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I've got three 433MHz receivers (all the same type) and I would like to increase the range on them (by which I mean the physical distance that the receiver can detect the signal from the transmitter). Changing the antenna on the transmitter (the little key fob/dongle thing) isn't an option for practicality reasons. One of these receivers is unfortunately housed in a sheet metal box (which can't be readily changed), so I would like to get the antenna outside the box, but I'm unsure as to how running it out of the enclosure interacts with the total length of wire used in the antenna itself, (i.e. the length exposed outside the enclosure vs total length to get back to where it is soldered to the receiver).

The receivers currently have short coiled wire antenna (they look like a spring, but are actually coiled wire). Since the receivers are stationary, I can take some liberty with a larger antenna. Googling suggests that a balanced dipole antenna with a balun is the way to go, with 178mm straight wire on each 'leg' (not sure of the right term) on the antenna. The problem is, I don't know the first thing about RF, so I haven't been able to discern what is a good guide for how to construct such an antenna.

Could anyone point me in the direction of a practical guide in this area that is technically sound?

EDIT - Hardware Details: The transmitter and receivers are Elsema PentaCode series devices: Transmitter: PCK43302 Receivers: PCR43301RE & PCR43302240R

Basic details are on page 3 of this document:

They're frequency hopping spread spectrum devices, with a freq range of 433.100 to 434.700MHz.

Target range is ~200m, not quite line of site (elevation diff of about 10m over 150m due to small hill that rolls off).

EDIT - Directions to Transmitters: So, the receiver's are stationary, but the transmitters are mobile. In the case of the gates, they're on access roads, meaning the transmitters can be sending a signal from either side of the gate (so, 180 degrees from each other). This is part of the problem, as a high gain antenna in one direction will hurt the radiation pattern 'out the back' (i.e. from the other direction), which isn't great given that the goal is to open it from both sides. Energy radiated 'to the sides' is wasted though. Is there an antenna design that can help achieve this?

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  • \$\begingroup\$ what do you mean increasing the range? you mean increasing the signal db? or increasing the range of frequencies? \$\endgroup\$ Dec 27, 2020 at 3:04
  • \$\begingroup\$ Sorry, I mean increasing the physical distance at which the receiver can detect the signal from the unmodified transmitter. \$\endgroup\$
    – Chris
    Dec 27, 2020 at 3:26
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    \$\begingroup\$ You should see some signifiant gain (increase in range) by simply pulling the antenna out of its metal enclosure, almost no matter how you'd pull it out (I find it odd that the device would have its antenna there). Just use a short feed. As for further increasing the gain, there's a lot you can do right, and a lot you can do wrong. What is the device, where is the antenna placed, how much do you want to increase the range etc.. can you add some pictures? \$\endgroup\$
    – P2000
    Dec 27, 2020 at 5:03
  • \$\begingroup\$ I've added some detail on the devices. I'll see what I can do about extending the antenna cable so that it's coil is at least outside the enclosure. Target range is ~200m, though we can live with less for the one inside the metal motor housing/enclosure. \$\endgroup\$
    – Chris
    Dec 27, 2020 at 10:01

2 Answers 2

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Full size antenna options would be a ¼ λ vertical monopole with one radial or a ½ λ horizontal / vertical dipole.

enter image description here

Holes are to be drilled in the enclosures to lead the elements out.

The ground point on the PCB is to be connected to the metal enclosure.

enter image description here

The unit may be oriented to have the dipole horizontal or vertical.

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  • \$\begingroup\$ From an orientation/polarization perspective, is 'vertical' considered to be when the driven element of the antenna is perpendicular to the plane of the receiver board? Also, is it correct that a 1/4 Lambda and a 1/2 Lambda use the same length elements and that it is just their orientation that results in the 1/4 and 1/2 lambda names for these antenna? \$\endgroup\$
    – Chris
    Dec 27, 2020 at 9:51
  • \$\begingroup\$ Thankyou, that is helpful. Sorry, I can't seem to upvote comments or answers as yet, but I will look into what you have mentioned to understand that a bit more. \$\endgroup\$
    – Chris
    Dec 27, 2020 at 10:02
  • \$\begingroup\$ 'Vertical' and 'horizontal' refer to the actual orientation and not with respect to the PCB. A ¼ λ vertical monopole would normally require a ground plane comprising 3 to 4 radials bent downwards, 45 °- 60° to horizontal, for a good match. A single radial alone could also make a difference. You are right about the element lengths and their orientation. The radials would generally be 20% longer. I am sorry I edited my comment and it appears after your response! \$\endgroup\$
    – vu2nan
    Dec 27, 2020 at 10:06
  • \$\begingroup\$ No problem, thanks for the extra details in the edits, they're definitely useful to me! \$\endgroup\$
    – Chris
    Dec 27, 2020 at 10:41
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433Mhz receiver, Is this the common receiver for sensors like temp, humidity, etc?

433Mhz receiver still using FM modulation but in the UHF frequency range. Which is if you want to upgrade to the better version of antenna it should be YAGI type according to many books of amateur frequency.

This is PDF for practical UHF antenna design

This is UHF frequency band

If you want better yet with this receiver you should get a UHF booster, it will not change your receiver internally but the amplitude of the signal received from the antenna. But again, I don't know what type of your receiver are.

EDIT from Edited question:

Use Elsema assembled built for this kind of device. you need 180deg from both sides which is highly unlikely to achieve on a high gain pattern that using a single side (directional).

This could be achieved with a bidirectional antenna or Omni-directional, which Elsema build.

  • Part Number ANT433M
  • Frequency 428 to 437MHz
  • Length 1 meter
  • Gain 6 dBi

This is better than you are using another or DIY antenna which requires you to calculate the RF.

This link to Elsema Antenna

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  • \$\begingroup\$ a Yagi-Uda is a poor match for a portable receiver unless it's pointing in the right direction. \$\endgroup\$ Dec 27, 2020 at 9:26
  • \$\begingroup\$ he didn't say it is portable which is what he stated on the original question: "so I would like to get the antenna outside the box" and he just wants physical distance is longer than the original one. So Yagi antenna is a better choice for UHF range and long distance. \$\endgroup\$ Dec 27, 2020 at 9:35
  • \$\begingroup\$ In this case the receivers are stationary, the transmitters are portable (and not practically modified in terms of their antenna). I can't go totally wild on the gain, as if the radiation pattern gets highly directional and to far away from isotropic then it won't be practical. I'm thinking the 3db to 6db gain in the most likely direction of use is helpful. I'll add some extra detail with respect to directions. \$\endgroup\$
    – Chris
    Dec 27, 2020 at 10:05
  • \$\begingroup\$ check again my edited answer. \$\endgroup\$ Dec 27, 2020 at 10:18
  • \$\begingroup\$ Thanks, I had completely missed their antenna options! To ask a really basic RF question: How can you have an omnidirectional antenna that still has gain, such as the ANT443S ? (I thought gain was measured relative to isotropic - i.e. omnidirectional? - but perhaps it's measured relative to the antenna supplied as standard or some such, otherwise I don't really understand how it can just be 'better everywhere'....?) \$\endgroup\$
    – Chris
    Dec 27, 2020 at 10:47

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