Beadle
Well-Known Member
What sort/value of capacitor do they use?
Ham radio earth connection.
- Thread starter Conachair
- Start date
maby
Well-Known Member
We are getting a bit off-topic here - I fully acknowledge that my home setup is far from optimum and i know the theory of how to fix it - simple practicalities are getting in the way. My question is how one can manage to transmit upwards of 100w SSB into an antenna which, by definition, will pass within a few feet of the transmitter without horrendous RF feedback. I do quite like the idea of operating Maritime Mobile, but I don't have time to develop the techniques by trial and error and I've never found any definitive description of how to build a workable antenna.
Beadle
Well-Known Member
I used to operate mobile with 150 watts with an aerial on he roof of the car no more than 4 feet from the transmitter.
I operated from home using an inverted V antenna which passed directly over the shack, using considerably more than 100 watts -again without RF "feedback"
You cant induce rf into a conductor which is held at earth potential AT RF which may well be different from DC.
My strong suspicion is that whats happening is that your antenna is inducing rf voltage into the 30ft earth lead. If you get rid of that you will probably get rid of the source of the rf "feedback"
The "trick" is to make sure the transmitter and the mike and everything else in he shack are always at earth potential.
If you consider the aerial - it is designed to induce a voltage into a conductor hundreds or even thousands of miles away. Whether the transmitter is 10 feet of 100 feet away isn't going to make that much difference. There will still be a strong rf field around it.
The thing is to ensure that the transmitter and its immediate peripherals remain at earth potential.
Same applies to a boat. There is no reason not use your kit in the boat - the sea makes a good earth very close to the transmitter - use backstay as an antenna - atu - and you'll work the world - why not? - everyone else does
I operated from home using an inverted V antenna which passed directly over the shack, using considerably more than 100 watts -again without RF "feedback"
You cant induce rf into a conductor which is held at earth potential AT RF which may well be different from DC.
My strong suspicion is that whats happening is that your antenna is inducing rf voltage into the 30ft earth lead. If you get rid of that you will probably get rid of the source of the rf "feedback"
The "trick" is to make sure the transmitter and the mike and everything else in he shack are always at earth potential.
If you consider the aerial - it is designed to induce a voltage into a conductor hundreds or even thousands of miles away. Whether the transmitter is 10 feet of 100 feet away isn't going to make that much difference. There will still be a strong rf field around it.
The thing is to ensure that the transmitter and its immediate peripherals remain at earth potential.
Same applies to a boat. There is no reason not use your kit in the boat - the sea makes a good earth very close to the transmitter - use backstay as an antenna - atu - and you'll work the world - why not? - everyone else does
Conachair
Guest
One article says Type X7R Monolithic Ceramic capacitor, 0.15uF x 4
http://www.sailmail.com/grounds.htm
Beadle
Well-Known Member
Thanks for this
john_morris_uk
Well-Known Member
The theory doesn't change with the power and I have operated HF transmitters running kilowatts into antennas only a few metres away from the transmitter. If you are having problems, there are problems with the set up.
Just to re-emphasise the point, I currently run an ICOM 706 at full power into the insulated backstay of our boat with not a trace of RF feedback at all. IMHO its all down to earthing and setting the thing up properly.
To use our SSB set-up as an example, the ATU is right under the deck near one of the backstay chainplates. The antenna wire goes through a waterproof gland immediately above the ATU and is then is run in a small rigid plastic pipe held off the lower part of the split backstay with stand off insulators made of bits of cable ties through bits of water pipe. Its stood off the bit of the backstay that isn't insulated by a couple of inches to ensure that there is minimum coupling to the rest of the rigging.
This might be a time to say that I don't believe that there is any problem having insulators in your backstay from a rigging point of view. The only problem is to your wallet having to pay for the things. When did anyone EVER hear of a boat losing its rig because the backstay insulators broke? It just doesn't happen in my experience. Rigs fail through fatigue of terminals and age of wire, mast collapse etc and I am not convinced that proper backstay insulators alter the odds of rig failure, but the insulators do give you a proper antenna.
The earth is via a thick tinned cable to a through hull fitting to an earth plate.
The advantage of having proper insulators is that it makes your backstay a vertical antenna and if the length of it is anything approaching a quarter wave and its got a decent earth connection then the angle of radiation is low which is exactly what is needed.
I really struggle with the notion that getting a poor earth on a boat is a problem. Seawater is a remarkably good conductor as far as RF is concerned. If you find that a counterpoise (which is an alternative option) is better than your earth connection to the sea-water, you are only demonstrating what a poor connection you had in the first place.
Connect the earth to the keel and to a plate etc. If you want to isolate it electrically for galvanic reasons, then there is NO PROBLEM having a suitable capacitor in the earth lead. It must be a low impedance high voltage capacitor suitable for high RF currents. These are available commercially for a few pounds.
If you have a poor or non existent earth connection (or the wire connecting your ATU to your earth is electrically long at the frequency you are using) then this is when you get all sorts of problems. The transceiver and all its wires become part of the counterpoise that your ATU is attempting to tune up against. High RF voltages can appear at all sorts of places and these can overwhelm the defensive ferrite beads and toroids that you fit. This is when you start getting RF feedback and unexpected RF in places with the computer restarting or shutting down.
