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Post by papa on Dec 22, 2021 20:27:01 GMT
RFMxx Radio Antenna Needed
When we use wireless radios (like RFM69 & RFM95), the antenna is a critical component.
See here about antenna sizes for RFM69 (& RFM95) radio frequencies. I also adapted the following from Table 1 at this site. It gives appropriate regions for the frequencies. Antenna sizes (1/4 wave) may be close but a little different from other tables:
Each country/region requires a radio frequency that is available for UNlicensed usage.
Available Unlicensed Frequency Bands Frequency Antenna length Regions433 MHz 173 mm Europe, Asia, Australia, U.S. (limited) 868 MHz 82 mm Europe only 915 MHz 78 mm U.S. and Australia (& Canada ??) Other research says, a 1/4 wave ANT or ANA (antenna) wire for 868 or 915 MHz can be about 3 inches (80mm), about 6.5 inches (165 mm) for 433MHz. Next, Sources for Simple Antennas
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Post by papa on Dec 22, 2021 20:28:32 GMT
Sources for Simple Antennas
Soldering a straight wire antenna to a radio's ANA connector can work adequately in a home & even into one's yard.
A coiled antenna (purchased or from a wired wrapped around a pencil) will probably work adequately, but compared to a straight wire, range & directionality will be affected. Of course, a coiled antenna takes less space than a straight one.
Next, Some Antenna Guidelines
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Post by papa on Dec 22, 2021 22:42:32 GMT
Some Antenna Guidelines Antenna performance (RSSI) is measured in DBs (decibels with a different meaning than for sound). Our antennas may function adequately given negative DBs. The more positive (that is, the less negative) our DB result, the better our antenna is performing. -50db is better than -70db.
Never operate a radio without an antenna which could be damaged. Keep the polarity (orienting the antenna horizontal or vertical) of sender & receiver antennas the same. Since an antenna's signal forms somewhat of a doughnut shape around the antenna, vertical orientation seems best when having reception issues.
Since an antenna's signal forms somewhat of a doughnut shape around the antenna, signal coverage is better in all directions horizontally. Directly below & above the antenna is not covered. The farther away horizontally from the antenna, the more there is some coverage above & below.
Having line of sight & the least obstacles between sender & receiver will get the longest distance of reception. For short distances, these radios can handle some obstacles like walls, etc.
Next, Increasing an Antenna's Gain
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Post by papa on Dec 25, 2021 15:56:21 GMT
Increasing an Antenna's Gain As said above, a single wire (of correct length) soldered at the radio's ANA pin is often sufficient. However, what if we need more gain? This sparkfun link summarizes approaches that are found in other locations. They make sense to me, but ( disclaimer) I have not needed to use them. The methods for increasing antenna gain are generally variations on this: " Antennas love to have a ground underneath them [ground plane]. A RFMxx board contains a ground, but, the larger the ground, the better." To the ground pin nearest the ANA pin, one can connect another 1/4 wavelength antenna wire. Or put a piece of conductive metal near & perpendicular to the antenna wire. (To avoid damaging electrical shorts, be careful that the only place the metal piece is connected is to the RFMxx radio's GND pin nearest ANA.) In this Andreas Spiess video & comments, he makes an antenna that uses 4 legs for a ground plane. He uses an electronic tool to fine tune the antenna. However, he also links a calculator & plans to achieve a "close enough" antenna. |
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