Well I guess I shouldn't complain because it works (at least for the 125Khz tags I've tested), but my voltages aren't great either. I'm working on my portable antenna but I suppose these are good enough, yes?
# LF antenna @ 11 mA / 14099 mV [1273 ohms] 125Khz
# LF antenna @ 23 mA / 28466 mV [1187 ohms] 134Khz
# HF antenna @ 21 mA / 5091 mV [235 ohms] 13.56Mhz
Oh, and since the object of the exercise was to determine the resonant frequency of the antenna, I've modded 'sweeplf' to do it for you:
proxmark3> sweeplf
> sweeplf
#db# Antenna resonates at:
#db# 134.831 kHz
I've tested and checked in your update to the Windows source, works fine.
I've also checked in an updated command.cpp -- it wasn't compiling in Windows. You may want to confirm my change is ok, it's line 706 in command.cpp in function CmdLoCommandRead:
- strcpy(&c.d.asBytes + strlen(c.d.asBytes),dummy);
+ strcpy((char *)&c.d.asBytes + strlen((char *)c.d.asBytes), dummy);
BTW, I also added the display of Cursor A and B positions, but since I don't have a Windows dev environment I didn't want to tamper with it's code so maybe someone who does could bring them into line?
Thanks!
]]>Thanks for the help!
]]>From what I gather, plugging the dt between zero and the time at the max value into the formula d18c7db gave us will give you the optimal frequency that your antenna is currently tuned to. I'm not sure why your dt value is so wacky, but when i click on the peak (in the windows version) while trying to tune my antenna, it gives me about 92. So 12,000,000/92 = 130434.78, which I believe is the Hz value of the peak. This is a pretty decent balance between 125khz and 134khz. If you're shooting for 125khz, you'd probably want the spike to be at 96, and ~89.5 for 134khz.
If you want to increase the dt of the spike, add more wire. Remove wire to decrease the dt.
-Ryan
]]>Here is a screenshot:
What is that telling me?
]]>Ideally you want to bring those two voltage values close to each other, at the moment your antenna looks like it's tuned towards the higher frequency. Use the losweep, losamples and plot commands and note the numeric value under the peak. That gives you the antenna tuned frequency like so freq = 12M/(value+1)
Try removing a couple of turns from the coil and recheck the values, if the frequencies move toward each other, continue removing turns, otherwise you might have to add turns.
]]>https://www.lafargue.name/article2751.html
Is this for 125 or 134, and what should the other one be?
Mine currently looks like this, so I'm not sure whether to adjust up or down...
> tune
# LF antenna @ 11 mA / 14501 mV [1273 ohms] 125Khz
# LF antenna @ 31 mA / 37194 mV [1187 ohms] 134Khz
# HF antenna @ 0 mA / 64 mV [235 ohms] 13.56Mhz