QUESTION

Question

Hello,

We  have used your M20057 Active antenna for GPS in a upcoming large scale product. we don't find any help or reference about how to choose the resistance AT1 & inductor L for AT2 . anyway for AT1 we short it with 0 ohm resistance to ground. but for AT2 inductor, its mentioned as TBD, please suggest us a reference value to start with, we use double sided Fr4 PCB 1.6mm and entire PCb size is around 30mmx50mm, with some other LTE & BLE modules.

we need help on this,urgently.Thank you

with regards,

Dr.N.Chandra Sekhar,M.tech,phd

Answer 1

Hello Chandra,

A good starting value for AT2 would be a 1.8nH inductor. AT1 short remain a 0 ohm resistor. PLease be sure to follow the suggested clearanced area around antenna the end of the module where the two antenna matching components are placed.

You can lift the capacitor between pins 4 and 6 then place a semi-rigid coax on pin 4 to measure the return loss of the antenna and tune AT2 until you are resonating at 1575MHz

Best regards,

Geoff S.

Comments

Hi,

How Are you? thanks for your reply..just as  you mentioned i tried to tune the board..

1. you mentioned lift the capacitor..where ,are you referencing any capacitors on the M25007-1 module or on the main board ..i mean capacitor which connect RFO & gps receiver input pin?

2. i tried to lift the capacitor which goes to gps recevier,and instead of making it feed to gps receiver pin, i connected to VNA, supplied 3V. then started checking.

3.sadly i had 2.2nH,4.1nH,1nH,5.1nH & 10nH inductors only..i observed following

 with 2.2nH -1568Mhz -25db

with remaining inductors it goes to 1560Mhz..

even when different 2.2nH inductors interchanged i saw that, some times it was 1563Mhz, some time 1565Mhz..some times 1568Mhz..i think this is because of tolerance with in the inductors.. so now my doubt is, what should be the range of inductors i should try, i think tunable inductance is not a solution.it has to manually interchange the fixed inductors and try..but also what should be the step size..i mean shall i go for 1.6nH,1.7nH,1.8nH,1.9nH,2nH..i mean 0.1nH steps or 1nH,2nH,3nH,4nH, like that.bcz in our surroundings i cant get inductors,i got to order from over seas, so based on your input i got to procure the proper range and proper step ,else i might end up in lot of time waste, already i lost 2 months,still not able to fix the problem

for fine tuning,when Inductors of proper value available, is there any way of tunning by adding capacitance,if so where shall i change..

is it okay to add capacitance in parallel to the At2 Inductor?

what should be the db value i should target for..bcz i see that some times when resonating, for a same frequency it gives -4db, some time, -12db, some time -25db..

i also observed that when a small 100pf capacitor is added in parallel to 2.2nH,it resonates at around 1578Mhz, but when hand goes closer to the pcb,the resonating freq shifts... where as when there is only inductor, when hand goes near to pcb, simply db values is changing but freq not shifting much

please help me tune this antenna ..Thank you very much

Answer 2

Hi,

How Are you? thanks for your reply..just as  you mentioned i tried to tune the board..

1. you mentioned lift the capacitor..where ,are you referencing any capacitors on the M25007-1 module or on the main board ..i mean capacitor which connect RFO & gps receiver input pin?

2. i tried to lift the capacitor which goes to gps recevier,and instead of making it feed to gps receiver pin, i connected to VNA, supplied 3V. then started checking.

3.sadly i had 2.2nH,4.1nH,1nH,5.1nH & 10nH inductors only..i observed following

 with 2.2nH -1568Mhz -25db

with remaining inductors it goes to 1560Mhz..

even when different 2.2nH inductors interchanged i saw that, some times it was 1563Mhz, some time 1565Mhz..some times 1568Mhz..i think this is because of tolerance with in the inductors.. so now my doubt is, what should be the range of inductors i should try, i think tunable inductance is not a solution.it has to manually interchange the fixed inductors and try..but also what should be the step size..i mean shall i go for 1.6nH,1.7nH,1.8nH,1.9nH,2nH..i mean 0.1nH steps or 1nH,2nH,3nH,4nH, like that.bcz in our surroundings i cant get inductors,i got to order from over seas, so based on your input i got to procure the proper range and proper step ,else i might end up in lot of time waste, already i lost 2 months,still not able to fix the problem

for fine tuning,when Inductors of proper value available, is there any way of tunning by adding capacitance,if so where shall i change..

is it okay to add capacitance in parallel to the At2 Inductor?

what should be the db value i should target for..bcz i see that some times when resonating, for a same frequency it gives -4db, some time, -12db, some time -25db..

i also observed that when a small 100pf capacitor is added in parallel to 2.2nH,it resonates at around 1578Mhz, but when hand goes closer to the pcb,the resonating freq shifts... where as when there is only inductor, when hand goes near to pcb, simply db values is changing but freq not shifting much

please help me tune this antenna ..Thank you very much