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Page history last edited by PBworks 12 years, 9 months ago

Type Accepted LPAM Transmitters



In order to relieve the fears of other services, the LPAM transmitter is of low power only. 10 watts RMS to be used with current type accepted amplitude modulation. And must have a low pass filter at the rf output to the antenna tuner or antenna system, if no tuner is used: of a 5 element filter type. It's cutoff off frequency must be before the 160 meter band frequencies.


Recommended Transmitter Specifications:


These specifications are those proposed for a future LPAM Service.


(a.) 10 watts RMS Carrier. For use with type accepted amplitude modulation.


(b.) The transmitter must use a low pass filter of the minimum of 5 elements in the rf output before an antenna tuner or, if no antenna tuner is used in the station, will be used in line with the rf to the antenna system. No transmitter adjustment for peak loading purposes shall use the rf filter after the antenna tuner stage, the filter shall always be located before the antenna tuner. The filter shall be such that it has a cutoff frequency before the 160 meter amateur radio band at 1.800 MHz. The attenuation after the cutoff frequency should be 50 dB or greater.


(c.) The audio modulation requires a low pass filter between the audio source and modulation stage. Or between the audio limiting stage and modulation stage.


* The audio filter attenuation shall be: 60 log10 (f/3) = decibels


Where ‘‘f’’ is the audio frequency in kHz. At audio frequencies above 20 kHz, the attenuation shall be at least 50 decibels greater than the attenuation at 1 kHz.


* This specification was borrowed from The Traveler's Information Radio Service or TIS in § 90.242 (b.) Technical standards 5:8 The specification seems well suited for this service and transmitter power class. Since this service is comparible to the same power class as the proposed LPAM Service, technical data from § 90.242 will be borrowed from for comparison.


Comment: It would be unreasonable for a so called LPAM engineer to oppose such a rational view of using needed rf low pass filters.


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