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Low Power RF & Wireless Connectivity
426.2uH Ferrite Rod Antenna
My TMS3705 application drives a 426.2uH 3 inch ferrite rod antenna using a 71 turn bobbin. tuned to 134.3kHz by the 3.3nf capacitor shown in the sample application circuit for the TMS3705 device. It is fed through a 27 ohm series resistor to reduce the Q to around 16. The coil voltage is 80vpp when driven from a 9v buffer..
It works to provide a desired 4-6 inch range using the RI-TRP-W9QL-30 tag. The coil is directly mounted on the PCB giving a fixed tail length of < 1 inch.
I am worried about the 426.2uH inductance which is very much higher than TI designed antennae and ask whether I should be concerned about this choice of inductance ?
All the TI TMS3705 based ref designs i am aware of use 440uH to 470uH coils...yours should be OK. Which ref design are you looking at?
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Yes nothing suggested a problem but I was just puzzled by the inductance when compared with most TI Antenna docs.
The TI Doc was Fig 4-1 SCBA020 . I have buffered the output to permit 9v antenna drive and used a ceramic 4mHz clock. The C2/C3 filter is as shown as are the gain resistors R1,R2.
The application is a cattle feeding gate. I have randomised the scan cycle to eliminate multiple receiver blocking - at l;east long enough for the cattle to notice. I also have an Ethernet design where all gates are synced by a UDP command.
I have found the TMS3507 very easy to work with and so far no problems in the field with a prototype release. The project is an update ofa product which I designed in 1969 so the RFID solution is long overdue !
Many thanks for your help.
You mean figure 4-2, correct? Anyway - the TMS3705 is current limited, so this this why we use recommend using a lower Q (higher R, higher L) style coil than the high Q 27uH LF antennas which are standard equipment for use with our high power RFMs (i.e. RI-RFM-007B, for example). If you wanted to raise the power output using the TMS3705, we could recommend you have a look at using the UCC27424 IC. The example schematic for that can be found here ==> http://www.ti.com/litv/zip/slac342 (see zip inside the zip called RI-ACC-ADR2_circuit_diagram)
Yes I have actually used the UCC27424 IC to allow the 9v drive but thanks for your help regarding the rationale behing the higher inductance Xl around 390 ohms. I may wish to reduce the inductance if we movbe to a long tail antenna.. My antenna voltage was actually 120v pp which makes more sense !
Hello Colin, can I find out a bit more about your project using 3705+27424 and capturing then transfering the animalID from one system to another?
I too am involved in the cattle/sheep rfid tag business... we have bitten the bullet and decided to design exclusively for HDX....the opposing FDX concept we beleive will "die on the vine"....HDX has won the battle here in Australia....
eventually we expect the rest of the world will follow...there are just to many HDX tags "out-there-now"....plus HDX is a superior system ...though "data collisions" due to multiple tags replying is a weakness...
.I see you are adressing this in your own way by randomizing the interrogation rate and accepting the occasional collision as the adjacent power durants intertwine.....well done...
we too have a variant of your concept...plus we go much further in imparting a form of collision avoidance into the RO HDX animal tag ....it is a bit like converting a "sows ear into a silk purse"....or from another view "like gluing two more cylinders onto a four cylinder car to get a six cylinder sports vehicle...etc...etc)
I have several other tasks in hand....all of which involve massive numbers of passing cattle /sheep ....in the cattle instance, streams of up to five abreast cows run down an alley way at up to 8km/hour...the alley width is three(yes 3 metre wide)....we do this well and wit TI modules...the instance is under development , with sheep and involves up to fourty thousand sheep (yes 40,000) in a sale yard ...
this is typical of a sheep sale here...and it is a burning issue with the industry...first they don't want the expense of fitting every sheep with a RFID ear-tag and secondly they have yet to be convinced reading on such a scale can be reliably done....we are confident it can...so we are now extending our cattle RFID reading experience over to sheep.
at the end of the food chain, in the abaitoir is a place for(your) extracting the dead-cow's HDX animal-number and copying it onto another tag imbedded into the hook that is carrying the carcus....that is just before the ear is cut off the carcus-hook now carries the tracability number...and so it goes.....this is another work in progress here.
So you see why I have an interest in your work and in particular want to get reinforcement that the 3705+27424 is a good little platform...I do not wish to reverse engineer the 003 module as it seems like a good option for that medium power between the "flea-power" of the 3705 and the "brute-power" of the 007....though if TI consented to supply circuits for the 003 and 007 It would be very interesting, but perhaps it is too much imposition on them....
until then, I will proceede down the 3705+27424 pathway for one key reason and that relates to the possibility of "tri-stating" the 27424...there are reasons ...don't know enough yet...we may yet just include some TI components into our own future board but until then will stay with existing TI modules.
this form gives me some confidence that a knowledge base exists and is accesable for me....
So Colin, are you prepared to talk with me about you project?....we both realize the issue of IP...so if done carefully it is worth trying to engage with you
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