Abgeschickt von Marius Rensen am 30 Mai, 2005 um 16:58:07
Antwort auf: Weather Satellites von David Speight am 30 Mai, 2005 um 14:42:49:
the problem is your antenna gain and polarisation. WXtoImg can decode also acceptable images with a smaller bandwith as 25-30 KHz.
Use a crossed dipole, this makes the reception of weak signals from the polar orbiter possible, without any nulls in the vertical antenna diagram, and no noise bars on the received picture.
Another excellent antenna is Quadrifilar antenna.
But also the receiver sensivity is a goal for good pictures.
Hope this will help you.
: Can any one help me?
: I have been recieving APT images from the NOAA polar orbiting satellites and decoding them with WXtiImg.
: Fin. but one problem is baffling me:
: (1) I am using an ICOM R7000, and a homebuilt 1/2 Wavelength Dipole. Each picture I decode is uniformly covered with 'white' noise which reduces picture quality, and when the satellite is directly 'overhead', there is a ~20 degree band across the middleof the picture that is totaly black! i.e. apparently no data.
: Now, (if you're still reading) I understand that the bandwidth (?) of the reciever has to be about 25kHz to decode the images, and my R7000 specifications claim a "Selectivity" of +/- 7.5kHz minimum @ -6dB.
: Does this mean that the reciever has a bandwidth too narrow for these images? and what is the significance of the black band in the pictures?
: Any help extremely appreciated!