Author Topic: Alternative PCB Dipole Designs (433, 868, and 915MHz)  (Read 15110 times)

perky

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #30 on: March 19, 2018, 08:29:10 PM »
Yes indeed. As I stated this was a quick test to illustrate my belief that the elements should be closer to the 78mm than 60mm that
the v3.0 boards were built. The photo shows that adding length made the antenna work better for the freq of interest ( 915 Mhz )

OK, I assume that the total length of the elements with the extensions was actually greater than 78mm, and you've done some calculations as to what the real velocity factor appears to be for the dielectric part using a combination of lower velocity rate for the part with the dielectric and 0.98 for the extensions, then calculated 78mm for elements from that assuming the elements have dielectric beneath them all the way along. If 78mm is the total measured with the extensions the length would need to be reduced. Just asking to be sure ;)

BTW here's a document that appears to show the empirically derived velocity factor of 0.82 for FR4 (page 7), and is inbetween the dielectric alone and air values due to the fields partially travelling through the dielectric and partially through the air:

https://www.silabs.com/documents/public/application-notes/AN639.pdf

Mark.
« Last Edit: March 19, 2018, 10:13:49 PM by TomWS »

luisgcu

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #31 on: March 29, 2018, 07:58:14 PM »
Wow tbalon that is one heck of a first post!  Welcome to the forums!  That is awesome that you tested my adaption of captcha's work, thanks for the data and write up.  I'm all too happy to increase the length of the resonators (even though the boards will be a little more expensive) if it means we all get better performance.  As I said when I set out on my adaption, I don't have a VNA and have no plans to buy one and learn how to use it, so hopefully captcha's work transfers directly.  It would seem that perhaps it doesn't and the design can be further optimized.  I happen to have the 868 and 433 MHz versions of my antenna here so I can do some RSSI measurements using those longer resonators and see if they do indeed improve upon the RSSI at 915MHz.  Longer term, I can post revision 4.0 designs which have longer resonators and hopefully you'll be willing to test them as well.  If you prefer not to buy copies of those boards, I can and ship them to you if you are in the US.  I'm curious to see what others think since RF is most certainly not my forte.
I recommend this vector antenna analyzer https://www.ebay.com/itm/N1201SA-UV-RF-Vector-Impedance-ANT-SWR-Antenna-Analyzer-Meter-140MHz-2-7GHZ/182592795913?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649 , I tested your antenna and I get pretty much the same result as @tbalon.
..Knowing other is wisdom,
knowing yourself is Enlightenment..

nick-crow

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #32 on: May 15, 2018, 04:00:31 AM »
Hi I'm using the 868mhz version for my flight instrument (paragliding) we use a lora system to allow us to see each over and be seen by ground stations which forwards to the web I'm interested in the radiation pattern of these pcb antennas to check if I have used it in the optimal position. 

https://imgur.com/a/X7oBwTE     

http://www.air-ware.co.uk/


Felix

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #33 on: May 22, 2018, 09:21:04 AM »
ChemE,

PCBs.io does not seem to allow download of your shared project, as opposed to OSHPark where you can download the files.
Can you post your latest design here in a ZIP or post it on OSHPark?
Or better yet post the Eagle files like you did for the first version?

Thanks!

FWIW Black is one of the worst possible silkscreen colors for a PCB especially for prototyping. Anything that completely masks the copper is a bad idea.
You can't see the copper and if you need to fiddle with the copper layer - like in this case cut the trace, you have to first scrape off the black paint to see what you're doing).
Purple is still not great either but at least the copper is visible. I will probably never use black again in any of my designs or prototypes.
« Last Edit: May 22, 2018, 09:24:48 AM by Felix »

TomWS

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #34 on: May 22, 2018, 10:34:17 AM »
Purple is still not great either but at least the copper is visible. I will probably never use black again in any of my designs or prototypes.
Black is the only choice on PCBs.io.  The good news is that you'll probably never receive your boards from PCBs.io, so it won't matter what color the mask is!  ;)


Felix

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #35 on: May 22, 2018, 11:35:21 AM »
Black is the only choice on PCBs.io.
Yeah too bad :(
If PCBs.io reads this, they should consider changes.

