For a second iteration of the 433 MHz transmission between Espressif ESP8266 modules, I switched to RF modules based on the SYN115 and SYN480R devices. Largely because these work much better with the 3.3v supply rail and signalling that the ESP8266 uses.

I have something working with a center loaded "whip", the design of which was found on the web, but I'm intrested in getting the maximum range from this that I can, so I'm considering a full sized 1/2 wave dipole.

it doesn't take more than a minute on the web to determine that the end-to-end length of the dipole needs to be 345.4 mm, meaning a couple of legs, each 172.7 mm long should do the trick.

OK so far, and I even know where I want to attach them:

SYN115 based transmitter module

shows the transmitter module, and the receiver has the exact same "contact" pattern. Very conveniently, Ant and Gnd are right next to each other, so this shouldn't be at all difficult.

Except Gnd also needs to have a separate wire running to the ESP8266 as part of the power supply and signalling to enable the OOK transmission.

So what is likely to happen if I have +3.3V, Data and Gnd wires coming out the middle of the dipole? What options do I have to prevent this being a problem, assuming it is one?

-- Edit --

To expand on this, it may help to describe exactly what I'm doing. I want to send a signal from a temperature sensor that's outside the house to a receiver inside the house. (*)

So the two "constraints" are (1) this has to be able to get through an exterior wall of the house, and (2) about all I have for mounting is the wall of the house itself. Which in turn means a ground plane is somewhat out of the question. Thus the desire for a 1/2 wave dipole, that'll mount perfectly on the side of the house if vertically aligned.

(*) Sure, I can easily buy an off the shelf unit, but that's not the point here. This is as much a learning experience for me as anything, thus the preference to build it myself, and learn as I do so.

  • \$\begingroup\$ Are you attaching the antenna directly to the PCB, or, are you using coaxial cable between the board and antenna? \$\endgroup\$
    – qrk
    Commented Apr 18, 2022 at 21:04
  • \$\begingroup\$ Right now, I'm attaching the whip antenna directly to the Ant connector on the PCB. I have considered a length of coax, but wasn't sure exactly which cable to get. I would not want to bet anything on the success of using a length of "random" coax, e.g. RG 58 or RG 6. On the other hand, buying a super cheap 433 MHz antenna for a few dollars on ebay, and then throwing away everything except the length of coax has a certain charm to it. \$\endgroup\$
    – dgnuff
    Commented Apr 18, 2022 at 23:46
  • \$\begingroup\$ There are 1/2 wave whip antennas. Why do you need legs? Something with 172.7 mm legs sounds like a 1/4 wave antenna where the legs act as ground plane replacement. This seems to be some manner of semi-illegal OOK ebay junk, so you can probably attach any form of metal junk and call it antenna though - just up the output power since you aren't concerned about radio compliance anyway. \$\endgroup\$
    – Lundin
    Commented Apr 19, 2022 at 13:07

1 Answer 1


If your cable with signal, power, and ground leads runs horizontally, at right angles to the vertically-oriented dipole antenna, you needn't worry too much about interaction with the RF field. Technically, you're connecting an unbalanced RF output to a balanced antenna, which can cause RF currents to flow on the cable, but with such low power you shouldn't see issues.

On the other hand, if you're running the cable vertically and next to one element of the dipole, you could have these kinds of problems. In this case, a sleeve dipole is advisable. Use a metal tube (thin wall conduit, for example) for the lower antenna element, and tuck the circuit and cable inside it. The PCB ground connects to the sleeve only at the upper end of the sleeve, nothing connects to the sleeve at the bottom. The upper dipole element does not have to match - it can just be a stiff wire.

  • \$\begingroup\$ Perfect, thanks. Since I'll be mounting the various pieces to the wall myself (joys of DIY :) ) I can arrange them any which way I want. Very conveniently, the three holes for Gnd, Data and Vcc are on 1/10th in centers, just begging for a short piece of header to be soldered into them. This naturally will cause the power/data lines to leave the assembly at exactly 90 degrees to the antenna. \$\endgroup\$
    – dgnuff
    Commented Apr 19, 2022 at 22:05

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