KB6NU's Ham Radio Blog

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2016 Extra Class Study Guide: E9H - Receiving antennas

Posted: 06 Mar 2016 07:52 AM PST
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E9H Receiving Antennas: radio direction finding antennas; Beverage
Antennas; specialized receiving antennas; longwire receiving antennas

Many antennas, such as the Beverage antenna, are designed to be receiving
antennas only. When constructing a Beverage antenna, one of the factors
that should be included in the design is that it should be one or more
wavelengths long to achieve good performance at the desired frequency.
(E9H01)

While directionality is a desirable feature for a receiving antenna, gain
often is not, especially on the low bands. The reason for this is that
atmospheric noise is so high that gain over a dipole is not important for
low band (160 meter and 80 meter) receiving antennas. (E9H02)

Direction finding antennas

Direction finding is an activity that’s both fun and useful. One of the
ways that it’s useful is to hunt down noise sources. It can also be used to
hunt down stations causing harmful interference.

A variety of directional antennas are used in direction finding, including
the shielded loop antenna. A receiving loop antenna consists of one or more
turns of wire wound in the shape of a large open coil. (E9H09) The output
voltage of a multi-turn receiving loop antenna be increased by increasing
either the number of wire turns in the loop or the area of the loop
structure or both. (E9H10)

An advantage of using a shielded loop antenna for direction finding is that
it is electro-statically balanced against ground, giving better nulls.
(E9H04) The main drawback of a wire-loop antenna for direction finding is
that it has a bidirectional pattern. (E9H05)

Sometimes a sense antenna is used with a direction finding antenna. The
function of a sense antenna is that it modifies the pattern of a DF antenna
array to provide a null in one direction. (E9H08)

Another way to obtain a null in only one direction is to build an antenna
array with a cardioid pattern. One way to do this is to build an array with
two dipoles fed in quadrature. A very sharp single null is a characteristic
of a cardioid-pattern antenna is useful for direction finding. (E9H11)

Another accessory that is often used in direction finding is an attenuator.
It is advisable to use an RF attenuator on a receiver being used for
direction finding because it prevents receiver overload which could make it
difficult to determine peaks or nulls. (E9H07)

If more than one operator can be mobilized for a direction-finding
operation, they could use the triangulation method for finding a noise
source or the source of a radio signal. When using the triangulation method
of direction finding, antenna headings from several different receiving
locations are used to locate the signal source. (E9H06)

The post 2016 Extra Class Study Guide: E9H Receiving antennas appeared
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2016 Extra Class Study Guide: E9G - The Smith Chart

Posted: 05 Mar 2016 04:50 PM PST
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A Smith chart is shown in Figure E9-3 above. (E9G05) It is a chart designed
to solve transmission line problems graphically. While a complete
discussion of the theory behind the Smith Chart is outside the scope of
this study guide, a good discussion of the Smith Chart can be found on the
ARRL website
(http://www.arrl.org/files/file/Anten...an%202012.pdf).

The coordinate system is used in a Smith chart is comprised of resistance
circles and reactance arcs. (E9G02) Resistance and reactance are the two
families of circles and arcs that make up a Smith chart. (E9G04)

The resistance axis is the only straight line shown on the Smith chart
shown in Figure E9-3. (E9G07) Points on this axis are pure resistances. In
practice, you want to position the chart so that 0 ohms is at the far left,
while infinity is at the far right.

The arcs on a Smith chart represent points with constant reactance. (E9G10)
On the Smith chart, shown in Figure E9-3, the name for the large outer
circle on which the reactance arcs terminate is the reactance axis. (E9G06)
Points on the reactance axis have a resistance of 0 ohms. When oriented so
that the resistance axis is horizontal, positive reactances are plotted
above the resistance axis and negative reactances below.

The process of normalization with regard to a Smith chart refers to
reassigning impedance values with regard to the prime center. (E9G08) The
prime center is the point marked 1.0 on the resistance axis. If you’re
working with a 50 ohm transmission line, you’d normally divide the
impedances by 50, meaning that a 50 ohm resistance would then be plotted on
the resistance axis at the point marked 1.0. A reactance of 50 + j100 would
be plotted on the resistance circle going through the prime center where it
intersects the reactance arc marked 2.0.

Impedance along transmission lines can be calculated using a Smith chart.
(E9G01) Impedance and SWR values in transmission lines are often determined
using a Smith chart. (E9G03) Standing-wave ratio circles are often added to
a Smith chart during the process of solving problems. (E9G09)

The wavelength scales on a Smith chart are calibrated in fractions of
transmission line electrical wavelength. (E9G11) These are useful when
trying to determine how long transmission lines must be when used to match
a load to a transmitter.

The post 2016 Extra Class Study Guide: E9G The Smith Chart appeared first
on KB6NUs Ham Radio Blog.


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The ARRL really needs to reach out more effectively

Posted: 05 Mar 2016 11:44 AM PST
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Ive criticized the ARRL in the past over their membership recruiting
efforts. I dont believe that theyre doing enough to attract new members and
retain existing members, and a few recent incidents have only solidified my
opinion.

A couple of months ago, one of my Elmerees was here at my house, and at one
point we started talking about the ARRL. He wasnt critical, per se, but
rather mostly indifferent about the ARRL. He just didnt see the value of
the ARRL.

A couple of weeks ago, I received an e-mail from a ham radio podcaster. He
forwarded to me a link to an online discussionÂ*thats highly critical of the
ARRL, especially the rate hike. He writes, Im not a member and prolly (sic)
wont ever join again after reading this. Im not looking to go to war with
the ARRL because I dont care enough about it right now in my life, but I
was curious once I read this.

And, then, theres this post on reddit. This poster complains about ARRL
recruitment techniques and the cost of membership. He writes, Has the ARRL
lost touch with reality? Are the ARRL lawyers really that expensive? (you
bet they are). While I appreciate everything they do, they need to wake up.

The latest was from a comment filed with the FCC on RM-11759. The commenter
says, The ARRL membership only accounts for a fraction of us armature (sic)
radio operators and doesn’t speak for the majority. Needless to say, he was
not in favor of the proposal.

I dont think that these are isolated cases. I think attitudes such as these
are common amongÂ*amateur radio operators, and if the ARRL doesnt take steps
to stem this tide, then the percentageÂ*of licensed hams that are ARRL
members is going to continue to decline. Perhaps more importantly, its
influence will decline.

Im happy to report that I did manage to convince my Elmeree to become an
ARRL member. Im not so sure about the podcaster. I sent him a long
response, noting some errors in the original post, but I havent heard back
from him.

I hope thatÂ*the ARRLs new CEO, NY2RF, will make membership recruitment and
involvementÂ*a priority. As Ive said before, more members means more money
for programs and lobbying and more volunteers willing to do more things. In
the end, that will make amateur radio stronger.

The post The ARRL really needs to reach out more effectively appeared first
on KB6NUs Ham Radio Blog.