[time-nuts] Best choice for GPS active antenna voltage?

Bob Camp kb8tq at n1k.org
Fri Aug 5 14:17:32 EDT 2016


If you are doing your own antenna supply:

1) Make very sure it is current limited at some rational level (say 150 ma). A 
resettable fuse may be fine for this. 

2) Make sure you have some way to detect a short on the antenna. 

3) Put in some sort of surge suppression. A microwave compatible TVS at the 
antenna input is the best / first step. Some form of isolation to the main supply is a good second step.

4) At least rate everything so a 12V supply could be cobbled into the circuit. You never know when 
you might get a good deal on a high voltage antenna. 

5) Unless you are only running mag mount “car” antennas, you need +5 / +3.3 selectable
on the board.

6) If you have to do your own RF isolation / DC injection, design it as a bandpass (or at least
a high pass) filter. The more energy you eliminate below 400 MHz, the less your TVS gets
hit with in most cases. 

Lots of fun..


> On Aug 5, 2016, at 10:51 AM, Nick Sayer via time-nuts <time-nuts at febo.com> wrote:
> In designing boards with the Venus838LPx-T module, I must supply external antenna power myself. This is in contrast to the PA6H I’ve been using which internally supplies 3.3v active antenna power (and measures it for loading to switch between the internal and external antenna. The Venue module does not have an internal antenna).
> I therefore have the opportunity to select between 3.3v and 5v power to feed the external antenna. I could in principle do something more exotic, but I can’t imagine another option that would be better.
> So far, 3.3v has worked with all of the antennae I’ve used, but the sample size is two (four if you count active GPS splitters in the mix).
> In perusing the list, it sounds to me like modern antennae expect 3.3v, but I thought I’d explicitly ask rather than assume.
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