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

[Mete Balci]

I am new to the topic of time measurement, freq. standards and GPSDO etc.
but would like to share my experience.

I have quite a bad location for a GPS/GNSS antenna, inside an apartment and
looking to the north, and I need ~20m of cable to get it to my desk (using
RG58). The only good thing is I have a pretty open view almost from the
west to the east. Directly in the north direction, there is literally no
GPS/GNSS orbit (it is fun to confirm this with an astronomy program), but I
catch the ones on the sides.

I have a DIY GPSDO made in Japan (as far as I know it is different from
BG7TBL), LeoBodnar dual output GPSDO, and ublox M8T and F9T modules. The
DIY Japanese one has a ublox 7th gen receiver, and it cannot lock most of
the time. I believe the sensitivity is too low. LeoBodnar has a ublox 8th
gen receiver. It was mostly working but sometimes losing the lock, so I
installed an inline amplifier and then it is working pretty OK (Japanese
one does not work well with the inline amplifier also), I never see the
LEDs blinking so I guess it never loses the lock. It is a nice device but
1) you cannot use ublox u-center software, 2) it does not have a PPS
output. I tried M8T and F9T modules also, and they also work pretty fine.
F9T is dual freq. and I can use it in Time mode so actually I am planning
to use it to discipline a RbXO.

A puzzling question is I have C/N0 values maximum around 35, usually
between 20-30. My understanding is normally it has to be more than 40. I
did not understand yet why it is low but my current guess is it is due to
interference etc. because the antenna is not at the roof. (further
complications, I think my building is a steel construction, the window is a
little inside with a surrounding steel structure like a very large diameter
but small length tube).

So if you have a limited sky view or dont have an antenna on the roof, I
recommend getting a GPSDO having at least a ublox 8th gen receiver or
equivalent. I would like to try a Thunderbolt for example but not sure
about their sensitivity, not even sure if the sensitivity of Thunderbolt E
would be OK for my location.

Mete

On Wed, Mar 2, 2022 at 1:45 AM Wes <wes at triconet.org> wrote:

> I just acquired my second Bodnar GPSDO, a single frequency model.  I have
> the
> two frequency model already.  They don't do 1pps.  They are sold in the US
> by
> Airspy but I have had better luck buying from SDR-Kits in the UK.  Not
> much
> difference in price, they are friendlier and the delivery is just as fast.
>
> Wes  N7WS.
>
> On 3/1/2022 4:11 PM, Tom Holmes wrote:
> > John...
> >
> > If you haven't already, look into the Leo Bodnar GPSDO. It is a couple
> hundred bucks US, and the people I know who have them
> > are  pretty happy with them. Not sure off the top of my head if they
> make a PPS, however.  And, he is in the UK.
> >
> > Tom Holmes, N8ZM
> >
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