GPS Frequency Standards and Active Antennas

[fineshot1]

I am hoping some of you have enough experience with some of the various vendors(ie: Symetricomm, Spectracom, Vectron, etc.)
of the GPS frequency standards to answer a question which is just a curiosity of mine. I do not have any equipment problems along
these lines.

Can you mix the active antennas of one vendor with the GPS receiver of another? Is there a standard among the vendors for the
active antenna supply voltage fed up the rf cable, or do they all go there own way when it comes to a supply voltage?

[Bill_G]

In general, yes - you can mix and match active antennas among the different time base manufacturers. Most of them run on 5vdc, and most of them provide +20db gain at 1575mhz. So, you can use a Motorola gps ant on a new Spectracom, or a mobile ant on a Dalman / Tait. As long as they using single coax shipping 5vdc to the antenna, you're okay.

There are some other configurations out there, and you are usually limited to using the antenna provided. The original Dalman sync unit was an example. They placed the receiver in the outdoor unit, and shipped serial data back to the indoor unit on a multi-conductor cable. When it died, we were stuck with their antenna, and it was no longer available. However, I rolled my own. They were using NMEA format. I combined a rcvr board and antenna in a box, and shipped it down using the original cable. I had to change the mating connector at the end of the cable.

[Bill_G]

A quick note about the gain the active antennas provide - You want loss in your line. You want the loss to equal the gain, or be as close to a zero sum as you can. Use the crappiest wire you can find for short runs, and the best for long runs. Any run under 25ft, use plain old RG58. For runs up to 50ft, use RG8. For runs up to 100ft, use LMR400. If you present too much gain at the front end, it will over drive the rcvr, and cause errors. That might not seem important if all you want is time, but several times a day there are only three birds visible. If two are distorted, you will lose time lock as well as position lock forcing the ref osc to fallback to it's internal clock which may or may not be good enough. At the very least, you'll get a minor alarm on the system, and depending on who is monitoring, you may get a service call when none is warranted.

[MSS-Dave]

I have 2 Symmetricom TS3000 clocks here. The antennas (and software in the unit) allow for an elevation mask in degrees if using the thing in areas where buildings or other obstructions block LOS up to 35-40 degrees above the horizon. Don't know how they do it but I'm pretty sure the antenna is propriatary to that unit.

Dave

[fineshot1]

ok - good info. thanks fellas. Anyone else having input would be welcome as well.