[time-nuts] HP58504A antenna

Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Jul 21 20:46:03 EDT 2008

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


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