgt0egAQITSPIn S9UH19SjhsDV_MQ058gXsHUSahW_B0VfuQaKEvQ8usaAqknEAL w_wcB

diver dave 08-28-2017 08:47 AM

Quote:

Originally Posted by WesK (Post 587693)
If the interference is when the unit is operating as a charger (connected to shore power), we can forget about all the "modified sine wave stuff".

Battery chargers are notorious for creating RF interference but it's rare to transmit on a VHF radio when plugged into shore power and charging the batteries.

RF Interference can be transmitted two ways, through the air like a small radio station or through the AC or DC power system. If it's being transmitted through the air, it might interfere with receiving devices like your VHF reception or AN/FM reception but your VHF won't retransmit it.

So - if everything you have posted is accurate, the interference is being carried on your DC power circuit and is entering the VHF through the power leads and is being retransmitted by the VHF.

So - You need to filter the DC leads as close to the charger as possible. You need to keep everything but DC voltage off the leads. A capacitor across the leads is a pretty basic filter and will short the interference from one lead to the other. This may solve your problem or you may need a more sophisticated filter with one or more capacitors and an inductor.

I suggest going to a place that installs high end car stereos and talking to them about filters. Keep in mind that this filter must pass 40 amps or more of DC current so a small, cheap filter may burn out.

BTW: One of the best ways for someone who doesn't want to buy expensive equipment to trace RF interference is to buy an "old time" hand held transistor radio. Tune it between stations and move it around until the static increases dramatically. That's where the RF is coming from.

agreed. And, I have a 1963 Zenith pocket AM radio for jobs like this.

olegreg 08-28-2017 08:52 AM

Dave,
Yeah,
.009 vac on the DC with charger off.
.115 with it on.
Wes,
This is definitely a 60/120 hz hum being transmitted .
I am am going to add a LC filter when I get back from our cruise. Kinda hard to find 40 amp chokes up here on the BC islands.
But in the end, I will change out the inverter /charger as there is no way to get around the fact that it is taking out appliances with inductive loads

diver dave 08-28-2017 09:06 AM

Wow, small world. I've been working on a device causing BC Hydro problems in substations. LIke, 90 seconds ago!

olegreg 08-28-2017 09:41 AM

Curious,
I used to work in that world before I retired.
Can you elaborate?


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