Author Topic: Alternative PCB Dipole Designs (433, 868, and 915MHz)  (Read 16937 times)

LukaQ

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #45 on: June 16, 2018, 05:01:55 AM »
coax needs to be long for 915 and antenna needs to be for 915
Btw, are you in EU?

mgrooms

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #46 on: June 17, 2018, 02:42:43 PM »
hello, do I need to make any distance cut in the pcb for a 915mhz?

I seem to be getting same/little worst results than with a simple wire.

thank you.

Yes. The consensus view was that the elements of Chem E's v.3 antenna are a little short for 915 MHz; so he intentionally made the elements on the v.4 antenna too long. They must be trimmed to a shorter length for operation on 915 MHz. The question is HOW MUCH they need to be trimmed.

Has anyone [with an antenna analyzer] determined the best trim-length for operation on the 915 MHz ISM band? [for the Chem E v.4 antenna]?

ChemE

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #47 on: June 17, 2018, 04:20:27 PM »
To my knowledge, no one yet has measured the newest design to determine its frequency or how much the elements need to be trimmed.  I know Felix has both the newest PCB antennas and the SWR analyzer.  I am very interested to see how the latest design turned out though.

Sergegsx

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #48 on: June 17, 2018, 05:02:03 PM »
coax needs to be long for 915 and antenna needs to be for 915
Btw, are you in EU?

I am in the EU yes.
Why?

LukaQ

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #49 on: June 18, 2018, 12:08:20 AM »
Just asking, because ISM band in EU is 868MHz or 433MHz, you want to use 915MHz, which is probably taken by some mobile phone operator in your region. It's ok, if your far away (>200m) from anyone or anything that operates in 915MHz region.

Felix

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #50 on: June 18, 2018, 11:59:03 AM »
To my knowledge, no one yet has measured the newest design to determine its frequency or how much the elements need to be trimmed.  I know Felix has both the newest PCB antennas and the SWR analyzer.  I am very interested to see how the latest design turned out though.
New dipoles will be available in the shop in a few days.
I will post analyzer results with at mm difference from 80mm to 72mm. The 915mhz will be resonant around 72.5-73 mm with a VSWR of < 1.1

kni

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #51 on: July 05, 2018, 02:30:56 PM »
Help. My brain is stuck in "does not compute".

I am looking to confirm the optimal 915MHz distance from the moteino antenna pad to the point on the antenna where the poles diverge.

Here is what I have:
- Previous generation of dipole antenna from the moteino store (black pcb)
- Male pcb SMA soldered to the antenna
- 15cm rg316 male sma to female sma jumper cable:
https://www.ebay.com/itm/5PCS-15cm-RG316-Cable-SMA-Male-To-SMA-Female-Jack-Jump-Pigtail-6in-BS1/263266232496?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

The plan is to cut off the male sma from the jumper cable and solder that end directly to the moteino's antenna pad. I would then attach the male sma connector on the antenna to the female sma connector on the jumper cable.

I'm getting hung up on the optimal length from point A to point B.

The first page of this thread says:
Quote
915MHz = 10.80cm implies a 9.2cm pigtail

From the table for insulated copper wire in the Antenna Theory blog, the length reads:
Quote
915MHz   16.4cm   16.4 x 0.95 x 0.95 = 14.8cm

Should the distance be 10.80cm, 14.8cm, or some other distance? I am certainly misunderstanding something and could use a bump to get me back on track.

« Last Edit: July 05, 2018, 02:43:05 PM by kni »

MonZon

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #52 on: September 06, 2018, 03:55:09 AM »
Hi all!

I've ordered 433MHz antennas from pcb.io and it appears that it is shorter than expected. It measures 267mm long whether my 435MHz dipoles are 305mm long. Also, my antenna analyzer says that it is tuned to 545MHz, so cutting it is not going to help. Is it pcb.io mistake, wrong link or something? I'll have to cut all of them to 868 or 915 and sell them.
« Last Edit: September 06, 2018, 04:19:07 AM by MonZon »

ChemE

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #53 on: September 07, 2018, 07:40:11 PM »
Not the wrong link or PCBs.io's fault; rather it is my fault.  I don't have a SWR to test these, so I just copied captcha's designs as far as radiator length goes.  Others have found that this combination of PCBs.io's fiberglass and captcha's lengths is tuned higher than desired.  I had posted a stop-gap version with slightly long resonators to cover the 915 and 868 users but the old 433 design wasn't updated so it is too high unfortunately.  Since you are trimming it anyway, would you be able to confirm the lengths which resonate at 868 and 915?  I do need to get an SWR and finish tweaking this project.

MonZon

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #54 on: September 12, 2018, 11:12:48 AM »
Okay then, I get it now.

I've cut one 433MHz antenna to 868MHz - it turned out 164mm long 1.2 SWR  8) (overall length, both sides together). As for 915 - I don't have anything with that frequency. If you really need me to cut it - I will, for the sake of this project  ??? But I don't really think it is necessary. It would be better to make those pcb's a tad longer, so anyone can trim them.

Do you mind sharing 433 and 868 dip trace files? I'm thinking to lengthen 433 version and order it again.
« Last Edit: September 12, 2018, 11:16:56 AM by MonZon »

MonZon

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #55 on: November 24, 2018, 06:56:31 AM »
Not the wrong link ...

Any updates? Can I have the files?

Slople

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #56 on: April 05, 2019, 05:46:14 AM »
Hey everyone

I hope this thread is still active?

I ordered some of ChemE's PCB-Antenna [868MHz], Revision 2 and would like to use them for my paragliding-FLARM-equipment (collision warning). FLARM works between 868.0 and 868.6MHz.
I will solder some coax-wire directly to the board and connect it via u.FL to the FLARM-board.

Could someone with more knowledge than me give me a hint:

1. do I need to shorten the original boards? If so, to what length?
2. which length should the coax be?

Thanks so much,
Raphael

Felix

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #57 on: April 08, 2019, 09:32:02 AM »
Answered here.
Please take a moment and do a basic search before posting a repeat question.

Slople

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #58 on: April 08, 2019, 10:44:03 AM »
Thank you Felix and sorry for not reading this before.

I was hoping, someone else already did what I have in mind, as my most sophisticated electronical measuring instrument is a multimeter ;-)

Regarding the coax-length, my first Google-result returned this: http://www.bellscb.com/cb_radio_hobby/how_long_should_my_coax_cable_be.htm - stating "For most cases when using a single antenna system with a 50 ohm coax feed ANY coaxial length will work providing the antenna is tuned properly at the feed-point of the antenna (where the coax attaches)."

The 2nd result is http://www.m5bxb.com/coaxlengthcalc.htm, which "recommends" "tuning" the coax-cable to 50 Ohm impedance and correct length. I fear this is beyond my knowledge :-(

LukaQ

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #59 on: April 28, 2019, 03:37:34 AM »
Just to let everyone know:

the 868MHz dipole antenna here has active side 64mm long, which corresponds to 1060MHz tuning. If you select VF on site below to 90% (insulated wire AND end effects dipole) and enter 1060, you will get 64mm. Which agrees with what is measure by n1201sa. This means that this PCB design is too short! For 868MHz, each pole would need to be 78mm. So if you get the 433MHz version, and make it shorter.

One thing to note also. If you use coax to extend the antenna away from board and you add 11.4cm from exposed to exposed active wire, tuning freq. moves down to about 1000MHz, still far above 868M. VSWR is at that point 4.2, which is bad. Without coax is even worse at 4.8
So this design need to have longer poles


http://wxtofly.net/wavecalc.htm