Author Topic: Issue with external antenna  (Read 1347 times)

d00m178

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Issue with external antenna
« on: January 21, 2018, 12:55:54 PM »
Hello all.

My project contains two devices based on moteino.
one device is "server", it is located outside, under a lot of snow and has several thermosensors.
it has UFL connector soldered to PCB.
UFL connected to pigtail with SMA connector.
to SMA connected feedline - coaxial cable (lenght about 3m) and on other side of cable - N-type connector which connected to DIY GP antenna also based on N-type connector.

another device is "client" and it is portable device which I use to receive data from server device.
it is small case with moteino + ftdi adapter which I connect to my smartphone via OTG cable and get data from server via UART.
client also has antenna, but this is antenna from old broken meteostation.
it looks like monopole antenna but when I disassembled it I noticed that inside it has PCB instead wire.
then I assembled it and soldered pigtail to Moteino PCB. In manual to meteostation stated that it use 915MHz as my LoRa RF module.
I think this antenna is dipole but I'm not sure.
So, this client works as expected - receive data from remote servers. Maximum range is about 5 km.

I have issue with second client device.
it similar to first client but antenna is different:
https://www.amazon.com/gp/product/B01HHPK7KS/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

also I soldered UFL connector on Moteino PCB and connect antenna via pigtail:
https://www.amazon.com/gp/product/B01CWJ5JS4/ref=oh_aui_detailpage_o07_s00?ie=UTF8&psc=1

and this client doesn't work as expected. I can't receive data on point where I succesfuly receive data with first client.
I can receive data only if I stay very close to server.
And I think issue with antenna.
I disassembled it, and inside it has wire with spring. Lengh of wire is about 8cm from begining of spring till end of wire.

then I started read a lot about antennas, how they works and about radiation patterns, but still don't understand why first client works better than second.
Seems my new antenna has very low range but I don't understand why.

My main questions:

- do I need install new antenna on metal ground plane? I suppose no, because for example a lot of wifi access points and routers with detachable antennas doesn't have metal ground plane at all.
their antennas just installed in plastic case and connected to PCB via pigtail like I did.
now it just connected to SMA connector and placed in case.

- what exactly name of my new antenna? how it should be placed/located for good working? what is the spring in my new antenna?

- I would like to make good DIY antenna for client - would someone please advice some manual for my needs?
I think monopole antenna not good for my needs, because it shouldn't be used in hand, close to body - I usually put client in my jacket pocket.
 
Thank you in advance.

LukaQ

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Re: Issue with external antenna
« Reply #1 on: January 22, 2018, 01:14:04 AM »
your antenna with ground plane is Marconi antenna, dipole. White if you don't add ground plane, it is only monopole, which the second one is and those of wifi routers and such. Ground plane would make other "leg" of dipole antenna
« Last Edit: January 22, 2018, 01:15:50 AM by LukaQ »

d00m178

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Re: Issue with external antenna
« Reply #2 on: January 22, 2018, 08:21:35 AM »
your antenna with ground plane is Marconi antenna, dipole. White if you don't add ground plane, it is only monopole, which the second one is and those of wifi routers and such. Ground plane would make other "leg" of dipole antenna

sorry for probably mistake in my post.

first picture - it is GP antenna which I use on server devices and it works ok. at least with my first client device.

And my main question is about second picture with black monopole antenna which I use on my second client device. I have issue only with this antenna and want to make new antenna on PCB for my client device, or fix the issue with current antenna (but have no idea how to do it)


LukaQ

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Re: Issue with external antenna
« Reply #3 on: January 23, 2018, 01:11:13 AM »
we don't know what the problem is, could be, that your gain is lower because you have monopole, could be that antenna is the wrong length. How long is the wire anyway?
How do you feed this antenna? There are a lot of questions to be asked first.

You can always make PCB antenna, if you don't want to have so many connectors, coax cables and so on

For current antenna, you would need it stretched length. That would need to be, probably 1/4 wave, a bit less actually. Next thing would be (I will assume you have pretty large distance to cover), to have ground plane (which has radius of 1/4 wave or more) or ground under antenna, so that you turn it into dipole OR add another length of same wire to make dipole itself.

Let's see in what direction you want to go

d00m178

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Re: Issue with external antenna
« Reply #4 on: January 23, 2018, 09:39:04 AM »
Today I disassembled it again and checked length - take a look at the picture.
so total length of wire is 9.2cm
length of coil (spring) about 2cm

I wonder - if I use 915Mhz RF so I need wire == 8.2cm but not 9.2!
maybe I need cut 1cm from the top of this wire?
Iím not sure because here is a coil on wire and I donít know what is purpose of this coil.

And I feed it via pigtail with length of 20cm with RP-SMA connector. Thats all.
One end of pigtail has UFL connector and it connected to MCU, second end has RP-SMA and it connected to antenna.

