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Old 29-05-2012, 09:01   #1
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Proper Length of Antenna and Other SSB Questions - Part II

Since my last post, I have purchased and connected a KISS counterpoise and took my nav station apart looking to see the connections between my ICOM 700 Pro and SGC SG-230 tuner. Turns out, the cable leading from the tuner to the radio was in fact composed of an outer and inner jacket, and beneath the outer jacket were four thin wires. None were connected to a power source. So I connected the red and black to a junction box that I had installed earlier to provide power to a Davis weather station and VHF radio. When I turned on the radio, chose a channel, and keyed the mike, I heard the tuner click and pop for the first time. I then connected to the Doo-Dah Net on Saturday - signal report good despite poor propagation; and the Waterway Net on Sunday - signal appeared weak but readable. We are making progress.
Which brings me to my most recent inquiries.
1. Curiously, the cable from the tuner connects not directly to the radio, but to a piece of pvc pipe approximately 9” long, and 3” in diameter, capped at both ends. On one end is a female PL-259 connectorwhich the tuner cable screws into. On the other end is a 6” piece of cable with another PL-259 connectorwhich screws into the ICOM. While hard to read the label appears to identify it as an “isolator.” Question #1, what is this and more importantly, should I keep it or remove it? If I remove it, I will have to substitute a piece of patch cable to complete the connection. I was planning on buying a RWF meter to install anyway, so would that take care of the issue.
2. Now I have the tuner wires connected to a junction box, which is powered when I flip a switch on the main electrical panel. Flipping that switch, however, also turns on a Davis weather station and supplies power to the VHF radio. You still have to turn the radio on to use it. The SSB, however, is powered directly from the batteries and does not go through the panel. Question #2, should I re-route the wires powering the tuner directly to the batteries - or to the junction box I have set up nearby to power only the SSB. I am concerned that when I flip the switch at the panel, that I am creating interference for the SSB from the VHF radio and weather station when they get powered. If I wire the tuner directly to the batteries or junction, would an on/off switch in the positive line of that power cable cause any problems?
3. There are no ferrites on the tuner cable or the power cable for the radio. If this radio has been opened so I can talk on the ham bands, what types of ferrites should I purchase to put on the tuner cable and radio power cable. Since I have a pactor modem also connected to the radio, should I put ferrites on those cables as well?. Are there ferrites for SSB frequencies and ferrites for ham band frequencies - or are they all the same?
Once again, thanks for your continued help on this. George

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Old 29-05-2012, 09:27   #2
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Re: Proper Length of Antenna and Other SSB Questions - Part II

The PVC pipe thing is indeed an isolator, and these are generally a good thing to have. They can help with R.F. ground-loop problems. You may not need it, but I can't think of a good reason to remove it (unless it's faulty). There's not much that can go bad inside the isolator -- it's essentially a bunch of ferrite toroid cores with the coax running through the middle.

As for adding ferrites to the power and control leads, it can't hurt. Here's a link to a presentation I recently gave about SSB and satphones, including a section on EMI: SHTP Communications 2012. About halfway through it I give some details on appropriate ferrites and their application. The particular ferrite I mention is optimized for SSB frequencies

I'm going to let someone else advise you on the power connection points. There are many ways to get this right. The SSB itself may benefit from a direct battery connection, but the tuner power connection is less critical, especially if you use ferrites.

Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
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Old 29-05-2012, 09:29   #3
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Re: Proper Length of Antenna and Other SSB Questions - Part II

Wire the tuner with its own switched power source. No need to turn on half the electroncs in the boat to power the tuner. You can go direct to the battery but, without a switch, the tuner will be on all the time and need a proper size fuse to protect the tuner and boat in case of a short. SSB's are best wired direct to the battery with fuses in both the positive and negative leads. No need to go through a junction box and separate switch as the radio has its own switch.

You shouldn't need any ferrites on the radio leads. The radio was probably made with the ham frequencies already enabled. You will probably need ferrites on the cables of the PACTOR modem, however.

Don't know what the device is that the coax between the radio and tuner goes through.
Peter O.
'Ae'a Pearson 35
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Old 30-05-2012, 06:09   #4
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If the Pactor cables have a cylindrical bulge near each end they are already "ferrited", or common mode choked would be the technical term. Mine have these, but cheaper ones may not.

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Old 31-05-2012, 10:48   #5
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Re: Proper Length of Antenna and Other SSB Questions - Part II

Thanks to all for their assistance. One last question to Paul, how do you know an isolator has gone bad? Does the fact I can transmit indicate it's ok? Thanks again. George
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antenna, ssb

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