Hi there,
thank you for valuable information I get everyday from the list.

After a very long time I managed to power up a Trimble GPSDO, connected
to an aexternal antenna.

UCCM >*IDN?
TRIMBLE,57964-15,86854165,V3.0.0.11-01
Datecode: 0814 (pretty old, but still in its teen years)

Some output from "common commands":

UCCM >SYSTem:STATus?

57964-15    serial number  86854165    firmware ver  3.0.0.11-01LINK
mode

Reference Status __________________________  Reference Outputs

XX Ref 8KHz 0: [LOS]
XX Ref 8KHz 1: [LOS]                          TFOM    4            FFOM
1
XX Ref 8KHz 2: [LOS]                          UCCM A Status[OCXO WARMUP]
XX Ref 8KHz 3: [LOS]

ACQUISITION ...................................................[GPS 1PPS
Valid]
Tracking: 8 ____  Not Tracking: 3 ________  Time

PRN  El  Az  C/N  PRN  El  Az                GPS      11:44:34    27
Jul 2021
32  39 107  46    3  10 226
1  28 284  37    16  6 189                ANT DLY  0 ns
10  40  51  42    14  8 327                Position

8  79 239  45                              MODE    Hold
23  7  49  38
21  52 297  43                              LAT      N  43:35:11.819
27  55 153  43                              LON      E  13:31:1.250
22  32 230  41                              HGT              +225.27
m (MSL)

ELEV MASK  5 deg

UCCM >POSSTATus

07/27/2021  11:44:57

Position: LAT(N  43:35:11.819) LON(E  13:31:1.250) H(        +225.27 m
MSL)

Geometry: PDOP(0.0) HDOP(0.0) VDOP(0.0)
num of visible sats >  10
num of sats tracked >  10
-------- Receiver Channel State --------
CH  0 > SateID(03) TrackMode(pos avail) SigValue(36)
CH  1 > SateID(32) TrackMode(pos avail) SigValue(47)
CH  2 > SateID(01) TrackMode(pos avail) SigValue(37)
CH  3 > SateID(16) TrackMode(pos avail) SigValue(34)
CH  4 > SateID(10) TrackMode(pos avail) SigValue(42)
CH  5 > SateID(08) TrackMode(pos avail) SigValue(44)
CH  6 > SateID(14) TrackMode(tracking ) SigValue(20)
CH  7 > SateID(23) TrackMode(pos avail) SigValue(37)
CH  8 > SateID(21) TrackMode(pos avail) SigValue(44)
CH  9 > SateID(27) TrackMode(pos avail) SigValue(43)
CH  10 > SateID(22) TrackMode(pos avail) SigValue(40)
CH  11 > SateID(00) TrackMode(tracking ) SigValue( 0)

Rcvr Status(1):

Antenna Voltage:  5000.00mV  , Antenna Current:    0.00mA

UCCM >status

            - UCCM Slot STATE-

1-1. #Now ACTIVE STATUS ---------------- [OCXO Warm]
1-2. #Before ACTIVE STATUS ------------- [Alarm]
2-1. #Reference Clock Operation -------- [Not Used]
2-2. #Current Reference Type ----------- [GPS]
2-3. #Current Select Reference --------- [GPS 1PPS]
2-4. #Current Reference Status --------- [Good Accuracy & Stable]
#GPS STATUS ----------------------- [Available]
#Priority Level ------------------- [LINK > GPS]
#ALARM STATUS
#H/W FAIL [ LINK ]
#OPERATION ALARM ------------------ [Antenna]
3-1. #PLL STATUS ----------------------- [DISABLE]
3-2. #Current PLL MODE ----------------- [OFFSET OBSERVATION MODE]

The issue I'm facing is following: even after a long uptime, I never com
to a "fast blinking led" and PLL status "enabled". Monitoring device
with LHv6, shows an "operation mode" alternating Locked (few seconds"
and "recvery". TFOM is quite always 3 or 4. Power supply is linear, with
output voltage 5.6V or 6V. I made many tests but had no luck.

Sys:stat showa a "phase" value moving from -1.4E-05,settling up to
-4.3E-06, settling. On an old post I read that it might be caused by the
oscillator drifting due to age.

Any guess? Do I have to throw the unit from the window? For your
reference, I have a samsung unit connected to same antenna via a
splitter. The GPSDO is performing very well.

Thank you in advance for help.
Best regards.

