Wednesday, October 28, 2009

The Basics for the New Ham, Bob, No. 75

Here are a few questions provided by Mike, KF7DTI for the newer ham...


What is “Legal” (1500 watts) vs. Proper ( 5 to 20 watts) and why…
 First of all, let's look at what the legal limit is: 1,500 watts PEP (Peak Envelope Power) this is defined as the average power provided to the transmission line over one cycle where the envelope is at it's peak.  The envelope is the carrier plus the modulation, so it is the average power of the signal at it's highest modulation.  This gives a good indication of the likelihood of the signal to interfere with neighboring frequencies.


So now we get to the real question, what is proper.  Well the regulations have something to say about that too.  We are required to use the lowest amount of power to accomplish the communications we are trying to do.  This is definitely a gray area and a guideline rather than a hard and fast rule.  Sometimes it can be obvious, you don't need 50 watts to talk on 2 meter simplex to your neighbor a few blocks away.  Sometimes it is not obvious at all, just how much power do you need to be heard by that rare DX station in a South Seas island that dozens of other hams are also trying to reach.  There are endless possibilities for arguments here but this is a sort of "good faith" rule.  You need to use your own best judgment to decide how much power is necessary.


The other reason to use less power is personal safety.  I won't go into the specifics but there is good reason that your handheld doesn't put out more than about 5 watts.  If you want to use your mobile rig as a portable, as many of us in emergency communications do, it is important to get the antenna away from your body and anyone elses.  Just how far is another judgment call but it helps if you also have it up high so that when it is radiating primarily in the horizontal direction, it will be above your and everyone else's heads.



Proper handling of my unit .. will my Mobile work OK in the Freezing snow?..  110 degree Desert Sun?... pouring Rain?
Your mobile rig is designed to stay in a vehicle and to operate in one too.  There are a handful of new weather-proof and even water-proof rigs on the market but leaving those out, you should use your rig where it will be kept dry and reasonably clean.  As for cold and heat, you should check your owner's manual to be sure but generally you can do very well in the cold.  When it gets hot you run the risk of overheating your rig when you run full power.  Once again, this is a gray area.  You can run at a pretty high ambient temperature as long as you use low power.  The more power you use, the lower the ambient temperature has to be.


What happens when my batteries get low?.. How can I tell?
I assume you mean your portable here.  You should here a beep to tell you.  HT's are notorious for beeping about 5 seconds before they shutdown.  None of the HT's that I'm aware of have battery charge indicators.  I may be wrong about this and if anyone knows of ones that do please speak up.

Why is my brand new Mobile that I just put in my  old TRUCK so staticy?
There are a couple of possible reasons.  The most likely is the old truck itself.  It is either emitting radiation from sparking or other electronics or it is causing fluctuations in the voltage where you are hooking up your radio.  For this reason it is usually suggested to connect your radio directly to the battery, properly fused of course.  Then all you have to worry about is the radiation caused by your truck.  The only way I know to diagnose and fix it is to try putting some filters on the wires and see what happens.  But this is a well known problem and there is a lot out there already to help diagnose it.  One reason it happens is that mobile and HT rigs usually don't have the good filtering that base stations do.  You can pay a lot for a Motorola or other rig designed for professional use in high radiation environments and do a lot better. 



I can use my old CB Radio Antenna as my Mobile antenna right?
I wouldn't try it.  Antennas are a huge subject that has been covered in various ERN's.  You can check the blog for more info.  In general, you can probably modify an old CB antenna if you know what you are doing to make it work for amateur radio, but you are almost certainly better buying an antenna build to do the job.  Or you can make your own from scratch.  Most people don't make their mobile anteannas though, that is better suited for base operations.


What is SWR and why do I care? (that is a good subject)
 SWR has been covered a few times and Lee has an exhaustive set of lectures on fundamental electronics leading up to impedance.  In short, SWR, the Standing Wave Ratio, is a measure of how much of an electronic signal that you are transmitting, is reflected at a junction.  The cause of the reflection is an impedance mismatch at the junction.  For example, if you connected your transceiver that has an impediance at it's output of 50 ohms to 75 ohm cable, you will get an impedance mismatch that will cause a high SWR.  Since most of us know to use 50 ohm cable the mismatch almost always comes at the connection to the antenna.  The impedance at the connection to an antenna is a very complex subject and can depend on the antenna height above ground and other factors.  For VHF/UHF it is simplified by the fact that the antenna is high above the ground compared to the wavelength so there is little variation.  That's why you can buy an antenna with a 50 ohm connector and be pretty confident that it actually is 50 ohms.


What does QSL, QTH, QRV, 73… etc. mean?..   When is OK to use “Shorthand” like that?
QSL, QTH, QRV and other three letter combinations starting with Q are known as Q signals.  They come to us from the days of CW where it was worthwhile to have a shortcut for some commonly used phrases.  Q was chosen since it is almost always followed by U so that by creating these combinations, not using U you could be assured that it was not a word.  If the Q signal is followed by a question mark it means that it is a question, if no question mark then it is a positive statement.

For example, probably the most common one heard is QSL.  You will hear it in place of Roger, Acknowledged, etc.  It means, "I acknowledge receipt" or with a question mark, "Do you acknowledge receipt."  This is also the reason for QSL cards, which are an acknowledgment of receipt of a contact form another station.  These are used to prove that you made a contact with that rare DX station.  By the way DX is just shorthand for distance and means a long distance, usually international.

73 goes back a long way as well and just means, "Best Wishes"

There are no hard and fast rules about using these.  The most important thing to keep in mind is that you want to make yourself clearly understood.  If the person or people you are communicating with understand the Q signals it is fine to use them.
 



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