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eHam Forums / Misc / RE: Adding an external antenna jack to a tablet
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on: November 27, 2012, 04:07:02 AM
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I've taken apart my MacBook Pro several times, and the AirPort card has two tiny coax connectors on it for the main and auxilliary antenna. The iPad's AirPort card has one coax connector on it. It's easy to disconnect this coax and connect your own, but it's very thin (maybe 1.32mm?) and any substantial length will be very lossy; it's designed for a short run from where the card is placed inside, to an area at the top of the screen near the surface.
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62
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eHam Forums / QRP / RE: Is the KX3 all it's cracked up to be or fake?
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on: November 25, 2012, 03:27:28 PM
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Note that Ten Tec has a policy of cutting off customers who criticize their radios, so look for anonymous reviews too when that comes out. A primary consideration for me is to have as many ways as possible to get a signal out, especially in an emergency. I don't want to carry multiple radios or radio/transverter etc. to accomplish this so the FT-817 wins hands down. On the other hand, on the negative side, your FT-817 is now a single point of failure. If you went out with a KX-3 and an HT, if one fails you still have the other. Also if the HT remains on and beaconing on the whole hike, you can be tracked while in digipeater range, and you can also monitor the repeaters and simplex calling frequencies while underway - not just when you've set up the station. How many hours scanning time do you get out of the 817s internal battery versus the Li-ion battery in an HT? There are indeed some areas with repeater coverage that lack cell phone coverage, but in a life-threatening wilderness emergency I'd try my cell phone and my Personal Locator Beacon before turning to my amateur radio; the exception might be areas where I'm likely to raise somebody who's closer to me than the rescue services. Back on the first hand, though, that's arguably more items that might be forgotten at home, and if you're out on a radio expedition you probably wouldn't forget the main rig. This is especially important in an emergency because if I must get a call for help out then I can first try area repeaters (list is printed before leaving and carried with me), if no go then I can try FM simplex, if no go then I can try HF. All with THE SAME RADIO. Precious seconds saved by not messing with multiple boxes! Do you walk around with the FT-817 in manpack form with both a tuned HF vertical and VHF/UHF antenna connected at all times? I think there's going to be some messing around with antennas, tuner and microphone anyhow. What if it rains sideways? Is it water proof? And having two FT-817s allows me to monitor and use both HF & VHF/UHF simultaneously. The same is true for a KX-3 and an HT, for less weight. (We've discussed full duplex and satellites earlier in the thread.)
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63
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eHam Forums / DXing / RE: LOTW
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on: November 22, 2012, 04:45:31 AM
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About all I can think of is that the data sent over weather nets could be of use within a storm's circulation when it knocks out power to the region.
That's a good point, but trained weather observers can also provide something that radar and automated weather stations can't: Actual human observation to see if that hook on the radar image is actually a tornado, size of hail, damage reports, and readings from non-automated weather stations that happen to be in a particularly interesting part of the storm (like the eye for example). I'm not saying shut down ARES (does ARES even need the League to function?). Yes, even though it uses a bottom-up approach, they need the local coordination and sometimes they also need help from neighboring sections or HQ, whether that be coordination of mutual aid, resources, or legal and regulatory issues. They pay lip service to serious DXers and contesters at best. We shouldn't fall into the trap of thinking that our niche of amateur radio should be the only one. If there's a big cover story about DXing, do the ARDF enthusiasts grumble about that? If an SSB contest is featured, will PSK fanatics be cutting their keyboard cables in protest? It's not like the ARRL stays on the same topic all the time either: They used to have a campaign about digital communications, then it was "when all else fails" (emcomm), and now it's "The DIY magic of amateur radio" (hacking and buidling stuff). Maybe the next promotion could appeal to radio orienteering or international friendships? The general public, politicians and media are understandably more responsive to information about emcomm than many other niches though, so don't expect that to go away. Trust me, if there were any component of LoTW that had to do with giving PR to emcomm, the League would be on it like white on rice and they'd have their platinum-plated quadruply-redundant bulletproof system in place. Of course they should, but no component of LotW should be part of emcomm anyway. If the system was something like the Red Cross "Safe and Well" system or another system handling emergency and disaster welfare communications, it would be especially important that it stayed up in an emergency. LotW is not critical infrastructure, nor was it meant to be. It's just a neat way to confirm a QSO for awards. And I've got QSLs ticking in here. Faster and cheaper than paper (though I like paper too).
