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John
The ground plane in the coach roof isn’t the best place to put it. You really want it in the bilge as close to the hull as practical. Since the boat was probably used in freshwater, the previous owner probably never bothered to put it in the bilge. I suppose it will probably work OK on higher frequencies, but I would expect that you’ll have difficulty on lower bands. You might consider running some copper flashing through the bilge.The problem with some types of HF digital communications is that the duty-cycle of the transmitter is too long. The radio can overheat. The radio won’t burn up, but it will reduce output power. There are some marine SSB rigs that have optional cooling fans that allow the rig to transmit longer, up to 100% duty cycle. I have an SGC-2000 marine SSB that offers such an option. I am sure there are others. I’m not aware of any ham rigs that do, but you can’t run a ham rig on the marine bands anyway. You can run Pactor on a ham rig in the ham bands. I’ve never bothered. There are other digital modes that are better for plain text communication such as PSK-31. If you want to get email offshore, you may need the more robust radio.
I’m probably not the right person to comment on what the best equipment is for Pactor. I have little experience with it. I’ve forwarded your message the the 424 group. There are a number of software programs that work on notebook computers and connect to your radio to support digital modes, but these programs are data-rate limited because the ham bands are restricted to low data-rate modes. If you want faster access, you probably need a special modem. Your email provider will likely have recommendations.
http://www.sailmail.com/
http://www.qsl.net/ve3cvg/digitalonhf/digital.htm
The nice thing about using your computer with your radio is that you can receive weather fax on your computer for very little cost.Although there are radios designed for both marine and ham bands, my own experience is that marine SSB rigs are not as capable as a good ham rig. They are designed for appliance operators. They lack features that would be valuable in making contacts in marginal or crowded conditions. Since the marine bands are channelized, I can see why there is little need to provide filtering for crowded conditions, but lacking controls for marginal propagation is puzzling. Still, most of the marine bands tout their ability to operate on ham bands. I have yet to see one that I would consider capable of performing well. My SGC radio didn’t even come with a tuning knob. I’ve since upgraded it, but the receiver isn’t very good in comparison to a decent ham rig.
I added a second HF rig. I now have both the SGC marine radio as well as an icom-706 ham rig. The 706 is OK, but not what I would consider a great rig either. The nice thing about the 706 is that is is very small and easy to mount. It also can be purchased used for as little as $400. It should also work with any ICOM tuner such as the one you already have installed. Since it is designed as a mobile rig, it has poor cooling and won’t handle a long duty cycle.
Mounting two rigs in your nav station can make it crowded. Since you can’t operate on the marine bands with a ham rig, I would suggest getting a marine SSB that will work with your email provider first. They can probably advise you regarding which rigs will work. If you get frustrated with poor receiver performance, you can add a ham rig later. If the M700 can be adapted to work, it might be a good start since you own it. You can always sell it on ebay later if you get something better.
I would suggest that you get your general class ham license in any case. Even if you don’t use the ham bands, you will find the knowledge invaluable. With a ham license, you can operate from home and get used to how the bands work before you go offshore. You can temporarily install your boat radio at your home as long as you operate only on the ham bands. You probably want to be comfortable using the hf bands before going offshore.
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Rich Carter
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Rich-
A couple electrical questions I hope you can help me with:
I’m still working on a ground plane. It is tied to the internal keel ballast, and to copper sheathing against the hull bottom. I’ve read that tying the ground plane to the stern pulpit and lifelines also helps. Question is, is there any danger of RF burns from the ground plane when transmitting?
Second question:
I’ve installed a DC genset in a box in the stb cockpit locker. For cooling purposes, I’ve removed the diodes to outside the box, but I’d like to redo them with more heavy duty stud diodes. Any idea for a reasonable source of large amp diodes? Alternator is rated at 160 amps output.
Thanks,
Quent -
Quent,
Here’s a link to a free downloadable manual that has lots of useful information.
http://www.sgcworld.com/Publications/Books/hfguidebook.pdfConnecting the lifelines and other metal stuff to the ground-plane can’t hurt, but it doesn’t substitute for a good RF ground. Don’t confuse an RF ground with a DC ground. Just because your ohm meter says zero ohms doesn’t mean that the RF electrical potential will be zero volts. You are dealing with the speed of light and relatively long conductive paths relative to the wavelength. You can have large standing waves anywhere in your antenna system. If properly installed, the grounds should be OK. It is possible to get burned while using your equipment if the paths are too long or if you don’t ground things properly. My suggestion is to keep your bonding system in good condition (this is the web of green wires that connect all your through-hulls to your engine block). Run some copper flashing in the bilge as shown on page-68 of the linked document. Make sure that you have a good ground from the radio chassis to your engine block using a heavy gauge wire using a short
run.
Also ground the antenna tuner in a similar fashion. Make sure that nobody touches the backstay when transmitting.As for your question about doides, 160 amps isn’t all that much. My alternator is about that size. A good alternator shop should have diodes that will work. Offhand, I don’t know where you could get substitutes except perhaps Mouser. Why are you relocating them? Only part of the heat generated is from the doides, most of it is from the coils. You need to have adequate cooling for the alternator or it will overheat. The genset needs fresh air too.
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Rich Carter
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Hi Rich-
Thanks for the advice and the manual. Probably, I’m overstudying these issues.
Can you recommend a good source for an SWR meter?
Regarding the diodes, the guys who build the Genie series DC gensets, similar to mine which I think is by Jack Rabbit, recommend external diodes even with a well ventilated box. It seems to work, as about 10% of the alternator output goes out in heat at the diodes, the extra holes in the case keep the stator and rotor cooler, and the diodes obviously don’t make any noise outside the box. I’m using the original button diodes in some aluminum angle as a heat sink, but I can’t get them pressed in tight enough. Stud diodes bolt in. Mouser doesn’t have anything big enough. Ebay occasionally has them, but the part specs are a bit confusing.
Quent
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