I didn't expect to see all this good RF discussion on the PIC list!  Just
goes to show,  the people who work with PIC's are applications-oriented.

The government does have some very impressive systems that are very
nearly jam resistant,  but they are extremely expensive,  AND take up
hundreds of MHz.  of spectrum to operate.

Brian Robinson

 ----------
From:  PICLIST [SMTP:PICLIST@MITVMA.MIT.EDU]
Sent:  Wednesday, July 01, 1998 3:44 PM
To:  PICLIST
Subject:  Re: Spread Spectrum radios

Remember, anything that is transmitted can be jammed. If a person is
close
to the reciever or transmitter it can be easily jammed. (I demonstrated
this to a salesman at a convention when he said "Our units cannot be
jammed" by just placing my handheld tranciever next to his reciver and
transmitting. It de-sensed his reciever so much that it could no longer
recieve it's data.) Spending huge cash on jam-proofing must have a really
good reason, and a business or home security system isn't one. (How many
B&E artists have a VanEck or other item with higher technology other than
a crow bar.) In fact, the government cant come up with a jam-proof
system.. they just transmit at Gagillion watts to overcome the jamming
signal.

On Wed, 1 Jul 1998, Brian Robinson wrote:

> It will be difficult to find a system that is both cheap and has a high
> jamming margin.  I don't the details on why you need a high jamming
> margin,  but there are a bunch of vendors selling cheap spread-spectrum
> LAN cards;  you could always just buy a few and see if they work in
your
> application.
>
> There are more expensive radios made for the transit (i.e., railroads,
>  metros) market that are more jam-resistant,  but also much more
> expensive.
>
> Hope this helps.
>
> Brian Robinson
> hbrobinson@lucent.com
>
>  ----------
> From:  PICLIST [SMTP:PICLIST@MITVMA.MIT.EDU]
> Sent:  Wednesday, July 01, 1998 9:57 AM
> To:  PICLIST
> Subject:  Spread Spectrum radios
>
> There has been a few threads on these type of radios and I wanted to
let
> the
> list know that in a few weeks there will be some relatively cheap
systems
> available which will have very high jamming margins. This will be both
> frequency hopping and also direct sequence.
>
> If of interest please let me know.
>
> Thanks,
>
> Peter Grey
> Neosystems
> Australia
>