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Author Topic: Lightning protection for FC-40 and random wire  (Read 1036 times)
KG4JIX
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« on: August 14, 2006, 05:26:10 AM »

I'm planning for a FT-897D radio with a remote FC-40 autotuner outside with a random wire antenna.  I have two questions about lightning protection.

Should I use a single-wire lightning arrester on the random wire just before the FC-40 to protect it?  I could put the arrester's ground to the RF ground there.  The RF ground will have a ground rod (bonded to single ground point, of course) and a buried counterpoise wire.

How can I protect the CAT cable between the tuner and the radio?  (Do I need to?)  I'm looking for specs on the cable so I can build one that is 40 foot long.  Without more info, I'll probably try to use an old RS232 cable (shielded) or UTP.  I'm concerned that a surge on this cable could take out either the FC-40 or the FT-897D.  Also, there doesn't seem to be an easy way to switch the cable to ground when I'm not using the radio.  I could have a DIN receptical with all pins grounded, but that seems inconvenient enough that I wouldn't always do it.

Thanks,
kg4jix/randy
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KB9CRY
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« Reply #1 on: August 14, 2006, 06:38:36 AM »

Should I use a single-wire lightning arrester on the random wire just before the FC-40 to protect it?

That would be a good idea.


I could put the arrester's ground to the RF ground there. The RF ground will have a ground rod (bonded to single ground point, of course) and a buried counterpoise wire.


You may want to consider more than one ground rod.  According to Polyphaser, for a three legged tower, they recommend 50 to 75 ft. of ground radials per leg, with rods spaced every 2X their length.  If you think of your wire as a single leg, then you'd want about 50 ft or more of ground radial beneath it.  The caveat to this is that if your wire was to take a direct strike (we normally should be more worried about the more frequent induced energy from nearby strikes), then it would fry quick but the arrestor may protect the tuner.

I know that ICE makes arrestors for CAT cables and you'd want to protect that cable a the shack entrance at the SPG.  This section can also have energy induced into it.

Don't forget to run a large wire (I use #4 bare solid) around the house and connect the SPG to the service entrance ground.  

Phil  KB9CRY


How can I protect the CAT cable between the tuner and the radio? (Do I need to?) I'm looking for specs on the cable so I can build one that is 40 foot long. Without more info, I'll probably try to use an old RS232 cable (shielded) or UTP. I'm concerned that a surge on this cable could take out either the FC-40 or the FT-897D. Also, there doesn't seem to be an easy way to switch the cable to ground when I'm not using the radio. I could have a DIN receptical with all pins grounded, but that seems inconvenient enough that I wouldn't always do it.
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KG4JIX
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« Reply #2 on: August 14, 2006, 01:25:35 PM »

Phil KB9CRY,

> You may want to consider more than one ground rod. According to Polyphaser, for a three legged tower, they recommend 50 to 75 ft. of ground radials per leg, with rods spaced every 2X their length. If you think of your wire as a single leg, then you'd want about 50 ft or more of ground radial beneath it.

I was already going to have a couple more ground rods to the north for other purposes, but I will go ahead and add one to the east and one to the south.  I'll use them as starting points to run smaller radials.


> I know that ICE makes arrestors for CAT cables and you'd want to protect that cable a the shack entrance at the SPG. This section can also have energy induced into it.

The only ICE arrestors that I've found that may work are for rotator lines or remote switches.  I don't know the specs of the CAT cable, so I don't know how they would work.  I've read somewhere that the signals are 0 to +5 volts, but I don't know if/how they are shielded.  If the cable needs a single shield, I guess I could just shield an enclosure with the rotator controller in it, connecting the shields to the enclosure.  I'm already concerned about RF in the shack because the feed end is 15 feet from the shack.

> Don't forget to run a large wire (I use #4 bare solid) around the house and connect the SPG to the service entrance ground.


I'm using #4 bare copper.  I will bond to the the service entrance.  It's 37 feet past the last ground rod I'm installing to the north.

Why place the ground around the house?  I live in a "garden home" subdivision where people are very concerned with appearances.  There is an exception in the covenents for ham antennas: that was a major requirement for me buying a house.  I want to set a precedent of putting up an antenna, but keep people happy by having nothing visible from the front of the house, and not much visible from anywhere else.  They would not be happy with me digging in the front yard, especially under the driveway.  However, if it's important enough, I can do it.  Among other things, I will inform the architectural committee about the antenna, and give them a copy of my license.  I will show them that I am using good engineering practices.  Can I justify the the loop around the house as sound practice?

By the way, is there a machine for pounding in five ground rods?  I'm not physically up to doing it again.

