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RF 433 or 315Mhz module antenna problem

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nikhilele

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rf module antenna in india

I have attached the schematic diagarm with little explanation on it.
the main part we have to see is the Antenna ouput of the RF module.

We have to connect this ouput to the antenna for this we use tracks to the antenna connector on PCB.
Now for short distances we can use this track(if made long) as anttena and for long distance we can connect external antenna.
now my questions are

1>
Just by having a 50ohm track at antenna ouput can behave as good antenna for short distance.

2>
The losses in the bend of the track are significant at these frequencies can we ignore that losses. or I have to make bend in other way.

3>
for calculating the width of the pcb for 50ohm line we need only the dielectric constant of pcb and thickness of pcb only.
I am using glass epoxy or similar pcb without any ground plane so we cannot use microstip line formula.


I will answer all your queries
thank you for each reply

added latter
I am not sure about track impedace
 

nikhilele

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good capacitor to use for 315 mhz antenna

i think it is better i should add ground plane that will make my calculation easier,
but i am woundering, adding a ground plane will decrease antenna range or not.
cause ground will be close and obviously electric field will be shorted.
I am not able to remeber my antenna class lectures.
help me on this

But I remember the antenna lines should be kept away from ground lines so i cannot keep ground plane below the antenna track.

so how should i make a track so that it can work in two situations.
short range communication track as antenna
long range communication track connects ouput to external antenna
 

nikhilele

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315mhz antenna

my problem is i want to use printed antenna for short distance and whenever i want to increase range i can add an external antenna to the antenna connector.
and I think this is not possible in loop antenna cause it is tuned and it is terminated at end with capacitor.

Added after 1 hours 52 minutes:

From further readings i have got that 50 ohm line does not radiates much. am i right.

then how to make a track which will radiate much and does not reflect much.
 

biff44

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antena 315mhz pcb trace

Your layout stinks! If there is no ground plane under that long meandering line, then it is not a 50 ohm transmission line! It might look more like a big inductor.

So your module probably does not work well when you try to attach an antenna to the connector.

It probably works better when you do not attach anything to the connector! But if you want to make it work well without an external antenna, the best thing would be to resonate the loop, as probably explained above.

You can not have it both ways! If you put a ground plane under the line, it will no longer act like a loop antenna. If you do not put a ground plane underthe line, it will not act as a 50 ohm line for the external antenna.

Maybe, just maybe, you can have it both ways if you had a jumper selection for internal loop or external antenna.
 

nikhilele

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rf module 315 mhz pcb antenna

Maybe, just maybe, you can have it both ways if you had a jumper selection for internal loop or external antenna.
I was thinking of this only.
I completly agree with all your points.

1>(a)
It is ok if I keep this long track for radiation how much thickness i have to keep for this track to have good radiation. as you said:
It probably works better when you do not attach anything to the connector! But if you want to make it work well without an external antenna, the best thing would be to resonate the loop, as probably explained above.
1>(b)

and for resonating i have to connect a capacitor at the end of the track, am i correct ?


2>
For connecting external antenna I will connect it very near to the antenna output pin so even if the line is not 50 ohm the losses will be less.
 

nikhilele

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315 mhz long range antenna

biff44 wrote:

Maybe, just maybe, you can have it both ways if you had a jumper selection for internal loop or external antenna.
So I am posting a new one

In this if I make this pcb trace reach again to the position where it started and then i connect a capacitor over there then it will make more better antenna or the antenna shown in the fig is alright for short range and for long range u have to connect external antenna.

thanks for answering my silly question
I learn this way only..
 

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