Scuttlebutt SSB radio net - Saturday

I tuned in at the appointed time(s) last evening but could only hear a very strong and persistent morse signal. Would it be worth trying again some other time and preferably on an Amateur frequency? What about setting up a "Scuttlenet" at the same time every evening? Any suggestions as to the most convenient time and what would be the best frequency?

Paul.
 
The Morse station was 4XZ and Israeli coastal station.

Suspect 8 MHz a bit too high in freq for that time, a channel around 2 MHz if there is one would probably give better local propogation.

I listened on 7MHz Ham band and lots of Eastern Europeans with good signals but no British stations and only 1 Belgian so success on 8 MHz was always questionable.
 
Hi Ships Cat,

Any ideas as to how one 'fixes' it?!!! /forums/images/graemlins/smile.gif Last night when I was trying to contact Jim on full power, only three LEDs flashed (synchro'd with speech) slightly and there was no sound from the aft siren. There see, an improvement already, and all down to this Forum I'll bet!! /forums/images/graemlins/wink.gif /forums/images/graemlins/wink.gif

Cheers Jerry
 
Very difficult to troubleshoot it without being on the boat, but the main issues are:

INADEQUATE EARTH

Most non metal boats I see have inadequate rf earths, often relying on the sintered blocks one can buy (absolutely inefficient from the comparison few tests I've done alongside boats fitted with them), etc or even just a single connection to an anode or other fitting. Need to remember that the DC negative on most transceivers and tuners is grounded to their chassis so that the boat's DC system is connected to RF ground, which can mean that rf ground currents can flow through your DC system (which may even act like radials) if the rf earthing is inadequate.

The important thing is area presented to the sea and on most non metal boats the biggest area is the keel ballast. It does not need to be in electrical contact with the sea, just close enough to it to allow capacitive coupling at HF frequencies.

A way mentioned frequently recently of solving these problems is to use radials as the ground system. I do not fancy this myself as they introduce more directionality to the antenna and also there are high rf voltages on the ends of the radials which pose a burn risk as well as an arcing risk to other cabling or grounded objects. I also think some of the comments about them coupling to the sea is a load of twaddle so one ends up with an antenna which is a vertical (eg backstay) with only one radial - an inefficient antenna.

Where people often lead themselves astray with the rf earth is that they do not know that anything works, to an extent. They think that just because they can contact other stations then it must be ok. They even think that by comparing themselves with other boats, they must be ok but forget that most other boats have pretty poor radio systems. A good test is that if an amateur you should be able to work shore stations anywhere in the world reasonably reliably on HF. Those shore stations do not need to be powerful or with big gain antennas. I can regularly work amateurs in their cars in UK on HF from the boat here in New Zealand. Amateurs here on land (with relatively simple stations such as only a vertical antenna) routinely work friends on well equipped yachts throughout an entire circumnavigation.

COMMON MODE CURRENTS

A good article on these is on the Airmail2000 site http://www.airmail2000.com/rfi.htm. Need to remember that the DC negative on most transceivers and tuners is grounded to their chassis so that common mode currents can run back through the boat's DC systems. For common mode currents the usual fix is to use clamp on ferrites or wind cables through a suitable composition toroid. More than one ferrite, or else multiple turns through one is often needed - is not always as simple as some say of just clamping on a ferrite. When using the clamp on ferrites clip the housing together then pull it up tight with a cable tie around the whole thing (contact between the two halves is important for the magnetic patch).

It is sometimes said that the ferrites by OEM's on some equipment eg computer monitor cables, dc buck converter or switch mode power supplies, cables are there to stop interference from rf from transmitters - again a load of twaddle, they are there to stop that equipment interfering with radio
receivers, not the other way around. The fitted ferrite may help, but it is no indication of the equipment's immunity from rf as some claim.

Metal boats can be especially susceptible to common mode currents if any fault in the radio grounding (internally) or rf grounding as there is often a very high capacitance between the hull and the boat's cable systems (the high capacitance creating a low rf impedance path from the cabling to the hull (ground).

PICKED UP RF

Any longish wires, especially outside the boat, will act as antennas and pick up rf. This can be less of a problem for cables inside the boat if the boat is metal and does not have big openings but metal boats are still susceptible to pickup on cables outside the boat and not shielded (eg cables in mast are normally shielded by the grounded mast in a metal boat but cables to things like wind generators and solar panels are not - can cause regulator drop out on those, for example). The normal approach is to use 0.01 micro-farad disc ceramic capacitors to bypass rf at critical places in the cabling systems. For example, things like speakers and sirens which sound when one tx (you mention a siren) are usually easily fixed by simply soldering a 0.01 micro-farad disc ceramic capacitor across their terminals. Solar regulators one can usually do the same thing (just try various combinations of 2 terminals using one capacitor 'til hit the correct 2 and fixed).

