Does an SSB need an antenna tuner???

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npf1

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Ok ... this has been bugging for sometime so I'm hoping the esteemed panel can enlighted me.

Most people I speak to, and not only the sales people, say that an ATU is essential. I have an SSB installed, without an ATU and it worked all the way across the pond last summer. My unit has a tune button (or can be set to tune up frequency change) and can be heard to do 'something' when it is pressed'.

Can anyone explain to me 1/ is a tuner ESSENTIAL or BETTER (and why) 2/ what the unit is doing when the tune button is pressed?

Many thanks
 
An SSB does normally need an ATU. A radio transmitter is designed to work with an antenna, which has certain impendence at the output frequency (normally 50 ohms). An ATU changes the impendence of the antenna so that it matches what the radio is looking for. When the impedance matches then all of the signal that is outputted by the radio is outputted by the antenna (apart from some which is lost as heat in the atu). When the impendence is not right the antenna outputs some of the output of the radio but the rest is reflected back into the radio, this is not good. The signal, which is reflected back, can damage the radio. (Modern transmitters will automatically reduce their power to try and prevent any damage) For SSB on a yacht you are normally using what is effectively a random length of wire, which is unlikely to have the right impendence and the impendence will change when you change channels on the radio.(Impendence changes with frequency)

What the Tune button does can vary from radio to radio. On most radios it makes the radio transmit on low power for a number of seconds. This is for automatic ATUs that automatically tune the antenna to match the frequency the transmitter is operating on.

In summary you can use SSB with out an ATU but you run the risk of frying your radio

I hope this has made some sense
Jonathan
 
Help, please, from some of ye radio/comms geeks here.

One of my sailing friends - all right, my only sailing friend - has just bought a used SSB radio. He has also just bought a sizeable copper sheet, which he plans to attach to the radio/boat in some undefined manner as a so-called 'ground plate'.

Now, I've trailed few things behind me in my years sailing, but a copper sheet as big as a dinghy? What's he up to, and is it certifiable? /forums/images/graemlins/confused.gif
 
All comments are correct. However we are assuming you are talking about a SSB transmitter for communications. Some transmitters have an ATU built in but most don't.
Some vehicles around here carry SSB for the outback. Some have an automatic ATU built into the base of a whip antenna. Some (older) whip antennas however are pretuned to several frequencies. There is a wire and plug that fits into a socket on the side of the coil that is part of the antenna bottom half. You change the plug to a different position when going to a different frequency. ie from 2mhz to 5 mhz to 7 mhz to 9 mhz to 13 mhz. Small changes of frequency are Ok.
So that is just another option but not practical on a boat where a long wire or whip antenna are used with an ATU sometimes called antenna coupler.
Strength of radio transmission is perceived on a very logrythmic scale.
So commercial shortwave stations can transmit 500000 watts while you SSB may transmit 100 watts or your phone 50 milliwatts. The received strength is better with more power but not directly proportional. To add to that all receivers have a circuit to make the strong signals less loud and the weak ones stronger ( or at least as good as possible.
So if your transmitter is only transmitting 5 watts into a untuned antenna it still may often appear to work ok. it is just that when communications are difficult you really want all the power you can get into the air. (not to mention the possibility although remote with modern transmitters of damage)
So bilbobaggins your friend is not certifiable just setting out to do it properly ie best ground connection. olewill
 
The definitive answer

ATU stands for Automatic Tuning Unit, so strictly is not essential because if you know what you are doing, you can use a manual tuning unit - its cheaper, but for 99.9% of us is much too fiddly to bother with.

Get yourself an ATU.
 
Yes most definitely, unless you have an antenna long enough to be resonant on a single frequency..but then you will be limited to single frequency working.
What the ATU does is to match a random length of wire to the output "impedance" of the transmitter.
This is because the PA (power amplifier) section of the transmitter must see broadly a 50 ohm aerial circuit. If it doesnt the ouput transistors will overheat, become less efficient and eventually go into a condition known as "thermal avalanche" where they are destroyed.
If the antenna is a poor match to the transmitter it will have what is known as a high VSWR (voltage Standing wave ratio).
In essence this means that as the antenna is a mismatch at the transmitting frequency, only a proportion of the power is radiated. The unradiated power (slightly simplified) travels back down the feed line and destroys the output transistors.

Inside the ATU there is usually an array of motorised coils or "inductances"
which automatically tune the antenna by adding or subtracting inductance/capacitance according to a preset algorithm.
They are usually arranged in what is known as a Pi Tank circuit, or sometimes a constant K "M" derived section..depending on whether the application is to tune
a dipole, or in an end fed shunt type "marconi" circuit for vertical wires.

Hope this expains a little.

Steve.
 
The 'ground' plate does not have to be in direct contact with the water so a large copper sheet stuck to the inside of the boat and connected to the earth connection of the ATU should work very well. In fact it doesn't need to be sheet metal, a mesh will do as well.
 
I've heard that the guardwire/ stanchion post array acts as a really good counter poise for a long wire (backstay) antenna . Any reports?

I'm soon to install my Icom 718 so tips would be appreciated ( I have a SG-239 ATU )
 
Thanks everyone for contributing. I'm beginning to understand it now! But still have more questions ...

The radios I have are an ICOM 700 and an ICOM 710, each with their own antenna and grounded to around 20 sq ft of copper mesh running under the deck. As I don't have tuners, I would be interested to know what my radios are doing when the Tune button is pressed.

Re the comment on the LRC SSB course, I found that course frustrating: lots on radio procedure and DSC but hardly anything on the understanding the radio, propogation, antennas etc, etc. So Abigail, I'm surprised at your confidence!

Has anyone installed an SWR Meter?
 
