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Forum Index : Microcontroller and PC projects : HC-12 Aerial orientation question
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| erbp Senior Member  Joined: 03/05/2016 Location: AustraliaPosts: 186 |
I have 2 x HC-12 modules, both just using the little helical wire aerial that they come with. How critical is it to have the modules positioned so that the aerials are in the same plane - both horizontal or both vertical? Does anyone have any experience or guesstimate as to how much impact having the aerials mis-aligned might have on communications (not sure how this would be expressed)? Thanks for any feedback, Phil. |
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TassyJim Guru  Joined: 07/08/2011 Location: AustraliaPosts: 5905 |
With perfect antennas the losses would be huge. At least 25dB Fortunately the little antennas are anything but perfect so the radiation pattern will be poor. The losses will be less than for perfect antennas but it is still advisable to keep them the same. Every dB counts. Jim VK7JH MMedit MMBasic Help |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 5727 |
In free space you might see a difference if you rotated one relative to the other, particularly end-on. However, if the signal has to pass through a wall then polarization probably makes far less difference than losses caused by the wall. It would be an interesting experiment. The "spring" antenna is probably very inefficient. The turns aren't separated from each other so it's unlikely to act as a directional helical circular polarized antenna, just as a straight wire that's a bit thicker and more rigid than usual. These factors do make a difference (by changing the Q factor a bit) but not at that power. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| erbp Senior Member Joined: 03/05/2016 Location: AustraliaPosts: 186 |
Thanks guys, I will ensure that I mount the modules so both aerials are aligned in the same plane. Cheers, Phil. |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9063 |
Good advise. Think of it like this: You have one antenna at 0', and the other at 90' You can BASICALLY say that: "90 degrees off, is 90% lost." Now, it is not QUITE that drastic, but yes - the horizontal(or vertical) plane DOES matter, range-wise. Smoke makes things work. When the smoke gets out, it stops! |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 5727 |
The main thing to watch is that the furthest end of the spring from the pcb is almost certainly the "hot" end to RF. Don't get that end close to any metalwork or you will definitely de-tune the system and your range will probably collapse. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9063 |
Yes, totally agree with that too. It's actually quite remarkable how anything metallic close to or beside the "Hot" end of the helical, can really ruin your day if you are playing with these(or any other) RF modules.  You wouldn't think it would matter THAT much, but it does! As I have always said: "RF is a rather unforgiving mistress." Usually one correct way to do things, and a plethora of wrong ways that screw everything up! Smoke makes things work. When the smoke gets out, it stops! |
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| DaveJacko Regular Member  Joined: 25/07/2019 Location: United KingdomPosts: 52 |
There's a thread on this subject from a few years ago.. https://www.thebackshed.com/forum/ViewTopic.php?TID=9267 yes, it's a pity the HC-12 does not report RSSI. Can anyone answer this question; does the amount of current consumed by the device correlate with the amount of RF energy coming out of the other end ? This would be handy for 'tuning an antenna with wire cutters' I assume what works for transmit would work for receive. I have had over a mile, little helical on bedroom window sill to a magmount ('for 433 MHz') on the roof of my Transit |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 5727 |
I hope you have got the frequency into the (tiny) unlicensed area of the band for the UK and have got the erp (effective radiated power and also tiny) within UK limits then ;) I wouldn't like to think you were getting a knock on the door from the MOD... Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9063 |
Yes indeed, and that is pretty much how I setup my HC12 networks. Transmitter nodes that use the little helical antennas to keep the transmitting nodes small, and a roof-mounted tuned antenna - in my case, a "Slim-Jim" antenna, sealed up in PVC pipe, sticking up in free air, well away from anything metallic. I then feed that into one of those broadband TV amplifier/signal booster things, and the output of THAT goes into my main receiving HC12 via SMA cables and F-adaptors to the tiny UFL SMD socket on the end of the HC12. With that arrangement, I can get miles and miles of range @ 100mW transmit power. But here in NZ, there are slices of the band that are "Unrestricted"(no license needed) with EIRP of up to 500mW, so that is just PERFECT - for me in NZ. As mentioned, don't run the maximum HC12 output of 100mW, if you are not allowed to in your country. I am just lucky that Radio Spectrum Management here in NZ has a few of those slots you can use. In my case, up around 458MHz. Smoke makes things work. When the smoke gets out, it stops! |
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