EMF Probe Project

Thread Starter

Butterworth

Joined May 6, 2009
135
I am not an expert on antennas.
You could try a big loop, or a coil wound on a ferrite rod. Have a look at
http://www.radio-electronics.com/info/antennas/ferrite_rod_antenna/ferrite_rod_antenna.php
http://www.stormwise.com/page26.htm

Google "ferrite rod". Some of the crystal radio parts suppliers sell ferrite rods.
I looked up the stormwise one, seems really promising, but if I were to use one of those 2000u rods, won't that throw off the whole circuit? I mean the basis of the design was around the inductor isn't it?
 

Ron H

Joined Apr 14, 2005
7,014
According to simulation, raising the inductance lowers both corner frequencies and raises the sensitivity.
In any case, your sensitivity will probably be directional, so rotating the antenna might pick up one source and lose another one.
 

Thread Starter

Butterworth

Joined May 6, 2009
135
According to simulation, raising the inductance lowers both corner frequencies and raises the sensitivity.
Interesting, is there a graph that plots out the inductance vs. sensitivity on that sim? Is is possible to post it?

In any case, your sensitivity will probably be directional, so rotating the antenna might pick up one source and lose another one.
Yes I found this while testing it around the house. It works best at right angles to the source.
 

Ron H

Joined Apr 14, 2005
7,014
Interesting, is there a graph that plots out the inductance vs. sensitivity on that sim? Is is possible to post it?



Yes I found this while testing it around the house. It works best at right angles to the source.
OK, here is the results of the sim, using 1mH and 10mH. No guarantees. I don't even know if I modeled the inductor stimulus correctly.
 

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Thread Starter

Butterworth

Joined May 6, 2009
135
OK, here is the results of the sim, using 1mH and 10mH. No guarantees. I don't even know if I modeled the inductor stimulus correctly.

Thank you Ron H, it looks like that the 10mH inductor gives you a good gain increase throughout the entire bandwidth, up until the higher end of the frequencies. I did notice that you modeled the TL074 though. Will this matter in real life testing that I have the TL084?
 

Ron H

Joined Apr 14, 2005
7,014
Thank you Ron H, it looks like that the 10mH inductor gives you a good gain increase throughout the entire bandwidth, up until the higher end of the frequencies. I did notice that you modeled the TL074 though. Will this matter in real life testing that I have the TL084?
TL084 should be fine.
 

Thread Starter

Butterworth

Joined May 6, 2009
135
So, now that we all had a relaxing weekend, I am sure that the BBQ's went well? :)

I have finally made the new PCB layout, if maybe Ron H or anyone else with much talent to spot my errors :)rolleyes:) would like to confirm that I finally got this one right, based on Schematic R1 that Ron H has so graciously provided, it would be greatly appreciated!

Attached is the new PCB layout. All thoughts and comments welcome! :)
 

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Thread Starter

Butterworth

Joined May 6, 2009
135
BUMP

Is no one able to give input on the circuit layout?

I could really use the help on this.

Thanks in advance, to anyone who is willing to help on this.
 

Ron H

Joined Apr 14, 2005
7,014
BUMP

Is no one able to give input on the circuit layout?

I could really use the help on this.

Thanks in advance, to anyone who is willing to help on this.
I checked it. It appears to be electrically correct, except you will have to mount the transistor on the bottom side of the board, according to the datasheet. The picture there is of the top side of the transistor.
I don't like the length of your ground trace, but it would be difficult to fix it on a single-sided board. Of particular concern is the length of the path from pin 4, through C5, to pin 11. It needs to be much shorter. If the circuit oscillates, connect another 100nF cap from pin 4 to pin 11 on the back side of the board, using very short leads.
 

Thread Starter

Butterworth

Joined May 6, 2009
135
I checked it. It appears to be electrically correct, except you will have to mount the transistor on the bottom side of the board, according to the datasheet. The picture there is of the top side of the transistor.
I don't like the length of your ground trace, but it would be difficult to fix it on a single-sided board. Of particular concern is the length of the path from pin 4, through C5, to pin 11. It needs to be much shorter. If the circuit oscillates, connect another 100nF cap from pin 4 to pin 11 on the back side of the board, using very short leads.[/QUOTE]

Thank you Rom H, I can see that the V- lead is too long, I will try to shorten it without sacrificing the layout, as well as fix the Q1 orientation! ;)

The V+ through R10 to pin 4 then throuh C5 can be shortened, I will try to fix that tomorrow along with the rest. - Will this be the major cause of oscillation? If I were to fix another 100nF cap on pins 4 & 11, it will be very hard for me to do so on the back side of the board, I do not have the proper drillset up to make the .82mm hole size without breaking the bit! :rolleyes:

Thank you for the professional input! I will make the changes and post the result.
 

Ron H

Joined Apr 14, 2005
7,014
The V+ lead to R10 is not an issue - only the loop from pin 4, through C5, and back around to pin 11.
When I said put the cap on the back side, I meant you could tack it to pins 4 and 11 with solder. You wouldn't need holes, although it would look "tacky".:D
Actually, you have spare holes next to the IC pins. What are those for?
 

Thread Starter

Butterworth

Joined May 6, 2009
135
I see, so if I can shorten the lead around from C5 to pin 11, it should help with oscillation?

I can solder the leads from another 100nF cap across pins 4 & 11 on top of IC1? I am not worried about asthetics. ;)

The holes are shown because of the program I use, its supposed to be filled on the top layer, not through holes.
 

Thread Starter

Butterworth

Joined May 6, 2009
135
Ok Ron H, this is the new layout based on the revision suggested. I did not include the 100nF cap across pins 4 & 11 because I can retro-fit that in later on if I need it.

I shortened (at least tried to shorten) the V- lead for HP1 and pin 11, and removed the V- lead after C5 to make it shorter. I also re-arranged the Q1 circuit to fit a bit more snug and to give access to the V- rail I ran from pin 11 on the bottom.

I hope this is better, let me know either way if it looks better or not.

Thanks.
 

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Ron H

Joined Apr 14, 2005
7,014
Your original layout had a shorter path length from pin 4, through C5, to pin 11. I have highlighted it in red on the old layout and the new one. I didn't check the rest of your new layout.
Are you aware that the 4 op amps on the chip are interchangeable? You don't have to use the pinouts that I showed on my schematic. If rearranging them can shorten the traces and make the layout simpler, then do it.
 

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Thread Starter

Butterworth

Joined May 6, 2009
135
Your original layout had a shorter path length from pin 4, through C5, to pin 11. I have highlighted it in red on the old layout and the new one. I didn't check the rest of your new layout.
Are you aware that the 4 op amps on the chip are interchangeable? You don't have to use the pinouts that I showed on my schematic. If rearranging them can shorten the traces and make the layout simpler, then do it.[/QUOTE]

You know that is something I didn't even think of! :p

I will see what I can come up with on Monday, I do not have the pcb file with me at this moment. Back to the drawing.... um, monitor? :D

I see about the ground trace between the old and new layouts, I will try the amp switching and see what comes of it.

Again Ron H, you have givin me great insight! Thank you again!
 

Thread Starter

Butterworth

Joined May 6, 2009
135
Hey Ron, I finally got to re-do the schematic, things have been very very busy lately, so that being said here is the new layout. I think it is ok in terms of having no errors, but you mentioned before that the traces were too long on the last schem, I tried to fix that by switching U2 & U3 on the layout.

(Please pay no mind to the holes on the schematic, the program I use defaults all pads as through holes for some reason. This board has no holes for traces! Only mounting holes on the corners.)

Let me know your thoughts or concerns!

Thanks! :)
 

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