[time-nuts] Re: GPSDO - GPS1300-10-1000 by RFX Ltd. UK

[Bob kb8tq]

Hi

A GPSDO with a poor sky view will not do well. They are designed with the
“assumption” that you will have a good lock unless the antenna gets hit by 
lightning ( or some other catastrophe ).

Assuming you are south of Hadrian’s Wall, you will have GPS sats overhead 
at least occasionally. The bulk of what you will be able to “see” will be to the 
south. If you really have a good antenna location and are a bit north, you may
be able to “see” sats on the other side of the north pole. More or less, there
is a big coverage blank area over the poles with GPS.

The closer you get to either pole, you will need to have a fairly good view closer
to the horizon than you would at the equator. Still something like a 20 degree 
view should be “good enough”.

One way to get an idea of what’s what is to buy a $10 USB plug in GPS. Fire
up any of the many tracking / display programs and see what sort of plots you get. 
It might be a bit cold to sit on the roof with a setup like this, but at least you
will get an idea.

Bob

> On Mar 1, 2022, at 5:11 PM, John Moran, Scawby Design <john at scawbydesign.co.uk> wrote:
> 
> Bob, Jim - Thanks for the detailed replies. You have both managed to confirm the difficulties and unknowns involved in being a fledgling TimeNut.
> 
> I think that is what prompted me to try to avoid as many unknowns as possible by buying one that was at least guaranteed to work, especially in the un-locked mode because I'm not sure what my GPS viewing here will be like until I have a unit to play with.
> 
> A problem we have over here is that there isn't the huge eBay market for such things, so choice is really limited to Chinese recycled/cloned stuff of unknown provenance. OK, I could buy from a US supplier but, and I will probably be jumped on for saying this, US suppliers seem incapable of finding reasonably priced delivery methods. A recent example was a nice slide rule I was interested in for $36, but carriage was $86 ... I didn't buy.
> 
> Getting back to GPSDOs - given that, when locked, they are probably all quoted as 'close to Caesium' (British), I will still buy a new one, but more reasonably priced and then try to acquire an SC-cut crystal to start making an OCXO to eventually form the heart of a GPSDO. I like the comments about holdover and recovery from holdover ... one of you keeps talking about rabbit holes, I think I see one looming.
> 
> John 
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