4 Way GPS Antenna Splitter w/DC & Amplifier

2-Way Amplified

© Brooke Clarke 2001 - 2007

Home Brew 4-Way Splitter
HP 58535A 2-Way Splitter

Home Brew 4-Way Splitter

This is a 4 way GPS splitter that includes amplification to make up for the 4-way divider loss.
The parts breakdown is:

One of the Motorola VP Encore receivers is powering the amplifier.  The 4-way divider has 2 diodes to route the DC bias so the port that has the 75 Ohm termination does not load the DC bias.  This system works well and was much lower in cost than a commercial GPS divider.

I moved the line amp outside about in the center of the coax feed to make up for coax loss.  Of course the actual GPS antenna, a Motorola hockey puck, has a built in amplifier.

19 April 2003 - By connecting the antenna from a Garmin GPS III Plus to one of the output ports and taping it to the antenna on a military PLGR GPS receiver the receiver works extremely well, locking onto signals that the Garmin can not capture with a direct antenna connection.

23 Aug 2003 - Added a Trimpack AN/PSN-10 GPS receiver to the system.  This required inserting two more of the DBS satellite amplifiers between one of the 4-way divider outputs and the trimpack.

5 Sep. 2003 - While experimenting with various amplifiers, I checked with an Ohm meter and the port I was using showed DC open.  Then applied 18 Volts to get full gain from the Radio Shack (RCA D903) amplifier and notices that it was drawing way more that 2 of the amps should draw.  Shut down and checked the amps while not connected to anything and all was well.  But when I looked at my reference GarminIII+ it was not tracking.  None of my GPS receivers were working.  Checked the Garmin using it's own antenna and it worked.  Checked outside and the mast top Motorola ANT97 is dead, it got fried by the 18 Volts, normally runs on +5.  Have a Timing 2000 on order.

What went wrong?
Ans: the open I saw was the routing diode in the 4-way divider, once the voltage got above 0.6 V the 18 volts was sent up to the inline amp and to the mast head active antenna.
The fix:  Add DC blocks (RS 15-1259) to all of the 4-way divider outputs, except for the one that powering the mast head antenna and in line DBS amp.

The system now looks like this:

HP 58535A 2-Way Splitter

Although I'm calling this an HP splitter, it was also branded Agilent or Symmetricon.  It's a 2-way splitter is intended for GPS use and has a DC path from Port 1 and Port 2 to the common antenna port.  When a positive voltage is at either port it's dropped by 0.137 V @ 1ma at the antenna port.  When +5 VDC is applied to either P1 or P2 a little more than 20 ma is being drawn with the antenna port open.  When a port has +5 applied there is no voltage on the other port so it's OK to connect two receivers where each has a DC output, like the Thunderbolt (+5) and the DAGR (+3) at the same time.  If either receiver goes off line the other will power the antenna.  But the receiver with the lower output voltage may generate an internal error message caused by insufficient current.
HP 58535A 2-Way Splitter

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