KB6NU's Ham Radio Blog

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Operating Notes: MNQP, 7P8C, new hams!

Posted: 10 Feb 2016 06:51 PM PST
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MNQP. Saturday, I defended my Minnesota QSO Party title. Last year, I
managed 21 CW QSOs, 13 phone QSOs, and 29 multipliers, forÂ*a total score of
1,972. This year, I managed 54 total QSOs (52 CW, 2 SSB) in 31 counties for
a score of 3,348. Im hoping thats good enough to get the rice!

7P8C. I managed to work the guys in Lesotho tonight on 30m. I called for 15
minutes before I got them. Im normally only good for about ten minutes in a
pileup, but tonights pileup wasnt quite so bad recent ones, so I stuck it
out.

New hams!Â*Today, the callsigns for most of those in my January 31, 2016
class were issued. I sent out an e-mail to all those whose licenses were
issued and invited them to call me on the W8UM repeater if they already had
a radio. That did prompt two of the, KE8DCQ and KE8DDU, to call me, and it
gave me great joy to provide them with their first QSO. Ill be sending them
their first QSL cards shortly.

The post Operating Notes: MNQP, 7P8C, new hams! appeared first on KB6NUs
Ham Radio Blog.


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2016 Extra Class study guide: E7G - Active filters and op amps

Posted: 10 Feb 2016 12:40 PM PST
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Five questions were eliminated from this section, making it a little
easier.Dan
E7G Active filters and op-amps: active audio filters; characteristics;
basic circuit design; operational amplifiers

Operational amplifiers, or op-amps for short, are very versatile
components. They can be used to build amplifiers, filter circuits, and many
other types of circuits that do analog signal processing.

An integrated circuit operational amplifier is a high-gain, direct-coupled
differential amplifier with very high input and very low output impedance.
(E7G12) The typical input impedance of an integrated circuit op-amp is very
high. (E7G03) The typical output impedance of an integrated circuit op-amp
is very low. (E7G01)

The gain of an ideal operational amplifier does not vary with frequency.
(E7G08) Most op amps aren’t ideal, though. While some modern op amps can be
used at high frequencies, many of the older ones can’t be used at
frequencies above a couple of MHz.

Ideally, with no input signal, there should be no voltage difference
between the two input terminals, and the output voltage should also be
zero. Since no electronic component is ideal, there will be a voltage
between these two terminals. We call this the input offset voltage. Put
another way, the op-amp input-offset voltage is the differential input
voltage needed to bring the open-loop output voltage to zero. (E7G04)

Because they are active components—that is to say that they amplify—filters
made with op amps are called active filters. The most appropriate use of an
op-amp active filter is as an audio filter in a receiver. (E7G06). The
values of capacitors and resistors external to the op-amp primarily
determine the gain and frequency characteristics of an op-amp RC active
filter.

Ringing is one undesirable characteristic of an op-amp filter. One effect
of ringing in a filter is that undesired oscillations to be added to the
desired signal. (E7G02) One way to prevent unwanted ringing and audio
instability in a multi-section op-amp RC audio filter circuit is to
restrict both gain and Q. (E7G05)

Calculating the gain of an op amp circuit is relatively straightforward.
The gain is simply RF/Rin. In figure E7-4 below, Rin = R1. Therefore, the
magnitude of voltage gain that can be expected from the circuit in Figure
E7-4 when R1 is 10 ohms and RF is 470 ohms is 470/10, or 47. (E7G07) The
absolute voltage gain that can be expected from the circuit in Figure E7-4
when R1 is 1800 ohms and RF is 68 kilohms is 68,000/1,800, or 38. (E7G10)
The absolute voltage gain that can be expected from the circuit in Figure
E7-4 when R1 is 3300 ohms and RF is 47 kilohms is 47,000/3,300, or 14.
(E7G11)



-2.3 volts will be the output voltage of the circuit shown in Figure E7-4
if R1 is 1000 ohms, RF is 10,000 ohms, and 0.23 volts dc is applied to the
input. (E7G09) The gain of the circuit will be 10,000/1,000 or 10, and the
output voltage will be equal to the input voltage times the gain. 0.23 V x
10 = 2.3 V, but since the input voltage is being applied to the negative
input, the output voltage will be negative.

The post 2016 Extra Class study guide: E7G Active filters and op amps
appeared first on KB6NUs Ham Radio Blog.