HP-Z3801A

Information about my HP-Z3801A's

I have bought two of these receivers. Why two you may ask, well I thought it would be nice to have one extra, if the main one would go bad for some reason. Hopefully I will then always have a nice clean 10 MHz reference in the house.

HP-Z3801A #1 has been modified to be able to talk RS-232C, while the other is untouched and coupled to the computer via a Moxa RS-422/485 ISA card in my server computer.

Presently receiver #1 is fed by a Motorola Timing-2000 antenna via 6 meters of Rg58 cable, and receiver #2 by a Magellan hockey puck like antenna with 6 meters of Rg174 cable. I intend to buy a GPS antenna splitter, probably four-way, and use the Timing-2000 antenna exclusively.

To see how my receivers behave, take a look at my GPSCon page.

Hardware

You will find five important connections on the HP-Z3801A

Antenna
Female N-connector, 50 ohm.

Power to antenna is 5 volts nominal, 50 mA maximum.
10 MHz
Female BNC-connector, 50 ohm.

Sine wave, 1.9 V_p-p into a 50 ohm load.

Computer

25-pole female D-SUB connector.

RS-422. If you want to use RS-232 instead this is possible with a small modification to the unit, look at http://www.ad6a.com/Z3801A.html for more information about this.

Pin number	Input/Output	Description
1		Cable shield
2 (A), 14 (B)	Output	Transmit data (TXD) - GPS Receiver output RS-422
3 (A), 16 (B)	Input	Receive data (RXD) - GPS Receiver input RS-422
7		Signal ground
15 (10 MHz_1-), 12 (10 MHz_1+)	Output	Differential pseudo ECL 10 MHz output
11 (10 MHz_2-), 24 (10 MHz_2+)	Output	Differential pseudo ECL 10 MHz output
17 (1 PPS_1-), 9 (1_PPS_1+)	Output	Differential pseudo ECL 1 PPS output
8 (1 PPS_2-), 21 (1_PPS_2+)	Output	Differential pseudo ECL 1 PPS output
All other pins		No connection

1 PPS output. Jitter of leading edge < 200 nanoseconds between pulses, accumulated time error < 7 microseconds per day unlocked, for 24 hours, after one day of stabilization and 2 day of locked operation with fixed antenna location, waveform pulse width 10 to 50 microseconds, time accuracy < 1 microseconds (locked to GPS.)

Baud rate. 19200 - 7 data bits, 1 start bit, 1 stop bit, odd parity, no flow control (fixed configuration.)

Power
3-pole (only upper and lower pin used) male AMP MATE-N-LOKII� connector. In Sweden you may buy the connector body and connectors from a company called Elfa, part number 44-183-15 and 44-199-66 respectively.

Top pin should go to plus, lowest pin to minus, and middle pin not connected. Use 18 AWG wire, i.e. 1 mm diameter, or 0.79 mm². Standard cables for 220 V here in Sweden would work, they are 0.75 mm².

DC power is according to the BSC standard (two versions exist, these values are for the most used one, the other one, BTS, wants +27 Vdc nominal) -54 Vdc nominal (-60 Vdc +/- 0.5 Vdc to -37 Vdc +/- 0.5 Vdc operating range.) Less than -46 Vdc +/- 0.5 Vdc starting (some units wants even more.) Nominal input power is less than 45 watts. At start the unit may draw up to 1 A of current when the ovens are warming up.

A very interesting plot on the voltage and current consumption may be viewed at http://www.mcn.org/m/w6str/Z3801A_Turnon.jpg (local copy)

Only a very simple power supply is needed. Below you may see a circuit diagram of the one I am building just now.
Ground
Ground stud. Connect to safety ground.

Software

There are a number of softwares available to communicate with the receiver. Microsoft Windows users will find some at http://realhamradio.com/GPS_Software.htm If you want to use Linux instead, take a look at http://www.febo.com/time-freq/gps/z3801a/tools.html I am also writing my own software, stay tune for more information on this.

To be able to communicate with the receiver you must have a RS-422 port on your computer, or modify the receiver to use RS-232 instead. Se above for more details.

The commands are not case significant. A list of commands may be found in the HP-Z3801A manual, or the HP-58503B and HP-59551A operating and programming manual.

Location
When received the receivers normally are in HOLD state, i.e. they still think that they are stationed at the cell phone site they were put at. To get it to know the new location you have to start a new survey to find out your location. This can be done by sending the command
```
:PTIME:GPSYSTEM:POSITION:SURVEY ONCE
```
If you know your location you may enter the location without doing a survey, or use it as a better starting point for a survey.

If your location is
```
North:   37 degrees, 19 minutes, and 32.5 seconds
West:   121 degrees, 59 minutes, and 51.2 seconds
Height: 40.12 meters
```
You should send the command
```
:PTIME:GPS:POS N,37,19,32.5,W,121,59,51.2,40.12
```
Antenna cable delay
Another good thing to do is to set the delay in the cable. The command is
```
:PTIME:GPSYSTEM:ADELAY <seconds>
```
Where <seconds> is written as 000E00, i.e. 30 ns (nanoseconds) is written as 30e-9. The equation to use to calculate the delay is
```
             L
delay = ------------
         K * 3*10^8
```
Where delay is delay in seconds, L is the length in meter, and K the velocity factor of the cable, i.e. K=0.66 for Rg58 cable.
Time
To get the system to display UTC time (if it still displays GPS time) you may change this with
```
:DIAG:GPS:UTC 1
```
Followed by
```
:SYST:PON
```
or, if that does not do it,
```
*TST?
```
will.
GPS receiver information
The following command will show you some data on the GPS receiver in your HP-Z3801A.
```
:DIAG:IDENTITY:GPS?
```

Pictures

	This is HP-Z3801A #1 running along nicely. It will eventually be placed in 19" panel together with its 48V power supply.
	This is the Motorola Timing-2000 antenna feeding HP-Z3801A #1 temporarily placed near a window facing east.
	HP-Z3801A #2 sitting on my desk awaiting setup near the server computer.
	HP-Z3801A #2 with top lid off.
	HP-Z3801A #2 with top lid off.
	HP-Z3801A #2 with top lid off.