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Forum Index : Microcontroller and PC projects : HC-12 Antennae
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| Andrew_G Guru  Joined: 18/10/2016 Location: AustraliaPosts: 871 |
Hello all, I now have quite a network of HC-12s reporting temperatures around the house and data from an external weather station. They are all at FU2/2400 baud and the battery powered ones sleep for ~10 minutes, wake, and then spit out data. To my "non-rigorous testing" there appears to be some variability in the success of transmission. Now that I am using either 3x AA batteries or 5V, I suspect it may be the antennae on either the remote or the base station (or both). I'm interested to know what the general practice is out there? - I am using the coiled "spring" straight out of the box but so that it extends beyond the PCB (I have seen one picture here where a shedder has the spring lying against the back of the PCB) - any comments? - the HC-12, and its antenna, are enclosed in a plastic box along with the MM, batteries etc - does that attenuate the signal and should I mount the antenna externally? - how much do PCBs, circuits and even batteries near or in line of sight to the receiver effect transmission? - should the "springs" be aligned (eg both vertical or both horizontal?) - any better antennae that may not be as vulnerable as a spring poking out through a box (the units have sockets to attach to them)? (I have a little gadget, based on an LCD backpack, that receives and displays all the HC-12 transmissions. I place this partway between sender and receiver and ~100% of expected transmissions are being made - but not all are being received at my base station. I also use a checksum approach (based on NMEA's) and apart from start-up ~all transmissions are intact) Many thanks, Andrew |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
Hi there. [:) For best range performance, use FU4 mode at 1200 baud. This is pretty much my go-to mode for HC-12's, and it does help the range greatly - even on those little helical ants. Replies to you specific points: 1) Yes, ant should stick out clear of any other objects, especially anything metallic. I know the arrangement you are referring to with the ant back against the module. That will work for short distance stuff, but the PCB close to the helical will de-tune it quite badly, and this will have the effect of limiting your range. 2) No, so long as the box is plastic, this won't affect the signal. A metal box is a real no-no with RF, if your helical is INSIDE the box. You can certainly use an external SMA-type antenna if you want. In that case, a metal box can be desirable, as when earthed, it will shield the module against unwanted interference. 3) ANYTHING metallic, including batteries and copper PCB anywhere near the antenna will have an effect on it's efficiency. Just how much of a problem that ends up being depends on the range you are wanting to achieve. For maximum range and performance, the antenna should be completely away from any other metallic object - including batteries. 4) Yes. If one helical is vertical, and the other is horizontal, the transmission planes will be 90 degrees out, and this will affect range. For short-range stuff, you can get away with putting the antenna at just about any angle. For maximum range and efficiency, the antennas need to be in the same plane. 5) Yes. You can use U.FL to SMA adaptor cables such as these ones here to connect your HC-12's U.FL socket to a panel SMA socket, and from there you can use any suitable external SMA antenna. Smoke makes things work. When the smoke gets out, it stops! |
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| Andrew_G Guru Joined: 18/10/2016 Location: AustraliaPosts: 871 |
Thanks Grogs. I chose FU2/2400 (apart from the name) to minimise power usage - which has been a problem for the 2x AA powered remotes. I can easily go to 1200 baud (each remote only sends about 20 ASCII characters every 10 minutes). Is FU2 at 1200 a sensible compromise? What you say supports my guess that it is likely to be the base station antennae that is the problem (it is fairly crowded inside its box and it would be easy to have an external antenna to it). Any guidance as to what a might be? Thanks again, Andrew |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
Any SMA antenna that suits your operating frequency. There are a ton of different ones in the 433MHz and 470MHz bands. I don't know if 470MHz is legal in Aussie - something you would have to check. Try searching eBay or AliExpress for "433MHz SMA antenna" - you should get heaps of hits.  Smoke makes things work. When the smoke gets out, it stops! |
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| Andrew_G Guru Joined: 18/10/2016 Location: AustraliaPosts: 871 |
Thanks Grogs, Will do. Cheers, Andrew |
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| Andrew_G Guru Joined: 18/10/2016 Location: AustraliaPosts: 871 |
An update. I ordered a brace of antennae and pigtails from AliExpress this morning and they have already been dispatched via slow boat from China. Cheers, Andrew |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
I like AliExpress and go to them more then eBay these days. Mainly as you can often select several shipping options. I always go for the AliExpress Standard Shipping, and most stuff I order gets here in about one week, which is pretty good. eBay offer free international shipping on most of the listings, but it can take weeks and weeks to get here.  Smoke makes things work. When the smoke gets out, it stops! |
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| cs41 Newbie  Joined: 08/08/2016 Location: AustraliaPosts: 27 |
A quick note re placing antennas inside boxes. As others have said metal boxes are definitely out. Some plastics are not so good. A quick check is to place the box in a microwave oven for 1/2 minute or so ( with a glass of water to protect the oven) and see if the plastic gets warm. If it does then it is absorbing energy and will reduce the signal level. If it stays cool it will be fine as a suitable enclosure. PVC pipe makes good antenna enclosures ( maybe with the HC12 in the pipe as well which will enable you to mount the HC12 and antenna in a better location.) but do check the pipe in the microwave oven first to make sure it is suitable. Hope this is useful. cs |
