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Old 11-08-2008, 08:32   #1
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Black Box Secrets - Revealed!

OK, this time it's a Blue Box :-)

I promised in another thread I'd post pictures of the little box I use to route coax lead-in cable from the dipoles I carry on the foredeck of Born Free.

First, some FAQs...

1. Why is this needed? Strictly speaking, it's not. However, it sure makes life a lot easier for those choosing to carry vertical dipoles aboard. Creating a semi-permanent point-of-attachment located just below the gooseneck allows you to keep the coax to the antenna fairly short, and to easily erect or dismantle the antenna if you wish. The shorter coax run also allows you to prepare for sea in a few seconds by simply untying the lower end of the dipole and pulling it aft into the shrouds.

2. Why two coax leads instead of one? Because it allows me to carry two dipoles simutaneously. Currently, I carry one for the 20m amateur band and one for the 8mHz marine band. Of course, you could arrange for just one if you only intended to use just one dipole.

3. How is the coax led below? In my case, there's a slotted extrusion at the trailing edge of my mast, so I just run the coax inside that slot, through the Spartite collar, and under the cabintop to an antenna switch located near the radios. This allows me to switch between the dipoles and the permanent backstay with SG-230 tuner. On other boats you might choose to run the coax inside the mast, or otherwise down to a thru-deck fitting.

4. Why a vertical dipole? Because it's simply the best performing ruggedized marine antenna you can carry aboard. It's performance is legendary, particularly on the higher bands (20m and above). Vertical dipoles require NO GROUND and NO TUNER, and you can pump as many watts into them as you want.

5. What's the downside of vertical dipoles? They are single-band only. Unless you have a very tall mast, the average cruising boat can only mount dipoles cut for frequencies above, say, 8-10 mHz. A 40m dipole would require a hoist of about 65'...too much for most boats.

6. What about the various methods to make dipoles shorter, or to use them on multiple bands? IMHO, all of these are impractical for a real seagoing antenna. The traps add weight and wind resistance, open-wire or twin-lead transmission lines are impractical, bent-leg dipoles are a pain to deploy, there's the waterproofing issue, etc., etc. Yes, you could probably use them at anchor and at dockside, but they are IMO impractical to take to sea.

OK, if you've suffered with me this far, you deserve to see the pix of my new black....er, blue box: Gallery :: Constructing a Marine Dipole Antenna

Bill
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Old 12-08-2008, 08:43   #2
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Nice idea!

Nice idea!

We're just about finished the refit of Beausoleil - the radios are the next project. I'm lucky enough to have two independent insulated backstays, so one will be for my Icom 706, and the other for the Icom M700 which came with the boat. But I do have a ~100' copperweld dipole which I had at home - driven by an AH-4 with ladder line, so I'm thinking of using it to make a 20m dipole and possibly another. I also have some old ss lifeline which would last a bit longer, but it's also much heavier. Decisions, decisions...

We'll be heading south in September, and will be in Annapolis for the boat show and will hang out for a month or so before heading further south. It'd be great to hook up with you sometime!
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Old 12-08-2008, 09:08   #3
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doesnt a 706 cover the same bands as a 700 albeit with a reduced max power, and some slight loss of band at the bottom of the range, but with a much easier fitting footprint???????
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Old 12-08-2008, 14:53   #4
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Filters for IC706MkIIG?

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Originally Posted by Talbot View Post
doesnt a 706 cover the same bands as a 700 albeit with a reduced max power, and some slight loss of band at the bottom of the range, but with a much easier fitting footprint???????
Number one issue is the M700 is a certified Marine SSB radio, whereas the IC706MkIIG is "only" an amateur radio...

Advantages of the 706 would be access to not only the amateur HF bands, but VHF/UHF (54-440Mhz) as well. It reaches down to 160m/1.8-2.0MHz with the right antenna. And the ability to use the Winlink2000 e-mail network...

Disadvantages are 100W output vs. 150W like you said (admittedly, not very bad from a technical point of view), and the very real fact that while the M700 is engineered to be more forgiving when battery power dips, the 706 is known to perform not quite up to snuff when supply voltage dips to 12V and below. And the fact that the 706 can be intimidating for those unfamiliar with its operation.

