[time-freq] time-freq Digest, Vol 32, Issue 1

[Tom Clark, K3IO]

> I have a new Efratom GPS timing antenna that I hope to use for a
> GPS-disciplined frequency standard.  The antenna itself is a black cone
> about the same shape and size as a disposable 10 ounce foam coffee cup.  The
> base of the antenna has a sticker that reads:  EFRATOM PN 012003-004 GPS
> ANTENNA.  The electrical connection is through a female TNC jack.  The
> antenna is mounted with four screws to the top of an aluminum fixture that
> has a female N connector on its bottom end.  The antenna and fixture, along
> with an Andrew cold-shrink kit and some hardware, are packaged in a foam
> tray that has the part number 104545-001.
>
> In order to use this antenna without either damaging it or operating it
> inefficiently, I need to know what voltage it is designed to accept.  My
> searches on the Internet have been fruitless.  Can anyone on this list share
> some details about its specs?
>
> 73, Eric Lemmon WB6FLY
Eric -- There is a very simple way to measure the required bias voltage 
if you have a small, variable voltage power supply. If the supply is one 
with a current meter, great. If not, scrounge up a way to measure ~50 ma 
current. Start with the voltage at zero. At some voltage, current will 
start to flow. At a bit higher voltage, the current will flatten out. 
The "flat top" voltage is near the voltage you need to apply.

Typically the LNA will be fed from an onboard 78xx (or similar) voltage 
regulator chip, so you can't really overdrive the LNA's bias. The 
voltage you hit with the test I described will be the 78xx output 
voltage plus the regulator's overhead.

Typically, similar antennas are designed for a 5v, 9v or 12v bias. Since 
the antenna is likely to have an on-board regulator, it's not easy to 
damage them.

73, Tom