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

Peter Bell bell.peter at gmail.com
Wed Nov 2 06:34:09 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).

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.


Pete Bell

On Wed, Nov 2, 2011 at 4:19 PM, David J Taylor
<david-taylor at blueyonder.co.uk> wrote:
>> I've made a small Web page describing what happened when I changed the
>> puck antenna on a Rapco 1804M for a more sensitive one.  The Rapco 1804M
>> expects a big outside antenna.
>>  http://www.satsignal.eu/ntp/Rapco-1804M-notes.html
> This page has now been updated to provide a comparison between three puck
> antennas - the Garmin GA 27 (BNC), a 3rd-party low-cost puck, and a Gilsson
> puck antenna.  It seems that the even higher signal level from the Gilsson
> benefits the 1804M more than the other two.
> Cheers,
> David
> --
> SatSignal software - quality software written to your requirements
> Web:  http://www.satsignal.eu
> Email:  david-taylor at blueyonder.co.uk
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