Rusty's Blog

I certainly wasn’t expecting it, but tonight I won my choice of one of three radios, or a 32″ TV. Considering the fact that I don’t watch all that much TV, that really means that I have my choich of the three radios.

The odd part is that I don’t currently have a lot of opportunity to make much use of even that. I won’t go into the issues involved, suffice it to say that getting an antenna in the air.

In a way it pushes a bit towards me looking at getting some land in an out of the way place, which has been a thought in my head for some time anyway.

Well research to do tonight, and thoughts to consider for the months to come.

Not an exercise posting.

I’ve mentioned before that I’m a ham. Might be considered an understatement there, but anyway. I was assembling a power adapter for one of my radio’s today, and went to test it. I tested it ‘wrong’ this time.

The correct method of testing a power cable is to take a multimeter, put it in ohm or short test, and make three or six tests, depending on whether it is a 2 conductor, or 3 conductor power cord. The first test is obvious, make sure you have connectivity from one end of the cord to the other, on the expected lead. In the process, you may also test to make sure that you are not providing a short between any two conductors.

What did I do? Plugged it in. Twice. The first time I wasn’t really expecting much, simply because the battery in question was dead. I kind of thought it was, but that’s a different matter.

The second time I was ticked. Then burned. Ticked first. I had plugged a radio into the cable, then plugged the cable into a battery. I was expecting the radio to power on. So when it didn’t, I was ticked. Then I realized that the wire was getting a bit warm. Well, ok, hot. No, HOT!

Can’t hold onto it long enough to separate it, but the wire attached directly to the battery is cool enough, so I ripped it off there. After the wire cooled off enough to handle, I separated the power poles, and have discarded the remains. the insulation melted, and smoked. As I say I had attempted to grab the wire to separate it ther, and ended up burning a thumb and finger.

Yes, smoke. Wire got hot enough that it melted. When that happens, unless you have some very special insulating material, it’s going to go up in smoke. Or at least melt significantly, and part of it will go up in smoke. But the important part here is that wire that’s hot enough to melt, will burn you, and most of the things you have in your house right now.

Getting back to a multi-meter, they do pass some voltage down the line. However the current involved is very small. If you have a short in the line, the meter pegs to zero ohms, or if the meter has a continuity tester, it will beep or emit a tone. There is a current limiting resistor in the path, so you won’t have the experience I ran into when plugging into a 7.5 amp hour battery.

“7.5 amp hour battery?” you ask. Ok, batteries are rated in ‘amp hour’ or in some cases ‘cold crank amps’ I won’t go into what cold crank amps is, it’s pretty specific to car starting batteries, and if you want to know more, I’d suggest looking to your auto mechanic. When batteries are rated in ‘amp hours’ though, or ‘milliamp hours’ it means that if you have a load that draws 1 amp, the battery should last this that many hours. In theory this is somewhat linear, in that if you have a 5 amp hour battery, that giving it a load of 5 amps will provide a useful life of 1 hour. It’s a nice theory, but the reality is that as the amperage load goes up, the battery life drops at a rate that is not linear. Take that same 5 amp hour battery and give it a 10 amp load, it will die in a bit less than half an hour. Give it a 20 amp load, and you’re probably going to be lucky to get 10 minutes out of the battery, much less 15 min.

So what sort of lifetime will a dead short give you? That’s an interesting question. In this case there was a stretch of wire, an estimate being about 12 inches, or about 2 feet of wire, that was actually producing a very low but existing resistance. I’m sure it was less than an ohm, but there was some resistance. More resistance than the leads that were directly attached to the battery. It was enough resistance that the flow of electrons generated heat. As noted above.

So approximately how many ohms of resistance? Or how many amps was the circuit drawing? Well, given that the resistance of the wire was less than an ohm, we can do some rough back of the envelope calculations. According to Ohms law, Voltage is the product of resistance and amperage. (Product means you multiply the other two elements.) In this case I happen to know that the voltage of the battery is 12, because that’s the variety of battery I was using.

So to get amperage, or resistance, I need to take what I ‘know’ and divide 12 by that to get the other. Since resistance can’t therefore be zero, or we would have a divide by zero problem, let’s use some sample loads and see what happens. Let’s say we have a 1 amp fuse in the circuit, and we turn a variable resistor until the 1 amp fuse blows. What is the resistance on the variable resistor? Presuming that the actual load that the fuse blows at is 1 amp, to determine the resistance, we divide the voltage, 12 by the amperage, 1 and we end up with a resistance of 12 ohms. If we get a 12 amp fuse, and adjust the resistor until it blows the fuse again, what do we get? Well, 12 volts divided by 12 amps, gives us 1 ohm. If you cause a 60 amp fuse to blow, the resistance has to be about 0.2 ohms.