Thanks,
kg4jix/randy.
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AI4NS
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« Reply #3 on: August 14, 2006, 03:09:10 PM »

You absolutely need to run the ground wire to your service entrance ground. You don't need to dig a trench, just poke it in the ground, under your mulch, etc. If you need to run it under the driveway, get some PVC pipe sections, and connect a hose to them and wash them under the driveway one section at a time then glue another section on, and continue, then feed your ground wire through. Rental places often have chipping hammers to break up concrete, tile, etc, and they have an adaptor to drive ground rods. Doesn't mushroom the end that way either.

Mike
AI4NS
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KG4JIX
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« Reply #4 on: August 14, 2006, 03:50:48 PM »

Mike AI4NS,

> You absolutely need to run the ground wire to your service entrance ground. You don't need to dig a trench, just poke it in the ground, under your mulch, etc. If you need to run it under the driveway, get some PVC pipe sections, and connect a hose to them and wash them under the driveway one section at a time then glue another section on, and continue, then feed your ground wire through. Rental places often have chipping hammers to break up concrete, tile, etc, and they have an adaptor to drive ground rods. Doesn't mushroom the end that way either.

I'm sorry.  I didn't communicate that well.  I absolutely will bond all grounds to the service entrance ground.  Also, all wires will enter the house through a grounded bulkhead with lightning arrestors.  All coax will have the shields grounded just before the arrestor, as well as at the antenna.  All ground wires will be kept as short as possible.

My question was why surround the house with a ground wire.  In other words, place a loop of ground wire arround the entire house.  I've seen that recommendation before, but I don't understand why it is important.  The ARRL Antenna Book (2000 ed.) shows that in the drawing in the section on lightning and EMP protection.

I understand why the other protections are needed.  I don't understand why circling the entire house is suggested.  I suspect that it is either to improve protection from EMP coming from different directions, or just to improve the overall ground system by having it go more places.

I appreciate your responding emphatically.  Not bonding to the service entrance ground is indeed dangerous.  Since my response wasn't clear, others reading this could have been mislead into that danger.

Thanks,
kg4jix/randy.
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KB9CRY
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« Reply #5 on: August 14, 2006, 07:19:35 PM »

You don't need to circle the entire house like you would circle the wagons, but that would be best.   Just run a wire, like others have suggested, from your SPG to the service entrance ground.  

Phil KB9CRY
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KB9CRY
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« Reply #6 on: August 15, 2006, 05:53:30 AM »

Give the guys at ICE a call and ask about network protectors:
How to Contact Us


U.S. Mail
I.C.E. - Industrial Communication Engineers, Ltd.
P.O. Box 18495
Indianapolis, IN 46218-0495
USA


Telephone
Toll-free: 1-800-423-2666
Phone Hours: Mon-Fri 10AM-6PM


FAX
FAX: 1-317-545-5412


Internet
Website: http://www.iceradioproducts.com
E-mail: help@iceradioproducts.com

You may also want to look at the Polyphaser website.
I'm sure these companies have something for Cat 5 cable.s
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KG4JIX
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« Reply #7 on: August 15, 2006, 05:28:24 PM »

KB9CRY,

> Give the guys at ICE a call and ask about network protectors:

> You may also want to look at the Polyphaser website.
I'm sure these companies have something for Cat 5 cable.s

I've been over their web sites.  I haven't talked with them bacause I don't know much about the CAT cable.  (That's not CAT as in Category 5, but Yaesu's interface port.)  For the FT-897D, it can be configured via menus to connect to a computer, a tuner (FT-30, FT-40, or LDG AT-897), or a linear amp.  The CT-82 Computer Interface Cable that comes with the FT-897D converts from the CAT interface to a RS232 one.  Based on a previous Yaesu product, I believe the CAT is using TTL levels for signals (0 to 5v) instead of the RS232 (-25 to +25v) ones.  The FC-40 ships with a 16' Control Cable that uses the CAT interface port.  That's what I need to extend to 40' and to add lightning protection.

The control cable is 8-pin mini-DIN.  All 8 pins are used and, since it's mini-DIN, I suspect that it's shielded as well.  There is 13.8v provided on the cable to power the tuner.  I've read about someone extending the cable to 60' using straight-through extension Apple serial cables.

ICE has a Rotator/Remote Switch cable protector that shunts at 20v that is a possibility.  I've also considered a RS232 protector.  I'd really like the spec on the cable, or hear from somebody that has it working.  Since the FC-40 is waterproof and designed for remote use, it seems to me that others will have added lightning protection, too.

Thanks,
kg4jix/randy.
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K9KJM
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« Reply #8 on: September 10, 2006, 06:40:27 PM »

Lightning arrestors, Coax switches to put antennas to ground, And multiple ground rods are important, But as already mentioned, BONDING all grounds together is what is really important!
For good up to date info: http://members.cox.net/pc-usa/station/ground0.htm
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