Cheap antenna impedance values, plausible ?

[kellogs]

Good day,

Got his cheap antenna: https://www.tme.eu/Document/ab28b11ed5a07f3d86b2cbf91b5e11e7/433M-ANT824.pdf

Trying to use it as a way to check my measurement-taking setup and equipment.

- NanoVNA calibrated at S11 port for 50 ohm
- Plastic stand for the antenna with good clearance around it
- measured at heights of 1.2m and 1.65m above the ground
- i was standing another ~ 1.5m away from the antenna with the VNA, reading it.

433.8 MHz: ~ 3.3 - j10 ohm
441 (+/- 2) MHz: ~ 29 (+/- 5) - j1 ohm

There is no official SR Passives contact info that I could find, so I am asking here: what is more likely, the antenna really is not very well tuned or my measurements are skewed ?

 

[dave3825]

Never knew wifi was 433mhz. Based on that, I would not take any other info they list with a grain of salt.

 

[wtp]

covers the ham band, so it should be HI-FI.

 

[mmckenna]

Never knew wifi was 433mhz. Based on that, I would not take any other info they list with a grain of salt.

433MHz is a Part 15 allocation and has been used for various wireless services. Not enough bandwidth for WiFi, but could certainly be used.
Also, different countries have different frequency allocations.

I wouldn't put a lot of faith into the specs for a low buck antenna like that. Very common to find cheap, after market radio antennas that are not resonate anywhere near the claims.

 

[Ubbe]

The antenna costs $2.82 from xonelec.com and seems to consist of two shortened helicoil elements, so no halfwave dipole gain to be expected, where probably one goes to the coax center lead and the other to the coax shield. It's 2% off in frequency and I wouldn't expect it to be more accurate than that in its manufacturing process.

/Ubbe