daleboutm
Member
I have a Bavaria 370 C with a steel keel. Is it possible to ground the Hf transceiver (i.c. the antenna tuner) by means of the steel keel (bolts) and the stainless tanks (water en fuel)?
ground for a HF transceiver
- Thread starter daleboutm
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hightech
Well-Known Member
William_H
Well-Known Member
Yes the keel should be a good ground for the HF tuner as also will be the running gear prop etc. If you have any concerns about making the connection ATU ground to keel prop then you can use a large capacitor to ermit the HF to pass but not the DC . You need high voltage capacitors ie 600 volt at .001 microfarrad. Fit about 10 in paralell you need the large number of capacitors to carry the RF current without cooking the capacitors.
The connection wire ground of the ATU to keel needs to be as short as possible using a braid or multiple thick wires. This reduces the inductancee of the lead. good luck olewill
The connection wire ground of the ATU to keel needs to be as short as possible using a braid or multiple thick wires. This reduces the inductancee of the lead. good luck olewill
mdrifter
Well-Known Member
You can tie in metal fuel & water tanks, engine and keel bolt to improve your effective ssb ground. The keel will act as a very effective capacitive ground connection despite layers of epoxy and anti-fouling. Currently we have no expensive external ground plates and yet have effective ssb communications. A good source of info is www.sgcworld.com The best material for atu ground connections is copper tape c. 2"-3" wide, a few thou thick; its surface area is the critical factor because that's where the ssb currents flow - thick wire or braid is not as effective.
shmoo
Well-Known Member
If you are going to follow the good advice here and use copper tape then actually connecting to to the keel becomes less important. Run lots (>5) of lengths of copper tape away from the tuner. Try to make at least one of the lengths 1/4 wave at each frequency you plan to use (tricky on the lower ones, I know). Some folks like to run the tape against the hull but I think it is better under the deck (i.e stuck to the ceiling) to give a better return to the antenna. This method also puts the boat electronics "outside" the field (ie not between antenna and radials)
Radio amateurs get good results from cars on HF. These are not in contact with sea water and have tiny antennas but they do have a big metal ground plane - aim to reproduce a "car".
Radio amateurs get good results from cars on HF. These are not in contact with sea water and have tiny antennas but they do have a big metal ground plane - aim to reproduce a "car".
mithril
Well-Known Member
Yes, why bother connecting to outside apendages. We use sheets of Aly foil (lamnated cooking foil) and lay it as sheets under the water and fuel tanks. As the bilges are clean and dry so are the foil sheets. We laminate so its thickness allows easy handling as we push a strip of about 2m under the tanks.
beneteau_305_553
Well-Known Member
I use only a connection to the guardwires via the stern rail. It worked really well for me across the atlantic this year.
Billjratt
Well-Known Member
I have to say I'm not sure of all these bogus ground planes in a marine/marina environment. You would have to be careful not to produce closed loop circuits and keep an eye on marina strays. I believe that if you're going to pump lots of RF watts, they should have a dedicated path - OK to the keel if there's no other connection to it, otherwise for me, it's a dynaplate. If the guardrails have a slashable safety string at the pushpit they weren't connected, if they didn't they were a loop(even if there was string at the pulpit, 'cos it's under salty water now and then) and they are a finite wavelength long, unlike the oggin.
roly_voya
Well-Known Member
I'm new at this but the books and advice I have seen so far suggests that sea water is a very poor absorber of RF energy so effectivly you cant 'ground' to it. Sounds odd that seawater is not a conductor but high frequency is funny stuff, not at all like DC or even mains. Effectively then the 'ground' needs to be the other halve of a dipole arial or as near as possible to another backstay but at or below water level and it 'radiates' RF engergy into the ground rather than conducts it - hence guard wires seem to work like dipoles and keels seem to act like a big resevouir that absorbs the energy.
john_morris_uk
Well-Known Member
[ QUOTE ]
I'm new at this but the books and advice I have seen so far suggests that sea water is a very poor absorber of RF energy so effectivly you cant 'ground' to it. Sounds odd that seawater is not a conductor but high frequency is funny stuff, not at all like DC or even mains. Effectively then the 'ground' needs to be the other halve of a dipole arial or as near as possible to another backstay but at or below water level and it 'radiates' RF engergy into the ground rather than conducts it - hence guard wires seem to work like dipoles and keels seem to act like a big resevouir that absorbs the energy.
[/ QUOTE ]
Hmm - not sure where to start disecting this lot. You are mistaken in lots of what you say or have read. I agree that HF is 'funny stuff' compared to DC or mains frequencies.
