Ham radio earth connection.

[Conachair]

Is there anything to be gained by connecting the ground tag on the back of a icom ic 7000 to the hull of a steel boat? There seems to be continuity to the neg anyway, and the neg is connected to the hull at the engine, the ground tag would be run back to the same point anyway.

Any thoughts?

 

[ffiill]

Hi-personally cannot remember detail but on an HF radio tranceiver technically its not an earth you are creating but a dipole aerial-similar to ground radials-so hull is as good as it gets-does not have to be physically grounded to water.Seemingly you can get similar effect on a glassfibre boat by laying copper gauze over the bilges,keel,water tanks.
Remember a US ham who used the aluminium frame and steel chassis of his mobile home to similar effect.
Came across one article on Google where a US Ham used gauze as above and the whole of his rig and mast as the aerial to considerable effect.
The other point is that the earth cable is usually of heavy duty woven variety similar to that used on cars
PS I thought I had seen you up for sale?-looked good the big stove and the pine paneling or am I thinking of another boat?

 

[Beadle]

Yes there is a point.

If you rely solely upon the -ve lead there will be rf currents flowing all along the path and in everything else connected to the -ve lead.

If it were my boat I would get some copper braid or similar substantial copper wire and connect the earth connector on the transceiver to the nearest point on the steel hull that I could make a good connection.

Assuming you have an ATU with an earth connector I would do a similar thing with that too, preferably to the same point as the transceiver. You cannot have too good an earth.

 

[Conachair]

Yes there is a point.

If you rely solely upon the -ve lead there will be rf currents flowing all along the path and in everything else connected to the -ve lead.

If it were my boat I would get some copper braid or similar substantial copper wire and connect the earth connector on the transceiver to the nearest point on the steel hull that I could make a good connection.

Assuming you have an ATU with an earth connector I would do a similar thing with that too, preferably to the same point as the transceiver. You cannot have too good an earth.

Problem is that having more than one connection from the hull to the battery neg is not a good idea on a steel boat. Could a capacitor be put in line to cut out dc currents? If so any idea what size?

Ta V much

ps. If the ground and batt neg have continuity - how does the rf -know- to go down the ground wire and not the neg? Though there are 3 sets of big ferrite beads on the power supply, which must help I suppose. Ta again.

 

[William_H]

HF radio earth

On Aluminium aircraft we went to some trouble to ground the radio at the mounting to the airframe but as said it is the ground connection at the ATU (antenna coupler) that matters. And of course on a steel boat make sure the antenna connection is as short as possible like no more than 6 inches from ATU to the feed through insulator to outside the hull and the antenna. good luck olewill

 

[maby]

I'll be interested to hear your experiences - been thinking of taking a transceiver onto the boat, but I'm not at all sure what kind of antenna to rig...

What bands are you intending to operate? How do you expect to get anywhere enough isolation between the antenna and the rig? my experience from home with a very small garden is that I get horrendous levels of RF feedback with the antenna ten or fifteen feet away...

Martin (G8FXC)

 

[Conachair]

I'll be interested to hear your experiences - been thinking of taking a transceiver onto the boat, but I'm not at all sure what kind of antenna to rig...

What bands are you intending to operate? How do you expect to get anywhere enough isolation between the antenna and the rig? my experience from home with a very small garden is that I get horrendous levels of RF feedback with the antenna ten or fifteen feet away...

Martin (G8FXC)

Ah, isolation , that old chestnut. Actually I'm not sure what you're talking about . Pretty much a full on novice with huge amount to learn. Don't have a license yet so can't transmit. Recieving seems good, using a dipole hauled up to the mast head on the topping lift. Considering the boat is a few feet away from huge buildings in the middle of london recieving seems to be good. Weatherfax from northwood and germany, and can just recieve images from weather satellites. PSK31 seems fine with signals from all over europe & russia.

Ah, I see what you mean now with isolation, well steel boat so that should help. Otherwise, everyone else does it so can't be that hard Getting a license in london when you don't know what's happening from one week to the next is proving tricky but one of these months I'll be able to transmit.

Long term I'll fit an insulated backstay. Ta

 

[Beadle]

Hmm - must confess I hadn't considered that aspect of a steel hull.

Perhaps if you connected the ATU and transceiver to the hull at the same point that the
-ve lead is bonded to the hull it may be a more acceptable solution. It will keep any stray currents out of the fabric of the hull - which I assume to be the problem.

I'm really not keen on the idea of a capacitor in the earth lead.

