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Old 23-05-2005, 12:20   #1
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A Simple RF Ground Test

An RF Ground Test Tip from Gordon West:

Q. Light up time
My electronics guru tells me that a single-point ground for my radios is not enough. Is he correct and is there a simple test I can do?

A. Gordon West replies: A single point ground is fine although there is also a simple test that will tell you how well your system is working. It’s not hard to do but it does have to be done at night. Once it's dark, get a small fluorescent tube and touch the glass part of the tube to the antenna wire leading either to the insulated backstay or to the fiberglass whip antenna. Have someone turn on the radio and then whistle quickly into the microphone. If the tube is making contact with the wire and things are working properly, the fluorescent tube should light up when the whistle sounds. The lit tube indicates that there is good current in the wire leading to the antenna. Good antenna current occurs because of a good seawater— single or multi-point— ground with copper foil. But beyond having a good seawater connection, adding more foil inside the hull generally won't make your system work any better. However to maintain good SSB and ham radio signals, you have to inspect the seawater ground regularly and make sure it is clean.

Gordon West is a communications and electronics expert who is also a specialist in marine radio communications

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Old 23-05-2005, 18:57   #2
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SSB RF grounds

Gord May and Gord West...good sources of info! This is one of my favorite subjects partly due to the vast amounts of apparently conflicting information from the "experts".

Assuming that an automatic tuner functions properly, the two worst aspects of an SSB installation is the radio frequency ground immediately from the tuner to the sea water and the loss of energy from the tuner high-voltage RF output lead into surrounding metal such as pulpits and shrouds.

Yes, a flat copper conductor tends to minimize the inductance of the ground lead yet they are usually uncoated, easily corroded, and not easy to dress or twist to accommodate a run to a hull fitting. They are also expensive. A better alternative is to use multiple parallel conductors for the ground "wire".

Buy marine grade wire, 14 GA, like 14-2 or 14-3. Measure the length, in feet, from the tuner ground connector to the sea water conductor through-hull. Divide the measurement by two and that is the minimum number of conductors to use for the high-frequency bands. For example, 8 feet divided by two equals 4 conductors. Use two 14-2 cables or a 14-2 and an 14-3 to make the ground lead. Strip the ends of the measured wire and twist them together to make a single conductor at each end for the attachments.

Use nylon cable ties to "marry" the cables intimately together along the run. This guarantees that the mutual inductance of the combined wires will cause the overall inductance to be the lowest value possible for the insulation thickness.

This technique is an improvement over that of the flat copper because it is relatively inexpensive, readily available, and easy to run in tight places and will not corrode. Imagine if the copper foil had many parallel "slits" in it's length that would not allow each adjacent copper conductor to touch its neighbor. THEN you would have an improved lower inductance lead than the strip with out the slits. That is what you have done with the multiple conductors.

Most SSB and HAM installations using automatic antenna tuners are designed to operate into a quarter-wave vertical antenna. The antenna "Begins" at the drive point which is physically where the ground and high-voltage wires exit the tuner. What we have just done is to create a "phantom ground" very close to the physical point of the tuner's ground lug.

When properly tuned, the high-voltage output lead is the point where maximum current flows. The current distribution falls off (shaped as a quarter cosine wave for you teckies) to zero at the top of the antenna radiator (which could be the bottom of your upper backstay insulator). Now here's the important part: The amount of energy that you can transfer to the atmosphere is directly proportional to the manner in which the CURRENT distribution "sees" open space without any surrounding metallic parasites. This means that if you run your high-voltage lead along the lower part of your backstay up to a lower insulator that you LOOSE energy into the lower backstay.

If you are smart you will NOT USE a lower insulator because of this phenomenon. Merely attach the high voltage lead to the inside chainplate contacting the also save on having to drill through the deck to feet a high-voltage lead. If you already have a lower insulator jump around it with rigging wire the same alloy as your backstay using S/S wire clamps (not hose clamps). Do not put goop over the connections...leave them bare to the air. NOW you will not be pumping energy into a parasitic parallel are USING the entire lower backstay as a radiator. There's not much that you can do to eliminate the loss from your stern pulpit.

What about the voltage on the exposed backstay? Here's the intersting physics that describes the voltage. The voltage distribution is ZERO at the turner output drive point and is desctribed by a quarter sine wave along the antenna, becomming maximum only AT THE UPPER INSULATOR!. The likelyhood of causing a shock is just about zero for another reason. You don't get shocked by RF you get burned only if you brush up against the upper end of the antenna.

I am very famaliar with RF burns having worked around 100kW SSB transmitters for several years. Anyway, why would you have anyone hanging onto the backstay when you are transmitting...their body, in proximity without touching the antenna, represents a "water loss" just like a parasitic parallel piece of reduces your effective radiated output power.

Now I realize that you will not want to trust to this explaination and will probably cover the lower 6-8 feet of the backstay with those plastic safety line covers just "to be sure".

