Jose Manuel wrote: > Hello all, > > I´d like to repair a HP58504A antenna that don´t deliver any output signal. > The current is about 30 mA ( I think too high), and the transistor (unknown > type) and the MMIC (uPC2749TB), seems to be with correct voltage. > > The resistive voltage divider feeding (from the +5V supply) the Vcc pin on the MMIC will draw about 15mA by itself plus 6mA for the MMIC is a total of 21 mA. The input stage has a total dc resistance of around 421 ohms to the drain, with 90.5 ohms from the source to ground, should the input transistor have a drain to source short the input stage current would be about 9.7mA giving a total of about 30.7mA.
To eliminate the possibility of a drain to source short, the drain to source voltage of the input device needs to be measured (or inferred from resistor measurements with the circuit unpowered and by measuring the voltage drop across the 100 ohm resistor in series with the drain with the circuit powered - this is unlikely to cause parasitic oscillations) without causing it to oscillate. > Does anyone have any experience or data about this antenna? > > I took an inside photo: http://www.ea1px.es/HP58504A.jpg Can the > transistor be identified by the color code? > > > > Thanks in advance, José, EA1PX > Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