[ QUOTE ]
....lots on radio procedure and DSC but hardly anything on the understanding the radio, propogation, antennas etc, etc.

[/ QUOTE ]

You may then be interested in getting an amateur licence. In UK it now requires 3 exams, the 1st two trivially easy, the 3rd quite interesting if that sort of thing interests you. You then have (legal) access to amateur maritime nets.

[ QUOTE ]
I would be interested to know what my radios are doing when the Tune button is pressed.

[/ QUOTE ]

Just transmitting a low power carrier

[ QUOTE ]
Has anyone installed an SWR Meter?

[/ QUOTE ]

There is no installation to do, just get a meter and a short length of coax with a plug at each end, connect it up and you are done. Most installations I see have them. You probably don’t want to do that until you have an ATU installed or it will scare you!!
 
You got a great deal of info in reply to your first query but judging from your last comments some of it might have caused confusion.

Imagine the ATU (whether Automatic or Aerial or Antenna) as simply matching up the size of the output "pipe" of your radio with the input "pipe" of the aerial. If you dont match them, then some of the output is reflected back and can do damage, though on modern radios its more likely to cause it simply to power down to protect itself. Incidentally, the degree of reflection is what you meanure with the SWR. 1 to 1 is as good as it gets, 3 or 4 to 1 is getting too much.

Part of this mismatch can come from an aerial being forced to operate outside its resonant frequency. Aerials are like violin strings - they have a resonant requency and can be tuned by adding bits on or taking them off. Thats what was being referred to by the Australian comments, and its also what the big metal lump is at the bottom of your VHF aerial. In effect, they trick the radio into thinking its connected to an aerial that is longer than it actually is and is therefore resonant at a lower frequency.

This approach is OK for a radio that uses a narrow band of frequencies like a VHF and you can even get whip aerials with all sorts of connections to allow you to use a wide range of HF frequencies, but you are using a piece of rigging which will only be resonant for one frequency in the 1.6mc/s to 28 mc/s range of your transmitter, probably somewhere around 20 mc/s . So you need a different aerail tuning set up on each frequency which is what and ATU would do for you.

Either of the radios / aerials you have could have an attached ATU - the ICOM one is the AT130HF. When you say "what is it doing when it is tuning", the answer is probably nothing unless the ATU is present. You might even have the ATU - its in a plastic box and is likely situated just under where the aerial lead leaves the inside of the hull for connection to the backstay. Entirely automatic - no knobs or anything to twiddle.

None of this will affect reception very much. As for transmission, even assuming that you have no ATU and are not frying your radio, whats the point in consuming 150 watts of battery power and emitting just 10 from the aerial?
 
Just an additional bit of waffle. " IMPEDANCE " is a measurement used in electronics but seen in nature and is simmilar in principle to resistance.
So a high pressure water pump to wash your hull can be seen as high impedance while a river driving a water wheel is low impedance. ie pressure versus volume. If you try to drive a water wheel with your high pressure low volume jet you wont do so well as a river of huge volume loow pressure . Likewise you might drive a tiny high powered/speed turbine from your pressure washer successfully buttry to use a river you would get nowhere. You have to match the load to the nature of the source.
An electrical example is the power to your spark plug is very high volltage very little current while your battery provides low voltage high current. A spark plug source is no good for charging a battery and a battery is no good for firing spark plugs.
An antenna with a tuner is designed to be dfed by 50 ohms characteristic impedance. The transmitter likewise is designed to provide power at a source impedance of 50 ohms. even the cable is designed for 50 ohms impedance. (a high voltage low current can leak across the insulation and be lost be capacitance effects while a low voltage high current can be lost by resistance and inductive effects in the cable. 50 ohms is the best compromise.(its like a hydraulic hose small with thick walls for high pressure large with thin walls for low pressure) (this is anot a perfect analogy however because electricity leaks all the time so thicker the walls the better but more important for high pressure )
Now as explained an antenna resonates at a frequency and this can be electrically adjuusted to resonate at a higher or lower frequency easily by a factor of 5. When the antenna is resonant it presents an impedance (ie the best ratio of voltage to current, for power transfer) which may be somewhere near 50 ohms. This impedance can be then transformed to exactly 50 ohms to get the best power transfer. All done by coils and capacitors either manually or elctrically tuned. There hows that for waffle olewill
 
Hmmm, Will, are you not getting mixed up here with the standard water analagy for teaching DC ohms law?
Impedence is a rather ethereal unit, often misunderstood, a bit like tesla's and webers/m2 for resistivity and permeability..or is that the other way round...anyway I digress...
Opposition to AC current flow is called reactance, and Ohms law for AC circuits holds true for it.
However, impedance is a measure of both reactive and resistive components combined. It can only be calculated vectorially..ie the square root of the sum of the squares for both X and R. (for series circuits).
Your analagy also neatly sidesteps a bunch of cable issues like velocity factor, and attenuation.
Anyway I can see where you are coming from...unfortunately the behaviour of RF often defies simplification..and is probably best left as a "black art", rather than lead people into a false sense of security by attempting to understate it.
If people need to know more, then I think it was Talbot who earlier said that the best course is to take the radio amateurs exam.

Steve.
 
I wonder if my mesh foredeck would work....hmmm?

Top_Cat_refurb_newdeck01_TH.jpg
 
I would not like to be part of the rf path between an on deck mesh and any conductor nearer the sea when transmitting.

RF can burn.

I have seen coax melt down in front of my eyes when a fault gave a bad mismatch on a shore based installation (150 watts A1 144 Mhz)

Iain
 
Note also that RF burns are pretty nasty, destroying the central part of nerve fibres - they hurt for a long time, can't be cooled by water, and are liable to get infected.
 
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