FreeLists / si-list / [SI-LIST] Re: ESD solution on antenna output

[Matthias Weingart <si-list@xxxxxxxxxxxxxxxx>]

We are some HAMs here and we have some practical experiences with 2.4GHz
Wlan adapters that use external (outdoor) antennas (PCI cards): Some of the
antennas does not have a DC path. From time to time (once a year) a card
(from any vendor) stops working, or at least the sensivity goes done
irreversible. Looking at the PCB the antenna input path looks like this -
SMB connector, xx pF capacitor in series, RF chip pin. No additional
protection is visible. We added a inductor (well only a wire with some
windings) to the SMB connector. The RF sensistivity was reduced somewhat (it
is only one "digit" of the RSSI indicator). After 3 years we are doing it
this way, we had no failure in the HF part of the cards any more. I think
the inductor works as a additional protection in addition to the the input
protection of the chip. The first part of energy is reduced by the input
protection, but latter the inductor gets more current and reduces the power
that the chip protection has to absorb.
 I simulated a human body model in Spice (150pF charged at 8kV, 330R, 50nH
in series) and without the inductor the energy that the protection diodes
need to absorb was much higher than the some what ringing voltage with
the additional inductor.

I would suggest to use the inductor, well it rings, but it does not add more
energy. In case of a (rare) spark a reception of the signal is not
possible at all, the ringing does not matter.

Spark gaps or gas discharge devices are much too slow. They only prevents the
device from burning in case of lightning (I guess).

M.

On Tue, Feb 03, 2004 at 08:58:39AM +0100, Bart Bouma wrote:

> I saw already several replies on your question, so I keep it short.
> An inductor is not the ideal way to protect against ESD-pulses.
> However, my experience is that an inductor can help to protect against 
> surge pulses at antenna inputs (TV-tuners).

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