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Old 01-06-2014, 19:10   #1
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Icom M802 & AT-140 Grounding???

I have an Icom M802 & AT-140 tuner that uses a wire mesh in the hull as an RF ground. The system works fine except I get some noise from the refrig & freezer compressors and the Simrad Autopilot. I have tried to isolate the noise at the compressors and autopilot computer without great success.

I was recently given advice to disconnect the RF ground from the M802 chassis & just connect the tuner to the RF ground. I was also given advice to connect the wire mesh RF ground to a bronze hull fitting to provide a better RF ground in contact with seawater. In the process of disconnecting the RF ground from the M802 chassis, I found that the M802 chassis is also common with the boats 12v DC ground so the original installation had the RF ground and ships DC ground tied together at the M802 chassis.

I have disconnected the M802 chassis from the RF ground and have connected the RF ground wire mesh to a brooze hull fitting and still have the RF ground connected to the tuner.

Am I on the right path or am I missing something. The ICOM manual says the the M802 chassis should be connected to the RF ground as well as the tuner????
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Old 01-06-2014, 19:49   #2
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Re: Icom M802 & AT-140 Grounding???

You are on the right track. Your M802 will be connected through the coax cable to the tuner and then to RF ground.

Have the changes you have made helped?
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Old 01-06-2014, 20:21   #3
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Re: Icom M802 & AT-140 Grounding???

HF frequencies actually propagate over the surface of materials rather than through them. The absolute need for a seawater conductive connection is actually an urban myth (poor physics). What actually happens with seawater coupling is that lower frequency noise in the negative/ground system is dampened by the seawater connection, consequently reducing the parasitic effect as a result of the higher frequency harmonics on the HF component of the system. Your copper mesh counterpoise connected to you engine block etc offers a good amount of surface area for your RF ground. Somewhere over 175sq.ft. of total surface area would be optimum but not always possible on a GRP boat.

You're probably fine with your current setup and you're going right direction and DeepFrz states. Decoupling your RF ground from your negative tie will go a long way to helping reduce the noise from your other devices. Typically, one of the worst offenders would be a PWM battery charger when it comes to SSB noise.

One of the reasons that people find that Kiss SSB works quite well is not because it's a perfect counterpoise solution, but because it is typically completely decoupled from the vessel's common negative/ground system and consequently not too noisy!
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Old 01-06-2014, 20:54   #4
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Re: Icom M802 & AT-140 Grounding???

We normally shut the fridge off when doing any HF radio communications. We have found we get noise from the auto pilot, some led lights, battery charger, cabin fans. Trying to eliminate all the noise well we put a number of chokes on the autopilot and that really helped but usually we just turn off the offending culprits when using the radio. We also have a 802 with a AT140 tuner and just run the ground to the nearest thru hull. Rock solid transmission.

Good luck
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Old 02-06-2014, 07:50   #5
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Re: Icom M802 & AT-140 Grounding???

BrightAyes,
Yes, you are in the right track in regards to "grounding" and wiring of the M-802 and AT-140...

But, this will typically have NO effect at all on radiated, on-board-generated, RFI (Radio Frequency Interference)....

Much of this is covered in the Sailmail Primer...
SailMail Primer


See detail here in red...
Quote:
Originally Posted by BrightAyes View Post
I have an Icom M802 & AT-140 tuner that uses a wire mesh in the hull as an RF ground. The system works fine except I get some noise from the refrig & freezer compressors and the Simrad Autopilot. I have tried to isolate the noise at the compressors and autopilot computer without great success.
Typical RFI/noises from Danfoss based refrigeration/freezers are lots of beeps, tones, and buzzes...(and this noise, as well as other noises from the Autopilot corepak/computer)
Typically these are RADIATED (i.e. "transmitted" thru the air) and received by your M-802/AT-140's antenna (backstay, I assume??)


So, the usual cures are mulit-fold (and most apply to BOTH the frig/freezer AND the autopilot):
a) Simply turn off the frig/freezer when using the radio (NOT such a great solution....but many times, just the a change in voltage and/or switching the frig off and then back on again a few minutes later is enough of a change to "move" the interference away from the frequency you're using, and you're good-to-go...)
Of course, turning off the autopilot is usually a non-starter...

b) Try to install your AT-140 and antenna as far away from your refrigeration compressors / controllers (and autopilot corepak) as possible (usually NOT very practical)

c) Make sure your GTO-15 antenna wire (that is the beginning of your antenna) that runs from the AT-140 output to your backstay is as far away as possible from the refrig compressors (and autopilot corepak) AND as short of length as possible....(do NOT lengthen it just to move it further away, as you want it to be as short as possible and run as directly as possibly to the backstay)

d) Do NOT ever run the GTO-15 wire along with any other wires!!!
ALWAYS keep the GTO-15 wire as far away from every other wire as possible....and never allow it to run parallel to other electronics wires....