Also what I mean about antenna on PCB (like in my first client device) - it is like these antennas:
https://www.aliexpress.com/item/GSM-3G-4G-built-in-antenna-PCB-plate-aerial-internal-IPEX-connector-2/32510874309.html?ws_ab_test=searchweb0_0,searchweb201602_3_10152_10151_10065_10344_10068_10342_10343_10340_10341_10543_10084_10617_10083_10616_10307_10615_10301_10313_10059_10534_100031_10604_10103_10607_10606_10142,searchweb201603_1,ppcSwitch_5&algo_expid=b53f3104-07a5-4244-9330-add07a89858c-4&algo_pvid=b53f3104-07a5-4244-9330-add07a89858c&priceBeautifyAB=1

https://www.aliexpress.com/item/GSM-3G-4G-LTE-internal-antenna-5dbi-high-gain-module-aerial-70-15mm-ipex-connector/32825294695.html?ws_ab_test=searchweb0_0,searchweb201602_3_10065_10344_10068_10342_10343_10340_10341_10543_10084_10617_10083_10616_10307_10615_10301_10313_10059_10534_100031_10604_10103_441_10607_442_10606_10142-normal#cfs,searchweb201603_25,ppcSwitch_5_ppcChannel&algo_expid=ae65d8aa-d95b-4698-8363-96fcdb179d85-4&algo_pvid=ae65d8aa-d95b-4698-8363-96fcdb179d85&priceBeautifyAB=1

because in my first client antenna inside in ordinary plastic tube was pretty the same piece of PCB. Unfortunately now I canít make a photo of it.
it very similar to this, on right side of module:
https://www.weathershack.com/images/products/davis-instruments/6250-2d.jpg


I just don't understand - why antenna from old weather station which used on first client device works better than this new antenna from amazon?
I know that in first case it is PCB antenna, and second - it is wire with coil, but what the main difference?
because first device works on range about 5 km, a second barely works on range 20-30 meters!
« Last Edit: January 23, 2018, 09:49:31 AM by d00m178 »

Felix

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Re: Issue with external antenna
« Reply #5 on: January 23, 2018, 10:30:14 AM »
I know that in first case it is PCB antenna, and second - it is wire with coil, but what the main difference?
because first device works on range about 5 km, a second barely works on range 20-30 meters!

Difference in build maybe?
Looking at those PCB antennas, they are GSM antennas, multiband and very wideband. The pigtails are probably not tuned to the narrowband you are using them at. I would look into different antennas. See the PCB dipoles by ChemE.

LukaQ

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Re: Issue with external antenna
« Reply #6 on: January 23, 2018, 11:45:03 AM »
I donít know what is purpose of this coil.
You would coil the wire the have shorter antenna, but still have it's length be for the freq. you want to use it for. And as far as I know, antenna come few % shorter then calculated, something about capacitive coupling to surrounding space (in some cases like remotes, that would be hand)


As far as PCB antennas go, from ONE source I found, still it is from company that do a lot of RF stuff, is that they have low gain, maybe that is why you have such performance.

Take a look

http://www.hoperf.com/upload/rf/ANTENNAS_MODULE.pdf

Does that bad antenna work the same on more then one module like that? have you tested that module with good and bad antenna, so that you know, that antenna is the problem


Kilo95

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Re: Issue with external antenna
« Reply #7 on: January 23, 2018, 12:33:28 PM »
I use a full wave wire monopole antenna on my Moteino connected to my PiGateway, half wave monopoles on my nodes, and one of ChemE's PCB antennas on my WeatherShield that is outside and 175 feet from my PiGateway. The halfwave monopoles work fine for me and the PCB antenna on the WS gives RSSI -80 to -100. good enough for me

d00m178

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Re: Issue with external antenna
« Reply #8 on: January 28, 2018, 07:15:04 AM »
I realized that last time I didn't attach pictures of disassembled antenna.
Here it is.

and now I realized that central wire of antenna may be longer because of the part of wire that soldered to copper wire with coil.
So total length of antenna could be 11.5 cm.
Am I right or no?

perky

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Re: Issue with external antenna
« Reply #9 on: January 28, 2018, 01:03:38 PM »
I use a full wave wire monopole antenna on my Moteino connected to my PiGateway, half wave monopoles on my nodes, and one of ChemE's PCB antennas on my WeatherShield that is outside and 175 feet from my PiGateway. The halfwave monopoles work fine for me and the PCB antenna on the WS gives RSSI -80 to -100. good enough for me
I'm a bit confused, are your full-wave and half wave monopoles really dipoles (centre fed)? End feeding a half wave of full wave monopole is high impedance, maybe 2000 ohms, so it would require an impedance matching circuit to get effeciency from it.

Mark.
« Last Edit: January 28, 2018, 01:59:24 PM by perky »

LukaQ

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Re: Issue with external antenna
« Reply #10 on: January 28, 2018, 01:52:17 PM »
I realized that last time I didn't attach pictures of disassembled antenna.
Here it is.

and now I realized that central wire of antenna may be longer because of the part of wire that soldered to copper wire with coil.
So total length of antenna could be 11.5 cm.
Am I right or no?
I'm pretty sure that 2cm is not 2cm if you uncoil it. wire length is measured of straight wire