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

["Grasso, Charles" <Charles.Grasso@xxxxxxxxxxxx>]

Irrespective of existing external antenna protection technology - it is
worth remembering the original post and I quote:

" My colleague (the designer) put it there to try and alleviate any
potential ESD problems. I have found that I cannot solve the ESD
susceptibility problem without removing it." 

Hence the suggestions for sparkgaps/discharge tubes of course there
are low capacitance "ESD" diodes used in USB2 that could also work.

So - having restated the problem - any folks out there have any other
ideas??


Best Regards
Charles Grasso
Senior Compliance Engineer
Echostar Communications Corp.
Tel:  303-706-5467
Fax: 303-799-6222
Cell: 303-204-2974
Email: charles.grasso@xxxxxxxxxxxx;  
Email Alternate: chasgrasso@xxxxxxxx
 

-----Original Message-----
From: Geoff Stokes [mailto:gstokes@xxxxxxxxx] 
Sent: Wednesday, February 04, 2004 2:51 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: ESD solution on antenna output

Hello Mathias

I've seen something like that before.  Your receiver has no off-chip
filtering apart from antenna tuning, so selectivity may be poor.  The
discharge energy is in the form of a fast spike with a decay.  There is a
lot of spectral energy in the high frequency spectrum, but with a suitable
filter, you only pass the part in the wanted signal spectrum, which is a
much smaller energy.  On an aircraft, you will generally find there is a
quarter wave choke in the form of a short circuit metal stub behind the
antenna connection which does most of the protection, where lightning is a
concern.  A wire choke can do the same, but the current carrying capability
is reduced.  A metal strip might be an improvement to your design.  At 2.4
GHz on an epoxy-fibreglass PCB (something like FR4), the microstrip quarter
wavelength is about 17 mm (I used AWR TxLine).  You could either print it or
just stick down some pieces of copper foil, soldered at the ends.  The width
is a compromise between rejection and signal loss - I suggest about 1 to 3
mm wide, maybe less if your PCB is multi-layer.

Cheers
Geoff

> -----Original Message-----
> From: Matthias Weingart [mailto:si-list@xxxxxxxxxxxxxxxx]
> Sent: 03 February 2004 18:49
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: ESD solution on antenna output
> 
> 
> 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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