433Mhz Remote Control Antenna Selection

Question

First I want to thank all of you who come here and help others. That is very kind and unselfish of you!

This is lengthy but I want to make sure I tell you everything you need to know to answer this for my application.

I can just bet you have answered this question in some form a hundred times since the fairly recent popularity of these things so I apologize if you have but I am still not clear about how to get the longest range with the simplest design.

I have searched and read so much about using 433mhz remotes that it gets more confusing the more I read because there seems to be as many opinions as facts.

I am an electrical controls engineer and have been trying to understand antenna design. For those of you that have a good understanding of this - congratulations!

My applications are simple but I suppose the implementation is not always so much.

I get those cheap 433 remotes from ebay sellers and some have better range than others. I bought a "Solid Remote" brand which is by far better than the others.

I easily get 500 feet with the solid remote.. https://www.solidremote.com/wp-content/uploads/2016/03/catrcr-768x1024.jpg

I pulled the antenna out from the box and straitened it out extending it straight up and put the receiver in my attic.

It came with two key fob remotes,

I also bought two of these https://www.ebay.com/itm/12V-4CH-Channel-Wireless-Remote-Control-Radio-Relay-Switch-Transceiver-Receiver/262511780529

I uncoiled the antenna and have it pointing straight up out of the box.

The solid remote is by far better in range. I take apart the key fobs and solder wires where the buttons are so I can connect them to external switches.

All that to ask a simple question that probably has a more complicated answer.

1.) Between these two, What is better for these devices? 1/4 wave monopole or 1/2 wave monopole?

2.) is a loaded monopole going to get better range? I made one of these https://www.instructables.com/id/433-MHz-Coil-loaded-antenna/ but my wire might be too big in diameter, I used 14 gauge bare copper. How does wire diameter affect the transmitter and receiver?

I read that a straightened out antenna is always better then a coiled one and the coil was only to make it fit in a small space. Then I found the loaded coil design that claims to be better.

So Perhaps without diving too deep you can tell me what will give me the best range of these options.

Thank you very much!

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No apologies needed! I understand everything you said here. Very good post.

I am using these cheapos because the applications I am using them for are so non critical, Just hobby stuff mostly. So I can connect the relays to my Allen Bradley PLC and do whatever with the trigger.

This post of your was excellent, instead of excoriating me for buying cheap arduino compatible stuff you helped a lot, I thought the key fobs transmitters would be problematic but interestingly the solid remote is actually pretty decent, the others not so much, of course they both have the loop antenna you referred to. I bought another that has a collapsible monopole attached to the transmitter pc board

https://www.ebay.com/itm/Wireless-Remote-Control-1000-Meters-Long-Range-NO-OFF-Switch-DC-12V-10A/382677576948 This uses a 12volt A23 Battery, Cold weather is a problem with the battery so I might stack a few button lithium batteries together and wire them outside of the transmitter.

I am using this one to monitor a mail box door, I put a reed switch on the door and wired it to one of the transmit buttons (there are actually two, one is hid under a cover)

I used some silicon to fasten the antenna on this one to the board because the solder point on the base of it is the only place it is secured.

I took out the coiled antenna out of the receiver and and straitened it out so both X AND R antennas are vertical. The transmitter is about 400 ft from the receiver and so far working ok, I am doing this for an elderly neighbor so they don't have to check their mailbox for nothing in this cold weather.

I did notice that the solid remote is using a bit more complex receiver then the others I bought, I think one of the differences is AGC on the solid remote.

I was wondering if I need to go this route, how I would attach a YAGI to one of these things,

Anyway thanks a lot for an excellent response. If you have some suggestions on other sources for inexpensive - may I say "cheap" remotes for some of my not critical hobby projects I would like to know.

