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Old 29-09-2015, 23:00   #1
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Airmar 200WX degrades VHF RSSI

I've got an Airmar 200WX weatherstation at the masthead, about a foot and a half from my VHF antenna. The VHF antenna is connected to a VESPER XB8000 transponder via Vesper antenna splitter. When the Airmar is up and running (via NMEA 2000), AIS reception is severely degraded. Targets only shows within 3 or 4 nm of the boat. The status page of the Vesper configuration utility shows an RSSI value of -70. Disconnect the 200WX from the N2K network, and the RSSI goes to -115, and targets over 40 miles out are displayed.

Have read that VHF transmissions can cause issues with data being sent from Weatherstation, but nothing about it interfering with VHF reception.

Anyone else have similar issues?
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Old 30-09-2015, 15:45   #2
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Re: Airmar 200WX degrades VHF RSSI

Yes, you definitely need to keep any electronic devices far away from your VHF antenna. My WX200 is 3 feet from our VHF.
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Old 02-10-2015, 15:26   #3
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Re: Airmar 200WX degrades VHF RSSI

mrp006,
The Airmar 200wx manual specifies mounting a minimum distance of 1 meter away from VHF antennas....but, you may be getting some (a lot?) of RFI being radiated from the NMEA 2000 wiring as well...

[Does anyone know if NMEA 2000 is FCC Part 15 compliant? I know it would be the individual devices that should be / would be tested/certified (and I'm doubtful that a masthead wind sensor would be sent for testing / cert), but I'm wondering about the NMEA 2000 network / standard, has NMEA made the network Part 15 compliant?]

This is just another example of the poorly designed / manufactured electronics these days, that radiate a LOT of RFI (Radio Frequency Interference).....typically well beyond that would be allowed under FCC Part 15 regulations, but most of this stuff never really even gets tested, let alone actually "certified"...
Quote:
Originally Posted by mrp0006 View Post
I've got an Airmar 200WX weatherstation at the masthead, about a foot and a half from my VHF antenna. The VHF antenna is connected to a VESPER XB8000 transponder via Vesper antenna splitter. When the Airmar is up and running (via NMEA 2000), AIS reception is severely degraded. Targets only shows within 3 or 4 nm of the boat. The status page of the Vesper configuration utility shows an RSSI value of -70. Disconnect the 200WX from the N2K network, and the RSSI goes to -115, and targets over 40 miles out are displayed.

Have read that VHF transmissions can cause issues with data being sent from Weatherstation, but nothing about it interfering with VHF reception.

Anyone else have similar issues?
Welcome to the modern era, where few care about radiated emissions from electronics...and even fewer care to manufacture systems that are compliant / certified!
And when you look at how the Asian electronic manufacturers treat the "rules" (I have best friends that work in EMC / RFI compliance testing/certification here in the US, and they tell me stories that will make wonder how much of this stuff is allowed to be imported into the US , or EU, and understand that the "enforcement", whether from governments or the WTO, is a fallacy these days!), you start to understand just how bad it might get!


If you wish to see just how bad this is getting, I just posted (in the thread on EPIRB interference) some information from this years ITU report on interference / significantly increased RF noise levels in the 406mhz to 406.1mhz EPIRB band! (primarily in Europe and Asia)

Here is just a brief quote, from the ITU report:
Quote:
The 406-406.1 MHz frequency band is exclusively allocated to the mobile-satellite service, which is currently used by the Cospas-Sarsat system, the purpose of which is to provide distress alert and location data to assist search and rescue (SAR) operations, using spacecraft and ground facilities to detect and locate the signals of distress beacons operating on 406 MHz.

According to Resolution 205 (Rev.WRC-12), the frequency band 406-406.1 MHz is constantly monitored. Several noise measurements have been conducted using all the three space components. In particular, measurements performed by the LEO component show that the level of noise over certain years (measured in the 406-406.1 MHz band) has increased by 15 to 20 dB above the interference level in some areas. This noise level is especially high over Europe and also in part of Asia. For most of the areas on the Earth (mainly over oceans), a distress beacon can be correctly received and processed by the SARP even for low levels. However, a general concern is raised on the reception and processing of weak distress signals, in certain areas, caused by an increase of noise especially in Europe and Asia.
Now, mrp0006, I'm sorry if I went off on a rant here, and didn't actually answer your question...

Bottom line:
I don't have a Airmar 200WX, nor do I have a NMEA 2000 network, so I cannot answer your query with direct knowledge, but my knowledgable guesses are:

a) your Airmar is much closer than the minimum specified distance of 1 meter, from your VHF antenna...
b) you may have NMEA 2000 network RFI / RF radiation that is causing this, as well...
c) You may have poor shielding / poor shield on your VHF antenna coaxial cable...
d) You may have a defective connector / poor connection of the WX200, and/or your VHF antenna, and/or your VHF radio, and/or your VHF/AIS antenna splitter, and/or your Vesper XB-8000....

And, quite possibly all four of the above!
But, again....even if you have one, two, three, or all of these problems above, the darn weather sensor should NEVER radiate enough energy to wipe-out all but the strongest VHF / AIS signals!! (and this is why I went off on my rant above....to show you why this is a problem these days!)


I do hope this helps!

Fair winds...

John
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Old 02-10-2015, 15:32   #4
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Re: Airmar 200WX degrades VHF RSSI

I wonder if a large balun like this Ferrite Products for RF Chokes, Baluns, and RFI Mitigation on the NMEA 2k cable would help.
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Old 02-10-2015, 15:49   #5
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Re: Airmar 200WX degrades VHF RSSI

Saltyhog,
Actually as long as you use the proper mix (For VHF freqs, use Mix 43 or 61), and run the NMEA 2000 cable thru a few times, this is a good idea, and couldn't hurt....
Quote:
Originally Posted by Saltyhog View Post
I wonder if a large balun like this Ferrite Products for RF Chokes, Baluns, and RFI Mitigation on the NMEA 2k cable would help.
But, FYI, with the extreme issue mrp has written about, it seems that this is a case of severe RFI, which might need further testing/investigating and a more substantial fix..


I suggest talking directly to Airmar engineering team, and if that gets him nowhere, then get someone on-board with some serious test equipment...(I've been paranoid bring some of my gear on-board, and that's in the cabin....I can't fathom bring it up the mast, so this might be an expensive troubleshooting mission!! Understand that an analyzer that can see these low-level signals at VHF freqs is at minimum a $4k - $5 instrument, and typically closer to $15k....and the consulting/testing work doesn't come cheap either!!
If he wasn't an entire continent away, I give some thought to doing this for him....but he'd owe me BIG TIME...)


BTW, fair-rite.com and palomar-engineers.com are good sources for ferrite info and devices...as is dxengineering and radioworks...


Fair winds...

John
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