[time-nuts] Monitoring the Rapco 1804M - how antenna changes affect the unit

David J Taylor david-taylor at blueyonder.co.uk
Wed Nov 2 07:10:53 EDT 2011

> Assuming it's using a timing-optimized receiver, the lack of a clear
> view to the sky is probably the biggest problem.  Once they have a
> valid almanac, they will normally select the satellites with the
> highest elevation angles - and if you have an obstructed view that
> might well include several that are not visible.  Obviously, the less
> channels on the receiver, the bigger an issue this is - on top of
> this, the timing receivers tend to be engineered to favor selectivity
> over sensitivity (the idea being that the gain is in the antenna and
> you can select it to match the cable losses).

Yes, that in consistent with what I'm seeing, Pete, thanks.  I am told 
that the actual receiver is a Trimble SVeeSix, so why I occasionally see 
eight reports from the Rapco firmware I don't understand.

> I have no idea if the firmware in the Rapco will support the 8-channel
> UT+ - but the fact that the monitoring software seems to have spaces
> for up to 8 SVs gives me some hope it might (or possibly there is some
> later FW that does).  This could be worth trying.
> Regards,
> Pete Bell

As the unit is only required for frequency, I am not intending to modify 
it.  It has OCXO with quite good specifications, so it will more than meet 
my needs.  It would likely meet my needs five minutes after being switched 

Thanks for your comments.  I've updated the Web page about the 6/8 
channels, and added a couple of pointers for those who might want to try 
the antennas.  An outside one with a clear sky view would like be better 
than any of these puck antennas.

SatSignal software - quality software written to your requirements
Web:  http://www.satsignal.eu
Email:  david-taylor at blueyonder.co.uk 

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