Author Topic: Small loop antennas @ 433 Mhz  (Read 36760 times)

WhiteHare

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Re: Small loop antennas @ 433 Mhz
« Reply #90 on: October 31, 2016, 11:24:52 AM »
In any event, it looks as though the small TH experimental node will now fit nicely inside a very small case (attached photo) which already has a bunch of vents.  With a tall gangling monopole antenna sticking out, it just wouldn't look as streamlined.  I haven't attached the TH sensor yet because I've run out of them, but I'm sure it will fit if I solder it directly.  Now I just need to figure out the best way to wire it for power.  I have some tabbed coincells on order from China, so that's one possibility.

That's the epilog.  I'll stop hijacking this thread now....   ;)

[Edit: P.S. I think the lesson here, at least for me, is to start with the case I want to use and work backward from that.  Otherwise, one can over-optimize for size and it won't really matter. Finding appropriate cases with good aesthetics isn't particularly easy. ]
« Last Edit: November 01, 2016, 07:21:15 AM by WhiteHare »

WhiteHare

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Re: Small loop antennas @ 433 Mhz
« Reply #91 on: November 01, 2016, 12:32:57 PM »
By the way, I just now did an off-the-cuff, very unscientific, test to get a rough gauge on the various antenna performances.  Comparing wire monopole, uSplatch, and Splatch antennas.  Before starting the test, I thought the monopole would be the clear winner, and the Splatch would handily beat the uSplatch.  Honestly, though, I didn't see a clear winner or loser.  For any one of them, the RSSI depends a lot on the vagaries of how it's orientated or situated.  So, with that in mind, I'd say they're all in about the same ballpark, give or take.  There are possibly better configurations that I haven't yet tested (such as with the Splatch in a vertical configuration), but those are the early preliminary results with the units I've already made (photos above).

perky

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Re: Small loop antennas @ 433 Mhz
« Reply #92 on: November 05, 2016, 10:35:40 AM »
Hey, I've just come across this article. Seems you can use the free NEC-2 software for antenna design, this normally only uses air dielectric, but you can fudge it to use FR4 dielectric with some simple hacks. They've come up with an inverted L type 915MHz design that apparently performs better than a monopole and is only 1.25" square:
http://www.edn.com/design/communications-networking/4332858/Small-915-MHz-antenna-beats-monopole
Mark.

joelucid

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Re: Small loop antennas @ 433 Mhz
« Reply #93 on: November 06, 2016, 01:33:29 AM »
Quote
Hey, I've just come across this article.

Looks interesting. They don't mention it but I'd assume you need a full sized ground plane for this antenna though. So the miniaturization only benefits one half of the antenna.

perky

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Re: Small loop antennas @ 433 Mhz
« Reply #94 on: November 06, 2016, 08:45:32 AM »
Yes, it's an inverted L folded monopole so I assume would require a ground plane. I was more interested in the fact you can simulate these with NEC-2 (4NEC2) and the FR4 hack. Pity there's no download for the NEC-2 design files...
Mark.

joelucid

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Re: Small loop antennas @ 433 Mhz
« Reply #95 on: November 22, 2016, 03:43:36 PM »
Guys, check out these very cool air trimmers I got today:



Here's the design I just threw together for it:




It's the Johanson 5851 (http://www.farnell.com/datasheets/35551.pdf) with a Q of >7500 at 100 Mhz. This thing should fly! I'll report back when I have the boards.

I paid like $7 each for the trimmers - so this is definitely for the enthusiast  ;)

Joe

tve

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Re: Small loop antennas @ 433 Mhz
« Reply #96 on: November 23, 2016, 02:05:38 AM »
I don't quite understand the uSplatch. Isn't a 50Ohm resistor across antenna and gnd pins essentially a 0dBi point source antenna? And the uSplatch has max gain of 0.3dBi, is that worth it? (Note that a 50Ohm RF resistor costs about the same as the uSplatch but is a lot smaller.) I'm sure I'm missing something :-)

WhiteHare

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Re: Small loop antennas @ 433 Mhz
« Reply #97 on: November 23, 2016, 09:59:12 AM »
I don't quite understand the uSplatch. Isn't a 50Ohm resistor across antenna and gnd pins essentially a 0dBi point source antenna? And the uSplatch has max gain of 0.3dBi, is that worth it? (Note that a 50Ohm RF resistor costs about the same as the uSplatch but is a lot smaller.) I'm sure I'm missing something :-)
I've tried it both ways, and simply put: the uSplatch is more efficient at converting electrical energy into RF energy at the target frequency.  If range isn't a concern, then I think an argument can be made for using a resistor antenna.  Likewise, if space isn't a concern, then a simple wire antenna like the standard issue Moteino uses remains a good choice.

