ateet101
Newbie level 6
Hi,
I have the following 3 antennas:
Tunable dipole: tuned to 375MHz for my measuements with known Gain
Broadband Dipole: 200-500MHz unknown Gain
UHF antenna: 240-380MHZ unknown Gain
I put the antennas 'Broadband Dipole' and 'UHF antenna' in an anechoic chamber 3 meters from each other. I measure -35dB in power on the network analyzer at 300-340MHz. Second, I replace the 'UHF antenna' with the 'Tunable Dipole'. I receive -37dB in Power. Let's say the known gain of the tunable dipole in 2dB between 300-340MHz.
Gain of UHF antenna = Gain of Tunable dipole + (Power to UHF Antenna - Power to Tunable dipole)
Gain of UHF antenna = 2dB + (-35dB - (-37dB)) = 4dB
The problem is when I move the Broadband Dipole to 5 feet. I understand that I should receive different power levels because the antennas are further away from each other, but my gain numbers are different too. After making the same calculations, i get 7dB of Gain.
Question: Why is there such a big difference of 3dB in Gain? Shouldn't the gain of the UHF antenna be the same regardless of position?
Thanks
I have the following 3 antennas:
Tunable dipole: tuned to 375MHz for my measuements with known Gain
Broadband Dipole: 200-500MHz unknown Gain
UHF antenna: 240-380MHZ unknown Gain
I put the antennas 'Broadband Dipole' and 'UHF antenna' in an anechoic chamber 3 meters from each other. I measure -35dB in power on the network analyzer at 300-340MHz. Second, I replace the 'UHF antenna' with the 'Tunable Dipole'. I receive -37dB in Power. Let's say the known gain of the tunable dipole in 2dB between 300-340MHz.
Gain of UHF antenna = Gain of Tunable dipole + (Power to UHF Antenna - Power to Tunable dipole)
Gain of UHF antenna = 2dB + (-35dB - (-37dB)) = 4dB
The problem is when I move the Broadband Dipole to 5 feet. I understand that I should receive different power levels because the antennas are further away from each other, but my gain numbers are different too. After making the same calculations, i get 7dB of Gain.
Question: Why is there such a big difference of 3dB in Gain? Shouldn't the gain of the UHF antenna be the same regardless of position?
Thanks