Analog Filters-Constant Delay . To anyone.

[Wirechief]

Hi Everyone, I have a question about an 8 pole, 6 zero constant delay filter? What does 6 zero mean and what operating parameter does it affect? I am one of the uninformed by the way. I asked Frequency Devices to send me one of their analog filter design guides and found this filter mentioned. I hope everybody is doing well here on the forum and we are sad about the losses that the detector crowd has experienced. God Bless all of you. John, Wirechief.

 

[Wirechief]

If I am reading right I understand that in A/D filtering that some accuracy is lost during sampling. Does this make analog filters more desireable among Engineers? I wonder how much accuracy is sacrificed. If I understand right Eric don't you prefer using analog filters in your detectors? I'm finding the subject of filtering interesting especially when it pertains to metal sensing. Again I'm in the uninformed catagory but want to learn as much as possible. Thank goodness for the filter! Thanks, John the Wirechief.

 

[Reg]

Hi Wirechief,

I was hoping someone would jump in on this question by now that knew what they were talking about, because I sure don't. It has been so long since I worked with Laplace transforms, I am just lucky enough to remember how to spell the words. Don't remember much else though. I took this class back around 1970 and haven't used it since, so I am just a little rusty.

Now, with that stated, I will try to limp through a basic answer to your question about poles and zeros.

Any filter network having a combination of specific inductance, capacitance, and resistances can be displayed in a mathematical equation having components in both the denominator and numerator. This equation will be the math equivalent of the actual filter or number of filter combinations.

Now, with that said, then the poles and zeros are determined by the solution to the equation(s) of the filter network. The zeros, I think are the solutions to the numerator and the poles are solutions to the denominator.

One can sort of think of the number of poles and zeros as the number of filters. My guess, and it is just a guess is the 6 poles refer to a high pass filter having 6 stages.

Again, don't take this info as being exact, but hopefully, it helps in explaining a little.

A thorough explanation really would require a working knowledge of differential equations and laplace transforms, something that faded out of my memory years ago.

Reg

 

[Wirechief]

Ok I see what it is indicating now. I enjoy building low power ham radio tranceivers which usually have crystal filters in them and we call them 2,3, or 4 pole filters according to how many stages that are built into the receiver. Thank you very much Reg for the info and I think of a metal detector as a radio with a portable antenna on the end of it. I will say that I have found metal detectors to be much more interesting than radios lately. I am looking at active filter designs and if you know of a good textbook on them let me know. Well God Bless and happy hunting Reg! John Wirechief.

 

[locusman]

I am new to this forum and have wanted to tinker with PI circuits also. What basic schematic are you referring to in your advice to your colleagues? It sounds like all of you were referring to the same design schematic. How do I get ahold of a copy of this schematic, if possible? Any information you could provide would be appreciated.

Mark

 

[Reg]

Hi Mark,

A good PI design to learn from is the Hammerhead (HH) PI designed by Carl Moreland. This is a good basic design that is easy to build and works quite well. To make things easier, Carl has or did have pc boards made which makes building the machine a whole lot easier than trying to make the pc board also. They are a high quality pc board.

Carl has also provided quite a bit of information about the circuitry and how it works in his write-up of the HH PI.

Here is the link to Carl's home page. Just select the Hammerhead project.

http://www.thunting.com/cgi-bin/geotech/pages/common/index.pl?page=main&file=main.dat

You might email Carl and ask if he still has any pc boards available if you are interested in building a PI.

Hope this helps.

Reg