Here are some 'better facts' from an ex RF engineer that might steer you in the right direction.
Seawater is quite a good ground for RF at HF. In fact the water table on land isn't that bad either. (Its no co-incidence that the BBC 198 Khz tranmitter is located on a bit of land with a very high water table - I used to sail on the gravel pit next door...)
If you have (any) wires near the transmitting antenna you stand a chance of getting funny effects from absorption and induced RF voltages and currents. This is why the guard rail as a continuous electrical loop might be a bad thing. (Look at any commercial HF radio antenna and note how all the guy wires on the masts are broken up into small - compared to the wavelength - lengths with insulators.)
Vertical antenna’s (like backstays) need an effective ground to function. Their efficiency is directly proportional to the efficiency of the ground connection. (In other words resistance and their associated losses in the ground circuit of a vertical antenna are direct losses in transmission efficiency.) It is in this context that the keel does not act as a reservoir for RF! It may or may not be an effective ground path for the antenna circuit.
I'm new at this but the books and advice I have seen so far suggests that sea water is a very poor absorber of RF energy so effectivly you cant 'ground' to it. Sounds odd that seawater is not a conductor but high frequency is funny stuff, not at all like DC or even mains. Effectively then the 'ground' needs to be the other halve of a dipole arial or as near as possible to another backstay but at or below water level and it 'radiates' RF engergy into the ground rather than conducts it - hence guard wires seem to work like dipoles and keels seem to act like a big resevouir that absorbs the energy.
[/ QUOTE ]
Hmm - not sure where to start disecting this lot. You are mistaken in lots of what you say or have read. I agree that HF is 'funny stuff' compared to DC or mains frequencies.
Here are some 'better facts' from an ex RF engineer that might steer you in the right direction.
Seawater is quite a good ground for RF at HF. In fact the water table on land isn't that bad either. (Its no co-incidence that the BBC 198 Khz tranmitter is located on a bit of land with a very high water table - I used to sail on the gravel pit next door...)
If you have (any) wires near the transmitting antenna you stand a chance of getting funny effects from absorption and induced RF voltages and currents. This is why the guard rail as a continuous electrical loop might be a bad thing. (Look at any commercial HF radio antenna and note how all the guy wires on the masts are broken up into small - compared to the wavelength - lengths with insulators.)
Vertical antenna’s (like backstays) need an effective ground to function. Their efficiency is directly proportional to the efficiency of the ground connection. (In other words resistance and their associated losses in the ground circuit of a vertical antenna are direct losses in transmission efficiency.) It is in this context that the keel does not act as a reservoir for RF! It may or may not be an effective ground path for the antenna circuit.
William_H
Well-Known Member
I tend to agree with John Morris in that with HF SSB things can be very strange. Gross inefficiencies in HF transmission and antenna matching can be tolerated and often not even noticed.
I have serious doubts about the idea of foil around the cabin but not connecting to the sea. Of course any conductor anywhere will act as at least a partial ground plane to the antenna tuner as does a car body but that doesn't mean it is as good as it can be. I certainly would connect to the keel etc either directly or by capacitor in the belief that this is the best ground plane. Yes connect metal fuel tanks as well and yes use copper strip. olewill
I have serious doubts about the idea of foil around the cabin but not connecting to the sea. Of course any conductor anywhere will act as at least a partial ground plane to the antenna tuner as does a car body but that doesn't mean it is as good as it can be. I certainly would connect to the keel etc either directly or by capacitor in the belief that this is the best ground plane. Yes connect metal fuel tanks as well and yes use copper strip. olewill
santeana
Well-Known Member
Good stuff, John, as far as what not to do. So what do you recommend for a backstay set-up? In particular will you please enlarge on the distinction you make between RF reservoir and antenna ground path. New to all this so apologies if I'm being dumb.
john_morris_uk
Well-Known Member
[ QUOTE ]
Good stuff, John, as far as what not to do. So what do you recommend for a backstay set-up? In particular will you please enlarge on the distinction you make between RF reservoir and antenna ground path. New to all this so apologies if I'm being dumb.
[/ QUOTE ]
The clue to the distinction between reservoir and ground path lies in the word 'path'. Reservoir implies some sort of storage where what we are really looking at is RF current. Vertical antennas which approach a quarterwave high (or are made to appear a quarterwave bu the antenna matching unit) are very low impedence. Impedence means 'resistance' in RF terms. Low impedence means high current. (in simple terms, ohms law still applies..) In a vertical antenna RF current in the antenna is matched by RF current in the ground system.
