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Electronics => Beginners => Topic started by: Arek_R on April 03, 2019, 11:01:04 pm

Title: RFM69HCW antenna question
Post by: Arek_R on April 03, 2019, 11:01:04 pm
Hi, I'm designing a receiver for electric skateboard using RFM69HCW, the requirement is to have a ceramic SMD antenna but also have the ability to somehow change/switch it to U.FL(pigtail?) coaxial connector, so off the shelf external antenna can be used instead if the signal with ceramic antenna won't be good enough.
I've seen some construction(see the pic) where track is split into two and placing small ceramic SMD capacitor will switch to either antenna.
Is it a good way to do it?
What capacitor should I use?
Is that capacitor going to descrease the range?
I'm a complete noob when it's about RF and I don't even know what keywords to use to google my answers regarding this so that's why I ask you.
The frequency is 433MHz

Thanks!
Title: Re: RFM69HCW antenna question
Post by: Arek_R on April 05, 2019, 12:45:58 pm
No RF guys over there? :/
Title: Re: RFM69HCW antenna question
Post by: senso on April 05, 2019, 02:06:52 pm
There are u.FL connectors that make a connection without and antenna connected, or break the connection and "route" the signal to the antenna when one is inserted, usually used for test points in modems/routers.
Title: Re: RFM69HCW antenna question
Post by: Arek_R on April 05, 2019, 04:43:34 pm
Oh wow that would be great, could you please provide example link?

EDIT: Alright I've found one, not under u.fl name at all, but dimensions seem to match:

https://www.digikey.com/product-detail/en/murata-electronics-north-america/MM8030-2610RJ3/490-5907-6-ND/3635134 (https://www.digikey.com/product-detail/en/murata-electronics-north-america/MM8030-2610RJ3/490-5907-6-ND/3635134)

But then it doesn't have a pin, it's a female version, I needed male version so people can just buy standard u.fl 433MHz antenna from ebay aliexpress amazon etc.
Or at least I have to find a plug that plugs into this.
Title: Re: RFM69HCW antenna question
Post by: Doctorandus_P on April 07, 2019, 04:01:48 pm
I'm no RF guy but I think the capacitor is not very critical and mostly forms a high pass filter.
I've also seen 0 Ohm jumpers to switch between the PCB antenna and the coax connector.

The layout / trace length of the RF side is pretty critical though. Adding a "normal" switch is a no-no.

Alternatively you can opt to put a connector between the RFM69 module and your uC board.
The RFM69 modules are prety cheap and you can easily swap the whole module if you want to use another antenna.
This way the RFM69 & antenna can be a single unit without having to mess with the RF side of things.