[time-nuts] HP58504A antenna
bruce.griffiths at xtra.co.nz
Tue Jul 22 00:51:30 EDT 2008
christopher hoover wrote:
> Jose wrote:
>> 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.
>> 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?
> I'm assuming correctly that the big blob of solder in the LL
> is the antenna connection, otherwise please ignore all of this.
> I suspect that "transistor" is really an MMIC in one of the
> fancier packages rather than a discrete transistor.
Circuit is exactly that to be expected with a discrete pHEMT or similar
> It looks to me as if the bias flows through the trace on the BR
> and then through a couple of 001 R's before the bias
> setting 221 R.
Nonsense they are 100 ohm resistors text is upside down.
1 ohm resistors wouldn't be particularly effective in the filters,
> This MMIC is before the filter, so it is probably been selected
> and biased to avoid IM problems.
Its unlikely to be an MMIC as they generally have all the bias parts
internal to the chip other than an output biasing resistor.
Also most MMICs do not have the input connected to dc ground.
> But I don't think 30 mA sounds too high.
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