On Tue, Jul 27, 2021 at 2:54 PM ordnit via time-nuts <
time-nuts@lists.febo.com> wrote:

Hi Ordnit,

I'm hardly an expert, but I wonder about the splitter. Is this a passive or
active splitter? If passive, it could be the input impedance of your
Samsung is much lower than for your new Trimble and it is making the signal
seen by the Trimble too weak. If you are willing to disconnect the Samsung
temporarily, perhaps you could try connecting your antenna to the Trimble
only and see what happens.

Don

The status shown looks mostly ok. Reference is GPS, plenty of satellites tracked, signal levels ok, etc. Your antenna alarm is due to the 0ma current - should not be a problem. But… your XDOP values are all 0 which seems suspicious and the status is still ‘OCXO Warmup’ (not 100% on that since I don’t have a Trimble unit, only Samsung and Symmetricom). I would suggest that you eliminate the splitter and connect directly to your antenna, just to eliminate things. Also, the OCXO could be substantially off frequency. If possible, I’d measure the EFC voltage and frequency. The output from DIAGnostic:LOG:READ:ALL? would also be useful.

You also might want to post to EEVBlog as there is a substantial thread on these UCCM units there at https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/

Most general purpose passive splitters for the L-band regime are
essentially variations
on the Watkinson splitter, which provides good isolation between the output
ports, if
(and only if) the input port is driven from a matched source.

So if your GPS antenna, whether active or passive, has a good output match
then
the Samsung's input impedance will not affect operation of the Trimble.
But, again,
this is true only if the antenna's output impedance is matched to the
splitter's
characteristic impedance (including consideration of any impedance
transformation
in the transmission line between the antenna and the splitter).

I cringe at the cavalier treatment given to line impedances used in GPS
systems.
AFAIK, all GPS equipment is designed for 50 ohms, yet a great deal of such
equipment is provided with 'F' connectors, which invite the use of
inexpensive RG-6
line, which is 75 ohm cable.  In addition to problems with impedances and
loading,
It's a built-in source of multipath, all at no extra charge!

Dana  K8YUM

On Tue, Jul 27, 2021 at 3:01 PM Don Cross cosinekitty@gmail.com wrote:

Hi

If you measure the input impedance of most low noise receivers, it’s not
going to be 50 ohms pure resistive. There are multiple reasons for this.
Since the “load” is not a match to either 50 or 75 ohm cable, it’s not that
big a deal.

The amp in the antenna with it’s post filtering may or may not present a
50 ohm source. They rarely hit a 14 db return loss spec in any case. Indeed
there are a lot of attenuators out there that don’t get to 14 db at 1.5 GHz.

Trimble did a lot of testing before they put the F connector on the TBolt.
They could find no impact at all.

Bob

I'm not worried about the F connector itself- rather, it's
irresistible temptation to use
wrong-impedance cables, often rather long ones.

Agreed that LNA inputs don't tend to make good matches, but that's what the
splitter
largely addresses.  It's the wrong impedance of the source that foils the
benefit of the
splitter, and which most people ignore altogether.  I think we'd get along
better if the
antenna output impedance were 75 ohms, F connectors were used, and 75 ohm
splitters were used.  Then good isolation would be preserved at low cost no
matter
what load impedances were present on the splitter's outputs.  The simple
mismatch
loss between 50 ohms and 75 ohms is pretty negligible in this context.

When I see an attenuator with only about 15 dB return loss at L-band, it
goes straight
into the trash.  To me, the anticipated main benefit of having a nanoVNA is
that I'll
be able to identify such defective items at flea markets before spending
money on it.
That is, if there are ever any more flea markets (because of Covid).  I'm
not optimistic.

Dana

On Wed, Jul 28, 2021 at 7:58 AM Bob kb8tq kb8tq@n1k.org wrote:

Hi there,
thank you for all the information.

I'm using a bullet antenna (don't remember the maker), on top of my
office. Cable has 50ohm impedance (ultraflex 7) and average quality N
connectors. Patch from splitter to receiver is 50ohm as well, but still
using RG58, will upgrade it asap.

Update on my issue:
Yesterday I made some testing, removing the splitter and nothing changed
(apart the samsung complaining about signal loss :)  ).

I removed the trimble board from its case, I gave a look to it and
powered up again: well... may be a kind of magic but it works. Now the
status led is blinking fast and this is the output I get from commands:

UCCM >STATus

            - UCCM Slot STATE-

1-1. #Now ACTIVE STATUS ---------------- [Master Manual]
1-2. #Before ACTIVE STATUS ------------- [OCXO Warm]
2-1. #Reference Clock Operation -------- [Not Used]
2-2. #Current Reference Type ----------- [GPS]
2-3. #Current Select Reference --------- [GPS 1PPS]
2-4. #Current Reference Status --------- [Good Accuracy & Stable]
#GPS STATUS ----------------------- [Available]
#Priority Level ------------------- [LINK > GPS]
#ALARM STATUS
#H/W FAIL [ LINK ]
#OPERATION ALARM ------------------ [Antenna]
3-1. #PLL STATUS ----------------------- [ENABLE]
3-2. #Current PLL MODE ----------------- [OFFSET OBSERVATION MODE]

UCCM >SYSTem:STATus?

