Greetings, I'm sure this is a pretty basic question. Which is good because my knowledge of electonics is pretty basic. 30 years ago I bought a CB radio, antenna, and an SWR meter. I believe SWR stands for Standing Wave Ratio. Anyway, this meter was for matching the antenna to the radio. Changing the position of the antenna on the car would affect the match. Now, I have an FM transmitter that I bought as a kit from Ramsey. It works well with included telescoping antenna. As long as the radio is within about 80 feet. The transmitter is used to listen on the radio to stations broadcasting on the web. The location of the antenna is pretty close to the center of a 10 acre parcel that is about 1000 feet long by 450 feet wide. The ideal antenna would be one that broadcasts in a rectangle of the same proportions so as not to break any FCC rules.So what I would like are pointers to likely antennas and how to build the SWR meter. I've googled but haven't been able to find something simple enough for me to understand. Any ideas are very welcome. I'm a machinist with many years experience so if anyone has any metalworking questions I'd be happy to try to come up with a good answer. Thanks, Eric R Snow, E T Precision Machine
Antenna advice please
Sep 10, 2005
4 Replies
Well, good luck on that one. Easier to arrange for it to rain only on 1/2 of your lot!
Unfortunately, modding the transmitter or the antenna will violate the part 15 rules for this device. Extending the range from 80 feet to 330 feet will require more power. Which won't be within the regs.
Sorry, Eric. Your transmitter doesn't produce enough power to move the needle on any SWR bridge (passive) that you can build.
The good news is that there's no real benefit to matching the antenna and line on a tiny TX like this.
Regards PN2222a
Let me introduce my partner,
2N2906.
The instructions from Ramsey state that other antennas can be used with this transmitter without violating FCC rules. Most important is to keep the signal within my property. ERS
Most important is found in paragraph (b) below. This means you can use any antenna you like, as long as your field strength (in any direction) does not exceed the value specified below.
[Code of Federal Regulations] [Title 47, Volume 1] [Revised as of October 1, 2004] From the U.S. Government Printing Office via GPO Access [CITE: 47CFR15.239] [Page 816-817]TITLE 47--TELECOMMUNICATION
CHAPTER I--FEDERAL COMMUNICATIONS COMMISSION
PART 15_RADIO FREQUENCY DEVICES--Table of Contents
Subpart C_Intentional Radiators
Sec. 15.239 Operation in the band 88-108 MHz.
(a) Emissions from the intentional radiator shall be confined within a band 200 kHz wide centered on the operating frequency. The 200 kHz band shall lie wholly within the frequency range of 88-108 MHz. (b) The field strength of any emissions within the permitted 200 kHz band shall not exceed 250 microvolts/meter at 3 meters. The emission limit in this paragraph is based on measurement instrumentation employing an average detector. The provisions in Sec. 15.35 for limiting peak emissions apply.
Greetings John, Of course you're correct. The FCC can't use the size of a piece of land as a gauge. And I seem to recall reading that even if the power does not exceed the above it must still not interfere with someone else recieving radio signals. Eric
Join the Discussion
Have something to add? Share your thoughts — no account required.
Didn't find your answer?
Ask the community — no account required