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Image Embedded Internal Filter for F-Scan2 users
 
Stephan2 Views: 4,297
Published: 15 years ago
 

Internal Filter for F-Scan2 users


Dear Group,

It has been a while since I did post on my development of my first F-Scan2 filter design. It is almost a year now! Interest revived when I attended the Frequency Research Workshop at Las Vegas a month ago. This workshop was held by Dr. Jeff Sutherland and was very interesting!

I was approached regarding my filter and I was not very happy with the external filter, it needed its own power supply, you needed to connect it to the F-Scan2 and it was expensive and time consuming to build!

So I looking for a cheap alternative and I looked at various filter ICs that are available and tried a switched-capacitor 5-pole Bessel filter form Linear Technology, the LTC1065CSW. It requires very few other external parts and draws very little power. I added an on-board DC-DC converter chip to generate te necessary -5V, the +5V suppls is available inside the F-Scan2. The filter worked like a charm right from the first prototype. The second revision made the board just a little larger than a US quarter!

The small size was achieved by state-of-the art surface mount technology and that also brought the cost down. I can offer this board for just $50. This is essentially at my cost, I don't even care if I recover my development costs. This is for you, the F-Scan2 user.

I have extensively posted documents about test on the F-Scan2 on the Yahoo FScan forum, not only on the filter but also on how to avoid spurious peaks that the F-Scan generates every 1365.5Hz, therefore named 'repeat pattern'.

If you are a user of the F-Scan2 or want to buy one, or just curious, then I recommend that you become a member there on this forum.

You can see the comparison in size how really small it is!

And here is how you can insert it into the F-Scan2:


Since opening the F-Scan2 could void its warranty, I am sending a filter to Thomas Boehme in Switzerland who builds the F-Scan2. I had the pleasure to meet Timo Boehme during the Las Vegas Frequency Research Workshop and we had a good discussion about the filter. If the filter is approved, there is still the issue on who Mr. Boehme will authorize to install that filter. However, those of you, who feel comfortable and have enough technical skill to use a screwdriver to open the cover of the F-Scan2 and insert it yourself, you may order the filter from me.

 

I announced the filter on the F-Scan2 forum and so far I have had already six responses with an order request! Every filter that I send is fully tested and it is a snap (Plug & Play) to install it as you can see from the picture above. You disconnect the finger electrode connector inside the F-Scan2, drop the board in and reconnect the finger electrode connector - done! The +5V power, ground and finger electrode signal are all on this three-pin header where the board is connected to. So there is no soldering or wiring necessary.

Q: What does the filter do?

A: It is a low-pass filter with its -3dB point at about 100Hz. It removes any noise or frequency bursts that leak through the body to the finger electrodes, which confuses the analog-to-digital converter (ADC) if the DIRP scan is at or comes close to 1365.5Hz or its harmonics. 1365.5 Hz is the sampling rate of the ADC during a DIRP and when a signal with the same frequency or harmonics of it is sampled, it shows 'spurious peaks' due to aliasing (the technical word in signal theory for this kind of behavior). Since the filter starts to suppress signals higher than about 225Hz (that is about twice the -3dB point and the filter starts to pick up) there are no more spurious peaks!

Q: If the filter cuts everything above 225Hz, how can the F-Scan2 work at higher frequencies?

A: The F-Scan2 sends out burst of frequencies as high as 15MHz and along with this there is a 6V DC voltage at the output of the F-Scan2 (hand electrode) but it measures only the slowly changing DC level as a result from the physiological response of the body to that frequency. So the ADC of the F-Scan does not measure the signal from the higher frequencies, it It would never be able to do that since it only samples the finger electrode input 16 times with a sampling rate of 1365.5Hz.

Q: Why should I use the filter, my DIRP works just fine.

A: You may or may not pick these repeat pattern peaks but how do you know? I have posted on this issue extensively on the Yahoo FScan forum (you have to become a member to view). I also posted and uploaded an Excel 'calculator' that allows you, without a filter, to avoid to hit these repeat pattern frequencies. It is quite straight forward how to use it. And you can download a free Excel viewer from Microsoft if you don't have Excel. In my uploaded PDF documents on the forum (in the 'files' folder) I also show how you can analyze your DIRP data once you have imported it into Excel. I have developed a logical Excel function that can show you possible locations of 'repeat pattern hits' in your data. But with a filter you don't ever have to worry about that and you get fewer hits during a DIRP and you don't waste time to zap hit that aren't real.

The images of the filter can also be found on the 'Zapper Image Gallery' in the F_Scan_Filter_Folder.

With best regards,

Stephan

 

 

 

 

 
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