At 08:33 AM 2/16/2005, Michael Tope wrote:
>If you want to be competitive on the low bands, Scott, the most
>important thing to consider is your ability to hear weak stations.
>Given the choice for example between a 300 ft tower in your
>current location with the encroaching development and all the
>noise sources and headaches that will be associated with this
>and a shorter tower in a more remote (e.g. quiet location), I
>would chose the quieter location with the shorter tower. Last
>fall I was sitting along a saltwater beach in Southern California
>in my truck using nothing but a screwdriver and I could hear TX9
>on Chesterfield Island on 75 meter SSB seemingly better than
>anyone on the west coast (it was clear that even the guys with
>good antennas were having trouble copying him). The
>combination of a saltwater horizon and a near zero local noise
>floor made a huge difference - there he was Q5 on the
>screwdriver while everyone else struggled to copy what he
>was saying. That was a real eye opening experience for me
>(I am used to being the guy who can't hear the DX).
>
>73 de Mike, W4EF.......................................
>
>
>----- Original Message -----
>From: "SJ W3TX" <superberthaguy@adelphia.net>
>To: <TowerTalk@contesting.com>
>Sent: Wednesday, February 16, 2005 4:48 AM
>Subject: [TowerTalk] World Class Station Conundrum - help!
Bringing up a very interesting point... Is it theoretically possible (with
unlimited processing power and perhaps a lot of receiving elements
available) to cancel the noise? After all, a gain antenna helps a bit
(because it "sees" less of the noise), but that's a directivity thing, not
a "gain" thing.
The noise in an urban/suburban site might appear pervasive and
omnidirectional, but is it really? If you set up two (tiny) antennas some
(small) distance apart in your backyard, how correlated is the noise
between the antennas? If it's correlated, then it can be cancelled.
There is some good literature on adaptive reception of skywave signals,
relying on polarization and pattern diversity, which essentially forms
adaptive beams on the incoming desired signals (and yes, it does work with
signals from the antenna elements that are below the noise level).
The question, with fancy receive processing, then becomes, "Is there noise
coming from 'exactly' the same direction as the desired signal?" How much
of that lowband interference (other than lightning) is skywave? How much
is local sources, propagating essentially horizontally (or by NVIS)?
(obviously, if you're hearing urban noise coming from the location of the
DX transmitter, propagating by the very same ionospheric path, you probably
don't have much hope...)
There's some interesting anecdotal reports from the lowfers and natural
noise recording folks where they use a whole stack of noise canceller boxes
(like the one from MFJ). There are, of course, more sophisticated (and
probably cheaper) ways to do this.
Jim, W6RMK
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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