I do have a question regarding the 706: I know it's probably worth the extra expense to pop for the CR-282 temp-stabilized crystal if I'm going to use it with a pactor modem, but what about the optional filters? Would the FL-103 (2.4kHz) be recommended?
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Old 12-08-2008, 15:02   #5
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I have not got as far in m research to know the details of the use, just as fa.r as identifying the 706 as a good option.

I intend pursuing this further by using the on-line Ham courses available from the States.

Meanwhile, I would appreciate info on the use of this filter, and what other filters for this systemnshould be used and why.
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Old 12-08-2008, 17:18   #6
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Capn Jon,

Would be pleased to hook up with you or any other SSB affectionados. I plan to be at the SSCA gam with my boat (Sept 20, I believe, in the Rhodes River at Camp Letts); and at the Annapolis Boat Show in October. Look for S/V Born Free!

The M700 is a wonderful older radio, IMHO. I have one in my home ham shack, and used it for several weeks on the Waterway Net in the mornings. Aside from the advantages already cited (marine certification, 150 watts, lower voltage tolerance, better frequency stability, etc.), it's a great radio. Understand that in my ham shack I have MANY HF radios...ham (including the 706MKIIG, a 900CAT, a 703, a KWM-2A, an FT-817, two QRP+, etc., etc.). In addition, I have several marine rigs (M700, TKM-707, and an FT-600 at the moment), and a number of military and commercial transceivers. I can switch between most of them instantaneously. Still, in this company of excellent radios, the old M700 shines. VERY NICE RADIO.

Ditto for the M710 and the M700 Pro. Have installed several of these and they're solid, very nice rigs. Sorry to say, I can't say the same for the M802. I believe Icom really fouled up with this design -- wouldn't have one aboard my boat -- though many sailors do just fine with the rig. It's not, as one of the radio's designers said to me recently, a "radio man's radio". It's designed for people who know nothing about radios. Yeah, right!

I guess that's the best that can be said about it. But, if that was really the guiding design parameter, I think they missed the mark by a mile. I won't bore you with the reasons, but could go on for several hours :-(

Re: filters for the 706, they couldn't hurt but I'd try Pactor first, maybe at lower than full power. The 706 is one of the dirtier ham rigs in existence, following the recent trend of Japanese manufacturers of creating little boxes which do everything but which have pretty awful specs in the splatter (spurious emissions) arena. Cutting back on the power level helps a bit.

If I seem to be knocking Icom, it's because of the frustration I and other radio guys feel. With very little effort and very little expense, Icom could have cleaned up the 706MKIIG and other radios they produce. So could other manufacturers. But they haven't, choosing to save a few bucks rather than produce a better radio. Some of the older ham radio designs are actually better in this regard. All of the marine radios are better, because they have to meet more rigid type-acceptance parameters.

Yes, there IS a real difference between ham rigs and marine rigs. Would that there weren't!

And, hey, I'd be more than willing to pay the $20-30 or so it would take to bring ham rigs up to marine rig specs :-)

Bill
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Old 13-08-2008, 10:11   #7
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Quote:
Originally Posted by btrayfors View Post
Capn Jon,

Would be pleased to hook up with you or any other SSB affectionados. I plan to be at the SSCA gam with my boat (Sept 20, I believe, in the Rhodes River at Camp Letts); and at the Annapolis Boat Show in October. Look for S/V Born Free!...
Then maybe we'll see you at the show!

Quote:
Originally Posted by btrayfors View Post
Re: filters for the 706, they couldn't hurt but I'd try Pactor first, maybe at lower than full power. The 706 is one of the dirtier ham rigs in existence, following the recent trend of Japanese manufacturers of creating little boxes which do everything but which have pretty awful specs in the splatter (spurious emissions) arena. Cutting back on the power level helps a bit.
...
With very little effort and very little expense, Icom could have cleaned up the 706MKIIG and other radios they produce. So could other manufacturers. But they haven't, choosing to save a few bucks rather than produce a better radio. Some of the older ham radio designs are actually better in this regard.
...
And, hey, I'd be more than willing to pay the $20-30 or so it would take to bring ham rigs up to marine rig specs :-)
Well, any recommended mods to clean this puppy up?

All the popular modifications at Hampedia and Mods.dk seem to just concentrate on opening up transmit for MARS and emergency use. I see one to further stabilize the XO by replacing a varicap with a 33pF ceramic capacitor, but can anything be done to the IF bandpass filters, or other sections? I have a soldering iron and I'm not afraid to use it!!!

Maybe this should be a new thread?
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