57964-15    serial number  86854165    firmware ver  3.0.0.11-01LINK
mode

Reference Status __________________________  Reference Outputs

XX Ref 8KHz 0: [LOS]
XX Ref 8KHz 1: [LOS]                          TFOM    3            FFOM
1
XX Ref 8KHz 2: [LOS]                          UCCM A Status[ACTIVE]
XX Ref 8KHz 3: [LOS]

ACQUISITION ...................................................[GPS 1PPS
Valid]
Tracking: 10 ___  Not Tracking: 0 ________  Time

PRN  El  Az  C/N  PRN  El  Az                GPS      07:35:47    29
Jul 2021
26  73 268  45
31  22 215  37                              ANT DLY  0 ns
16  45 309  42                              Position

10  11 170  38                              MODE    Hold
29  32  77  43
25  6 141  34                              LAT      N  43:35:11.808
18  79  73  45                              LON      E  13:31:1.216
5  18  45  39                              HGT              +228.84
m (MSL)
23  31 143  42
27  19 281  40

UCCM >posstatus

07/29/2021  07:36:06

Position: LAT(N  43:35:11.808) LON(E  13:31:1.216) H( +228.84 m MSL)

Geometry: PDOP(0.0) HDOP(0.0) VDOP(0.0)
num of visible sats >  10
num of sats tracked >  10
-------- Receiver Channel State --------
CH  0 > SateID(26) TrackMode(pos avail) SigValue(46)
CH  1 > SateID(31) TrackMode(pos avail) SigValue(36)
CH  2 > SateID(16) TrackMode(pos avail) SigValue(42)
CH  3 > SateID(10) TrackMode(pos avail) SigValue(37)
CH  4 > SateID(29) TrackMode(pos avail) SigValue(42)
CH  5 > SateID(25) TrackMode(pos avail) SigValue(36)
CH  6 > SateID(18) TrackMode(pos avail) SigValue(45)
CH  7 > SateID(05) TrackMode(pos avail) SigValue(40)
CH  8 > SateID(23) TrackMode(pos avail) SigValue(43)
CH  9 > SateID(27) TrackMode(pos avail) SigValue(38)
CH  10 > SateID(00) TrackMode(tracking ) SigValue( 0)
CH  11 > SateID(00) TrackMode(tracking ) SigValue( 0)

Rcvr Status(1):

Antenna Voltage:  5000.00mV  , Antenna Current:    0.00mA

UCCM >DIAGnostic:LOG:READ:ALL?

Log status:  22 entries

L00:21/07/28.06:00:47 Self survey started
L01:21/07/28.06:05:30 Ref Change: GPS
L02:21/07/28.06:09:10 Ref Change: No reference
L03:21/07/28.06:09:25 Ref Change: GPS
L04:21/07/28.06:09:54 Ref Change: No reference
L05:21/07/28.06:10:07 Ref Change: GPS
L06:21/07/28.06:32:45 Ref Change: No reference
L07:21/07/28.06:33:07 Ref Change: GPS
L08:21/07/28.06:34:42 Self survey completed
L09:21/07/28.06:36:13 Ref Change: No reference
L10:21/07/28.06:36:25 Ref Change: GPS
L11:21/07/28.06:58:13 Ref Change: No reference
L12:21/07/28.06:58:25 Ref Change: GPS
L13:21/07/28.07:07:27 Ref Change: No reference
L14:21/07/28.07:07:43 Ref Change: GPS
L15:21/07/28.07:31:43 Ref Change: No reference
L16:21/07/28.07:31:55 Ref Change: GPS
L17:21/07/28.08:35:59 GPS Antenna open
L18:21/07/28.08:36:01 Ref Change: No reference
L19:21/07/28.08:36:30 Ref Change: GPS
L20:21/07/28.12:13:02 Output mode: Active
L21:21/07/28.12:13:02 A/S change: Slave(HIGH)

So far, so good.

PS: I don't belive in magic, so I guess that some glue I used to hold
the board, added some capacitive side effects. Let's keep it going,
wating for a new GPSDO to join the collection.

Best regards!