[time-nuts] "Deaf" receivers ?

[shouldbe q931]

I recently acquired a pair of Meinberg M600's (with GPS-CON downconverters).

>From the usual auction site got a dual band antenna (for
futureproofing), a 2nd hand mini-circuits ZN4PD1-63W-S+, several SMA
BIAS-TEE to prevent DC issues, and an assortment of coax cables to
connect everything up.

To power the antenna I used a ublox M8Q series without a BIAS-TEE
connected to the splitter, and then tested with another ublox (a NEO
7M) via a BIAS-TEE that it could also see satellites and that both
could get a 3D fix.

When I connected up each of the M600's, they eventually acquired
positions and acheived sync, but while the ublox receivers rarely do
not show a 3d fix, both of the M600's will show the a similar number
of satellites in view as the ublox, and sometimes more than one "Good"
satellite, but the "Selected Satellite Set:" never seems to change
from "00 00 00 00".

I presume that as its a timing device, that once it has surveyed its
position, it only needs one satellite to solve for time, and the MRS
status shows "Signal available, Is master, Is locked, Is accurate"
with an offset that is usually within -50 to -120ns but I'm lost as to
what the "Selected Satellite Set:" should be displaying.

At the moment, one of the Meinbergs shows 10 in view and one good, and
one of the ublox shows 12 in view and 8 used.

I tried with one of the Meinberg's (via the GPS-CON) connected
directly to the antenna with no improvement, and tried with a patch
antenna directly connected, again with no improvement, and different
ports on the splitter etc.

The antenna location is by no means ideal (west facing window in
fairly central London), but none of the ublox receivers (just basic
Max8 and Neo7m, no timing ones yet)  have had any trouble getting and
keeping a 3D fix.

>From my "naive" viewpoint, it looks as if the Meinbergs are a little
"deaf", but I'm guessing that I'm missing something.

Any suggestions gratefully received.

Cheers

Arne