[time-nuts] True position unlocking

[Björn]

Hi Taka,

Sent from my iPhone

> On 10 Apr 2019, at 22:23, Taka Kamiya via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> I have somewhat of a result.  
> 
> I rigged up an antenna outside.  It has 360 degree view above 30 degrees above horizon.  (it's located at middle of my front yard).
> Using 40dB antenna, lock was faster but it still lost sync every now and then.  RE-lock was faster as well.  Then, I disconnected its power supply (which is a switching power supply) and fed it from my lab supply.  The power is spec'd 0.5mv ripple.  It locked about the same as above and lost it once in few minutes.  But once it relocked, it is staying locked.  It's been running 2 hours locked solid.  It would have lost it few times by now.
> So the issue likely is the power source.  Yay!
> 
If you can have a look at the SNR for the individual satellites you should have a much quicker feedback on receiver status than waiting for unlock.

Look at the highest elevation satellites and try to maximize their signal strength.

Then with more time at hand - can Lady Heather do it’s fine “signal strength vs az/el”-plot with this receiver?

High elevation satellites can be +20db stronger/clearer than satellites down along the horizon. The receiver can only track a satellite down to a certain SNR (usually between 20 and 30 but it varies between models). If you have ‘the highest elevation’-satellite at say 50db then a low elevation satellite might come in at 30db and still be trackable. If your high elevation satellite is tracking at say 35db then lower elevation satellites will not be tracked at all - and the receiver will track much less satellites than are actually visible from your antenna. Also low SNR satellites will be somewhat noisier.

After a day or two LH should have a “painted” azimuth/elevation plot on SNR. Compare that while changing PSU or antenna gain. Also compare with what your well performing receivers show.

Antenna signal gain... most modern receiver will happily eat a wide range of rf signal strengths. Some receivers - mostly older - have a narrow gap where they perform optimally. There should be information in the receiver documentation somewhere. Then you can check with adding antenna gain - cable attenuation - splitter attenuation + any amplifiers (maybe within the splitter) etc.

Good luck!

Kind regards,

      Björn