I have also observed the low sensitivity of the T-Bolt here. The older one (red box with built-in DC/DC converters) barely worked with the Trimble Bullet antenna I got with it, but works fine with an HP 58532A and also with a small mag-mount Trimble model. The two newer T-Bolts (group buy) appear a little more sensitive, they are usable with the bullet, but barely.
Didier Sent from my Verizon Wireless BlackBerry -----Original Message----- From: [email protected] Sender: [email protected] Date: Fri, 31 Dec 2010 00:44:42 To: <[email protected]> Reply-To: Discussion of precise time and frequency measurement <[email protected]> Subject: Re: [time-nuts] GPS Antenna Chris-- The thunderbolt receiver is notably deaf. While a more-or-less standard 24dB antenna will work, you'll get better results with a higher gain antenna, such as one made for this kind of work. eBay may be your friend. The HP/Symmetricom 58532A is 30dB of gain (or a little more). A chap in HK sells them for $40 a pop, $10 shipping, really hard to go wrong. (Don't confuse with the Symmetricom Timing Antenna, which has a GPS receiver built into it and isn't suitable for our type of craziness.) I swapped out an older 24dB active antenna with a 58532A and saw a noticeable improvement in stability at the tbolt outputs. Two GPS receivers from one GPS antenna -- the kicker is providing DC power to the amplifier in the antenna. HP/Symmetricom make a nice bit of kit for doing this, Mini-Circuits has one as well, GPS signal splitters. They have fairly narrow bandpass filters and a low-noise amplifier to overcome the loss in the splitter, and a DC network to supply power to the amplifier and the antenna from the GPS receiver. The HP/Symmetricom unit is the 58535A. N connectors. You can pound nails with it. It's heavier than a thunderbolt, maybe twice as heavy. I use one for driving two thunderbolts off the same antenna. Also available in a 4 port version. If you're good at surface mount rework, you can increase the gain a bit, as the output ports have pads on them (to increase isolation/return loss). There's a MiniCircuits one, the MCL ZAPD-3DB-1575-3 GPS Antenna Amplifier Splitter , on eBay currently for the remarkably low price of $25. Usually these suckers go for $100 or more, as the sellers usually understand that they've got a specialized bit of kit and price it accordingly. Expensive, but if you're going to be driving multiple GPS receivers and comparing them, the alternative (using separate antennas) leads to madness. Of course if you're reading this list, you're well on the path as it is! Watchful waiting on eBay -- I watched a few of the splitters go for $150 or more, and pounced when I saw one for a price I was willing to pay. That MiniCircuits one looks like a good deal... If you want to do lightning protection, Ham Radio Outlet in Anaheim, or one of the other Ham Radio stores can get you a protector with N connectors that's rated for 1 - 2 GHz. Not cheap, but then again, neither is your house. We aren't in Florida, but it only takes one... 73 bob k6rtm in not yet raining silicon valley ------------------------------ Message: 7 Date: Thu, 30 Dec 2010 15:25:46 -0800 From: Chris Albertson <[email protected]> Subject: [time-nuts] GPS Antenna To: Discussion of precise time and frequency measurement <[email protected]> Message-ID: <[email protected]> Content-Type: text/plain; charset=ISO-8859-1 A few questions about GPS antenna.... 1) I read the Thunderbolt user manual and did not find any meaningful spec on the antenna except that it is amplified and uses DC power in the coax. What signal level is the Thunderbolt expecting? oes it want a 24dB antenna or more or much less? 2) I want to feed two GPS units with one roof mounted antenna. I figure that splitters are just a transformers and will not pass DC to power the antenna. There must be an easy way around this. 3) Do people really run coax straight from a GPS antenna into their house with no protection from lightening? Maybe a GPS antenna is a small target compared to a 100 foot wire antenna in Florida -- ===== Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
