KB6NU's Ham Radio Blog

///////////////////////////////////////////
2016 Extra Class study guide: E2E - HF operating methods

Posted: 22 Mar 2016 08:29 AM PDT
http://feedproxy.google.com/~r/kb6nu...m_medium=email

E2E Operating methods: operating HF digital modes

Perhaps the most popular digital mode these days is PSK31. PSK stands for
“phase shift keying.� One of its main advantages is that it had a very
narrow bandwidth—only 31 Hz. In fact, PSK31 is the digital communications
mode that has the narrowest bandwidth. (E2E10)

One of the ways is achieves this narrow bandwidth is that uses variable
length coding. That is to say, characters have different numbers of bits,
depending on how frequently they appear in normal text. PSK31 is an HF
digital mode that uses variable-length coding for bandwidth efficiency.
(E2E09)

Another type of modulation commonly used on the HF bands is frequency-shift
keying, or FSK. RTTY, for example uses FSK modulation. FSK is a type of
modulation that is common for data emissions below 30 MHz. (E2E01) One type
of FSK modulation is MFSK16. The typical bandwidth of a properly modulated
MFSK16 signal is 316 Hz. (E2E07)

Amateur transceivers use two different methods to modulate a signal using
FSK: direct FSK and audio FSK. The difference between direct FSK and audio
FSK is that direct FSK applies the data signal to the transmitter VFO.
(E2E11) When using audio FSK, audio, typically from a computer sound card,
is used to shift the frequency of the transmitted signal.

To tune an FSK signal, one often uses a crossed-ellipse display. You have
properly tuned a signal when one of the ellipses is as vertical as
possible, and the other is as horizontal as possible. When one of the
ellipses in an FSK crossed-ellipse display suddenly disappears, selective
fading has occurred. (E2E04)

PACTOR is one digital mode that uses FSK. It also uses the ARQ protocol to
detect errors. Because of this, PACTOR is an HF digital mode that can be
used to transfer binary files. (E2E08)

Another way to detect and correct errors in a data transmission is forward
error correction. The letters FEC mean Forward Error Correction when
talking about digital operation. (E2E02)

No matter what type of modulation you use, data transmission over an HF
radio link is very slow. 300 baud is the most common data rate used for HF
packet communications. (E2E06) In fact, due to bandwidth limitations, 300
baud is the maximum data rate.

Some HF digital modes operate automatically, that is to say the software
running these digital modes automatically initiate and maintain the
connection. One technique for doing this is called Automatic Link Enable
(ALE). Stations using the Automatic Link Enable (ALE) protocol use
automatic control. (E2E12)

Of course, as we all know, when using HF links, any number of things can go
wrong. All of these choices are correct when considering the possible
reasons that attempts to initiate contact with a digital station on a clear
frequency are unsuccessful: (E2E13)

Your transmit frequency is incorrect
The protocol version you are using is not the supported by the digital
station
Another station you are unable to hear is using the frequency


The post 2016 Extra Class study guide: E2E – HF operating methods appeared
first on KB6NUs Ham Radio Blog.


///////////////////////////////////////////
White paper describes active antennas

Posted: 21 Mar 2016 02:08 PM PDT
http://feedproxy.google.com/~r/kb6nu...m_medium=email


For some receiving applications, active antennas may be a good choice. You
can even buy them on Amazon (Sony AN-LP1, MFJ-1020C).Â*Many shortwave
listeners use active antennas they can use them over a wide frequency range
and are very small.
The R&S HE016 Active Antenna System is a combination of the Active Rod
Antenna R&S®HE010 and two crossed HF dipole antennas. The two horizontal
dipole antennas are combined via a 90° coupler to produce an
omnidirectional radiation pattern.

To learn more about active antennas, you can download a new Rohde&Schwarz
application note, Active Antennas for Radiomonitoring. This application
note:

Â*Describes howÂ*active antennas work.
Explains their characteristic parameters, including:

impedance
antenna factor
antenna noise
sensitivity
gain
non-linear distortion
dynamic range


Gives examples of how to use them.


The final section, for example, describes how to use themÂ*for HF reception.
It discusses how the ionosphere affects signal polarization, how to select
an appropriate antenna, and the effects of installation height.

The antennas described by this app note are really a step (or two) above
the kinds of active antennas that most SWLs and hams use, and the app note
includes more than youll probably want to know about them. But, it will
give you something to think about if youre tempted to plunk down $100 or
more for that Sony or MFJ antenna.

The post White paper describes active antennas appeared first on KB6NUs Ham
Radio Blog.