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Author Topic: What inductor is this specifically?  (Read 744 times)
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I am trying to figure out what inductor is on this PCB, can someone help me identify it?  Thanks!

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http://how-to.wikia.com/wiki/How_to_identify_inductor_markings
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Would it be safe to say that http://www.ebay.com/itm/5pcs-Common-Mode-line-filter-10mmx6mmx5mm-Inductor-1mH-1A-/150924583713?pt=LH_DefaultDomain_0&hash=item2323ce6321 would be a drop-in replacement then?
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How many wires does the inductor have comming out of it. There are four on a common mode choke.
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It appears from looking at the PCB (Front and back), that the power rail goes straight through the inductor (2 points).  The purpose of this circuit is to filter 1.2GHz noise on power rail.  Instead of spending $15 on a pre-made one I would rather just get the proper inductors and do it myself smiley.  If anyone can point me in the direction of figuring out what inductor would work for specific frequencies (And filter caps too), that would be awesome.  I want to make one for 433mhz as well.
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So it looks like it is a Pi circuit, last schematic here.
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

However, for such high frequencies you need a ferrite to wind the coil on that is good at those frequencies. You also need capacitors that will work at those frequencies. These tend to be small ceramic ones.
However, there are components called feed through capacitors that are designed to be mounted on a chassis and the power actually goes through the capacitor.
Make sure that the inductive reactance Xl = 2Pi FL is about ten times as the capacitive reactance Xc = 1/ 2Pi FC
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It looks to me like a 1000uH (1mH) shielded power inductor.  Digikey has about 14 PAGES of these, in various sizes and current/power ratings (the latter is likely to be important.)  You can probably come close by picking one that looks the same and has the same size (measure it) (or just pick the highest power rating in that size.)  For a better match, try to measure the DC resistance of your existing coil and match that as well.

The eBay part looks like something entirely different.
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It looks to me like a 1000uH (1mH) shielded power inductor.  Digikey has about 14 PAGES of these, in various sizes and current/power ratings (the latter is likely to be important.)  You can probably come close by picking one that looks the same and has the same size (measure it) (or just pick the highest power rating in that size.)  For a better match, try to measure the DC resistance of your existing coil and match that as well.

The eBay part looks like something entirely different.

I don't have one to measure, I am just basically building that circuit myself.  My gut feeling was to look for something that looked the same, now though I know what to look for specifically! 

Shielding certainly is important too, this is going to be used on an FPV plane and my goal is to make all electronics as efficient as possible, and there are so many things going on in such a tight space, you have analog video on 1.3GHz being TX'd at 700mw, I am going to have a 433MHz transceiver operating bidirectional at 100mw, quite a bit of servos, motor, lights, so I want to make sure electrically everything is as perfect as possible smiley.
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That's at least 4 orders of magnitude too large an inductor for 1.2GHz! It will filter out noise in the 10kHz to 100kHz range pretty well and have a self-resonant frequency around 1MHz I suspect.  For 1.2GHz you use ferrite beads threaded on the power rails, and plenty of ceramic decoupling.  Each RF section in its own metal box with feed-thru caps to route power and low-freq signals in and out is standard - have a look at some amateur radio UHF transmitter designs,
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So you do not believe the above PCB design would actually filter 1.2GHz noise?  It's supposed to filter power to the 1.3GHz TX itself according to it's specifications, not on the 433MHz link.
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Filtering power to a 1.3GHz transmitter is not the same as filtering out 1.3GHz.
Yes it will filter noise but not the noise of the transmitter.
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It looks to me like something designed to filter motor noise (servos, brushed or brushless main motor) out of the power going to the sensitive RF components (receiver, etc)
With the components shown (100uF caps, 1000uH inductor), you should get a low-pass filter with a cutoff frequency of about 700 Hz.  Higher frequencies would be filtered out too (more, in fact), up to practical limits of the components (which are going to be very real, once you get to RF frequencies.)
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It look to me that you are looking for a problem to throw a solution at. Can you clearly state what 'noise' (frequency and amplitude) you are trying to filter out from what? That is, what are you specifically trying to protect from 'noise' and what do you think are the source(s) of that noise? Only then can you start to apply different and/or effective filtering methods.

Lefty
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I am trying to be preventative of issues.  Ultimately the efficiency of range is what I am looking for, I want a clean noise floor both EMI and RF for the 100mw 433MHz data link to be able to both transmit and receive to the greatest distance possible, and for my 1.3GHz video link to get the best range possible without anything interfering with anything else.  There will be a motor and servos running on the same battery too, as well as autopilot, OSD, GPS, Etc, so I think filtering will make all of the difference to get the best performance.

That particular product in my OP according to it's specs are supposed to filter something from 1000MHz to 1400MHz noise, I guess the idea is to prevent noise from getting into the video TX, but I don't know enough about RF to know really if this circuit was good for the purpose or not. 

I am still waiting on some components to get in, plus I think I am going to order one of those USB SDR's (Capable of 50MHz to roughly 2.2MHz), which I could use as an RF meter to test RF noise, and I will see if my DSO Nano is capable of spotting any power noise on the power rails.

At this moment I am trying to really pre-plan everything as much as I can.

One thing I know is that 433MHz has the ability to create harmonics close to 1.3GHz, and 1.3GHz can effect GPS, but luckily the airframe I am installing this onto is quite large so separation for RF components should be pretty good, but it also means longer wires and EMI to consider, toroids will be used on pretty much everything getting a power rail smiley.
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I am trying to be preventative of issues.  Ultimately the efficiency of range is what I am looking for, I want a clean noise floor both EMI and RF for the 100mw 433MHz data link to be able to both transmit and receive to the greatest distance possible, and for my 1.3GHz video link to get the best range possible without anything interfering with anything else.  There will be a motor and servos running on the same battery too, as well as autopilot, OSD, GPS, Etc, so I think filtering will make all of the difference to get the best performance.

I understand the concern, just question the method, or rather the lack of engineering methods being applied.

That particular product in my OP according to it's specs are supposed to filter something from 1000MHz to 1400MHz noise, I guess the idea is to prevent noise from getting into the video TX, but I don't know enough about RF to know really if this circuit was good for the purpose or not.

Not with caps that large, it simply can't be a bandpass or bandstop filter with corners at 1000 and 1400 Mhz. It is most likely a low pass Pi filter, but have no idea if it's still effective in it's stop band up to >1000Mhz.

I am still waiting on some components to get in, plus I think I am going to order one of those USB SDR's (Capable of 50MHz to roughly 2.2MHz), which I could use as an RF meter to test RF noise, and I will see if my DSO Nano is capable of spotting any power noise on the power rails.

Generally RF spectrum analyzers are the instrument of choice to look at and measure noise floor at any specific frequency(s) of interest.

At this moment I am trying to really pre-plan everything as much as I can.

One thing I know is that 433MHz has the ability to create harmonics close to 1.3GHz, and 1.3GHz can effect GPS, but luckily the airframe I am installing this onto is quite large so separation for RF components should be pretty good, but it also means longer wires and EMI to consider, toroids will be used on pretty much everything getting a power rail smiley.

Yea, that is a lot of stuff, and every installation tends to be unique when it comes to RF interference, EMI, etc.

Good luck
Lefty

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