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eHam Forums / Antennas and Towers and more / RE: LIGHTNING PROTECTION
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on: November 22, 2012, 02:15:17 AM
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When you say "lightning protection", what exactly do you mean? Are you thinking about just grounding the antenna coax before entering the house and maybe putting a transient arrestor on it, and bonding the coax ground to the electrical service ground? Yeah, you should do that. Or are you thinking about a lightning protection system with air terminals, heavy lightning conductors and ground rods for protecting the house against a direct strike? You probably don't need to go that far. The amount of effort put into lightning protection and grounding should be at least up to the standard of the local electrical code (NEC in the US, NEK 400 in Norway, BS 7430 in the UK, etc.), but a wish to go beyond those standards should be tempered by the risk of lightning damage. Here's a Weather Channel map of lightning risk in the US for example: http://www.weather.com/encyclopedia/charts/lightning_risk.htmlIn low lightning areas, it's not common for residential buildings to need a lightning protection system, except for highrises, hospitals, etc. Are ham-band antennas more prone to attract lightning than a TV antenna at the same height? No. The lightning doesn't care what service the antenna is used on, it only cares about its physical shape and impedance to ground. There is an element of chance of course - your neighbor might not have incurred damage, but you might get just the "right" conditions next summer. Is ham gear. both hollow- and solid-state more prone to lightning and other collateral damage than consumer electronics? I don't think so; it would be more expensive to replace though.
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eHam Forums / Misc / RE: 30m ssb?
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on: November 22, 2012, 01:38:26 AM
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The Norwegian regulation only specifies band boundaries, not modulation types, but it does say that the IARU and NRRL band plan should be followed - so there's band planning by reference.
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eHam Forums / DXing / RE: LOTW
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on: November 19, 2012, 02:58:30 PM
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Maybe if they stopped funneling a huge percentage of their resources into the Hamsexy/Shack-on-a-belt Emcomm crowd they'd have a little something left in the kitty for a program that adds to their international stature. It wouldn't exactly do any good for international stature and good will for the ARRL or ham radio as a whole if they shut down ARES, the NTS, Ham Aid, etc. to turn LotW into Fort Knox. "Sorry, earthquake victims in the Caribbean, California or wherever - we shut down that emcomm stuff to buy a 99.999999% uptime quadruple-redundant system to manage our hobby diploma program." Also, realize that contesting, DX and Emcomm is not opposing goals. A good contest station will probably be a good traffic handling station; a good DXer probably knows the right mode and frequency to reach a particular disaster-stricken area in the 3rd world (and might even know every active ham who lives there); political representatives probably find it easier to let us use valuable frequencies to tell each other that we're 59 years old, talk about antennas and complain about the president all day, when they understand that amateur operating skills can be used for organized emergency response from time to time. Even with a few days of downtime in a year, LotW doesn't really have to have better uptime than it does already - it just needs to catch up on the backlog when it does go down.
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eHam Forums / Antennas and Towers and more / RE: Station ground question.
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on: November 19, 2012, 01:25:12 PM
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Yeah, more exactly the surge arrestor only has to deal with the voltage difference between the center and shield that remains when the strike comes to the entry panel. I suspect there's not much point in over-designing Polyphaser EMP arrestors to handle higher voltages than they already do since at one point the differential will spark through the coax dielectric, or jump acros the feed point anyway. Or turn it into a fluid. A long run of (preferably buried) coax will work to limit strike energy all on its own, and is hopefully augmented by ground kits (connection from shield to the grounding system) along the way, so the arrestor only has to deal with any differential that remains. On the flip side, if the lowest impedance path from the antenna to ground goes through the arrestor and into the house, it doesn't matter if you had the world's best arrestor there since the most of the strike will enter the house anyway - through the shield. Now theoretically, even if you have the strike going through your station, if you have a ground system that ties everything together with low enough impedance, everything should rise in potential at approximately the same time, but I sure don't want to be there to test it out if it happens.  PS: I'm an engineer, but not an electrical engineer, so take the above with some salt.
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eHam Forums / Antennas and Towers and more / RE: Station ground question.
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on: November 18, 2012, 03:16:46 PM
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Thanks for the links guys - I have some reading to do. I think I might make some CAD drawings of the various home station grounding scenarios to have something more concrete to run calculations on. early streamer emission (ESE) I did some literature searching about ESE couple of months ago, and as far as I can find, there's no evidence that ESE actually can prevent lightning strikes from happening - as is often claimed by ESE proponents - or that they work better than regular air electrodes like points or balls. The only possible exception might be ground-to-cloud strikes from towers more than 300 feet high, for which there is simply insufficient evidence to show anything conclusively. The strike is going to come somewhere in the area - but with a lightning protection system you can try to help it strike where you want it to go. My question is (and I have not seen this discussed) about how far away from the base of the foundation should that circle be spaced? Would I place that ring of ground rods as close to the foundation as possible or is that critical? It should be outside the drip line of your roof - you want the ground ring it in wet ground. Or something like that. Here in Norway NEK 400 specifies 0.5 m away from the foundation.