As I said before, a good ground system is essential for a vertical antenna to work efficiently. Good ground systems also lower the angle of radiation - another bonus.
Practical answer: You need to discover the most efficient way of connecting the ground connection of the antenna matching unit to the seawater. The metal work in the boat (including foil etc) will connect capacitively to the surrounding water - but probably not very well. A large area of copper plate stuck to the hull, or one of those sintered plates is probably the best solution. I am not sure what fouling does to the efficiency of the sintered plate, but perhaps someone else will tell? The manufacturers all say things like 'not effected by marine growth' - but they woould say that...
Good stuff, John, as far as what not to do. So what do you recommend for a backstay set-up? In particular will you please enlarge on the distinction you make between RF reservoir and antenna ground path. New to all this so apologies if I'm being dumb.
[/ QUOTE ]
The clue to the distinction between reservoir and ground path lies in the word 'path'. Reservoir implies some sort of storage where what we are really looking at is RF current. Vertical antennas which approach a quarterwave high (or are made to appear a quarterwave bu the antenna matching unit) are very low impedence. Impedence means 'resistance' in RF terms. Low impedence means high current. (in simple terms, ohms law still applies..) In a vertical antenna RF current in the antenna is matched by RF current in the ground system.
As I said before, a good ground system is essential for a vertical antenna to work efficiently. Good ground systems also lower the angle of radiation - another bonus.
Practical answer: You need to discover the most efficient way of connecting the ground connection of the antenna matching unit to the seawater. The metal work in the boat (including foil etc) will connect capacitively to the surrounding water - but probably not very well. A large area of copper plate stuck to the hull, or one of those sintered plates is probably the best solution. I am not sure what fouling does to the efficiency of the sintered plate, but perhaps someone else will tell? The manufacturers all say things like 'not effected by marine growth' - but they woould say that...
santeana
Well-Known Member
Thank you. So a direct path to ground (sea water) is more effecient (and better) than a reservoir or other indirect capacitive method. Hadn't appreciated in your first note the distinction of one over the other.
Following on from Roly; if two yachts with identical antenna/equipment used the ballast as the 'route' to ground and one had internal ballast and the other bolt-on external, what practical performance differential would you expect.
Following on from Roly; if two yachts with identical antenna/equipment used the ballast as the 'route' to ground and one had internal ballast and the other bolt-on external, what practical performance differential would you expect.
john_morris_uk
Well-Known Member
[ QUOTE ]
Thank you. So a direct path to ground (sea water) is more effecient (and better) than a reservoir or other indirect capacitive method. Hadn't appreciated in your first note the distinction of one over the other.
Following on from Roly; if two yachts with identical antenna/equipment used the ballast as the 'route' to ground and one had internal ballast and the other bolt-on external, what practical performance differential would you expect.
[/ QUOTE ]I would be happier if you stopped using the term 'reservoir'.
The one that perfoms the best will be the one that has the least RF resistance in the ground path. I would expect that to be the one with a direct connection to the sea, provided it's a low resistance connection through large braid or copper tape and to a large enough contact area with the sea-water.
Thank you. So a direct path to ground (sea water) is more effecient (and better) than a reservoir or other indirect capacitive method. Hadn't appreciated in your first note the distinction of one over the other.
Following on from Roly; if two yachts with identical antenna/equipment used the ballast as the 'route' to ground and one had internal ballast and the other bolt-on external, what practical performance differential would you expect.
[/ QUOTE ]I would be happier if you stopped using the term 'reservoir'.
The one that perfoms the best will be the one that has the least RF resistance in the ground path. I would expect that to be the one with a direct connection to the sea, provided it's a low resistance connection through large braid or copper tape and to a large enough contact area with the sea-water.
PhilipH
Well-Known Member
William
You are just the man I have been looking for. I have an aluminium hulled boat and want to fit an ICOM 801E. Now I do think that all things electronic and electrical contain an element of magic and mystery - in other words I'm a bit thick about these matters. Anyway, to get to the point I have been advised to fit (a) capacitor(s) between the ATU and the hull which will be the ground (no need for, in fact definitely no no copper). However, I have not been able to get advice on which capacitors to buy, who from and how to fit them - the ATU will be attached to the pushpit as it's in a waterproof box. Would I need to fit the capacitors inside a waterproof locker? Also, just how does one attach whatever comes off the other end of the capacitors to the hull? Drill and tap in a bolt or what?