Answer 1

In a past life I worked with this stuff. We built 390MHz radios and then transitioned to 433MHz. The company built equipment that was cheap and robust and cheap and small and cheap and useful and did I mention cheap. I was not the RF/antenna designer but I worked pretty closely with them. It was a while ago, but here are the bits of (hopefully) helpful information I can pass along:

• At 390MHz our standard specification was 1000 ft of open-field range. I would suspect 433MHz should be able to achieve similar, well beyond the 500 ft that you're getting.
• But with that said, range-testing was always a big exercise in frustration. Finding a good test environment (free of multi-path effects or interference) is difficult, and we would always find that range-testing results would vary from one day to the next, or even one hour to the next. So unless you've run your tests a few times over, and/or "at the same time", then you may not be able to trust your test results.
• BTW one common interference source is poorly-spliced TV cable connections and amplifiers. You might wind up learning how many of your neighbors are stealing cable ;-)
• The antenna design process was actually pretty empirical (which isn't too surprising when your antenna is just a piece of wire), there were often cycles of test/cut shorter by 1cm/repeat during the design process.
• The antenna was just a quarter-wave whip with ground plane or a long trace on the board to act as the other side of the dipole.
• As some people have hinted in the comments, you might be jumping to conclusions by looking at the antennas. The difference you are seeing between these two radios might have a lot more to do with the quality of their receive (and possibly transmit) circuitry than with the antennas themselves.

But to address your actual questions:

• First and foremost, these products have probably already optimized their antennas as much as possible, and there is little you can do to improve it.
• ...unless you want to put a directional antenna in there, in which case you should be able to enjoy some pretty big gains.
• Once the proper matching (e.g. quarter-wave or half-wave) has been achieved, then a larger antenna is always better. RF field strengths are commonly measured in volts/meter, so then intuitively larger antenna means larger signal. The loaded coil just helps you to get a proper wavelength match with a physically smaller antenna.
• Another huge thing to watch out for is the antenna pattern. A lot of the literature out there shows nice ideal antenna patterns but in the real world the antenna pattern is always a lot more "lumpy", and the difference between a "hot spot" and a "cold spot" in the antenna pattern can be a big difference in the range you'll achive.
  • In the range-testing I mentioned earlier, this led to the "range test dance" where you would have to orient the transmitter in all kinds of different positions to find the best part of the antenna pattern.
  • ...and we've all done the trick where we press the car remote against our chin or forehead, haven't we?
  • For the receiver antenna (wire whip) the pattern is probably pretty omnidirectional as long as you are perpendicular to the direction of that wire whip.
  • For the transmit antenna things get trickier. It is probably using a small loop antenna as the transmit antenna, and that loop antenna has a bunch of circuitry and/or a battery on one side all helping to foul up the antenna pattern. The result will definitely be "lumpy". I can't find any great examples of what it might look like, but this antenna pattern (NB not from a loop antenna) is a decent facsimile of what those loop antenna patterns looked like. You might need to twist and turn to find the best orientation.
• Another big problem to watch out for is the so-called hand shift. In these super-low-cost transmitter designs, your oscillator is your antenna. In other words, you have a tuned LC tank circuit that resonates, and the transmit loop antenna forms the L part of that LC circuit. The circuit winds up being pretty sensitive to parasitic capacitance; when the transmitter is held in your hand the parasitic capacitance due to your hand will shift the RF center frequency. This is typically a much larger effect on range than antenna efficiency! In practice, the radio is typically built to resonate a little bit off-frequency to pre-compensate for this (i.e. the hand shift will bring the frequency to where you want it).

Bottom Line / TL;DR version: while your question is about antennas and antenna design, you would be wise to check a few other things besides the antenna first. Environmental interference, poor receiver circuitry, frequency shifts (such as hand shift), and nulls in the transmit antenna pattern can be much bigger problems and adjusting the receiver antenna won't do much to help. If you're determined to try and improve the antenna, attaching a directional antenna is strongly recommended. If you're going to try and build a better whip antenna, then good luck but there probably aren't gains left to be had.

Hope this helps. Sorry, I didn't really deliver on the "without diving too deep" front. ;-)