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Posted: 7/20/2008 7:35:37 PM EDT
[Last Edit: 7/20/2008 7:42:57 PM EDT by ChuckG]
Some of these may border on stupidity.. please bear with me..

I'd like to play safe as I live in the most lighting prone area in the U.S.. That said, I don't really want to string up permanent antennas outside in plain view either. Given those two considerations I am wondering if installing both a dipole and dual band 2m/70cm mobile antenna in the attic is a viable solution and how well they might work.

First.. Is an antennae reasonably safe from lightning strike when situated inside an enclosed attic? And how much signal sacrifice can be expected by not having it a full 30" off the ground and enclosed? Looking at my house I'd say the peak of the attic is approx 15' up. What about a ground independent mobile antennae for 2m/70cm like the SBB-5NMO.. should it perform fairly decent at 15' inside the attic? Base unit will have a tuner and can pump max 100W HF, 50W 2m, and 20W 70cm.

Now these attic solutions are really for just playing around. Should the S really HTF and I need all the reception that can be realized.. I have trees (if they are there after a hurricane) far enough apart (60m) to string up a pretty long wire easily 30" off the ground.. same goes for the 2m/70m antennae. Question is.. if I use trees for towers would utilizing a grounded I.C.E. device inline of the feed line provide sufficient lightning protection for the operator and equipment?

Edited for grammar

Link Posted: 7/21/2008 9:33:43 AM EDT
Attic mounted antennas will work but with a loss of performance, and is not a really good solution for lightning protection as lightning can just as easily strike the house as an antenna outside. HF antennas especially will usually pick up a tremendous amount of noise from electronics in the home, as well as create a high RF exposure inside the home potentially causing problems with other items in the home as well as biological exposure. Construction materials absorb or reflect RF energy creating signal loss and pattern distortions. High voltage nodes on HF antennas can arc to nearby conductors or set fire to wood or other non conductors that it might be in contact with, for this reason as well as RF exposure I would recommend limiting transmitter power to probably 50 watts, less if you're using a tuner with an unmatched antenna if you're using an HF antenna in the attic.

Using the antennas outdoors and away from the house/shack and using a good lighting protection product (the ICE is very good) connected to a good grounding system is the best solution for overall performance. Make sure you protect and bond all your grounding (antenna, and power drop ground need to be bonded outside the house)
Link Posted: 7/21/2008 12:40:54 PM EDT
[Last Edit: 7/21/2008 12:45:52 PM EDT by ChuckG]
I've tried to do a little research on this and some say there is some added protection from direct antennae strike while others seem to think otherwise. The common theme I noted is that an antennae in the attic could still accumulate energy from an indirect strike and channel it down the feed line. So that leaves me wondering if grounding the attic antenna to a house ground and utilizing an I.C.E device on the feed line should suffice.

I guess my biggest question is would an antennae in the attic make the house more likely to be struck by lightning? Antennas in the attic or not, I'd image a direct strike on the house is going to cause allot of damage throughout the house based on standard building codes.

The signal degradation, antennae insulation (fire hazard), RF interference, Bio hazard concerns are all noted. I think allot of these can be mitigated by a thoughtful installation and attention to when the antennae is utilized (wife out shopping; kids at school; tx power as you mentioned). But I am talking myself into what I want.

My predicament is I do not want to make this into a major hobby as I have enough of those already. The radio would be for emergencies and occasional use to familiarize myself with it (I say that now). So I really do not want to get into a properly bonded ground system so I can string up permanent external antennas all of which I don't want to see anyhow.

Although an option, I'd prefer not to have to put up temporary (field expedient) antennas outside every time I decide to switch on the radio. But I if that is the best option considering, and I can only use it on fair weather days, then that is what I'll have to work with.

D@mn.. this is allot of work.. but I think still a better, cover all bases, SHTF comms option than even a Sat phone

Edited: For Grammar
Link Posted: 7/21/2008 1:05:39 PM EDT
[Last Edit: 7/21/2008 1:11:19 PM EDT by Gamma762]
You're not likely to either attract or repel lightning with anything that you do around your house. If you imagine a 150 foot diameter ball rolling around the skyline above your house and general area, anything that the ball touches (treetops, house roof, power lines, antennas or towers, etc) is subject to a direct lightning strike. High conductivity things like metal antenna towers might seem to be a huge "lightning rod" that would attract lightning but in practice the difference is not that large. A CG lightning strike travels thousands of feet through air to reach the ground and typically goes wherever it wants based on ground conductivity and other factors. Personally I've seen direct strikes to an open field just a couple hundred yards from a 500 foot high broadcast tower with an extensive ground system - if anything would be a "lightning rod" that would be it.

The indirect effects you mention are another source of concern and one of the biggest reasons why your attic antenna doesn't really make that much difference especially with an HF antenna. Lightning generates both a localized magnetic field pulse as well as a radio frequency pulse (short range EMP) which is rich in radio frequencies from medium wave (AM broadcast) up to about 100MHz if memory serves - which will be intercepted and converted to electrical current by your HF antenna (since that's what an antenna does) creating the potential for damage to your radios and other household items from any nearby strikes.

The only way to protect the equipment is to divert that energy somewhere that has the capacity to absorb that kind of energy quickly enough, and where it doesn't cause harm (ie, a lightning protection grounding system). Putting more distance between the antennas and the equipment helps as it gives the ground system time to dissipate the energy before it reaches the equipment.

You can have some good functional HF antennas with not a lot of "environmental impact" as far as the looks of your home and yard, especially if you have a reasonable supply of trees. Also, becoming a good HF operator is something that takes a little experience, it's not just a turn-on-the-radio-and-talk operation, so you want something that you can use more often.
Link Posted: 7/21/2008 5:35:57 PM EDT
Just my experience here and yours may vary but I have an 20m/40m shortened dipole strung up flat in the attic of my house and a 2m/70cm Arrow open stub jpole also in the attic. The only problem I have had with RF is my PC speakers need to be OFF or else I get a nice dath vader effect :-) other than that I have been able to work southern Brasil, Hawaii and all over the CONUS with 100W. try it out, use common sense and have fun.

-A
Link Posted: 7/21/2008 6:06:53 PM EDT
I had a couple Arrow solid element yagi antennas along with a Arrow J-Pole antenna in my attic at my last place. They both worked extremely well. I was able to hit repeaters up in the mountains 100 miles away with ease. I highly recommend their antennas and Al is a great guy to deal with.

www.arrowantennas.com



--Scott
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