Now I have also had the following advice directly fromICOM, which again is like something from a Philip Pullman book to me: "Thanks for the enquiry. As the M801 is a 'floating ground' design it should not be necessary to fit an isolating capacitor in the ground lead to the earthing point. This is normally only necessary when the installed equipment has the negative supply connected to chassis and it is possible for DC current to flow through the ground lead."
Your advice would be much appreciated.
You are just the man I have been looking for. I have an aluminium hulled boat and want to fit an ICOM 801E. Now I do think that all things electronic and electrical contain an element of magic and mystery - in other words I'm a bit thick about these matters. Anyway, to get to the point I have been advised to fit (a) capacitor(s) between the ATU and the hull which will be the ground (no need for, in fact definitely no no copper). However, I have not been able to get advice on which capacitors to buy, who from and how to fit them - the ATU will be attached to the pushpit as it's in a waterproof box. Would I need to fit the capacitors inside a waterproof locker? Also, just how does one attach whatever comes off the other end of the capacitors to the hull? Drill and tap in a bolt or what?
Now I have also had the following advice directly fromICOM, which again is like something from a Philip Pullman book to me: "Thanks for the enquiry. As the M801 is a 'floating ground' design it should not be necessary to fit an isolating capacitor in the ground lead to the earthing point. This is normally only necessary when the installed equipment has the negative supply connected to chassis and it is possible for DC current to flow through the ground lead."
Your advice would be much appreciated.
William_H
Well-Known Member
Hello Phillip thanks for the PM I will reply on this forum in the hope that John Morris will check what I write. This whole area is a bit mysterious and we tend to revert to theoretical best cos you can't tell the difference often in practice. To answer Ron's question.
Now it would seem that Icom have answered your question quite precisely ie no capacitors needed as case of the icom (presumably the tuner) is isolated from DC ground. Hopefully that also extends to isolation of the transceiver from ground as it will be connected by the coax cable. A multimeter on ohms scale should enable you to check that there is isolation from both +ve and -ve power wires to the ground connection of the transceiver and tuner with all connected together.
If however you don't trust them or want capacitor isolation... (electrolysis corrosion of the hull is your biggest worry)
I suggest that unless you can find a high current high voltage capacitor designed for this work that you use multiple small ceramic capcitors in paralell. Use the 600v ceramic ones simply cos they are bigger more robust and use a value like .005 or even .001 microfarrad ( also descrbed as 5 or 10 nf. (nanofarrads) use about 10 in paralell to minimise the inductance. The total capacitance is the sum of all those connected. They are cheap enough.
If under the deck, the box is not necessary but they need to be physically protected. Drill a hole through a stringer or similar and fit a copper lug to solder the capacitor leads to. Mount another lug on a piece of insulation to support the wire to the tuner and the ends of the capacitors. Put lots of Duralac around the lug on the aluminium but make sure there is a low resistance connection lug to the hull.
If you don't use capacitors then you still need to make a good connection to the Al hull. Cable should be clamped onto bare Al then covered in Duralac or similar corrosion inhibitor. It would be agood idea to dismantle this connection every season just to make sure it is a good connection with not too much corrosion.
Good luck olewill
Now it would seem that Icom have answered your question quite precisely ie no capacitors needed as case of the icom (presumably the tuner) is isolated from DC ground. Hopefully that also extends to isolation of the transceiver from ground as it will be connected by the coax cable. A multimeter on ohms scale should enable you to check that there is isolation from both +ve and -ve power wires to the ground connection of the transceiver and tuner with all connected together.
If however you don't trust them or want capacitor isolation... (electrolysis corrosion of the hull is your biggest worry)
I suggest that unless you can find a high current high voltage capacitor designed for this work that you use multiple small ceramic capcitors in paralell. Use the 600v ceramic ones simply cos they are bigger more robust and use a value like .005 or even .001 microfarrad ( also descrbed as 5 or 10 nf. (nanofarrads) use about 10 in paralell to minimise the inductance. The total capacitance is the sum of all those connected. They are cheap enough.
If under the deck, the box is not necessary but they need to be physically protected. Drill a hole through a stringer or similar and fit a copper lug to solder the capacitor leads to. Mount another lug on a piece of insulation to support the wire to the tuner and the ends of the capacitors. Put lots of Duralac around the lug on the aluminium but make sure there is a low resistance connection lug to the hull.
