[ANSS-netops] ANSS-netops Digest, Vol 26, Issue 1

[Greg Steiner]

Juan,
There are other frequencies available for low bandwidth digital 
communication, the main problem is finding sources for the hardware to 
use these frequencies. A lot of them are for use only with serial 
(rs-232) style signals.
When I was at CERI we had to deal with multiple users in this band. 
there are 2 solutions that you might want to try before you abandon 
those frequencies.
1st, you might try using more directional antennas. small parabolic 
dishes (2-3ft provide a narrow beam width for your signal. Not only does 
this concentrate the energy you are radiating, it also minimizes off 
azimuth received energy as well. Inside of Memphis we resorted to a 6ft 
dish at the Memphis end of the link for just this reason! Unfortunately 
these types of antennas cost about 2K and require a substantial mount so 
they aren't blown around too much.
2nd,
You might try changing the polarity of your radiation from vertical to 
horizontal or vise versa. Sometimes a slight repositioning of the 
antenna can also help a great deal.
Don't be tempted to use the small omni type antennas as they are the 
worst possible solution to the problem. Small yagis are better but still 
have quite a few side lobes with significant gain in them. Flat panel 
antennas are better, but the parabolic dishes are the best when it comes 
to eliminating interference.

You may want to look at the pattern of the interference. One thing this 
band suffers from is interference from microwave ovens. because the 
operation of this type of device produces a large amount of noise 
adjacent to the actual band used by the telemetry equipment it may be 
possible to filter this out using cavity type filters. All rf spectrum 
is crowded today and you have to use best practice not only for antennas 
but feedlines, connectors and all the parts of the system.
Hope this helps.

On 2/3/2011 6:00 AM, anss-netops-request at geohazards.usgs.gov wrote:
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> Today's Topics:
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>     1. 2.4GHZ problems (Juan B Lugo Toro)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 2 Feb 2011 09:56:16 -0400
> From: Juan B Lugo Toro<juanb.lugo at upr.edu>
> To: anss-netops at geohazards.usgs.gov
> Subject: [ANSS-netops] 2.4GHZ problems
> Message-ID:
> 	<AANLkTinu0TJ2v7RQEo86QE4BctWT8mHX4TCJ5d6EAk+S at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Hi
>
> We, at PRSN has been using the 2.4ghz radios but some weeks ago we started
> having problems in some sites. I understand that because it is an open
> frequency it is too busy. I was thinking to move to 5.0ghz but it will be a
> matter of time to start having problems. I will appreciate any suggestion. I
> am thinking on a private frequency but I will like to know first if there is
> already a government frequency available on that range like the VHF and UHF
> bands that we can use.
>
> Thanks in advance
> Juan Lugo
>
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