If you want, you can use the power law now to determine how many watts are being generated. Power in Watts is equivalent to voltage times amperage. So the 60 amp draw on a 12 volt battery gives you a power draw of 720 watt load. Considering that a light bulb that draws 200 watts is hot enough to melt and ignite nylon that is not in contact with the light bulb, that’s theoretically close enough to what I saw for the purpose of this blog. If you want to try the experiment, might I suggest doing so at a good electronics and electrical bench, on isolated circuits. So let’s say that 2 feet of this wire adds approximately .2 ohms of resistance to the load.

Be careful doing this stuff. I actually had fomal training in soldering, and electronics. If you’ve followed the entire blog to this point, you’re well on your way to being a geek. You will probably do the same thing that I just demonstrated that someone with formal training in this stuff, should have known not to do. I had the fortune of doing it with something that theoretically should not cause a problem. However 60 amps is nothing to play around with. For that matter it takes less than .2 amps to stop your heart. I would certainly much rather not have your doing something like that on my conscience. So let your Power Shorts be the ones that leave you feeling you can run 10 miles without breaking a sweat. Not leaving you concerned about the safety of your home.

And I’ve determined at least part of what’s wrong with my APRS stuff in my car.

No, I won’t go into what APRS is, beyond saying it’s part of the amateur radio hobby. If you have found my blog, and you have questions, there are loads of resources that will tell you more than I am about to say. So go search and find. As some might say, the truth is out there.

In my car there’s a link from under my dash, to the trunk that provides a power conduit for my APRS tracker, gps and radio. A couple of months ago, the fuse blew. I replaced it, and it blew again. That can only mean a couple of things, neither of them really good.. Either something in my dash was blowing the fuse, or something in the  trunk, or on the way to the trunk. Sinc that was easier to ‘fix’, by clipping the lead to the trunk, I did that, replaced the fuse again, and happy dash. So something on the way to, or in the trunk is being a problem.

On rading how to get my position to show up for SkyWarn this week, and noticing the interest in possible watcher’s for this evening, I decided that today was the day to find and fix whatever is wrong with the APRS stuff in my trunk. And I may yet get something ‘working,’ though at the apparent expense of a radio that I wasn’t planning on replacing. Well, that’s why you make plans, so that life can alter them. Right?

Troubleshooting. Check the wire to the trunk. Not shorted between the leads. good conductivity end to end. Check.

APRS tracker? Check that’s working.

Spare battery from the trunk to power up the radio?  Well, not the best, but we’ve got something to work with. Check.

Plug the battery into the distribution system, Dead battery. Hmm. Ok, only thing I haven’t checked here separately was the radio. Pop the power cable for that off the distribution block. check draw across the leads, Short. Ok, that looks like where my problem is. What am I going to have to do to solve? Well, quick solution would be to hang the connector off a different radio, except that the connection for the APRS tracker to the radio was a custom job. I’ll just have to creat another custom I guess. So what radio? Well, the Quick and dirty solution is to use another radio already mounted in the trunk. It has the advantage of being right there. The disadvantage is that the wiring for the mike is diferent. And from a quick look at the drawings of the two connectors, while I could probably cobble together a quick sollution, that’s not the ‘right’ thing to do.

Why not? Well, that radio is in the trunk for a specific reason. That reason has nothingto do with APRS, and I don’t want to break things that way. So, using that radio is ‘out.’ Even if it is possible.

Long term I want a different radio in there any way, and now is the time to build that up. Of course now I have to dig up the specs for setting that radio up for APRS. That’s not particularly difficult, as I have already done some stuff like that, it’s just going to take a bit of soldering, and waiting until I have a connector of the appropriate type for that radio. There is one already here some place, and I’ll spend a bit of time looking yet tonight, but I suspect that I will have to wait till I can gt to the hardware store tomorrow for the final solution. We’ll see.

More to follow.

This past Sunday I helped with the operations of the Iron Man Bike Ride in Lakevill, MN. Things didn’t go quite as planned. It wasn’t a complete failure byb any means, but it was obvious from early in the day that the weather could have been a lot more cooperative And then some.

