log detector

[ws0822]

Does anybody know what is log detector? I need some information about the function of log detector....
i have tried search at google but it seem like only few information is available.
Actually i found this thing at this website (https://www.qsl.net/pa3ckr/signalgenerator/). And i cant understand what is the function of log detector and its uses in frequency sweeping to determine frequency respond of a circuit under test. Can any one please give some explanation about that? Thx in advance...

 

[Sceadwian]

The third refrence to log detector provided by Google seems to describe things pretty well!

 

[ronsimpson]

ws0822,

What is the frequency range? There are RF log detectors and some audio parts.

 

[Gobbledok]

Log Detectors are also called "Automatic Toilet Flushers"

 

[RCinFLA]

Log detector are used to compress a signal level into a usable range that provides more dynamic ranging display. Example would be to provide dB scaled output level.

There are also log compressing amplifier chains that expand the overall dynamic range of the amplifier string in front of detector.

 

[ronsimpson]

Years ago people that sold trees to the lumber mill would make their mark on a tree and then push it into the river. At the limber mill they counted how many trees came from each person up stream. The logs are headed down stream at the same time as boats pass up and down the river. Up stream boats had a log detector (person) on the bow of the boat. If the log detector failed you ran the risk of getting wet.

 

[ws0822]

okay... i think i have some ideas about log detector already.... thx you guys =)
btw, for the sweep frequency part in the website, he used shift register and dac to sweeping up and down around a given frequency and display the x-axis of oscilloscope.
So i think the x-axis is in linear scale, is it possible to change it to log scale?

 

[RCinFLA]

Yes, there are sweep displays on some spectrum analyzer and just about all impedance/network analyzers that allow log sweep. For broadband filters it give a better view of corner frequencies and multi-octive skirt response.

 

[bountyhunter]

Does anybody know what is log detector? I need some information about the function of log detector....

I designed this one to drive an analog power meter. It takes the voltage signal coming from a stereo amplifier output and gives a display that is "log scale". It also has a peak detector before the log amp stage because log amps have very poor bandwidth.

 

[JimB]

Log Detector.

If you have a look at the AD8307 datasheet,

You can find it here:
https://www.electro-tech-online.com/custompdfs/2012/03/AD8307.pdf

There is a section which describes in detail how it works.

I have used the 8307 in a power meter which I built a couple of years ago, it was a nice easy chip to use and the results were exactly as predicted by the datasheet.

My power meter was for low level RF signals between 100khz and 500Mhz and power levels of -70 to +15dbm.
The display is a digital meter calibrated in dbm.

JimB