If you don't use capacitors then you still need to make a good connection to the Al hull. Cable should be clamped onto bare Al then covered in Duralac or similar corrosion inhibitor. It would be agood idea to dismantle this connection every season just to make sure it is a good connection with not too much corrosion.
Good luck olewill
john_morris_uk
Well-Known Member
[ QUOTE ]
Hello Phillip thanks for the PM I will reply on this forum in the hope that John Morris will check what I write. This whole area is a bit mysterious and we tend to revert to theoretical best cos you can't tell the difference often in practice. To answer Ron's question.
Now it would seem that Icom have answered your question quite precisely ie no capacitors needed as case of the icom (presumably the tuner) is isolated from DC ground. Hopefully that also extends to isolation of the transceiver from ground as it will be connected by the coax cable. A multimeter on ohms scale should enable you to check that there is isolation from both +ve and -ve power wires to the ground connection of the transceiver and tuner with all connected together.
If however you don't trust them or want capacitor isolation... (electrolysis corrosion of the hull is your biggest worry)
I suggest that unless you can find a high current high voltage capacitor designed for this work that you use multiple small ceramic capcitors in paralell. Use the 600v ceramic ones simply cos they are bigger more robust and use a value like .005 or even .001 microfarrad ( also descrbed as 5 or 10 nf. (nanofarrads) use about 10 in paralell to minimise the inductance. The total capacitance is the sum of all those connected. They are cheap enough.
If under the deck, the box is not necessary but they need to be physically protected. Drill a hole through a stringer or similar and fit a copper lug to solder the capacitor leads to. Mount another lug on a piece of insulation to support the wire to the tuner and the ends of the capacitors. Put lots of Duralac around the lug on the aluminium but make sure there is a low resistance connection lug to the hull.
If you don't use capacitors then you still need to make a good connection to the Al hull. Cable should be clamped onto bare Al then covered in Duralac or similar corrosion inhibitor. It would be agood idea to dismantle this connection every season just to make sure it is a good connection with not too much corrosion.
Good luck olewill
[/ QUOTE ] Sound as a pound William. (Should I say that to an ozzie - perhaps it should be 'sound as an ozzie dollar'?) I believe your comments are accurate and sound in RF and boaty electrical terms. I am sure that if he has a good insulated backstay and connections to the Antenna Matching Unit as suggested, he will have a first class HF set-up.
Hello Phillip thanks for the PM I will reply on this forum in the hope that John Morris will check what I write. This whole area is a bit mysterious and we tend to revert to theoretical best cos you can't tell the difference often in practice. To answer Ron's question.
Now it would seem that Icom have answered your question quite precisely ie no capacitors needed as case of the icom (presumably the tuner) is isolated from DC ground. Hopefully that also extends to isolation of the transceiver from ground as it will be connected by the coax cable. A multimeter on ohms scale should enable you to check that there is isolation from both +ve and -ve power wires to the ground connection of the transceiver and tuner with all connected together.
If however you don't trust them or want capacitor isolation... (electrolysis corrosion of the hull is your biggest worry)
I suggest that unless you can find a high current high voltage capacitor designed for this work that you use multiple small ceramic capcitors in paralell. Use the 600v ceramic ones simply cos they are bigger more robust and use a value like .005 or even .001 microfarrad ( also descrbed as 5 or 10 nf. (nanofarrads) use about 10 in paralell to minimise the inductance. The total capacitance is the sum of all those connected. They are cheap enough.
If under the deck, the box is not necessary but they need to be physically protected. Drill a hole through a stringer or similar and fit a copper lug to solder the capacitor leads to. Mount another lug on a piece of insulation to support the wire to the tuner and the ends of the capacitors. Put lots of Duralac around the lug on the aluminium but make sure there is a low resistance connection lug to the hull.
If you don't use capacitors then you still need to make a good connection to the Al hull. Cable should be clamped onto bare Al then covered in Duralac or similar corrosion inhibitor. It would be agood idea to dismantle this connection every season just to make sure it is a good connection with not too much corrosion.
Good luck olewill
[/ QUOTE ] Sound as a pound William. (Should I say that to an ozzie - perhaps it should be 'sound as an ozzie dollar'?) I believe your comments are accurate and sound in RF and boaty electrical terms. I am sure that if he has a good insulated backstay and connections to the Antenna Matching Unit as suggested, he will have a first class HF set-up.
PhilipH
Well-Known Member
Thank you very much - this is so helpful. Thanks also to John Morris for his review.
This forum is worth its weight in whisky.
Best regards
Philip
This forum is worth its weight in whisky.
Best regards
Philip