14-30 MHz Magnetic Loop Antenna

The small magnetic loop antenna is a compact efficient antenna that is ideal for portable deployment or for limited spaces and that can be improvised inexpensively.  The antenna is essentially a tuned circuit with an inductor formed by a loop of wire measuring less than 1/4 wavelength and resonated to the operating frequency with a capacitor.  Due to its low radiation resistance and large circulating current, the loop must be constructed of a large outer diameter conductor of low resistance for best efficiency.  Typically these loops are built from coaxial cable, hardline, or copper or aluminum tubing.  These loops have a very narrow bandwidth and require a variable capacitor (and preferably a reduction drive) to be resonated at the operating frequency.  Air variable capacitors or vacuum variable capacitors are used due to the voltage on the order of several thousand volts that is developed across the capacitor.  In order to maintain the lowest possible series resistance, soldered connections and a “butterfly” or split-stator capacitor are preferred. The addition of a fixed capacitor in parallel with the variable capacitor will allow operation of this antenna on 7 or 10 MHz at reduced efficiency by Dr. Carol F. Milazzo, KP4MD

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Construction of a Compact and Efficient Portable High Frequency Antenna

Thank you very much for the work done Carol F. Milazzo, KP4MD

Annunci

New Yaesu FTdx-1200

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Download FTDX 1200 Brochure 

CocoaModem 2.0

CocoaModem is a Mac OS X application which implements modems (modulator-demodulators) for some of the Amateur Radio modulation modes. cocoaModem’s name is a reference to the MacOS X Cocoa framework that it uses.

The cocoaModem application is free and can be downloaded from the Downloads tab at the top of this page. cocoaModem is built as a Universal Binary and runs natively on both Intel based and PowerPC based Macintosh computers and is localized for Japanese Mac OS X.

An online User’s Manual is available through the User’s Manual tab above. The What’s New page lists what has changed since the previously released version of cocoaModem.

cocoaModem 2.0 works under Mac OS X 10.4 (Tiger), Mac OS X 10.5 (Leopard), Mac OS X 10.6 (Snow Leopard) and Mac OS X 10.7 (Lion).

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Downloads

Mac Ham Radio Devoted entirely to amateur radio operators using macintosh

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Data Format for Korean OSSI CubeSat

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AMSAT-UK

Open Source Satellite Initiative Korean CubeSat OSSI-1Information has been released on the data format to be used by the Open Source Satellite Initiative (OSSI) CubeSat developed by Hojun Song DS1SBO.

The OSSI Data Format spreadsheet can be seen at https://docs.google.com/spreadsheet/ccc?key=0AjtQ6cJ4QOqJdGpHNnRtUWZJV0w4TTFKRU9WYTZqc3c#gid=5

OSSI-1 is planned to launch April 19, 2013 into a 575 km 63° inclination orbit on a Soyuz-2-1b rocket from the Baikonur launch facility in Kazakhstan along with the Bion-M1 satellite and the SOMP, BEESAT 2, BEESAT 3 and Dove-2 CubeSats. The OSSI VHF beacon is understood to be using 12 WPM CW.

Open Source Satellite Initiative OSSI CubeSat Wiki http://www.uk.amsat.org/?p=12231

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144 MHz Halo Antenna

Construction of a Low Cost Omnidirectional Horizontally Polarized Antenna for 144 MHz

 

 

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Antenna HALO per i 144 MHz. La realizzazione di un’antenna può sembrare, alcune volte difficoltosa. Molte di queste infatti necessitano di particolari accorgimenti costruttivi che rendono l’antenna robusta e sicura alle intemperie. Non sempre però questi accorgimenti costruttivi si rendono necessari, come ad esempio quando si desidera sperimentare una antenna nuova e con forme diverse da quelle che solitamente siamo abituati a vedere.

Una di queste antenne è la HALO. Questa antenna a colpo d’occhio stupisce per la strana forma che ha, ma se la si guarda con attenzione si può vedere che non è altro che un dipolo a mezz’onda munito di Gamma Match che viene piegato in modo da formare un cerchio: questo accorgimento costruttivo riduce lo spazio occupato dall’estensione del normale dipolo, ma ne mantiene la direttività.

In pratica, piegando il dipolo in modo da formare un cerchio riduciamo lo spazio occupato dal normale dipolo quando esso, esteso, gira: questo particolare accorgimento non rende l’antenna omnidirezionale in quanto il dipolo pur avendo acquisito la forma di un cerchio mantiene la direttività, pertanto l’antenna dovrà essere orientata verso il corrispondente in modo da avere il maggior segnale possibile. Un’antenna di questo tipo si presta molto bene per l’uso mobile.