e) Once you've done the above, then it may (usually) comes down to "choking-off" (and/or shielding) this radiated RFI at the source....
Understand that all the wiring that connects to these devices (refrig/freezer and autopilot corepak) act as ANTENNAS radiating/transmitting this noise/RFI....
Anything you can do to move these farther away, shield these devices, and "choke-off" this radiated RFI from these "antennas"....will go a long way in eliminating the RFI altogether....(but sometimes it is expensive to completely eliminate all RFI)

Clip-on ferrites are going to be your new best friend here!!
Buy a lot of them (maybe a dozen or more)....(all Raymarine electronics come with them, just for this purpose!)

Place them on ALL electronics wiring, especially on ALL autopilot wiring....and on all refrigeration wiring....
And, do this RIGHT AT THE devices, RIGHT as the wires leave the autopilot and refrig units...(thereby "choking-off" much of this radiated RFI...
Do NOT be stingy here....use a lot of ferrites and/or of you can loop the wiring thru the same ferrite 2 or 3 times that is even better (and their "choking" ability is multiplied exponentially (up to a point, anyway)....

I recommend DX Engineering and Radioworks....they both have the correct ferrite mix for HF RFI and both are used to dealing with HF radio users (mainly hams) who have RFI problems (although usually it's the HF radios causing the interference to other devices...

RF suppression snap-on Ferrite beads- DX Engineering

RFI


Also, take note that while it probably will be of little help in your specific problem described, using a "line isolator" on the coaxial cable (installed at the AT-140) is not only normal installation procedure, it is VERY practice to keep your radio's transmitted signal from causing interference to other devices on-board....and if you're ordering ferries anyway, you might as well buy/install a line isolator and coax jumper...

DX Engineering Maxi-CoreŽ Feedline Current Chokes DXE-FCC050-H05-A - Free Shipping on Orders Over $99 at DX Engineering

T-4

Line Isolator System



f) There are also "RFI shielded" refrigeration controllers....but they're expensive....(I think the Adler Barbour RFI-shielded BD50 controller is about $700....so, if all the above doesn't eliminate enough of the RFI, there is a rather expensive approach that will....and FYI, some have also done a DIY shield and using ferrites along with this DIY shield, has proven to be an excellent solution....but not one I'd recommend to a non-technical person)





I was recently given advice to disconnect the RF ground from the M802 chassis & just connect the tuner to the RF ground.
This is standard and normal practice, regardless of what the Icom manual says....(remember Icom manuals need to be "lawyer-proofed" and much is written that is not technically accurate)




I was also given advice to connect the wire mesh RF ground to a bronze hull fitting to provide a better RF ground in contact with seawater.
Yes, a direct sea water connection IS best (notwithstanding the misunderstandings of others)....
But, in most cases (99.9%) of RFI interfering with your RECEPTION on the radio, it will have NO effect at all...

BTW, I'm more concerned that there is "wire mesh" being used here...
This is very telling and NOT ever recommended for RF use (again notwithstanding that many laypersons seem to like its flexibility)....
"Wire mesh", unless it is contained within a jacket of some type so it cannot move AND protected from corrosion, can cause a LOT of RFI itself...
The "semi-conduction" of RF across all the small junctions as they move around, can cause a lot of RFI....and once these become corroded, they are no longer very conductive at RF and many times the problem gets worse....(and at best they cease to function as much of a ground connection...)

Copper strapping is used for RF grounding (both on-shore in all commercial environments, such as radio installations, cellular installations, etc. and on boats....), wire mesh is never recommended and I'd be happier recommending a large copper wire rather than "wire mesh"...

But, perhaps this is bronze mesh, or tinned copper mesh, that was glassed into the hull upon construction, so it does not move and is protected from corrosion???
If this is the case, just make sure the ends that you connect to are clean and shinny....and ignore my rant above...

Oh, and further, you should be using a water-resistant conductive grease on all your "ground" connections...
Penetrox-A is great stuff....its messy, but I've been using it for > 30 years and it works GREAT...
DX Engineering Penetrox A Anti-Oxidants DXE-P8A - Free Shipping on Orders Over $99 at DX Engineering





In the process of disconnecting the RF ground from the M802 chassis, I found that the M802 chassis is also common with the boats 12v DC ground so the original installation had the RF ground and ships DC ground tied together at the M802 chassis.
I have disconnected the M802 chassis from the RF ground and have connected the RF ground wire mesh to a brooze hull fitting and still have the RF ground connected to the tuner.
This is typical, and you disconnecting this is fine....(although some do find it works fine for them to have this connection, most do not...)
As you can see in the Sailmail Primer, having the RF ground connected to ONLY the AT-140 is the recommended way of doing it...
SailMail Primer




Am I on the right path or am I missing something. The ICOM manual says the the M802 chassis should be connected to the RF ground as well as the tuner??
Yes, you're on the right path....see all the above for details...
And, ask further questions as needed...


