[time-nuts] Spring cleaning and antenna placement

Brooke Clarke brooke at pacific.net
Mon Apr 20 02:10:57 UTC 2009


Hi Magnus:

The improvement is probably due to a noise figure reduction from use of the LNA 
if it's near the antenna rather than at the receiver end of the cable run.

Have Fun,

Brooke Clarke
http://www.prc68.com

Magnus Danielson wrote:
> Magnus Danielson skrev:
>> bg at lysator.liu.se skrev:
>>>> If you are in Scandinavia, the GPS birds will not spend much time (if
>>>> any?) to the north of you. Slide 12 of
>>>> http://web.ics.purdue.edu/~ecalais/teaching/geodesy/Satellite_orbits.pdf 
>>>>
>>>> suggests that the most northerly orbital point is at the latitude of
>>>> Denmark.
>>> With a decent antenna siting you see plenty of SVs to the north. Magnus
>>> problem is that there are lots of rather close by trees and stuff. These
>>> trees are also much taller than the antenna position.
>>
>> Indeed. The southbound sats goes almost over the head, but I also get 
>> long tracking periods for sats way up to the north.
>>
>> Since the house sits partly in a valey and the neighborhood is rich of 
>> trees there is plenty of foilage. To the north is a building, two 
>> stories high and ground level for it is just above the upper of mine, 
>> which pick up the extreme north direction.
>>
>> The location also requires an antenna mast forr the TV reception. With 
>> modern digital transmission it is best to have a good margin for 
>> reception, or there is no TV at all.
>>
>> If I had a flat roof I might just put a ladder up to the antenna, but 
>> unfortunately not so.
>>
>> Sky-view of GPS antennas was not of concern when picking this house. 
>> Maybe it should be for the next.
> 
> To follow up on this... I have now received my LNAs and I have installed 
> one. The LNA gives me a 16 dB boost, but lack of a bias tee force me to 
> use a passive splitter to act as the bias tee, and that sets me back 6 
> dB, so I effectively only gets 10 dB of boost, but the effect is 
> certainly there, the Z-12 tracks significantly better.
> 
> Just goes to show that LNA may come to assistance. Thought this may be 
> useful to some. A second LNA could boost me up even more, but using a 
> proper bias tee should give me about 6 dB.
> 
> Cheers,
> Magnus
> 
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