Ht Hytower

Multi-band vertical antenna



Fig. 3. Twenty and 75 meter frequency translation relationships to 5 MHz vfo+


Fig. 3. Twenty and 75 meter frequency translation relationships to 5 MHz vfo+

used In the switched carrier technique. See Fig. 1. Pure SSB filters are most selective on only one skirt. In this case, discrete cutoff frequencies and their relative attenuations are usually specified.

3) Ultimate attenuation. The amount of attenuation given to signals appearing out. side the selective skirt of the filter is normally referred to as ultimate attenuation. Generally —40 db is considered adequate as a design minimum. —50 db to —60 db ultimate attenuation is preferred.

Ham filter ' Standards11 arrive

In 1957, a 9.0 MHz symmetrical bandpass filter for amateur SSU use was introduced by McCoy Electronics Company, This filter was supplied with matching oscillator crystals for both upper and lower sideband operation and designated as type SSB-9. It was designed for a 6 db bandwidth of 2,7 kHz and a shape factor of 1.8:1, 40 db to 6 db.

The frequency of 9.0 MHz was chosen for this filter "first" because of the ease in hetro-dyning to 20 to 75 meters with only a single conversion stages. Fig, 3 is a graph of the 20 to 75 meter frequency translation relationships with a vfo operating in the 4 MHz range*

Popular demand for a filter of the SSB-9 type prompted design of a second generation filter series. The "Silver Sentinel" (McCoy type 32BI) and the "Golden Guardian" (type 48B1) evolved from the original SSB-9 designs.

The popularity of 9,0 MHz SSB filters has today spread throughout the world, YHI operators generally contend that high-frequency crystal filters were primarily responsible for the growth of SSB on the 50T 144 and 220 MHz bands, Manufacturers of amateur and commercial radio equipment have recognized the value of high quality crystal filters and are today producing amateur equipment capable of meeting rigorous commercial standards.

More than twenty years have elapsed since the birth of amateur SSB, Advances in state-of-the-art continue to tax the imagination. Amateur radio enthusiasts have played a major role in this progress arid should be proud to have pioneered these advances,

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