Posts Tagged ‘polar coordinates’
Handiham World for 30 May 2012
Welcome to Handiham World.
You can do it!
Listen to this podcast in its entirety here: http://handiham.org/audio/handiham053012.mp3
Today, just as we did last week, we are going to begin with Troubleshooting 101 as part of our initiative to help new ham radio operators (and even some of us older ones) learn how to do some basic troubleshooting for ourselves. Yes, it can be tempting to ask someone else to do things for us. This can become a bad habit when it keeps us from learning new things, especially things that we could – with a bit of practice – learn to do for ourselves. Knowing these basic things can serve us well in the future when no help is available.
Let’s get to today’s troubleshooting question:
Question: I carry my HT everywhere, and recently I was outdoors when it started to rain. Luckily I was close to a picnic shelter and was able to stay dry until the rain passed. It did get me thinking about what I would do if my radio did get wet though. Any ideas?
It is summertime, and we do want to be outdoors, and naturally we want to take ham radio along for the walk! Part of always carrying a radio is the possibility that you – and the radio – will get wet. But there is wet and then there is really soaked. The two are pretty different, but you are probably going to want to act quickly in either case to protect the radio.
Recently I read a story in WIRED about how some really high percentage of cell phone users drop their phones in the toilet. I think it was something like 25%! Unless you have a waterproof radio, you are probably not going to be able to fish it out of the bowl in time to avoid damage.
Let’s assume you have a typical HT that is not marketed as waterproof, submersible, or even water-resistant. It can likely survive a bit of surface moisture, such as getting caught in a rainstorm, as long as you act quickly to get it out of the direct rainfall, power it off, and dry the outside as quickly as possible. It might also be a good idea to remove the battery. If the radio falls into the water, it is a different ballgame. As soon as the radio begins to sink, water pressure increases and forces moisture into the radio’s case in a way that does not happen in a simple rainstorm. That means that you have to act very quickly to get the radio out of the water and remove the battery. The next step is to dry the outside of the radio as quickly as possible, then (with the battery still removed), place the radio and battery pack in a dry container with a desiccant, sealing the container so that the moisture is drawn out of the radio by the desiccant. Are you wondering what a desiccant is? I am sure you have run across those little packets of silica gel that are sometimes packed with electronic devices. They remove humidity that might damage the electronics. If you don’t have silica gel packets handy (most of us just throw them away because they have a finite life anyway), you can put the radio in a container with uncooked rice overnight. The rice will help to draw moisture out of the electronics. When you dig the HT out of the rice in the morning, put it on a nice, dry paper towel. Is there any sign of moisture still on the towel? If so, you might need to repeat the rice treatment. In any case, you will not be powering up the radio for days – that means keeping the battery out. You want to make sure that the radio is completely dry before putting the battery back in. If you can perform the drying out procedures in an environment with already low humidity, that is best. An air-conditioned, dehumidified house trumps a humid garage workbench. I would avoid using a hair drier to try to heat the radio. You do not want to add heat that can speed up chemical reactions or damage the electronics or even melt the case. I would not want to try the radio for at least a week so that I was darned sure all the water was out.
Let’s consider the best plan of all: prevention. It is much better not to have to dry out a wet radio, so we want to follow some basic procedures to keep our electronics dry, rain or shine. If you take your HT everywhere, always keep a small plastic bag in your pocket. The plastic bag can be used to stow your electronics should you get caught in a downpour. Since I have my little doggie Jasper with me when I am out walking, a dog waste bag does the job of radio protector in an emergency. These bags come in little rolls and are available anywhere pet supplies are sold, or you can just stuff a zip-style plastic food bag into a pocket. If you are boating or in a wet environment, you can just store the HT in a plastic bag when it is not in use.
You should also plan ahead, developing good habits when around water. Keep your HT in a case that will keep it from falling out. If you keep it in a pocket, be sure it is a pocket that is deep enough to keep it from working its way out when you sit down. One danger of using pockets instead of a belt clip and case is that you can forget your cell phone or HT in that pocket and run it through the washing machine. Don’t laugh – it happens! If you do use pants pockets for your radio and phone, get in the habit of quickly patting each pocket when changing clothes so that you will feel the HT or phone and remember to remove it. At Dayton earlier this month I was using the restroom in Hara Arena and there was some guy sitting in one of the stalls having a phone conversation on his cell phone. Not only is this kind of clueless socially, it is also the reason cell phones go for a swim in the toilet. Never use your HT or phone in the bathroom, because the bathroom has more water hazards than the golf course after a thunderstorm. Similarly, it is best to keep the HT somewhere away from the kitchen counter, another place where spills happen and are even expected.
