Subject: 641
Posted: 22 November 2009 at 1:58pm
Hi Dave,
There are a few possibilities here... first is that the M1 mini doesn't have enough output power to fully energize the antenna. Building a smaller sized antenna should help this, but also cutting the width of the copper tape down to a 1mm pathway with a 1mm spacing between should help. In reality, it took me several days to get the antenna shown in the book to work, and never even got close to working as well as the commercial Fieg antenna I bought. Unfortunately I'm not an educated engineer, I'm just a garage engineer, and passive system antenna design is not my forte.
The other possibility is that the M1-mini may have the capacitive components on the board and only require an antenna loop of a specific Henry measurement. I've not checked the documentation, but that might be the case... which would mean your capacitive work on the antenna is redundant and throwing everything off once you connect it to the board.
To help verify this, first check the waveform coming from the M1-mini with no antenna attached. You should at least see a 13.56MHz carrier signal being generated. Then check the waveforms on the antenna when connected to the function generator, then check them when the antenna is connected to the M1-mini... if the waveform distorts or completely disappears when connected to the M1-mini then most likely the board has capacitive elements on it and you just need to provide an appropriately tuned coil antenna.
On the other hand, if you can confirm with the o-scope that the antenna is resonating at 13.56MHz when connected to the M1-mini, then I'd cut down the pathways to 1mm wide and then focus on getting the amplitude as high as possible.
Hope that helps :)