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| Andrew_G Guru Joined: 18/10/2016 Location: AustraliaPosts: 871 |
Now that is a plan! I'll give it a go. I might take the screws out too. Cheers, Andrew |
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redrok Senior Member  Joined: 15/09/2014 Location: United StatesPosts: 209 |
Hi Andrew_G; Those little coiled antenna are essentially what is called a "Vertical Ground Plane" antenna, even if it doesn't look like it. Normally the simple Vertical has a 1/4 wavelength element and a ground plane or counterpoise. The term "Vertical" is referring to the orientation from the counterpoise, or strait away from the counterpoise. Not the physical orientation. Sometimes there are "Lading Coils" or inductors as part of the antenna. This has the effect of shortening the strait part of the antenna. In this case, there is so much loading the strait part is so short it's nonexistent. Nun the less, it's still a vertical and the alignment is along the length of the coil. Radiation is perpendicular to the element. If you have room in the box, just eliminate the coil and use a length of wire that is 1/4 wavelength long. This usually couples better as it's physically longer. In most all cases all the antennas should be oriented in the same way, more or less parallel. If you want to extend the range further place a sheet of metal behind the antenna and about 1/4 wavelength away and aimed at the master antenna. This works with the coil version also. You can go to an extreme and make a small Yagi antenna for it and get hundreds of feet of range. Speed Of Light = 300 million m/S Freq = in MHz (300 / Freq-Mhz) = Wavelength in meters (300 / Freq-Mhz) / 4 = 1/4 Wavelengths in meters redrok AD0TJ |
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| Andrew_G Guru Joined: 18/10/2016 Location: AustraliaPosts: 871 |
Redrok, many thanks for your explanation (and the time it took). If my maths is correct a 433MHz system would require a 173mm piece of wire? Cheers, Andrew |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
Yes, although due to the "end effect" and a few other quirks of propagation, you would normally use something like 0.95 times the calculated value. (chop off an extra 8mm) The actual amount depends on wire diameter etc but for receiving, anywhere near 170mm is close enough. Jim VK7JH MMedit |
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| Andrew_G Guru Joined: 18/10/2016 Location: AustraliaPosts: 871 |
Thanks Jim. I assume that: - it should be straight(ish), eg I could dangle it below the remote station box, and - that any connection beyond the 165mm (eg within the plastic box) should be shielded. (bearing in mind that I have some antennae coming from China (see above) that I can use for the critical links) Cheers, Andrew |
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| Andrew_G Guru Joined: 18/10/2016 Location: AustraliaPosts: 871 |
@CS41, Now that the missus is awake I could fire up the microwave. The glass of water was warm but the box was "as cool as a mother-in-law's kiss" (the finest box that Jaycar can sell). Thanks, Andrew |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
If you are putting the HC12 outdoors, I would stick it and the wire inside a length of conduit/pipe. If the receiver is inside and the antenna outside, I use one of the magnetic base antennas that are common on ebay. Jim VK7JH MMedit |
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| Andrew_G Guru Joined: 18/10/2016 Location: AustraliaPosts: 871 |
Thanks Jim, Andrew |
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palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 1993 |
If you do need better range I have the plans for a simple 433Mhz Yagi antenna that I can send you. Paul. "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| Andrew_G Guru Joined: 18/10/2016 Location: AustraliaPosts: 871 |
Paul, sorry for the delay, I have been MIA for a few days. Yes I'm interested in your antenna. I'll PM my email address (or post them here if you wish). Regards, Andrew |
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| redrok Senior Member Joined: 15/09/2014 Location: United StatesPosts: 209 |
Hi All; Just wondering? Is there a problem with BlueTooth at long distances? Not signal strength, that can be fixed. I'm wondering if there are "Timing" issues? redrok |
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| Andrew_G Guru Joined: 18/10/2016 Location: AustraliaPosts: 871 |
Hi Redrok, BlueTooth is out of my league but I am happy with the little HC-12 units. I am trying to pack a lot into a small box and was checking (what I suspected) about orientation etc. The responses have helped me a lot. I'll put external antennae on some but not others. If by "timing" you mean "collision" of data streams - yes I think it may be an issue. At present I have five remotes sending say 20 ASCII characters (at 2400 baud) every 10 minutes - so it is OK. (There is one other sending data every 10 seconds. That may cause problems so I may have to separate sender and receiver off to another channel). At present there is no common time-base so even if the start times were staggered clock drift could lead to problems. Given that they sleep for nearly all of the 10 minutes between transmissions I can't see a sensible way of coordinating time. I guess I could, at say 04:00, broadcast the time (and date) every say 10 seconds until they have all responded "OK Time reset" (or whatever) and then stagger their transmissions (I could also keep the remotes awake longer around 04:00). For the battery powered remotes it is not critical if I miss a few 10 minute streams of data. Does that help explain what I am doing? Cheers, Andrew |
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