Operating instructions

20 Choosing a Ham Radio
processing, with more aggressive levels also giving the signals a “digital” sound. Noise
blanking (NB) is used to remove repetitive noise pulses, such as those from an automo-
bile’s ignition system or power-line noise from nearby ac utility lines. Noise blanking is
very useful in mobile HF radios and noise reduction can be used for all SSB and CW HF
operating.
DSP can also be used to create a notch filter. Not only can the filter’s notch frequency
be manually adjusted, just like an electronic notch filter, but many DSP notch filters can
automatically detect the frequency of the interfering tone and tune the notch filter (Auto-
matic Notch Filter or ANF). Some radios even have the ability to “notch out” more than
one tone at a time!
Radios with more DSP functions also allow you to control the filter response—how
aggressively nearby signals are rejected. A filter that allows some of those signals to be
heard has a “soft” response, while one that rejects the signals more completely is “sharp”
or “steep”. Soft filters result in more natural sounding audio, but do not reject interfering
signals as well. If the DSP functions are also applied to the output signal, you may also be
able to tailor your transmitted audio to suit your voice, adding more average power and
increasing the intelligibility of your signal.
Memories
HF transceivers use memories and VFOs in much the same way that VHF/UHF mod-
els do. Start by reading the VHF/UHF section on memories. HF radios often offer band
memories as well, sometimes referred to as band-stacking registers. These memories store
one to several settings of the VFO on each of the HF bands. Pressing a band-select key on
the radio’s front panel cycles through these memories. This is useful if you use the same
frequency on a regular basis.
Scratchpad memory is a set of temporary memories for use when you are just tuning
around the bands and want to save a frequency and mode setting without dedicating a
memory. Like VHF/UHF radio memories, the memories store not just the frequency, but
also the mode, filter and other settings.
To find out how many memories you’ll want on your HF radio, count all the nets and
emergency frequencies you might use, some of the frequencies for WWV and WWVH
(www.nist.gov—the US time and frequency standard stations), calling frequencies for
your most-used modes, propagation beacons, and any other frequencies of interest. Add
some extra memories for expansion.
Scanning
Scanning is also provided in mid- to top-scale HF radios, just as in the VHF/UHF ra-
dios (read the VHF/UHF scanning section for a discussion of the terms). The most popu-
lar scanning mode on HF is range scanning in which the radio tunes continuously across
a portion of the band, looking for any signal. Scanning is less useful on HF, however,
because of the higher noise levels and the wider range of usable signals, making it difficult
to set a single level to use as the scanning threshold.
Antennas
If antennas are the most important part of an amateur station, that is doubly true on HF
where long-distance contacts place a premium on the antenna’s ability to transmit and
receive efficiently. Antennas are generally rated in terms of gain—how well they con-
centrate signals in a preferred direction. Gain is specified in dB and every 3 dB of gain
doubles your signal’s strength.
The simplest antenna (and a very effective one) is a half-wave dipole made of wire,
one-half wavelength long, and installed horizontally. You can build it yourself as de-