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| − | ==The HF Communications Receiver==
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| − | A receiver for monitoring ''voice'' HF utilities must have the following features:
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| − | * Coverage from 100 kHz to 30 MHz
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| − | * Upper sideband (USB) and lower sideband (LSB) modes
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| − | * Good stability (doesn't drift off frequency)
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| − | * Good selectivity (able to seperate 2 stations that are close to one another in frequency)
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| − | Many receivers and portables marketed as shortwave or world band radios will satisfy
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| − | these requirements. The majority of voice communications use USB, but LSB is
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| − | certainly possible (foreign fishing fleets have been known to use LSB); therefore, whatever you
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| − | select '''must''' have USB and LSB capabilities. The lower band limit of
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| − | 100 kHz is typical of many HF radios, but many marine transmissions occur
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| − | at 2 MHz and above. Other features such as memory channels and alpha tagging
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| − | are desirable, but not necessary. See the [[:Category:Receiver Reviews|Receiver Reviews]] article for several links on this important topic.
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| − | ===But What if I want to Decode Digital Signals?===
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| − | This is one area where the field gets a bit more expensive. While it's true that many radios (and some wide banded radios like the AOR8200) will decode ALE and HFDL signals, as you get into the more complex modes, the needs for a better receiver become rapidly apparent. Read the [[A Few Words on Receivers]] article for a more complete discussion on this topic.
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| − | ==Propagation and You==
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| − | Your ability to receive HF maritime communications is affected by signal propagation
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| − | conditions in the atmosphere. Many factors affect propagation, including sunspots, solar
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| − | flares, and the time of day. Frequencies above 10 mhz or so are usable during the
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| − | local daytime, while frequencies below 10 mhz will be usable at night.
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| − | If you are a newcomer to this topic, reading a good primer would be a great benefit. Don't
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| − | get discouraged about all the jargon; whole books and very technical scientific papers have
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| − | been written on the subject; but it's unnecessary to have a degree to gain a basic understanding.
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| − | To get you started, please see the [http://www.ae4rv.com/tn/propflash.htm Propagation Primer]
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| − | website by Geoffrey Noles AE4RV (requires Flash player).
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| − | ==Antennas==
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| − | Your station is only as good as the antenna you can use. The best antennas for
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| − | receiving HF maritime comms is going to depend largely on what you can put up
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| − | and what kind of receiver you are using. Generally, something that is relatively broadbanded -
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| − | such as a random wire or inverted L - will be the best one to get you started. Our [[HF Antennas]]
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| − | page has a number of possibilities, including some that are already assembled - all you need to do
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| − | is supply the feedline and proper connectors.
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| − | If you live in an urban area, or are plagued with noise problems, consider utilizing
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| − | a loop antenna. MW DXers have been utilizing loops for their directional capabilities almost since
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| − | the beginning of the broadcast industy; they are useful for HF listening because they are less
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| − | sensitive to certain kinds of electrical noise. If you're interested in this topic, please
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| − | see our [[Loops]] page.
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| − | Another possibility is to use a Magnetic Longwire Balun(MLB) with a good grade of coax to feed an inverted L design. Plans exist on building baluns on the Shortwave SWL Antenna Yahoo group; or you can purchase the popular PAR EF-SWL antenna, which uses a similar principle. The [[HF Antennas]] article has information on these topics as well.
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| − | Unfortunately, many lower end communications receivers, as well as Software Defined Radios, may be overloaded by local MW and/or FM stations, causing noise and other artifacts in the HF spectrum. You may need to add some front-end filters - the very bottom of our [[HF Equipment and Accessories]] has a selection of these.
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