If Joe succeeds in his experiment, then it should outperform the uSplatch, and that would be great.  I certainly do admire his tenacity in pursuing it, and I look forward to hearing how it turns out.
« Last Edit: November 23, 2016, 10:37:25 AM by WhiteHare »

tve

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Re: Small loop antennas @ 433 Mhz
« Reply #98 on: November 23, 2016, 11:39:08 AM »
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I've tried it both ways

Ah, you compared with a 50 Ohm RF chip resistor soldered across ant and gnd on the rfm69 module? By RF resistor I mean something like http://www.digikey.com/product-detail/en/vishay-thin-film/FC0603E50R0BTBST1/FC0603-50BFCT-ND/1769793

perky

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Re: Small loop antennas @ 433 Mhz
« Reply #99 on: November 23, 2016, 01:43:45 PM »
Dummy resistor loads will only 'leak' some radiation, but it's tiny compared to a proper resonating antenna with a reasonable radiation length. Remember with a dummy load practically all the energy goes into resistive heating of the resistor rather than being transmitted, and it is physically small.
Mark.

joelucid

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Re: Small loop antennas @ 433 Mhz
« Reply #100 on: November 23, 2016, 01:50:51 PM »
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Dummy resistor loads will only 'leak' some radiation, but it's tiny compared to a proper resonating antenna with a reasonable radiation length. Remember with a dummy load practically all the energy goes into resistive heating of the resistor rather than being transmitted, and it is physically small.

Right. That's a long way of saying that they don't make any sense  ;)

captcha

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Re: Small loop antennas @ 433 Mhz
« Reply #101 on: November 23, 2016, 04:11:25 PM »
Quote from: joelucid
they don't make any sense

Oh, I beg to differ here.

A purely resistive 50 ohm dummy load would have superior impedance matching to the radio over any of the commercial or home brew antennas for these radios. If I'm bench-testing between two or more radios the resistor is also a far more compact solution and more than adequate to test comms in close quarters.

With an in-line rf power meter, dummy loads are also the best option to verify the transmitter's output power.

They have their place, but they finish last when you're after an antenna system to achieve long-range comms.

joelucid

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Re: Small loop antennas @ 433 Mhz
« Reply #102 on: November 23, 2016, 04:32:43 PM »
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A purely resistive 50 ohm dummy load would have superior impedance matching to the radio over any of the commercial or home brew antennas for these radios.

But what's the point? Sure 100% of tx power gets transmitted to the antenna and ... burned off as heat. No matter how bad your match with a real antenna - you'll always come out better than with a resistor. 100% of 0 is still 0.

But yeah they have their place - as long as its not sending or receiving rf  ;)

perky

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Re: Small loop antennas @ 433 Mhz
« Reply #103 on: November 23, 2016, 04:58:27 PM »
Oh, I beg to differ here.

A purely resistive 50 ohm dummy load would have superior impedance matching to the radio over any of the commercial or home brew antennas for these radios. If I'm bench-testing between two or more radios the resistor is also a far more compact solution and more than adequate to test comms in close quarters.

With an in-line rf power meter, dummy loads are also the best option to verify the transmitter's output power.

They have their place, but they finish last when you're after an antenna system to achieve long-range comms.

The resistor will have a finite size, also some inductance and capaitance. It'll act like a very, very low efficiency antenna with a very, very high loss as almost all of the power is converted into heat. The radios are very sensitive nowadays, so it will pick up and transmit some signals but its gain will be through the floor. You might on the bench be able to simulate receiving from a long distant transmitter,or it being a transmitter that is a long way away from its receiver when the devices are right next to each other, but for any other practical purpose they are useless as antennae.
Mark.

captcha

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Re: Small loop antennas @ 433 Mhz
« Reply #104 on: November 23, 2016, 05:35:08 PM »
Yep, couldn't agree more.

Instead of dummy load, I think a more appropriate name would be dummy antenna because as loads these resistors are quite effective.. :-)