 

[Beadle]

I'll be interested to hear your experiences - been thinking of taking a transceiver onto the boat, but I'm not at all sure what kind of antenna to rig...

What bands are you intending to operate? How do you expect to get anywhere enough isolation between the antenna and the rig? my experience from home with a very small garden is that I get horrendous levels of RF feedback with the antenna ten or fifteen feet away...

Martin (G8FXC)

I too am unsure of what you mean be "RF feedback"

I'm equally unsure of what "isolation" between rig and antenna means. One is connected to the other.

How does this feedback make its presence felt?

What aerial and earth arrangements have you installed?

What frequencies are we considering?

 

[maby]

RF Feedback - roughly the equivalent of hooking a microphone and speakers up to an audio amplifier and letting them get too close to each other. If the antenna is close to the rig, the transmitted signal can get back in via the microphone cable and speaker leads. Any slight non-linearity in the microphone amplifier demodulates the signal and you get feedback. OK - it doesn't manifest itself as the clean ringing that goes with audio feedback - you get distortion on the transmitted audio and a wide, dirty transmitted signal.

My garden is very small and my HF antennae are uncomfortably close to the rig. In my case it's worse on 20m and 40m - if I wind the output power up to 100w, the signal starts to distort. Same power levels into a dummy load and it's clean. I've heard of people insulating the shrouds or forestay/backstay and loading them up, but your transmitter is going to be just a few feet below the antenna and I would expect to suffer from terrible RF feedback.

Before anyone points out that every boat has a VHF transceiver driving a mast-head antenna, there are a couple of big differences. In the first place, your marine VHF is running quite low power - 25w maximum. Also, it's running on VHF, and the antenna is several wavelengths away from the transmitter, and finally, it's running FM modulation which cannot be demodulated by a simple non-linearity in the microphone amplifier - hence no feedback.

 

[Bilgediver]

I too am unsure of what you mean be "RF feedback"

I'm equally unsure of what "isolation" between rig and antenna means. One is connected to the other.

How does this feedback make its presence felt?

What aerial and earth arrangements have you installed?

What frequencies are we considering?

RF feed back is as its name implies. You get RF noise finding its way back into the radio input from the transmit signal. This is especially a problem on digital modes where the RF finds its way back into the sound card input along the feed lines. This can be especially bad with poor antenna installations. It is detected by listening to the output signal tones from time to time with a monitor radio and checking they are crystal clear and sharp with no muffling overtones.

One way of reducing the risk of feed back it is to place ferrite collars on all leads to and from the soundcard etc. These are available in Maplins and just snap over the leads and click closed.

You may also see the effects of RF feed back on the signal level with it being unsteady and rising sharply when RF feed back occurs. Also listen for a steady back ground hum etc indicating possible earthing faults as this will degrade your signal.

I always monitor the output sounds on digi modes but then I always listened to the fax machine in the office as this was the first indiction of a fault and often told what the fault was

Beware you need to be carefull not to blow the monitor radio. I use another ham receiver with the antenna disconnected but have used a Sony SSB on occasions.

 

[maby]

RF feed back is as its name implies. You get RF noise finding its way back into the radio input from the transmit signal. This is especially a problem on digital modes where the RF finds its way back into the sound card input along the feed lines. This can be especially bad with poor antenna installations. It is detected by listening to the output signal tones from time to time with a monitor radio and checking they are crystal clear and sharp with no muffling overtones.

....

If I transmit full power on 20 or 40, my mouse and keyboard simply stop working and I have to reboot the PC. All cables are festooned with ferrite beads - no avail - most PCs simply get very offended by a hundred watts at 14MHz in close proximity! All the cordless phones in the house ring as well!

 

[Beadle]

Reading the symptoms my thoughts centre on earthing.

A mike lead should be screened and the screen earthed.

But a few more questions:

1 How is the station earthed?
2 How long is the wire connecting the station to the actual earth rod or whatever means of earthing you use.
3 Do you have any form of rf filtering in the mains supply?
4 Is the "shack" ground floor or 1st floor?
5 What sort of aerial do you use?
6 Do you use an ATU?

Sorry about the inquisition, but I try to avoid blind guesswork

 

[KellysEye]

>There seems to be continuity to the neg anyway, and the neg is connected to the hull at the engine, the ground tag would be run back to the same point anyway.

