Debugging a helical antenna installation

Martijn van Oosterhout kleptog at
Sun Aug 5 13:23:01 EST 2001

On Sun, Aug 05, 2001 at 10:19:36AM +1000, Alan Wilkie wrote:
> external antenna.  The cable runs we're using for testing are fairly
> short (5 or 6 metres) so I don't think cable losses are going to be a
> problem.

What kind of cable is it? When we were doing this we made sure there was a
maximum of 2m of cable at each end and that was pretty expensive cable.
We're dealing with 2.4GHz here and you'd be suprised at the kind of cable
losses you can get.

> Needless to say, the reason I'm writing this is that we've had no
> success getting the cards to associate, even when they're 10m apart. 
> It's as if there's no signal at all getting into/out of the helicals. 
> We've checked all the obvious things and there are no shorts, the right
> pins are connected to the right places, etc.

This is a bad sign. When we just put them down in the same room, not even
orienting them, we'd get higher signal levels than with no antenna.

> What are the critical factors that affect these things?  Accuracy of the
> construction?  Connectors?  Soldering directly to the board?  How do you
> test them (i.e. who's likely to have a 2.4GHz signal generator and
> spectrum analyser)?  Do they saturate if you have them too close
> together?

With those full length ISA cards we had to chop the cable to get the
connector off and we had minor difficulties with the joints, but other than
that it seemed to work OK. From what I remember it's cable losses and
impedance that are your major issues.

Martijn van Oosterhout <kleptog at>
> It would be nice if someone came up with a certification system that
> actually separated those who can barely regurgitate what they crammed over
> the last few weeks from those who command secret ninja networking powers.

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