"Reg Williams" wrote in message
...

I have been trying for some time to decode L band signals from the Inmarsat
satellite 3-F2 with no success. I am located 20 miles west of Gloucester
UK.Lat 51 degrees N.
There are no obstacles as far as I am aware to block the signal at 30
degrees elevation. The antenna is pointing in the direction of 54 degrees
west. So I guess it may be down to the equipment. This is a 60cm dish with a
Log periodic pcb antenna 850-6500Mhz manufactured by WA5VJB pointing at the
dish. A short coax length is connected to the antenna via a pcb mount sma
connector to a LNA4All Low Noise Amplifier and then to a rtl 2832u r820t
dongle plugged into my laptop. The software is sdrsharp. I have tried
receiving signals generally around 1.545 Ghz. Not sure about the log
periodic. I guess the fact there is a short circuit when using an ohm meter
between the outer and inner soldering points before fitting the sma
connector is part of the characteristic of the antenna. From info I have
read, the signal is quite strong and can be picked up easily, so it seems
strange I cannot pick it up. Any thoughts or guidance i would be grateful.
Thanks
Reg

Key to successful use of a dish antenna is the feed illumination. (Note
that transmit and receive are reciprocal, so the term applies to receive,
also.)

The feed should illuminate the entire dish but the illumination should fall
off outside the area of the dish. First, the feed point has to be placed at
the focal point of the dish, which is easily found by the formula he
http://www.analyzemath.com/parabola/parabola_focus.html

Second, the feed's geometry determines the illumination of the dish. Having
too many elements will illuminate only a small part of the dish; having just
a single dipole will waste the available signal.

60 cm is a standard Inmarsat dish size, so don’t let that bother you. At
L-band, such an antenna doesn't have a particularly narrow beam; US Navy
ships use unstabilized Inmarsat dishes but pitch and roll do NOT cause a
loss of signal, if that helps.

"Sal"