I hope this helps..

fair winds..

John
s/v Annie Laurie
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Old 02-06-2014, 08:00   #6
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Re: Icom M802 & AT-140 Grounding???

Cavalier,
While I'm sure you're well intentioned here...but since I majored in Physics and have 40 years experience in RF, and have run my own electronics firm for over 30 years now....
Can I politely say your information is wrong...(and even if not flawed, is quite a ways beyond what anyone else here needs/desires..)


If you wish to be 100% accurate there is no "absolute need" for any ground at all....as the transmitter's signals will still radiate and the receiver will still work fine....
But, here we are trying to solve intricate RFI issues....
And, while "grounding" is a favorite internet subject to pontificate about, the fact is here in this situation it is almost irrelevant...

So, since this discussion / solution to "BrightAyes" problem has little to do with "grounding", I'm not going to ramble on about it, nor comment on the KISS....other than to say that your information and reasoning is wrong....sorry about that...



I do wish you fair winds and sunny skies..

John
s/v Annie Laurie
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Old 02-06-2014, 10:04   #7
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Re: Icom M802 & AT-140 Grounding???

Quote:
Originally Posted by ka4wja View Post
..but since I majored in Physics ....
Excellent, at least there's two of us in this world!

Quote:
Originally Posted by ka4wja View Post
..Can I politely say your information is wrong...So, since this discussion / solution to "BrightAyes" problem has little to do with "grounding", I'm not going to ramble on about it, nor comment on the KISS....other than to say that your information and reasoning is wrong....sorry about that...
Just stating "you're wrong" doesn't serve much of an educational purpose for anybody other than to help lower your own elevated blood-pressure.

I'd agree with you that the RF interference being caused by all of the other motors, PWMs etc. in their boat most likely has little to do with the common grounding. However, it is always useful to go over the system to ensure that unnecessary noise isn't being introduced via the power supply and its vestiges.

Just on Friday of last week, I finished debugging the controller boards for a Pulsed-neutron Generator. We were having major issues with noise coming into the Analogue input channels of the system, especially from the feedback from the RF cavity we'd built for the pulser. Or so we thought. After endless modifications to cable screening, local filters up and down-stream of OPAmps, hardware rectification and software filtering. We hooked a scope on to the lab power supplies. There was a phenomenal amount of noise coming from the switching DC supplies. Once we put in DC-DC line conditioners our problems resolved themselves. Now, and as we originally thought, the source of the noise was external RFI or cross-talk even-though we'd laid out the PCBs specifically (through best practice) to reduce the possibilities of such occurrences. In the end of the day it was noise coming in through the output from the [relatively] low cost +/-12VDC power supplies.

To be useful, I'd recommend that the OP read a little further around the subject of RF, antennas, counterpoises etc.. Evidently, there's a small library available on the subject, but one recommendation would be:
Introduction to RF Propagation, John S. Seybold (John Wiley & Sons, Oct 3, 2005).
Pages 48 onwards are particularly well written and are very clear.

Will reading the book help the OP solve their current issue? probably not. Will the acquired understanding equip the OP with more knowledge to help debug a future problem? Most certainly.

I find that most of the threads on this forum give an OP a multitude of differing opinions and facts (some at odds with others), this may seem an unnecessary distraction. However, decisions are very easy when you're armed with everything you need to know - and very difficult when you're missing information.

I'm sorry if you felt that my comments in the prior post represented "a little too much information" for the thread - however, i'll continue to post in a similar manner, too much information (even if perceived as incorrect) is better than no information at all!
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Old 02-06-2014, 13:25   #8
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Re: Icom M802 & AT-140 Grounding???

John, I don't see what Cavalier originally posted could be construed as wrong. He advocated decoupling the DC ground from the RF counterpoise - which is widely considered a good practice. He stated that the absolute need for a conductive seawater coupling as a counterpoise was a myth, and is widely supported in that statement by pretty much everyone in HF radio (we don't have a direct connection to seawater either). He then states that PWM devices create a lot of noise - that too is established fact as far as I can tell.

Maybe it is because he mentioned the KISS? All he did was say that maybe the reason it works well for some people is because it forces a decoupling of the DC ground from the RF counterpoise on noisy boats. That is hardly a recommendation or endorsement of the system.

So what about that post is wrong?

His second post, however- there is a lot of fodder in that one! I'm personally surprised that someone working with RF cavities producing feedback didn't go immediately to the DC power supply to look for the cause. High quality DC power supply designs are critical in RF trapping cavity applications...

Mark
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