Pay attention to these few simple concepts and you will make a more reasonable installation than you might otherwise.



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Old 24-05-2005, 00:14   #3
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That is the story of my life, "a day late and a dollar short". I had my backstay insulated last week. Two insulators instead of one. Oh, well, I will save the article for the next installation.

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Old 02-10-2005, 19:25   #4
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I have a 43ft steel hull + decks yacht.
Should I mount the SSB Tuner inside or outside the hull? Should I ground the Tuner and the other components individually to the hull where they are mounted or run a seperate ground to connect these and then only ground it all once next to the tuner to the hull?
If I mount the tuner inside, what is the best way to get the antenna signal out of the hull and onto the backstay?
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Old 03-10-2005, 20:29   #5
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steel hull and deck with HF SSB

Preferably mount the tuner as close to the "drive point" of the antenna as possible unless you can guarantee that the so-called "high-voltage" lead from the tuner is geometrically part of the 1/4 wave antenna radiator (which it always is electrically anyway). It is no problem to pass the tuner HV lead to the antenna through the steel deck as long as the distance from the tuner to the deck is equal to or less than 2 feet. Use an ordinary through the deck insulated fitting appropriate to the diameter of the HV lead for water integrity.

From a purist standpoint I would prefer to have the tuner immediately below the deck as long as the antenna radiator begins from the deck level, which is VERY unusual. The reason is that steel absorbs the magnetic field of electromagnetic radiation and, in general, is better at "shielding" than non-ferrous materials which absorb the electrical field. Absorbing the magnetic field close to a source is more effective than absorbing the electric field, in general.

Your antenna grount/tuner ground/RF ground should be all copper, regardless of whether or not it is connected to the hull. Keep in mind that steel is about 50 times more resistive than is copper and, therefore, the hull cannot be relied upon to provide a good RF ground even though it undoubtedly adds to the RF "ground" capability of a well coppered RF ground installation. Treat your hull as though it were an insulator, at first when considering RF, then consider where to make copper connections to it later AFTER you already have a good installation.
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Old 25-10-2005, 09:52   #6
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Existing SSB

I have just bought a 'new' boat. It has an SEA 225 SSB. Unfortunatley, I cannot get the thing to work - but that might be for multiple reasons. I plan to upgrade the system anyway to an Icom 802 probably.

How do I know if the ground (counterpoise) is sufficient? I will be sailing to Europe, so long range capability is important.

FWIW, there are numerous tracks of 4" wide copper strips leading all over the place, there's a copper mesh screen lying in the quarterberth - probably 3' x 5' and there are 4 dynaplates on the hull - at roughly the 4 corners of the boat.

I'm having a tough time working out if what I have is OK and also in knowing how to test it - especially difficult since I cant get the bloody thing to do anything but hiss at me!
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Old 25-10-2005, 10:18   #7
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Hi Bill

One important point to make is that no cruising boat under a fewhundred feet or more likely has a true "counterpoise" for the HF band because a counterpoise for that band would have to be about 100 feet in all directions from a vertical quarter wave radiator element. A counterpoise forms a quarter wave reflector for the radiator which, otherwise might be a half-wave balanced radiator of twice the quarter wave length.

What your predecessor attempted to do was create a capacitor which would couple the ac frequency to the salt water. Such buried copper is a waste of time if you already have a Dynaplate which makes a dc direct connection.

Yes, you will hear stories of how someone's "small" copper mesh worked wonderfully for them yet what I keep teaching is that all one has to do is generate an effective radiated power of around a few milliwatts in order to be heard on the far side of the earth with a good receive antenna. So, with extremely lousy antenna and tuner and transmission installations one can actually communicate with apparent "wonderful" results. That is UNTIL your boat is somewhere where the weak resulting output just will not radiate sufficiently to get to that same receive antenna. For some reason areas around Panama are like that...there are many others.

What you need to do first is take the transceiver to a shop where they can measure the output power on all bands as well as verify the calibration of the frequency.

We can talk next what to do about the transmission line, tuner, and antenna.
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Old 27-10-2005, 06:39   #8

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For all antennas?

Do all antennas on a boat follow the same rule? I mean I do not have a SSB radio at this time, but would like to make sure my VHF and other comm antennas are getting the best signal possible.

What is one to do with these types of antennas?
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Old 27-10-2005, 17:02   #9
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Yes, in essence, all antennas follow the same "rules" of physics. A technician, or informed individual, can normally easily use a good quality SWR meter, like a Bird Wattmeter with various frequency "slugs" and dummy loads to measure the output power of a trasmitter and the standing-wave-ratio at various physical points along the route to the antenna.

