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> AD8307 analog devices dc ~ 500 mhz 92 db log amp sa X2@
AD8307 analog devices dc ~ 500 mhz 92 db log amp sa X2@
Here you are looking at two pieces of AD8307 Logarithmic Amplifier from Analog Devices which by its ultra linear db-to-voltage characteristic provides over 90 dB in measurement range. This chip outputs a DC voltage according to the input power level and provides an stable 25mV per dB on its output pin 4, measurebble with a Digital Volt Meter.
This chip works for frequency range from DC to 500MHz. However as you can see from characteristic charts below (Fig 33 / 34 from datasheet), AD8307 has its best performance at 10MHz against other frequencies. It has the widest dynamic range from -75dBm to +15dBm (total 90 dB), very linear in log reponse chart while still within 1 dB error.
As the iput signal is downconverted to much lower IF frequency (usually at 10.7 MHz or 21.4 MHz) so it can be characterized on a Spectrum Analyzer (SA) or Scaler Network Analyzer (SNA), a wide dynamic range of power measurement is made possible with this chip when you tap it into the IF circuitry.
They have been so popular that it becomes an industrial standard for an RF Power Meter on 500MHz range or SA/SNA. There have been quite a lot of projects on this chip and you can easily find them on the internet.
As stated above, it outputs a stable 25mV/dB so match with this same scaling factor of another chip AD603, a low noise, Variable Gain Amplifier. A combination of these two provides over 120dB on the measurement range. Details of the AD603 can be found on its separate page of my listing here. The basic circuitry of 120dB measurement range can be found on my other listing at a more attractive bundle price (AD8307 & AD603) .
One thing I have to point out, there are two packages for the AD8307. One is the convectional DIP package and the other is SMD package. Only the SMD package, the AD8307AR work up to 500MHz. The high parasitics on the long leads of AD8307AN makes them works below 100MHz, with accuracy.
Along with the AD603, AD8307 is getting hard to find so they are getting more expensive as well. Now you can grab some for a try on these projects before they are gone ! at a very attractive price than any other sources.
Download AD8307 datasheet here
Power Meter designed by OZ2CPU. and published in October 2002, ELEKTOR MAGAZINE.
Portable RF Sniffer and Power Meter by Paul Wade, W1GHZ.
Simple RF-Power Measurement by Wes Hayward, W7ZOI, and Bob Larkin, W7PUA.
