I bought this 433Mhz transmitter/receiver that has two different antennas included. I managed to solder the receiver antenna to the transmitter. Is this a problem?

Shouldn't they have the same length since they work on the same frequency?

Edit: I found the technical difference between the antennas:

  • Transmitter: external antenna: 25cm ordinary multi-core or single-core line
  • Receiver: External antenna: 32CM single core wire, wound into a spiral.

Edit 2: I contacted the seller and got the following reply (I calculated the lengths) enter image description here


migrated from arduino.stackexchange.com May 19 '18 at 0:50

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    \$\begingroup\$ Looks like the wire length is the same, just one is spread out more. \$\endgroup\$ – Majenko May 15 '18 at 11:58
  • \$\begingroup\$ I've re-opened this so it can be migrated to Electronics SE. The question would be better answered ther.e \$\endgroup\$ – Nick Gammon May 19 '18 at 0:50

With the small differences between the two antennas, and the fact that they are both coiled -- there is little difference substituting one for the other would be.

An ideal antenna has no coil, but then it would have to be over a meter long at 433MHz. By adding inductance (the coil), the antenna can be resonant near 433MHz without needing the length. The sacrifice is sensitivity, but since both antennas are coiled, there's little you gain from one over the other.

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    \$\begingroup\$ but why do they offer two different antennas? It makes no sense to produce two different one if there is no difference. Do u call 7cm difference minimal for such small antennas? \$\endgroup\$ – jwillmer May 15 '18 at 13:01
  • \$\begingroup\$ Probably they want the TX antenna to be better impedance matched with the transmitter, to reduce reflected energy having to be dissipated by the transmitter. And for the RX antenna, longer means it's more sensitive. Are those really 7cm different in length? From the photos, it looks much less. \$\endgroup\$ – jose can u c May 15 '18 at 13:05
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    \$\begingroup\$ I suspect the two coils give a different radiation pattern. TX may give a longer range at the expense of vertical directionality, whereas the RX may give lower sensitivity but with a slightly improved omni-directional pattern or maybe the other way around, not sure. Either way you want the one with the more tight donut pattern to be the fixed station and the one with the better omni-directional spread to be the mobile station (eg keyfob). \$\endgroup\$ – Majenko May 15 '18 at 13:07
  • \$\begingroup\$ well the total length difference is 7 cm. They are wound into a spiral. \$\endgroup\$ – jwillmer May 15 '18 at 13:08
  • \$\begingroup\$ Suffice it to say that there is no inherent difference between a receive antenna and a transmit antenna. However, balancing compactness and optimal performance could lead to design decisions that result in slightly different antenna design. Ultimately, though, it's unlikely that swapping the "TX" and "RX" antennas on these modules will make a significant difference. \$\endgroup\$ – jose can u c May 15 '18 at 13:28

433 MHz Tx/Rx needs a 17cm antenna. 25 and 32cm are incorrect lengths. 32cm will likely work better, being closer to 1/2 wavelength than 25 is.

See this stackexchange discussion https://electronics.stackexchange.com/questions/132051/433mhz-quarter-wave-length-antenna-longer-is-better?utm_medium=organic&utm_source=google_rich_qa&utm_campaign=google_rich_qa

  • \$\begingroup\$ Thanky for the link, it is very informative but I could not find out why they sell two types of antennas and explicitly mark them as receiver or transmitter antenna. If you are right they could just sell one antenna type for both. \$\endgroup\$ – jwillmer May 16 '18 at 7:33

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