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eHam Forums / Antennas and Towers and more / RE: Station ground question.
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on: November 15, 2012, 04:24:35 PM
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WX7G, I still think your lightning calculations look suspiciously simplistic. They do not take into account the cone of influence of a ground rod, physical distance between rods, the area of influence around the buried ground wire itself, bends in the wire, the local ground resistance, etc.
It's easy for me to understand the rule of thumb that the ground conductor should be at least the same gauge as the sum of the other conductors (they limit the incoming current by their limited current carrying capacity, though there is the added complication of skin effect and and their continued conductivity after transition to vapor form though). But I still can't understand how you figure that a cluster of three ground rods will receive exactly 3/4 of the energy while the fourth ground rod at the other end of the house gets 1/4 of the energy no matter what the impedance between them is.
Are you still claiming that you could hang the bonding conductor on the wall and it would be as good as burying it? (I apologize if I misunderstood last time.)
Have you reconsidered the possibility for arching through walls? (As in, I think it's not a good idea to hang the coax on the exterior wall when you route it to the AC entry point. I think the coax should approach the house at a right angle to prevent flashing through the wall or inducing current in the wiring inside the house, while you said it was fine to hang the coax on the exterior wall all along the house if you want?)
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eHam Forums / Antennas and Towers and more / RE: Station ground question.
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on: November 15, 2012, 08:50:51 AM
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The Norwegian electrical standard - NEK 400 - requires all protective ground leads, metallic pipes (even non-metallic drain pipes in some cases), and coax shields to be connected to a common ground terminal.
What does BS 7430 and EN 62305 say?
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eHam Forums / Antennas and Towers and more / RE: Station ground question.
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on: November 15, 2012, 03:12:31 AM
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For commercial sites that can be operated safely during a thunderstorm, we're basically talking installing the radios themselves in a special equipment room/building with heavy duty protection, but that is also electrically separate from the shelter that the operators sit in, with fiber optic cable being the only connection, right? Even if the strike turns out to be too much for the equipment room to handle, none of the strike energy makes it into the shelter. Such an installation would be out of reach for most hams.
If you're happy to sacrifice your TS-2000, I guess you could install it in a box at the bottom of the tower with its own battery, and use your HT and skycommand to operate it remotely.
For N1RND though: Bury a ground ring of heavy copper wire around your house, bonded to the ground rods on both sides. You already said you unplug when not on the air - but I'd consider grounding the coax outdoors too. If you leave the coax "floating" and a nearby strike induces current in the vertical, it could jump to the electrical system through the wall or something?
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eHam Forums / Antennas and Towers and more / RE: Station ground question.
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on: November 14, 2012, 03:33:40 PM
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When talking about lightning protection, it's a lot easier to protect coax than ladder line. If you have a ladder line fed antenna, consider putting the balanced tuner outside and only bringing coax (with ground kits and protectors) inside. My problem is the service and station grounds are at opposite ends of the house.
While the ideal situation is to have a common entry point, if you bind the grounds together with an outdoor buried ground wire it can be close to what you get with a common entry point. The electrical code usually demands that all grounds are bonded together, so it might be illegal or against insurance terms to not do it. What you have to decide is how and where you bond RF ground with safety ground and lightning ground - when using unbalanced antennas the exact "tuning" of the ground system matters. I think the good way to do this would be to attend to safety and lightning ground first, and then tune the RF ground by adding radials, counterpoises and "artificial ground". For example, a tower may have three or four buried radials made of different lengths of heavy copper wire for lightning protection; on top of the soil there might be a large number of thin RF radials. Not only would putting on the lightning radials last mean digging up the RF radials - they could be detuned. If you look at the Motorola grounding guideline, they indeed recommend a common entry point, but to bond the entry points together through the outdoor ground ring if there are more of them.
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eHam Forums / Emergency Communications / RE: Future of Emergency Power: Small, Mobile Nuclear Power Plants (from Army)
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on: November 13, 2012, 12:55:03 AM
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In the post-Sandy situation, there isn't really a lack of generation. It's a question of lines being down and substations being flooded.
There could be other emergencies where major trunk lines get knocked out, or generation gets hit, where mobile power plants might come in handy. I'm thinking mobile natural gas power plants mainly - those already exist.
There is considerable interest about thorium power plants here in Norway, in some parts of the political scene, but unfortunately others don't see the need They ask why should Norway work for clean power for the world when we have so much hydro power and natural gas here, and isn't nuclear bad. The obvious answer is that if Norwegian companies got ahead in the thorium technology they'd earn boatloads of money, and much of the rest of the world could replace coal and gas plants with clean power without the nuclear waste products of fission - and if you're really serious about man-made climate change (and not using it as an excuse for some hidden agenda) it's the only reasonable thing to do.
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