Antennas for HC-12 module... what's the difference?

Today I got HC-12 modules, with two different wire antennas. Both are supposedly for 433 MHz but one is decidedly bigger than the other. The silvery one came with the module and is much smaller than expected; the golden one I ordered separately and is the size I expected.

I know next to nothing about antennas, I normally stick to the rule "bigger is better". Of course I'm looking for maximum range - in the final version of this project I think I'll be using external antennas (attached to the U.FL connector).

this ebay vendor shows various coil spring antennas for different bands:


you might be able to mine some info there.

It looks like one is twice as long as the other. Antenna are often in sizes of a quarter of a wavelength long, well one quarter, one half and one whole wavelength. A coil is a way of reducing this length even further. So I would expect them not to actually measure the wavelength anyway. Either way different lengths normally present different impedances and for best results the output impedance of the transmitter and the input impedance of the antenna must match. The matching is done using inductors and capacitors.

Unfortunately this is not easy to measure. One way is to use an SWR meter ( Standing Wave Ratio ) but they normally need quite a bit of power for them to work, well at least the low cost ones. The radiation pattern for each antenna is the same and the actually performance difference is marginal.

Most likley both will work.
The top one has a differant pitch than the bottom so is a differant length for the same frequency.
If you want maximum range though, dont use either, but use the normal 1/4 wave antenna which is 17 cm long.

If you want maximum range though, dont use either, but use the normal 1/4 wave antenna which is 17 cm long.

Unfortunately you need a ground plane or ground radials with a 1/4 wave, which are another 17+ cm long.
Actually, you also need that with that 'spring' type aerial.
Ignore it, and the 360 degree footprint is affected and range is reduced.

I prefer a 'sleeve' type aerial for max range (if needed). Easily constructed from thin/braided/50ohm coax.
'spring' type aerials is just a space-saving solution, but ok for short range.

Thanks for the replies, I obviously have a lot to learn when it comes to antenna design :slight_smile:

A ground plane, that's tricky considering the limited space. Does a ~60x80mm PCB ground plane qualify? Most traces will be on the other side of the PCB, which has a power plane.

The next iteration will be with external antenna - coax to the U.FL connector, antenna mounted in a hole in the plastic enclosure. So the ground plane (of the PCB) would be a bit away from the antenna. Alignment is another issue; most likely they would end up being in line, not perpendicular, due to the shape of the whole design. Doesn't sound optimal to me.

A ground plane does not have to be a continuous conducting sheet, it can be just horizontal wires connected to ground.
For best results these wires, or continuous conducting surface should extend a quarter of a wavelength in all directions from the base of the vertical antenna. However, smaller ones are better than none at all.

That PCB size does not qualify as groundplane for that frequency, but a power wire (if any) hanging down could.
As said, footprint is affected by the groundplane. That could be positive or negative in one direction.
A sleeve aerial eliminates that, because the ground element is buildin and straight.