Antenna design for LIPD 433Mhz

[Lin Farquhar]

I'm looking for a simple antenna, possibly an end fed dipole. to extend the range of cheap 433.92 hybrid transmitters (garage door opener type).
I'm fairly well versed in digital electronics but RF is not my strong point. The antenna would operate in a marine environment but I can construct it to withstand the sun and salt. I am looking for an electrical design. Any hints would be much appreciated, LF

[bodgy]

I can only speak for the UK and Australia, but wouldn't extending the range of the transmitter put you in danger of violating the no licence requirements?<p>I suppose you could always try enhancing the receivers capability, by putting a TV aerial amplifier on its input, but I can see problems there.<p>Colin

[russlk]

A directional antenna will increase the range without needing to increase the power. I can't help with that, but at this high frequency several possibilities exist.

[rfpowerdude]

I am using some RF Monolithics transceivers for this kind of app. I made a printed loop antenna that is pretty much omnidirectional. There is a nice app note on loop antenna design I have at work, but I can't remember where I got it. I'll get it on Monday.<p>Any kind of directivity enhancement on the transmitter end could put you in violation of FCC Part 15 Unlicensed Transmitters. Unless the output power is already low. The restriction on this power is a field strength of 50mV/meter at 3 meters. This works out to be about -1.5dBm into a 0dBi omni antenna.<p>It was suggested some work on the receiver end would be advantageous. A low noise amp at the receiver input will lower the overal noise figure of the receiver and in effect, increase the range. A more directional antenna at the receiver would also help.<p>I would have to see what your system looks like to make an optimum reccommendation.<p>--
joe

[dyarker]

You can't (legally) change the antenna on a no-licence transmitter. The transmitted power in any direction is what must designed to. Not the power out of the transmitter to the antenna.<p>That's why manufacturers must use soldered in, reverse connectors, or custom connectors on the antennas. To keep users from changing them.<p>Directional antennas on receivers has more benefit anyway. (If the direction from the transmitter stays the same.) The received power level is increased by the same amount, plus the received noise from the back and sides is reduced. So you get more range with a better antenna on the receiver than on the transmitter.<p>You didn't say the relative positions of transmitter and receiver. But a small LP antenna on the receiver on shore, would have about a 150° "window" for transmitters on boats.

[Lin Farquhar]

Thanks for all suggestions so far.
I'm using a yagi with folded dipole at TX end but am looking for a receiver antenna (vertical) that is simple to make (cheap!!!).
I've thought about a Jpole/zepp but everything I've seen is optimised for 50 ohm feedline whereas I need open wire 300 ohm (ish) matching.