Wednesday, April 1, 2015

Hams to lose frequency allocations above 2 Meters

The FCC and Homeland Security have been conducting a systematic and on-going survey of amateur radio frequency use in response to requests from communications industry lobbyists.  The survey has consisted in frequency monitoring and statistical analysis of usage rates and has covered the the past 7 years.

Communications industry lobbyists have complained that amateur frequency allocations in the UHF and higher have caused security concerns related to RF infrastructure and had made the claim that radio amateurs were not making appropriate use of the spectrum.

A new classified report confirms accounts of malicious and childish behavior, not only on the frequencies in the UHF and above, but also on the VHF, HF and LF spectrum allocations.  Recordings of amateurs using profanity, rebroadcasting copyrighted music, engaging in hate speech, etc., reinforced those claims.

A spokesperson for the FCC said, "The very valuable RF spectrum allocated to radio amateurs is being either misused or not used at all."  Amateur radio repeaters, which are used to extend the range of low powered radios, are often idle for days at a time, and in instances when they are in use are mostly used as a chat room for commuters.

The FCC had pointed out the role amateurs play in emergency communications, however the director of Homeland Security made assurances that local, state and federal emergency management agencies, were more than up to the task and not in need of assistance from civilian amateurs.  One official told congress, "let the professionals do their jobs, that's what we pay them for and it's also the reason we give them all that money to buy equipment.  In these modern times of wi-fi, smartphones, Twitter and Facebook there's more than enough ways for people to communicate."

The FCC and Homeland Security have identified the radio frequencies from 148 MHz and up as those the amateurs will no longer have access to beginning within the week.  "The amateurs will need to immediately cease operation on those frequencies and be subject to arrest, fines and imprisonment.
Amateurs will be given until April 30th to remove all equipment capable of transmitting on frequencies in excess of 148 MHz including walkie-talkies, mobile radios, base stations and all associated repeater systems.

The spectrum above 148 MHz will be sold at auction in the coming months and is estimated to be worth over a billion dollars in revenue to the government.

Sunday, January 25, 2015

Using Algebra to Derive New Formulas

Using Algebra to Derive New Formulas and Solve others

To follow this you are going to need to know some algebra.  If you need a refresher, I recommend  I am first going to show how to use algebra to find the temperature at which both a Fahrenheit and Celsius thermometer would be showing the same number.  That is, what temperature is the same in degrees Fahrenheit and Celsius.  You can think of this like using 2 different rulers to measure your height.  One in feet and one in meters.  Your height is the same no matter which you use, just the number will be different, i.e. 6 feet or 182.88 centimeters.

First we start with the conversion formulas.  To convert from degrees Celsius (C) to Fahrenheit (F), we multiply the temperature by 1.8 (also regularly stated as 9/5) then add 32.  So 20 degrees C = 68 degrees F.

Converting from F to C the formula is degrees F minus 32 then that result divided by 1.8:

To calculate the temperature where these are equal to each other, we set the 2 formulas equal to each other, use just one variable for temperature, e.g. “t” and solve for that variable:

The idea is to get the t all by itself and we do this by performing the inverse operations on various parts of the equation, remembering to do the same operation on BOTH sides!  First we’ll get rid of the 1.8 on the bottom of the right side by multiplying both sides by 1.8:

 The 1.8’s on the right side cancel leaving just the t - 32 and we multiply the 2 terms inside the parenthesis on the left side each by 1.8, giving us:

Now subtract t from both sides:

Doing the math this leaves us with:

Next we subtract 57.6 from both sides:

This gives us:

Next we divide both sides by 2.24 to get the t by itself (this is the same as multiplying by 1/2.24):

The result of this is:

You can check this by inserting minus 40 into the 2 equations above and you’ll see the conversions both come out to minus 40.

Now as they say, I showed you that so I can show you this, specifically, how to derive a new formula.

In the license books we’ve seen examples, usually poorly explained, where a new formula is derived by substituting values.  In the case of the power formula, P = E I, we are told to substitute the ohms law equivalents of E and I to get 2 new formulas.

The example I’m going to show you is from the ARRL Extra Class license manual which is only shown worked through superficially.  The assumption being that either the student is well versed in algebra, or will go to one of the many resources available online or elsewhere to bone up on it.

However, I have found that many who come to ham radio, especially those who come to it after a prolonged time away from high school or college, may have forgotten most, if not all that they’ve learned.  So I’d like to build on the previous example and work through the derivation of the formula for calculating resonant frequency of LC circuits.

The definition of LC circuit resonance is given as the frequency where both inductive reactance (XL) and capacitive reactance (XC) are equal.  Each reactance being 180 degrees out of phase with the other means that their reactances will cancel out leaving only a purely resistive load.  Let’s first look at the formulas for each, then we’ll set them equal to each other and solve for frequency to get the resonant frequency formula.

Setting them equal:

We want to find “f” so we’ll multiply both sides by f to remove it from the bottom of the right side.

Combining the f’s on the left and cancelling on the right leaves us with:

Next I’m going to get rid of the 2πL on the left by dividing both sides by 2πL (this is the same as multiplying by the reciprocal 1/L)

When we do the math we cancel the 2πL on the left side and multiply the top and bottom on the right, combining the like terms to get:

We now take the square root of both sides…
 This gives us:

…and that’s the formula for resonant frequency!  Not too bad, right?