I am wary of fitting capacitors across the conductors in some non DC systems cables though (such as in instrument buses such as SeaTalk) - in any event it should not be necessary.

Disc ceramic capacitors (or monolithic ceramic capacitors) must be used as other common types can present a high impedance to rf. Ferrite (either clamp on or cable would through a toroid) will also help, but contrary to what others may say, you often actually need quite a lot of them (else 10 or 12 turns through a suitable composition toroid) to reduce rf picked up on cables.

Generally, rf pickup will only be a problem if picked up in cables which are grounded (either directly or capacitively though running parallel to another grounded cable though some part of its length). So building the boat so that their is a high degree of isolation between DC systems and the rf ground and anything else connected to the sea (as it is the rf ground too) is a big help. Anything that needs to be earthed (eg the AC and tuner) should be star connected back to a single earthing point so the possibility of earth loops is minimised (see common mode currents above). This means avoiding systems where the DC negative is grounded to the AC earth or to any other metal connected to the sea (despite forum cries to the contrary this is the modern approach, especially with metal boats). In our own boat, for example, the DC (including the engine) is completely isolated from the AC/rf ground.

Finally, ignore most of what you are told in forums, most of it is absolute rubbish.

Hope that gives some ideas, but as you can see, it is very hard to identify a specific boat's particular problems from afar. I'll sit back and await the flak /forums/images/graemlins/crazy.gif.

John
 
Good treatise John - as usual.

I would be interested to know how you isolate the engine and the whole DC stuff from "earth".

I am assuming that the sea is the RF earth via keel or plate or something similar.

Surely the engine must have contact with sea - or must it?
 
Hi Bergman

The propeller shaft is insulated from the engine by an insulated flexible plastic disc coupling and insulated from the hull by running in Thordon bearings in the shaft log. The engine sensors and alternators are all isolated from the engine itself except for the starting heaters (which we don't need to use here) which use the engine as part of their return but are, of course, isolated when not turned on (also the switch is for them, of course, momentary).

I have never done a check of smaller pleasure boat engines as to how many are available with isolated sensors, etc but certainly the large engines that go into bigger commercial boats are readily available. I know of one forumite, at least, who has isolated his alternators from the engine by modifying them but do not know if he did the sensors (isolating the alternators alone is of value if they are directly connected without an isolation switch to the batteries as this gives an isolated system when the engine is isolated when not in use, which is most of the time in a sailboat, by a 2 pole switch).

The DC system is entirely isolated from AC ground ie the DC negative is not strapped to AC ground as some recommend - ABYC, as far as I know, still require DC negative to be strapped to AC ground but I think that is just a remnant that has not caught up with current practise. Certainly, for the larger new builds that I am involved with, isolated system is usual. Some forumites have contested that (none that I know who have actual involvement in specifying new builds in the industry) but another forumite who I know for certain has been strongly involved in the new build industry concurs with what I say.

Our boat is steel so the hull is the rf ground. Our ssb radio does not have its chassis isolated from DC negative so that means, of course, that connection of the rf ground to the hull at the ATU would strap the boats DC negative to the ground if it was not isolated. We use a capacitor (of the type I think Paul has described and provided a link to) in the ATU to ground conductor to isolate it for DC in order to maintain DC separate from the AC earth.

The only unresolved issue we have is not interference from the radio but interference from our shore battery charger, which of course is not of any impact when off shore power. Apart from putting a low level hum into the received audio it also lays it on the TX audio as well. The VHF was affected as well but I cured that by placing a standard 3 wire noise filter in its DC lines (such as is used for car audio systems, but a big 30 amp one to minimise voltage drop - they have a considerable volt drop at their rated capacity) and no doubt could do the same for the ssb. But my experience is that with ssb's being so voltage conscious with respect to power output, such a device would have to be greatly oversized to avoid power output drop. A DC-DC converter or placing the radio on and AC to DC supply would probably also work but it is not an issue that has driven me to fixing it as it is easy to just turn the charger off if in the marina. I mention this as is also a common problem encountered.

I think that perhaps hum and common mode type loops are more prevalent on metal boats due to the capacitive coupling between all cabling and the hull (have not really investigated this on other boats but measured it once on our boat and forgotten what it was exactly but something in order of 10's of micro-farads so effectively a short circuit at rf).

We have run up to 500 watts SSB on board and 250 watts continuous modes with no problems, but currently use an Icom IC-M802, 150 watts (if battery voltage right up /forums/images/graemlins/frown.gif).

John
 
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