a little RF help needed - Page 1
Forum section: electronics / projects

author: KTP
author_rank: Frequent Contributor
timestamp: September 19, 2010, 05:17:21 pm
content: Hi guys,I have been tinkering with the MSP430-RF2500 2.5Ghz transceivers after getting the pair for $25 from TI with the half price coupon.They use a very poor gain chip antenna so don't really have much range to speak of, but it is probably on the order of 15-20m line of sight. They are incredibly small and low power though.Anyway, I am interested in modifying one of them to act as a direction finder for the other (maybe put the other one inside the TV remote or my car keys) just for fun and to play around with writting a little code to detect the signal strength (I believe this is available over the SPI from the CC2500 RF chip.I have not had a course in antennas yet in my EE program, so would really love a bit of advice on what might work as a quicky directional antenna to replace the chip one.Thanks

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: September 19, 2010, 05:30:17 pm
content: As I've said dozens of times around the net; I may be 10 kinds of geek, but RF geek isn't one of them.That said, I've used this site a couple of times with good results, but with much lower frequencies.Surely someone on here can say if you can use a Yagi at 2500 MHz.http://bfn.org/~bn589/antenna.html

author: Unknown
author_rank: Unknown
timestamp: September 19, 2010, 05:47:14 pm
content: I'm not an RF expert either. There are some DIY designs for Wifi (2.4GHz) floating around. The frequency may be close enough that it works with minor modifications, or even without any (can't imagine them being too selective). I once made a biquad antenna for Wifi, it seemed to work fine (much better than the rubber duck antenna, although I had no way of measuring antenna performance), but that sounds like it might be too bulky for this application.

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: September 19, 2010, 06:01:03 pm
content: Duh ...WiFi .... I didn't think of that.You can find loads of cheap wifi antennas on eBay. Just copy the following line to the eBay search window and you'll see over 1,000 of them.(wifi, 802.11, 2.4GHz) antenna (yagi, directional) -cable -omni

author: KTP
author_rank: Frequent Contributor
timestamp: September 19, 2010, 07:22:15 pm
content: Right...I didn't realize there were so many directional wifi antennas available!The frequency of the TI part is 2.4Ghz...I mistyped when I said 2.5Ghz.I even found a fairly amusing video on making a directional wifi antenna out of a tin can:

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: September 19, 2010, 07:32:57 pm
content: Cute video.If you Google "DIY Cantenna" you'll find gobs of plans/projects based on the now famous Pringles can.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 19, 2010, 07:38:18 pm
content: You got mini 2,4G transmitters , and they are for portable use , those antennas or any antenna it supposed that it will amplify an specific output and above .Its best to stick in the original design , so to not loose the portability ..Other than the antenna , the quality of the receiver are crucial about getting an extended range,I do not believe that those are good enough , or equal to the ones found on the 100$ routers .Oh yea I have plenty of WiFi stuff in my workshop , 3Com bridges 2,4 & 5 G and Linksys ,and all type of Antennas even original LinkSys , and directional ones.Not to speak about special cables for the 2.4G .

author: joelby
author_rank: Frequent Contributor
timestamp: September 20, 2010, 01:28:01 am
content: You can try replacing the antenna with anything else, but it's possible that it won't help at all due to impedance mismatches. There's an article that gives you an idea of the procedure here:http://colinkarpfinger.com/blog/2010/the-dropouts-guide-to-antenna-design/, but this is for designing PCB trace antennas rather than pre-fabricated ones. Basically, the idea is the same but instead of modifying the antenna you'll fiddle with the matching circuit.