KB6NU's Ham Radio Blog

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Social Media meets ham radio

Posted: 14 Jan 2016 12:22 PM PST
http://feedproxy.google.com/~r/kb6nu...m_medium=email


Im not sure theres a real point to this post, but Im going to blather on a
bit about social media and amateur radio.

Twitter.Â*I like Twitter. I have more than 3,000 followers on Twitter, and
its not only helped me sell more books, Ive found out about a lot of great
projects, and Ive met and corresponded with a lot of great hams there. Its
a lot of fun.
Facebook. I have a Facebook account and I even have a page for my study
guides. I dont like using Facebook, though, and avoid it when I can.
Reddit. Reddit hosts a very active amateur radio forum. What I like about
Reddit is that these guys, unlike say the forums on eHam.Net or QRZ.Com are
really interested in doing stuff, not just complaining or arguing. A lot of
the hams on Reddit, and its associated IRC channel (talk about retro!),
#redditnet, have used my study guides, and apparently, Im quite popular
there.
Blab. Blab is an interesting concept. Its kind of informal streaming video.
You get on and just start blabbing. I suggested having a regular Blab
session to talk aboutÂ*ham radio topics. It would be sort of like an
interactive podcast. I didnt get a lot of positive feedback, though, so Ive
kind of dropped the idea. Perhaps what I should do is just do it. Im not
sure its worth the effort, though.


The biggest problem, of course, is that participating on these social
networks takes a lot of time, time that could be used for building stuff or
getting on the air. Even so, I would say that, overall, using them has
certainly increased my enjoyment of amateur radio and has connected me to
people that I probably would not have connected with otherwise.

What do you think? What social media accounts do you have? Which do you
prefer? What have they done for you?

The post Social Media meets ham radio appeared first on KB6NUs Ham Radio
Blog.


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2016 Extra Class study guide - E5C: Impedance plots and coordinate systems

Posted: 14 Jan 2016 10:31 AM PST
http://feedproxy.google.com/~r/kb6nu...m_medium=email


A lot of Â*questions have changed in this section. Theyve taken out all of
the questions requiring you to calculate impedances and phase angles,
although they have added questions about what these values mean. Overall,
there was a net loss of six questions in this sectionDan



Most often when we plot values on a graph, we use the rectangular, or
Cartesian, coordinate system. The two numbers that are used to define a
point on a graph using rectangular coordinates are the coordinate values
along the horizontal and vertical axes. (E5C11) In the graph above, point P
is at x,y.

Rectangular coordinates is the coordinate system often used to display the
resistive, inductive, and/or capacitive reactance components of an
impedance. (E5C13) In rectangular notation, –jX represents a capacitive
reactance. (E5C01) The impedance 50–j25 represents 50 ohms resistance in
series with 25 ohms capacitive reactance. (E5C06)

When using rectangular coordinates to graph the impedance of a circuit, the
horizontal axis represents the resistive component. (E5C09) When using
rectangular coordinates to graph the impedance of a circuit, the vertical
axis represents the reactive component. (E5C10)

To figure out the impedance of a circuit, you first plot the inductive
reactance on the positive y-axis and the capacitive reactance on the
negative y-axis. The net reactance, X, will be the sum of the two
reactances. After you’ve computed the net reactance, you plot the
resistance on the x-axis and compute the magnitude of the impedance, shown
by r in the graph above. If you consider that r is the third side of a
right triangle made up of the sides r, x, and y, r is equal to the square
root of x2 and y2.

If you plot the impedance of a circuit using the rectangular coordinate
system and find the impedance point falls on the right side of the graph on
the horizontal axis, you know that the circuit impedance is equivalent to a
pure resistance. (E5C12)

When thinking about how capacitive reactances, inductive reactances, and
resistance combine, it’s useful to think in terms of polar coordinates.
Polar coordinates is the coordinate system often used to display the phase
angle of a circuit containing resistance, inductive and/or capacitive
reactance. (E5C08) In a polar-coordinate system, each point on the graph
has two values, a magnitude (shown by r in the figure above) and an angle
(shown by θ in the figure above).

In polar coordinates, impedances are described by phase angle and
amplitude. (E5C02) These kinds of quantities are sometimes called vectors.
A vector is a quantity with both magnitude and an angular component. (E5C07)

In polar coordinates, a positive phase angle represents an inductive
reactance. (E5C03) In polar coordinates, a negative phase angle represents
a capacitive reactance. (E5C04) Phasor diagram is the name of the diagram
used to show the phase relationship between impedances and resistances at a
given frequency. (E5C05)





Now, let’s take a look at some actual circuits.

On Figure E5-2, the point that best represents the impedance of a series
circuit consisting of a 400 ohm resistor and a 38 picofarad capacitor at 14
MHz is Point 4. (E5C14) Right off the bat, we know that the only choices
are really Points 2, 4, and 6 because the resistance is 400 ohms. Next, we
calculate the capacitive reactance:

XC = 1/2πfC = 1/(2 × 3.14 × 14106 × 38×10-12) ≈ 300 ohms

Because the reactance is capacitive, it’s plotted as a negative value.

On Figure E5-2, the point that best represents the impedance of a series
circuit consisting of a 300 ohm resistor and an 18 microhenry inductor at
3.505 MHz is Point 3. (E5C15) The resistance is 300 ohms and the reactance
is:

XL = 2πfL = 2 × 3.14 × 3.505106 × 18×10-6) ≈ 400 ohms

And, since the reactance is inductive, it’s plotted as a postive value.

On Figure E5-2, the point that best represents the impedance of a series
circuit consisting of a 300 ohm resistor and a 19 picofarad capacitor at
21.200 MHz is Point 1. (E5C16) The resistance is 300 ohms, and the
reactance is:

XC = 1/2πfC = 1/(2 × 3.14 × 21.2106 × 19×10-12) ≈ 400 ohms

Because the reactance is capacitive, it’s plotted as a negative value.

On Figure E5-2, the point that best represents the impedance of a series
circuit consisting of a 300-ohm resistor, a 0.64-microhenry inductor and an
85-picofarad capacitor at 29.400 MHz is Point 8. (E5C17) This problem is a
little tougher because it has both capacitive and inductive reactance.

XC = 1/2πfC = 1/(2 × 3.14 × 29.4106 × 85×10-12) ≈ 63.7 ohms

XL = 2πfL = 2 × 3.14 × 29.4106 × 0.64×10-6) ≈ 118.2 ohms

X = XL XC = 118.2 63.7 = 55.5 ohms

Because the net reactance is inductive, it is plotted as a positive value,
and because the resistance is 300 ohms, the answer is Point 8.

The post 2016 Extra Class study guide E5C: Impedance plots and coordinate
systems appeared first on KB6NUs Ham Radio Blog.