Antenna design for dummies for 315MHz RF receiver?

Thread Starter

ibrewster

Joined Feb 12, 2020
2
I am building a receiver to use with the HomeLink mirror in my car (so I can actually do something wit it other than just open the garage door). To that end, I picked up a 315MHz RF receiver like this one: https://www.amazon.com/4-Channel-Wireless-MELIFE-Transmitter-Receiver/dp/B07S51NBFF?th=1 (photo attached) From what I can tell, it's just a small RF receiver with a coil antenna, and a bunch of extra circuitry to interface with the relays and coded remotes.

I got everything hooked up and programed the way I wanted, and tested that it worked. Unfortunately, the range stank - I could be sitting in my car just outside the garage, and push the button, and the receiver just inside the garage would get nothing. Basically, it only seems to work reliably if there was absolutely nothing between the transmitter and receiver.

After doing some research, I found a number of posts claiming that coil antennas can be tricky to get right, so with nothing to loose I tried straightening the wire and pulling it outside of the (wooden) box I installed everything in. This did seem to help somewhat, and testing actually looked pretty good, but when I tried it from inside my car (using the mirror buttons or the handheld remotes), I was back to no real functionality - it would work if I had direct line of sight with no obstacles, but as soon as there was anything between transmitter and receiver, it was back to not receiving. Further research informed me that the "ideal" antenna length would be 23.81cm long, but that's about as far as I could get - the rest of my research turned up stuff about "dipole antennas" and connecting to the "ground plane", which I honestly don't understand. So that leaves me with a few questions I'm hoping can be answered here:

1) The current coil antenna, once straightened, appears to be about the right length, but a significant portion of it is still inside the container, surrounded by other electrical stuff I have crammed in there. Might putting a longer wire on, such that the 23.8cm could all be *outside* the enclosure help?

2) Regarding dipole/ground plane, is that as simple as attaching a second wire of the proper length to the ground connector of the receiver and run it outside the box, or is there more to it? Would that be likely to improve reception?

3) Might the receiver itself be the issue - that is, might I be able to improve the situation by using a different, higher-quality receiver module than what is on that board? I don't need the relays - all I need is to be able to generate a 4 channel digital output that I can feed into a micro controller (Specifically, a CherryPy). I'm not afraid of having to do a bit of programming, however.

At the end of the day, I don't need a huge range. I just need the device, sitting inside my garage, to be able to reliably pick up signals from my car at the end of the driveway (about 20 feet or so, clear line of sight). I wouldn't have thought that would be all that difficult, but what do I know? :)

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Thread Starter

ibrewster

Joined Feb 12, 2020
2
For what it's worth, simply changing the antenna from a horizontal orientation to a vertical one helped significantly, at least in initial testing. I wouldn't have expected that, but hey - whatever works!
 

Janis59

Joined Aug 21, 2017
1,216
The best way to act is to switch before spiral the simple VNA and read it. Because of Wuhan virus epidemy some Nano-VNA today cost so small as 39 USD only (I bought mine half year ago for 100). Sterilize it in direct sunlight, wash a hands well and use a face-mask, and after day it will be completely safe for use to solve Your problem. And by-the-way, probably one hunger-striken cheeneese village all inhabitants will be saved from death of malnutritian for some period due these coins.
 
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