As for myself, I knew I wouldn’t be in quite as early as I would like to have been. My work schedule is such that Saturday night I got to work at 7:00 PM to work through till 7:00 am Sunday morning. If this were any other company, I would have asked for and gotten a vacation day, but someone decided that my employer should run the department I’m a part of at the bare minimum, and if someone want’s a weekend off they can just trade with someone else for it. Well, considering what I do at the moment, that would be a bit rough, as the people I might trade withare not as ready or interested in trading as we would like. So it didn’t happen. I hear some good things are in the works related to that for the future, but I’ll wait and see on those changes.

In any case, as I was walking from my car to work Saturday night I rememberd that I had not put my HT on the charger before I left for work. While the battery was not dead by any means, it was far from being as fully charged as I would have liked. Where I was going Sunday is notorious for having bad radio coverage. They added a new repeater this year, which provided somewhat better coverage, but it ws still far from perfect.

In fact I ended up setting up a radio in my car as a cross-band repeater. I need to add a small box to my trunk now to add in an ider for when I do that. As it was, I picked the same repeater, and a non-local repeater pair on a different band, and set the radio in the car on the second band to reverse the rx/tx pair on that band so that I didn’t need to do anything ’strange’ on my HT. With the exception of when another radio was in the area using the same repeaer, I pretty much had no problems at all on the net. I’ve heard a few people crossbanding, and all you end up with is the low frequencies, or something like that. In my case I was very happy with the results, and heard no complaints on my transmitions.

One of the things that we do at the rest stop is take down the rider numbers for any rider who drops out of the event. While there are riders who treat the event as a race, you’ll not that this is not a triathalon, and ‘race’ is not in the name of the event. The vast majority of the riders are in it simply to demonstrate to themselves that they can. And when it comes down to it, a surprising number of riders can ride 100 miles. (162 km for the rest of the world.)

The stop I was supporting is at the 70 mile mark for the 100 mile route. as a quick estimate, I would say that between 200 and 300 riders passed through the station and about 40 riders dropped out there. The number of people who dropped out is easier to estimate, simply because we had to report the rider number for each rider who dropped out. That number goes back to our network control operator, who passes the number on to the ride officials who can use that number to let friends and family members of the rider know where the rider is if they drop out. This also helps to prevent any uniquely identifiable information about the rider becoming known by people not involved in the ride. This is done for most races and events where Amature Radio operators are involved.

One problem that occasionally comes up is where one person reports a number, and the next person in the chain notes that that number isn’t in their list of numbers to report. So one or the other person has invalid information. I’m not really sure what can be done about that, but one of the things that I would like to see is an improvement in the reporting process. Riders should be able to present their rider number in a way that is pretty much self confirming. We’re getting close. Bar codes migh do it, or some form of RFID as runners use in marathons. However even those present problems with disapearing and the like. So we do the best that we can.

And we are looking at making improvements. A few years back APRS got to a point where it is inexpensive enough that almost any ham (amateur operator) can add the equipment to their car that allows them to show exactly where they are. Likewise the hardware is portable enough that you can set up a vehicle temporarily so that it can be tracked at any time.

So for events like the Iron Man Bike ride, it makes sense to add a tracker to support vehicles.

One of the things that can be done with the same service however is to be able to send other messages. Location information is simply numbers. Usually it is the latitude and longitude with an accuracy down to about 20 feet. There is no reaso to restrict the content of a transmission to location information though, another option would be to send the rider numbers via APRS.

One of the reasons that we were so busy with reporting rider numbers this year was the weather. At least one rider declared that he could handle the cold, and he could handle the rain, but the combination was just too much. We badly needed the rain, and I agree that if the temperature had been similar to that of the previous week, it would have been a very different situation.

For some 4 hours (and then a bit) I helped provide information to riders and get help for riders as well. I finally was able to get to sleep last night a bit after 9 pm. All in all, I think it was a good day.

I have posted photos from both Field Day 2008, and CONvergence 2008. I did not post all o fmy CONvergence photos. If you are aware that I took your picture, and want to see it posted, Please let me know. I also took down a few photos that just didn’t turn out well.

For both, I have limited the posted image size to 1500 pixels in the larger dimension. If you are looking for a higher quality image, I do shoot 6 m raw in pentax format, and can provide either full sized jpeg images, or the raw image if you are interested in manipulating that for a different effect.

My Picasaweb album is http://picasaweb.google.com/rusty0101 and these are the latest two albums in the gallary. Comments here, or in the album are acceptable. If you are in a specific image, and do not want it on the album, I can take it down, please let me know.

Thanks everyone