To sum up: there is no inherent problem is having lots of RF - even hundreds of watts) going into an antenna a few metres from your transmitter. Just make sure that the RF is really going into the antenna and that the earth system is good and all will be OK.
Even the best set up system might induce high RF voltages in bits of your boats wiring and it happens that I can light up my compass on indicator light on some frequencies. Its just an amusing aside and does no harm - I will fix it if I get round to it...
My biggest problem at the moment is the noisy interference generated by the alternator and its smart charger when the engine is running - but that's another issue.
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William_H
Well-Known Member
HF antenna earthing
recently I saw a friend's HF SSB installation in a Beneteu. He said he knew what to do for the installation so I did not get involved. However I noticed that LED indicators for electrics tended to light up when he talked on SSB. Subsequently on voyage he found the HF did not work well. I think this due to bad earthing at the ATU. It is an auto ATU so I can only presume that it tuned itself up to look like a low VSWR while all the time because of bad earthing at the ATU the coax outer had become a radiating part of the antenna. He probably had bad RF feedback as well.
It seems to me this whole earthing thing is a real unknown. If the earth cable is long it becomes a radiating part of the antenna like part of a dipole. However it also seems that if the earth is replaced by a correct length ground radial (counterpoise) then it does work as a dipole with great success.
Certainly a steel hull must be real bonus when earthing. Not so easy on a F/g hull. I can only advocate short earth lead to large earth area (sea) and get the antenna wire outside and up as soon as possible. olewill
recently I saw a friend's HF SSB installation in a Beneteu. He said he knew what to do for the installation so I did not get involved. However I noticed that LED indicators for electrics tended to light up when he talked on SSB. Subsequently on voyage he found the HF did not work well. I think this due to bad earthing at the ATU. It is an auto ATU so I can only presume that it tuned itself up to look like a low VSWR while all the time because of bad earthing at the ATU the coax outer had become a radiating part of the antenna. He probably had bad RF feedback as well.
It seems to me this whole earthing thing is a real unknown. If the earth cable is long it becomes a radiating part of the antenna like part of a dipole. However it also seems that if the earth is replaced by a correct length ground radial (counterpoise) then it does work as a dipole with great success.
Certainly a steel hull must be real bonus when earthing. Not so easy on a F/g hull. I can only advocate short earth lead to large earth area (sea) and get the antenna wire outside and up as soon as possible. olewill
Beadle
Well-Known Member
I agree
Earthing generally is one of the most significant factors in operating an amateur radio station. Its important for safety and also for effectiveness.
I think you have to look at the whole thing as a "system" starting with the earth then to the aerial and including the ATU.
Particularly so with an unbalanced aerial such as the ones invariably used on a boat.
Earthing generally is one of the most significant factors in operating an amateur radio station. Its important for safety and also for effectiveness.
I think you have to look at the whole thing as a "system" starting with the earth then to the aerial and including the ATU.
Particularly so with an unbalanced aerial such as the ones invariably used on a boat.
KellysEye
Well-Known Member
>It seems to me this whole earthing thing is a real unknown. If the earth cable is long it becomes a radiating part of the antenna like part of a dipole.
On a boat earthing is easy. The earth cable isn't part of the dipole the sea is, via the hull. If you don't have a metal boat then the way to go is connect metal inside the boat and run it to the earth on the radio. Don't connect disimilar metals. To get maximum performance run copper foil along the bilges for the length of the boat then connect that to the radio. That will give the same performance as a metal boat.
On a boat earthing is easy. The earth cable isn't part of the dipole the sea is, via the hull. If you don't have a metal boat then the way to go is connect metal inside the boat and run it to the earth on the radio. Don't connect disimilar metals. To get maximum performance run copper foil along the bilges for the length of the boat then connect that to the radio. That will give the same performance as a metal boat.
ffiill
Well-Known Member
Aerials
Insulated backstays are the usual but have been known to break-you can get a haul up the mast patent wire inside a braided rope/or make one yourself-the hollow braid takes the load off the wire and acts as an extra insulator.
The article I read on Google also made mention of some form of dipole-usually an iverted V-if you can get the angle right-as I recall it needs to be greater than 90 degree-may well be poss. on my ketch using main to missen as part of system
Insulated backstays are the usual but have been known to break-you can get a haul up the mast patent wire inside a braided rope/or make one yourself-the hollow braid takes the load off the wire and acts as an extra insulator.
The article I read on Google also made mention of some form of dipole-usually an iverted V-if you can get the angle right-as I recall it needs to be greater than 90 degree-may well be poss. on my ketch using main to missen as part of system
KellysEye
Well-Known Member
>Insulated backstays are the usual but have been known to break.
We've had four insulatorrs on the one of the backsatays and triatic stay for 13 years with no problems. Also I've never heard of insulators failing, so I don't think that's true. Have you got any examples?
We've had four insulatorrs on the one of the backsatays and triatic stay for 13 years with no problems. Also I've never heard of insulators failing, so I don't think that's true. Have you got any examples?
john_morris_uk
Well-Known Member
I agree! - See my previous post in this thread...
