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Your cable impedance is 50 Ohm, port impedance is 50 Ohm likely and impedance of your antenna is small ohms of fraction of ohm. Mismatch, energy does not go into antenna.
vfone, this is correct - antenna by itself resonates at 7.1MHz, when transmitter connected - at 6.3MHz.
Why after matching with parallel inductor antenna will not radiate the same - because of losses in matching inductor?
It is part of the circuit. I believe it is there to compensate capacitance of mosfet but can not say for sure. I tried shorting it, changed it's value. It did not result in improvement.
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Also note, mosfet on the schematic is not correct part number. I do not have correct...
Brian,
I guess I did not make myself clear. The L and C values for the antenna are values derived from measurements of existing antenna. I can not reduce value of C1.
Andrey
Of course FvM, Inductor in parallel! How can I forget? Thank you FvM!
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Please find attached schematic.
I see now how to tune it higher - add parallel inductor. What impedance to match it to? It is not 50 Ohm, FET will present dfferent impedance in 'on' and 'off' states.?
HF (8.2MHz) loop antenna is resonant at 6.3 MHz (lower than required) without any capacitors across terminals. How to re-match it to make it resonant at 8.2MHz?
Antenna is driven by a MOSFET driven by on-off digital pulses - like a switch. Antenna is connected to Drain of MOSFET and there is...
"... I have never seen an antenna engineer to put focus on antenna being square to maximize gain..."
now you see one. If you understand how patch radiates it is obvious that antenna width effects both it's gain and impedance.
I make 9dBi patch antennas (real dBi, not the directivity but gain with respect to isotropic; results are verified in controlled anechoic environment using Satimo tester) can even attempt to make 10dBi patch.
Practical solution to your problem will be dual-band antenna operating at both 916 and 433 MHz. In this case you need no switches no diplexers no any other frequency-selective arrangement. You connect said antenna to your dual-band CC1125 transceiver as per it's application note and switch...
can you make it work from 500MHz and fit into 100mm square? Not sure without trying or modeling. (Thanks to Hagster for pointing that.) If you are getting close try loading it: cut teeth (log periodic tooth antenna, again: idea courtesy of Hagster); sandwitch it between two blocks of plastic.
I do not know. You have a graph - figure it out.
0x54 corresponds to 84 decimal, according to your graph it is ~-80 dB. At 1ft?
Free space path loss calculator:
https://www.pasternack.com/t-calculator-fspl.aspx
gives us for 400MHz at 1m 24.5dB path loss.
start by taking few points at few close...
Assume your link is line-of-sight. If so you are 40 - 50 dB short of link budget (following your own calculations). Something is wrong in your system. First you figure out what is wrong.
Is your link really line-of-sight? How high radios are above the ground? What RSSI you get reported from...
STM electronics has application note AN1806 with detailed description how to design and tune 13.56 antenna. And other tools - search for it. Other companies who manufacture reader and tag IC's likely have it too.
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