For example, it is normal to verify that a marine VHF transceiver will put out 1W (and not more) on the low power setting and 25W (no more) on the high power setting into a dummy load. Then if one is thorough one goes to the masthead and measures the ouput power from the end of the coax into a dummy load to check the loss of the transmission line (there will be some significant loss at VHF yet perhaps not at HF in the case of your SSB installation). Then while at the masthead the SWR is measured to the antenna at the drive point. It is here that a notable measurement is made because the loss of the transmission line actually ameloriates somewhat the SWR if measured only at the transmitter output with the antenna on the other end of the stick. The SWR will not be 1:1 it will be less and may vary across the band according to the bandwidth of the antenna.

Often you "see" 5/8 wavelength masthead VHF antennas and they offer good compromise on "getting out" and receiving along with a SWR that is usually higher than what you can get with a good cut of 1/4 wave whip. A good 1/4 wave whip at a masthead is more difficult to make "ideal" than is the 5/8 wavelength loaded coil whip. In addition, the base loading coil of the 5/8 whip provides an automatic "short" to ground thereby leaking any static charg build-up at the top of the mast to give static lightning discharge protection that a quarter wave whip cannot give.

As you can tell by now there is a lot to this stuff and antenna design experts are really good engineers.
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Old 20-06-2009, 04:20   #10
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SSB Grounding

(sorry to all if any mistake but I am french speaking...)
Good morning Rick.
Thanks for all your comments about grounding and antenna connection.
I have a 37 feet GRP sailing boat based in the Med.
SSB is an ICOM IC-M802.
I had made a super ( as it was qualified -very strong signal- by some of the Winlink 2K MBO's I use for Airmail post) grounding by having 3M self adhesive copper strap all over the hull below water line and attached to one of my keel bolt but unfortunately corrosion as done its effect and I have to redo my grounding.
Having read your comments I will thus use marine grade wires in order to realize a new grounding.
I hope (as it is totally different from what I have read up to now - flat strap or copper net , never round cables ...) I will get the same result but should you have any comment to do or should you have any additional hint I would be more than happy to ear from you before I start the work.
Now about my antenna I have an other question.
I use and will continue to use a long wire which I hoist with one of my 2 spin halyard when needed.
One insulator on the top and one at the end from which a 2 feet cable goes connected to a antenna connector attached to the hull (hole has already been made...)and which in its turn is connected by a 2 feet cable to the tunner.
It would be nice If I could attach an image but...
Would it be better to take the bottom insulator out of the line and have the cable antenna directly connected to the antenna connector attached to the hull?
If yes I will also then try to make the connections in copper!
Thanks in advance for any reply I might receive.
73's to all.
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Old 20-06-2009, 05:59   #11
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I am not an expert, but I have experimented with different SSB installation techniques. One thing I found helpful was having a friend, a patient friend with another SSB. I set up different counterpoise for the transceiver that I could quickly switch between and would test on air. There were only a couple of surprises, but they made a significant difference. It was simple and easy to do as well as reliable.

My system has been pretty robust and reliable. I have an ICOM M700PRO. The transceiver is grounded to the same bronz thru hull as the counterpoise (see below). About 18ft of RG-8U coax runs to an SGC-230 tuner in the stern at the base of the insulated backstay. A short piece of heavy gauge wire connects the tuner to the backstay antenna. I cut 3" wide strips of copper foil from a roll of copper flashing from a HW store. The long run (approx 50ft) of copper is connected directly to the tuner ground and runs through the billge. At some point, this foil connects to a bronz thru hull. A simple, basic installation.

I did try connecting to the dynaplate I have, but that was not superior at all. I also tried connecting to the lifelines and aluminum toe rail, these were also not superior.

I considered using radials (lengths of wire cut to half wavelengths), but the cost was actually greater than the copper flashing (that might not be true now) and made runs through the boat more effort. I would have added a couple radials, but this was considered overkill and I agree.

Again...not an expert, just an exemplar for your use as a springboard to further discussion. And again....experimentation was invaluable, I highly recommend doing this.

Hope this helps


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Old 20-06-2009, 07:20   #12
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Thank you John.
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Old 20-06-2009, 07:56   #13
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A small neon bulb makes an even simpler tool that West's suggestion and is more easily visible in the bright sun. Using a neon bulb is a trick which has been around since the early days of radio (and neon) which I'm surprised he doesn't know.
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Old 20-06-2009, 11:50   #14
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Thank you.
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Old 20-06-2009, 11:50   #15
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A simple test for your counterpoise is to take a roll of aluminum foil and throw about 15-20 ft in the water. Then establish contact with a distant station and ask for a signal report. Then attach the end of the foil to tuner ground and ask for another signal report. Try it a few times with and without the foil, and if the other station can't tell the difference between the signals, throwing more money and time at your counterpoise isn't going to improve things.

ON3CHD, if you connect your counterpoise to a keel bolt, you should put a capacitor in that circuit to avoid electrolysis problems. It will let the RF current pass, but block the DC.

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