jbpeckham
Newbie
Sorry if this looks similar to some other questions. I promise I've had a (quick) look around and can't find quite what I'm looking for.
Objective
I'm trying to design a remote control for a domestic system.
The prototype worked OK, using cheap and nasty 433 MHz OOK modules with straight 17.3cm monopole antennas. I'd like to build a version of the remote control which looks good enough to hold in the hand without a case. I'll design a good-looking PCB, epoxy it and make a sanded wood grip for the back of it.
But, that means I want something 'a bit more pro' than a bit of bent copper nicked from a power cable. Something like a quarter-wave monopole connected by an SMA. It doesn't have to go far - only a few metres and through a ceiling.
So, would this work?
RF Measures considered:
Possible unknowns:
Objective
I'm trying to design a remote control for a domestic system.
The prototype worked OK, using cheap and nasty 433 MHz OOK modules with straight 17.3cm monopole antennas. I'd like to build a version of the remote control which looks good enough to hold in the hand without a case. I'll design a good-looking PCB, epoxy it and make a sanded wood grip for the back of it.
But, that means I want something 'a bit more pro' than a bit of bent copper nicked from a power cable. Something like a quarter-wave monopole connected by an SMA. It doesn't have to go far - only a few metres and through a ceiling.
So, would this work?
- Design a PCB to hold the MCU, inputs, power, etc. etc.
- Connect the 433 MHz OOK Transmitter parallel to and above the PCB via header pins
- Connect the Transmitter's ANT pad back down to the PCB by a header pin
- Trace the RF signal to the SMA, which is also connected to the Ground Plane
RF Measures considered:
- Transmission line on PCB < 10mm (wavelength of 433 MHz at ~0.5c would be approx. 350mm)
- Impedance roughly matched to 50 Ohm: for 1oz copper under a solder mask and on the other side of a 1.4mm board from a ground plane, I figure ~100 mils trace width.
- Transmission line on the opposite side of the PCB from the SMA connector (to minimise the effect of the through-hole stub)
- Ground plane on the same side of the PCB from the SMA connector
- I'll do my best to get a good solder joint
Possible unknowns:
- I understand the antenna ideally has a ground plane to reflect RF radiation off. That doesn't really exist here in any meaningful size. I guess that's OK though because the prototype worked?
- Is the coiled stubby antenna going to be any less effective than the straight wire used before?
- I've not considered any impedance matching of the header pin, and also assumed that any circuitry inside the off-the-shelf Tx module is irrelevant.
- I don't know if mounting the Tx module parallel to the main PCB is better or worse than perpendicular.
- I've seen some recommend a ground plane on both sides. Is that better, and would it change the impedance matching calculations?
- It's just a monopole antenna and the ground connection back to the Tx module is distant from the antenna connection (next to the Data and VCC pins). Does that change anything?
- My soldering is inconsistent