Select Other Pages Here a) GPS antenns and receivers b) GPS to TNC data cables c) TNC GPS Data interconnect d) TNC-interconnect cables d+e) TNC-Radio interconnect e) Radio-interconnect cables h) Power Splitter Harness i) Mag-mount antennas o) Cable and Wiring Overview -) Baker-to-Vegas HQ Page
GPS Antennas! We have two pictures below, to give you a better look at the antennas that we talk about on the item a page.
One possibility is to use a "micro-patch antenna", as described in a QST article. (We tried extending the Garmin antenna with a length of feedline, but found this to be unacceptable. The gain of the antenna dropped of quickly as we extended the feedline. Remember that most coax has a high loss factor at the microwave frequencies used by the GPS satellites.) Since we may need to use a 2-3 meter feedline to extend the antenna, we'll probably need to use antennas with MMIC amplifiers built in.
The micro-patch antenna has been built with an added (MMIC) pre-amp built into the antenna. This improves the original design, by giving more signal going into the feedline, which gives us more signal coming out the other end. Most GPS receivers supply some small amount of power to the antenna feedline, but you need to be careful that you don't connect an antenna to your receiver that will draw too much power. (This raises another point...these "active antennas" will rapidly drain your small, internal batteries. You should consider using an external power supply with more capacity if you plan to use pre-amplified antennas for an extended period of time.)
QST Magazine recently published an article about MMIC amplifiers. If you want to build your own active antenna, check the November 1997 issue, page 32 for that article.
There were many good reports from users of the antennas built by LRF designs. However, Mr. LRF took a new job with Garmin, so he had to stop making the antennas. The good news is, that the antennas were made available again, produced by another Ham (Jim Duncan, KU0G). The product was renamed the Blackjack antenna, but unfortunately he stopped making them in 1998.
Shown in the following photo, you see a Garmin GPS II receiver above the ruler, as well as three antennas. From left to right, they are the Blackjack passive antenna, Jano Metal Products passive antenna, and the active antenna from Lowe UK.
The Blackjack antennas are no longer made by Jim Duncan, KU0G, and we don't have any pointers to any other folks selling these antennas. These were originally the Little Red Fox design.
The Jano Metal Products (SM-65) antenna is passive has tab/ears that could be useful for permanent mounting. The unit performs well for the sattelites low on the horizon, as well as the overhead birds. These have a 3-meter (~10-feet) coax lead, with a male SMA connector. Price is $32 (US), I believe, in single units.
There is also an active, magnetic-mount version of the antenna available! The SM-66 antenna is the same physical size as the passive unit shown in the pictures. The test figures show that these antennas will outberform the Lowe units by about 5+ dB! (Trimble and Lowe units are rated at 25 dB, and the Jano unit is rated at 30 dB. My testing with one of these antennas showed excellent gain, and about 30 ma current draw on the Garmin 12XL with this unit attached. The antenna I received came with a molded connector that mates with the small, MCX connectors on the Garmin 12XL, and the magnets are "strong" performers. These antennas come with 3-meters (10 feet) of micro-coax as well. The price on the active antenna is $48 (US).
You can also request that either model be terminated with a different connector, and they will do that at the factory for $10 (US) each. This may save you from trying to find/buy/make adapters for connecting these antennas to your GPS receiver. They say that they have a variety of connector types available, and that retermination may only add a day or two to shipment. (Orders normally ship within 24 hours.)
(Word from the factory in early November is that the passive antennas are currently in stock, but the active units are beginning production, so delivery coul take a little longer. In my opinion, the active units are probably worth the wait, if you want an amplified antenna.)
Jano Metal Products, P.O.B. 11343, Station H, Napean, Ontario, Canada (K2J 3Y4). voice: 1-800-736-3740 - fax: 1-800-347-9638 voice: 1-613-825-7611 - fax: 1-613-825-7610 And, any day now, they will have info about the antennas on the Jano Group web site.
The active antenna from Lowe Electronics, UK, is a staellar performer. But, the performance will cost you some battery life. These units come with a long lead of coax, with a male BNC connector. The unit cost was $65(US) funds. www.lowe.co.uk/gpsant.html, but be forewarned that they have a picture on the page that is 185 kB, and it takes a bit of time if you're using a modem to browse. It's a nice picture of the antenna, but the picture file is BIG. We have also heard that these antennas are available from a U.S. distributor called E.B. Electronics, for about $10 less.
In the picture below, you can see a close-up of the undersides of the Jano Metals antenna (on the left) and the Lowe antenna (on the right).
I've also heard that TNC maker PacComm is reselling a Trimble antenna for $50 plus shipping. Delivery could take up to 2 weeks after the order is placed, according to the email messages I saw in the APRS SIG. Call 800-486-7388 to inquire.
TAPR also has some antennas for sale. More info is available at the TAPR web site (www.tapr.org).The TAPR GPS Index has a bunch of deals for GPS core receivers, as well as antennas.
Copyright 1996-2002, David K. Z. Harris, N6UOW Questions? Comments? Additions? Email b2v at baker2vegas.org Developed on a PowerBook DUO 230! Illustration Artwork: CLARIS DRAW Pro Web Page Creation: CLARIS Home Page 2.0 Photo Scanning: STORM Technologies EasyPhoto