Showing posts from January, 2017

Power measurements of DVB-T transmitters

Power measurements of DVB-T transmitters- first draft Introduction I have been puzzled for some time about how power of DVB-T amplifiers were measured relative to other modes. This is an important issue in DATV as DVB-T has been criticized as inefficient compared to DVB-S. It would appear that some of the debate comes down to how the power is measured. Most amateurs use simple diode power meters that do not give an accurate reading for DVB-T.

In this post, I outline the theory and practice of measuring DVB-T power correctly with either a thermal power sensor meter or envelope power using a spectrum analyser. It is important that the correct measurements be used otherwise it is comparing apples with oranges. Different power measurements are accepted in amateur radio, vis, CW (peak power, key down) compared to SSB (peak envelope power).

I wonder if another measurement unit for digital modes may be more appropriate, such as the data rate to the DC power input and spectrum width, bits/se…

Commercial DVB-T Amplifiers and filters and implications for DATV

Commercial DVB-T Amplifiers and filters and implications for DATV (first draft) Introduction Commercial solid-state DVB-T amplifiers use about 250 W "pallet" amplifiers; a pair of  amplifiers, each using a pair of LMDOS transistors in a single package. The circuit boards are mounted on a piece of thick copper then on a heat sink. To get higher power, 1 to 50 KW, many pallet amplifiers are used in parallel with a system of splitters and combiners. The amplifier output passes through a series of filters, to stay within a standardized spectrum mask to limit adjacent channel interference. To conclude I note some implications for DATV.
Pallet amplifers A typical pallet amplifier is pictured below (bought on eBay). The gold rectangle on the left splits the input to a pair of Doherty amplifiers, while the one on the right combines the amplified signal to the output. The combiner uses a type of circulator to dump RF to a dummy load, the black rectangles on either side of the combin…