Not sure what a ground tag is. However as said above the ground makes up hallf the aerial, so a ground is a must. If the current ground goes to the engine and the engine is grounded to the hull then nothing more needs to be done. If the engine isn't grounded to the hull then remove the SSB ground from the engine and attach the ground to the hull. That is standard on a steel boat because the bigger the ground the better and the hull is in the water, the engine isn't.

 

[Conachair]

Hmm - must confess I hadn't considered that aspect of a steel hull.

Perhaps if you connected the ATU and transceiver to the hull at the same point that the
-ve lead is bonded to the hull it may be a more acceptable solution. It will keep any stray currents out of the fabric of the hull - which I assume to be the problem.

I'm really not keen on the idea of a capacitor in the earth lead.

Think that will be what will happen on the longer run. Big earth bus bar near the engine and everything back to that.

Though plenty people seem to get on fine using capacitors on steel hulls. I'm at the mercy of all at the moment knowing so little but generally less is more on a boat.

 

[Reverend Ludd]

You might find this an interesting read

http://www.accidentalcruiser.com/features/Installing%20HF%20Radio.html

 

[maby]

Reading the symptoms my thoughts centre on earthing.

A mike lead should be screened and the screen earthed.

But a few more questions:

1 How is the station earthed?
2 How long is the wire connecting the station to the actual earth rod or whatever means of earthing you use.
3 Do you have any form of rf filtering in the mains supply?
4 Is the "shack" ground floor or 1st floor?
5 What sort of aerial do you use?
6 Do you use an ATU?

Sorry about the inquisition, but I try to avoid blind guesswork

Well, there's no doubt that my home installation is not well earthed - 1st floor shack with a decent earth rod and an attempt at a ground plane. Earth wire is probably about thirty feet long! I have a variety of aerials - ranging from a highly compressed multi-band vertical in the garden through a fairly large diameter wire loop running round the roof to an MFJ mag loop mounted high in the loft. Obviously, with such poor earthing, the balanced antennae are more successful and the MFJ mag loop is really quite good on 20m and up - it's just inconvenient because the tuning is so narrow. I have an MFJ antenna tuner - one of the higher power models with the roller-coaster coil, but in practice it's only really used for antenna switching and power metering - I did try hooking up a random wire to the long-wire post, but even 10 watts for tune up killed my computer and made the house telephones jangle!

 

[maby]

You might find this an interesting read

http://www.accidentalcruiser.com/features/Installing%20HF%20Radio.html

Hmmm, bit more complicated and intrusive than I would want. I've been wondering about the feasibility of mounting a standard base-loaded HF mobile whip on the pushpit?

 

[Beadle]

"I did try hooking up a random wire to the long-wire post, but even 10 watts for tune up killed my computer and made the house telephones jangle!"

That brings back a few memories.

I am deeply suspicious of the 30ft earth lead.

I used to have a similar arrangement - but somewhat shorter lead - it resonated on 15m band.

When I transmitted everything in the shack was hot with rf. I had all valve gear so didn't affect xmission quality much but getting rf burns off everything I touched became really boring.

I would be tempted to disconnect the earth all together and make a 1/4 wave radial for each band you use.

Connect one end of the radials to the earth on the ATU and run the radials out and along the ground, making sure the far ends are NOT touching the ground.

You should (must) use insulated wire for the radials (perhaps I should call them Counterpoises).

The vertical aerial should have its own set of true radials from the base laid on the ground (or buried) radially around the antenna.

You MUST leave the mains earth connected for safety

Do not have any other earth connection anywhere.

If you have a balanced aerial - a dipole for example, use a balun in the centre to connect to coax feeder- Not sure if the mag loop is balanced or not - if it is try a balun on that.

The vertical is unbalanced so should be ok fed by coax.

Best of luck - drop me a PM - let me know how it goes.

 

[KellysEye]

>How do you expect to get anywhere enough isolation between the antenna and the rig? my experience from home with a very small garden is that I get horrendous levels of RF feedback with the antenna ten or fifteen feet away...

Yachts have insulators on their backstay, typical distance between them is around 33 feet. If the backstay is fairly short the insulator must be 12 inches from the mast otherwise the signal will jump over and the mast would be live*. The radio close to the aerial shouldn't be a problem, ours is about 10 feet away. The ATU must be as close as possible to the aerial because it tricks the aerial into thinking it is different lengths and and a long wire would degrade the signal or worse wouldn't tune properly.

* HF cooks your hand from the inside if you touch the aerial or anything else live. As a party trick you can light a cigarette on the aerial when transmitting.