Finally, there is the drenching in something other than plain water. I’m afraid there is not much you can do about a radio that takes a salt water swim or a hot coffee bath. If disaster happens, the procedure is the same: remove from the liquid as quickly as possible while watching out for your own safety, take out the battery, and dry out as quickly as possible with absorbent towels on the outside and the dry rice treatment. Hopefully salt has not penetrated the radio, but if it has there may not be much you can do. The salt deposits left behind can become conductive in high humidity conditions, causing shorts. I am not a fan of disassembling electronics to give them a cleaning with distilled water or solvent, as that is a job for trained bench technicians. Considering the cost of bench time, it is likely that a salt water swim will mean it is cheaper to buy a new radio. Similarly, a drenching with sugar-infused soft drinks can leave a real mess of residue behind. If this mess gets onto circuit boards it can also absorb moisture and cause shorts, even after the drying out process. It will also gum up push buttons on the HT’s keypad. The bottom line: Don’t have your HT anywhere near such possible spills in the first place. If one does occur, follow the emergency procedure:
- Remove the radio as quickly as possible from the spill.
- Remove the battery.
- Blot the surface with a fresh paper towel or other absorbent cloth.
- Dry in a container of uncooked rice.
While your gooped-up radio is drying out, you can start shopping for a new one. It never hurts to be prepared for the possibility that your old HT is down for the count.
Email me at [email protected] with your questions & comments.
Patrick Tice, WA0TDA
A dip in the pool
It’s time to test our knowledge by taking a dip in the pool – the question pool, that is!
Today we are busting our brains with a question from the Extra Class pool:
E5C16 asks: “In polar coordinates, what is the impedance of a circuit that has an admittance of 7.09 millisiemens at 45 degrees?”
Possible answers are:
A. 5.03 E-06 ohms at an angle of 45 degrees
B. 141 ohms at an angle of -45 degrees
C. 19,900 ohms at an angle of -45 degrees
D. 141 ohms at an angle of 45 degrees
Now, you may be asking yourself, “Why should I worry about this particular question when the current question pool is only good until the end of June?”
The answer about why you should understand this question (and more importantly the answer) is that it is exactly the same question, including the question number, that appears in both the current pool AND that brand-new pool!
We can’t go into super-detail about how to work these out, but you can find the process easily enough in the ARRL or Gordo books or in the Handiham audio lecture series.
Briefly, here is the skinny:o Ohms at such and such an angle. If you have forgotten what admittance is, it is simply the reciprocal of impedance. If you don’t know what impedance is, you need to go back and hit the books. Anyway, here is how such a conversion works:
- The absolute value of Z (the impedance) equals 1 over .00709 (which is the 7.09 milliseimens converted into seimens by moving the decimal point three places to the left. The “1 over” part comes from the fact that we are working with a reciprocal, which means we flip the numerator and the denominator to get “1 over some other number”, which is a reciprocal.
- With me so far?
- Good; so now you just divide 1 by .00709 using your calculator. You get 141.0437 etc., etc., so you round that to 141 ohms.
- You look at the question and the possible answers again. Hey, answers B & D each have 141 in them! Now you have a 50-50 chance of guessing which one is right!
- But the question specifies “…at 45 degrees”, and we have done nothing with that number yet. We need to consider that phase angle “theta” equals zero degrees minus the 45 degrees we have been given. So zero minus 45 equals minus 45 degrees.
- Now we look at our two possible choices. Answer B is the one that says 141 ohms at an angle of -45 degrees, while answer D says 141 ohms at an angle of 45 degrees. Because you have cleverly subtracted 45 from zero to get -45 degrees, you pick answer B, 141 ohms at an angle of -45 degrees.
Here is a little memory trick: Always remember that admittance questions involve a reciprocal, you you are going to be dividing some small number into one. It will be expressed as one over the other number. You need to remember to convert to seimens by moving the decimal point. Then if the angle you are given is positive, such as 45 degrees, the final answer will likely be negative, such as -45 in this case. The reason for all this angle stuff is that we are not dealing with direct current. We are dealing with alternating current, which is always changing, so we have to pick a point in its alternating cycle where our specifications can be listed numerically.