Hello all,
I am currently working on finalizing some paperwork with regards to a 900 MHz transmitter for the FCC. They claim that they need this piece of information, specifically for IC documentation. I know a handful of things about RF and antennas, but I do not know enough to feel confident about any numbers that result from experimentation, theoretical equations, and the like. Here is what I have done:
Antenna characteristics:
Length: 18mm
Nturns: 8
Diameter of loop: 4mm
Freq: 900 MHz
Utilizing an equation taken from a paper on helical antennas, I have obtained the following:
g[dBi] = 10.25+1.22*(L / lambda)-0.0726*((L / lambda)^2)
I obtain 10.3 dBi gain reading using approximately the values of antenna characteristics listed above.
Next, a colleague constantly activated a transmitter with NO antenna oriented such that the receiving antenna and transmitter shared the same axis (pointed at one another directly). Then, a spectrum analyzer was used to record the average of peak readings of the transmission. Then, the antenna was replaced, and the readings were taken again.
75 dBuV/m with antenna, 54 dBuV/m without antenna; or 5,623 uV and 501 uV in non-log units. (20 log10(G) used). Dividing 5,623/501 and taking the log10 and multiplying by 10 yields, what Wikipedia claims to be, dBi units. The result obtained was about 10.5 dBi.
My questions:
Is this correct practice, both theoretical and experimental?
Are these measurements consistent with what others have observed for small RF helical antennas operating in normal mode?
The FCC person claims to often hear of readings of 0 dBi, or even -1 to -2 dBi. Should I reconsider what work I've done above, or are those readings a result of someone else not knowing what's going on?
Thank you very much in advance everybody.
Paul
I am currently working on finalizing some paperwork with regards to a 900 MHz transmitter for the FCC. They claim that they need this piece of information, specifically for IC documentation. I know a handful of things about RF and antennas, but I do not know enough to feel confident about any numbers that result from experimentation, theoretical equations, and the like. Here is what I have done:
Antenna characteristics:
Length: 18mm
Nturns: 8
Diameter of loop: 4mm
Freq: 900 MHz
Utilizing an equation taken from a paper on helical antennas, I have obtained the following:
g[dBi] = 10.25+1.22*(L / lambda)-0.0726*((L / lambda)^2)
I obtain 10.3 dBi gain reading using approximately the values of antenna characteristics listed above.
Next, a colleague constantly activated a transmitter with NO antenna oriented such that the receiving antenna and transmitter shared the same axis (pointed at one another directly). Then, a spectrum analyzer was used to record the average of peak readings of the transmission. Then, the antenna was replaced, and the readings were taken again.
75 dBuV/m with antenna, 54 dBuV/m without antenna; or 5,623 uV and 501 uV in non-log units. (20 log10(G) used). Dividing 5,623/501 and taking the log10 and multiplying by 10 yields, what Wikipedia claims to be, dBi units. The result obtained was about 10.5 dBi.
My questions:
Is this correct practice, both theoretical and experimental?
Are these measurements consistent with what others have observed for small RF helical antennas operating in normal mode?
The FCC person claims to often hear of readings of 0 dBi, or even -1 to -2 dBi. Should I reconsider what work I've done above, or are those readings a result of someone else not knowing what's going on?
Thank you very much in advance everybody.
Paul