[time-nuts] GPS backup for the stationary time and frequencyuser

[Magnus Danielson]

On 10/08/2010 08:22 PM, jimlux wrote:
> Brooke Clarke wrote:
>> Hi Jim:
>>
>> I've got a spare Ku band satellite dish and would like to use it for GPS.
>> In an ideal application the GPS antenna would be mounted in the normal
>> manner and above it would be a sub-reflector aimed at the Ku dish.
>> That way the antenna might pickup sats near the horizon directly and
>> from a narrow part of the sky by means of the dish.
>> The dish might be aimed at a WAAS GPS sat.
>> I've heard that you can just use the TV dish with a normal GPS
>> antenna, and it gas gain even though the polarization is reversed.
>>
>>
>
> Give it a shot. The other thing is that if you have your GPS antenna
> facing straight up, at the focus of the dish, you're looking at the side
> of the gps antenna, where the polarization might be less circular.
>
> But one thing to think about here... a standard Ku dish isn't very big..
>
> At GPS frequencies, you're looking at 20 cm wavelength. The dish is
> perhaps 2, maybe 3 wavelengths across. That's not a huge amount of gain.
>
> You might do just as well with a flat cookie sheet.

Well, a 1 m dish gives you 48 dB gain at L1 if I calculate correctly. 
The normal antenna is at 6 db of antenna gain?

Even if less than perfect, not too big size is needed to get meaningful 
antenna gain.

Cheers,
Magnus