This is the one @PulsarForce made which @Compgeek used
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This ^
Great work team, I got here just as the dust settled!
Well, you’re now tuned and at a safe (for the electronics) voltage - it’s a very good place to be! If you replace that with a lower value to get up around 25v you’ll get more power and some better range but definitely on the right track!
How do you figure out what resistance you need?
That depends mainly on what tools you have available: if you have an LCR meter you can measure the properties of your antenna and potentially the properties of the existing antenna and then use transfer function equations to find the resonant frequency and resonant gain and try to match the gain (and obviously 125kHz resonant frequency).
The other way is to use trial and error, changing resistors and coil windings and then running hw tune each time until you reach an acceptable balance of voltage, range and frequency.
Personally, I’d go for the second option even if I did have a LCR meter, since I don’t know the output capacitance / inductance on the PM3 easy board to begin with, which means that the equations need to be in relation to the existing antenna rather than theoretical ideal values (i.e. the same reason as why ProxLF only works on the RDV4)
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Changing the resistor doesn’t impact the tuning, its DC resistance that changes, nothing that affects the AC Impedance.
The easiest way is to just try different values until you get close, the ‘hw tune’ command gives you the info you need so you don’t need any other test and measurement tools.
If you want to get all precise on RF design, you could, but not really worth doing. Your other option is to try and match the DC resistance of the stock antenna to get you in the ballpark - but you’re already close, so I’d just play with the value.
This includes the resistance, since resistance is the real part of AC impedance. However, you are right that the frequency of the tuned antenna should theoretically stay the same (though the properties of the resistor used may make this not the case)
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BTW, would you mind sharing what LCR values you got for your antenna and the existing one? I’d love to know!
Well, yes, but to clarify what I meant, the change will be linear with no frequency component, so although altered in actual impedance it would be evenly affected across the frequency range
As for LCR values, I think I’m close to the stock one, I only have a cheap meter but if I get time will dig it out and measure - haven’t got the figures to hand, it was all back of the envelope and not properly documented. Being a one off I documented process not specifics
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I’m sure I’m a little too late here, but a little trick if you don’t have exactly the right resistor is to use 2 in parallel, it will cut the resistance in half. You can do the math on it too and use different ones in series/parallel to make unusual resistance values, but that’s not as fun as just mix and matching random resistors up in series/parallel.
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I love this. I salvage a TON of parts from old electronics and SMD components are often overlooked
Such a goldmine or little odds and ends to make your projects work
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How long was the rod that you ended up using? I am going to try and make this to hopefully read by possibly dead NExT as a last ditch effort.
@Compgeek top post has some great info, if you were going to try this
and this may come in handy also 
(@pulsarforce is @compgeek brother, who also made a homebrew antenna)
@PeachSqueezer made a different version also, so he may be able to give you some pointers also.
I read the 9mm as the diameter, I meant the length they ended up cutting it to.
25 to 35mm. It is in one of the posts mentioned above.
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I ended up somewhere around 40mm, my first attempt at 25ish was too short.
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Resurrecting. Does anyone have a good source for ferrite rods in the US? Also, what’s the ferrite mix that you all used?
Batteries. Afghans just burn them then pull the carbon rods out. Don’t know if it’s the same but…… worth a shot haha.
I ended up buying mine from Digikey.
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Thanks! This got me to where I needed to be.
I xref’ed the mix 78 available with Fair-Rite’s listing.
From their site Mix 78 is best for “power applications for frequencies up to 200 kHz and low loss inductive applications to 500 kHz.”
They even specifically mention RFID rods.
Ordered a couple.
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