T&T: AIS

[Peter Bennett]

Sunday, January 7, 2007, 3:54:30 PM, Jeffrey wrote:

>> Perhaps I have a bad receiver.....but if it works for a few 
>> ships as it does with the 3db antenna and many more with the 
>> 9db antenna I  would rather think it is a transmit issue.
>> 
>> Comments??
>> 

JS> About every 3dB doubles the power being transmitted out.  In addition, when
JS> you consider the cable and connector loss of the coax to the 3db antenna,
JS> you're probably losing almost all of the 3db gain.  The reality is that your
JS> 3dB antenna is providing no amplification and the 9dB one is probably
JS> providing 4x gain.  That could explain the results you are experiencing.

JS> It could also be that there is a problem with the 3dB antenna, cable, or
JS> connectors.  That should be easy to rule out.  The thing is that if you have
JS> any distance between the receiver and the antenna, a 3dB antenna isn't a
JS> good idea.

JS> ================
JS> Jeffrey Siegel

There should be no problem using a 3dB antenna, even with 40 ft or so
of cable.  Normal practice on sailboats is to have a 3 dB antenna at
the masthead, frequently fed with RG8X (.250" dia) cable.

However, in this case, I do suspect that there is a problem in the
antenna or cable.  I'd suggest the OP try connecting the AIS antenna
cable to his VHF receiver, and see what he can receive that way - if
he can't receive almost as well with that antenna and cable as he can
with his normal 9dB antenna, there is almost certainly something wrong
with the new AIS antenna and cable.


-- 
Peter Bennett, VE7CEI    Vancouver, B.C., Canada
Lien Hwa 28 (AKA Polaris 30) "Sea Spray"
GPS and NMEA info: http://vancouver-webpages.com/peter 
Vancouver Power Squadron: http://vancouver.powersquadron.ca