The good news is that you'll probably never receive your boards from PCBs.io, so it won't matter what color the mask is!  ;)
Did you not get yours lately?

I need proto boards FAST, I usually use OSHPark RUSH service if it's urgent, sometimes I get automatically upgraded for free :)
They arrive within 8-10 days from ordering. 3 boards is enough for prototyping.

TomWS

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #36 on: May 22, 2018, 12:09:52 PM »
Did you not get yours lately?
The last time I ordered boards from them (and I DO MEAN the LAST time), it took 39 days to get the boards with 2 day shipping...
This was in March/April.

Their online 'status' information is meaningless and they provide no feedback or response to queries.  Net:  Too long and too much uncertainty.

OshPark is my goto...

ChemE

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #37 on: May 22, 2018, 12:11:57 PM »
ChemE,

PCBs.io does not seem to allow download of your shared project, as opposed to OSHPark where you can download the files.
Can you post your latest design here in a ZIP or post it on OSHPark?
Or better yet post the Eagle files like you did for the first version?

Thanks!

Sure Felix, here they are.  I should note that this newer design has not yet been verified to be centered at 915MHz and I left it a little long in case some trimming was needed.  Life has been busy and I've put this project down for the moment.

Felix

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #38 on: May 22, 2018, 12:16:36 PM »
Sure Felix, here they are.  I should note that this newer design has not yet been verified to be centered at 915MHz and I left it a little long in case some trimming was needed.  Life has been busy and I've put this project down for the moment.
ChemE,
Thanks!
I got the N1201SA Analyzer which has confirmed the findings reported by tbalon.
I can try the new design when I get some time, thanks for sharing the new design!
I see you kept the radiators width the same, any thoughts on this and the supposed wideband they bring with this design?

Tom,
RE PCBs.io - I reckon they are in a hard market. OSHPark is probably very established. And with such delays being self repelling, any OSHPark competitors cannot really survive, UNLESS they come up with an edge product or service, that's the only way.

ChemE

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #39 on: May 22, 2018, 01:00:12 PM »
Yes, the feedback that I've gotten so far is the LoRa community crave wideband antennas because of the way it uses spread-spectrum and the wider radiators do indeed result in an impressively wideband dipole.  I would think given this, there is no reason to switch back to narrow radiators.

Leo did tell me that they switched board houses for a few batches and this created a long delay that was unexpected but also not likely to recur.  I am still happy to use PCBs.io but I understand why others have moved on.

mgrooms

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #40 on: May 29, 2018, 12:46:06 PM »
Felix,

I don't think I ever got the antennas I ordered from PCBios either. It took so long I forgot about them. Will have to check when I get home.

I see you received your N1201SA. Do you mind sharing your ordering experience / who you bought from? I'm ready to pull the trigger on one, but don't want to over pay, nor wait 45 days for it to arrive.

Thanks,
- Matt

« Last Edit: May 31, 2018, 08:16:43 PM by mgrooms »

Felix

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #41 on: May 29, 2018, 02:54:56 PM »
I bought it from an US ebay seller, if you search for it there should only be a few US sellers. I didnt want to wait so long for something like that either. I paid under $200 i think.
Also I got it from here so if something is wrong with such an instrument I can return and get my cash back quickly.

So far so good, I havent played with it a whole lot, just tested a few things and learned how to get around through the UI. Pretty cool toy, I dont really have a way to benchmark it but the results are pretty convincing and within expectations, plus scores of online reviews seem to back that these are legit analyzers.

UDPATE: this is the item I got from ebay:
https://www.ebay.com/itm/N1201SA-UV-RF-Vector-Impedance-ANT-SWR-Antenna-Analyzer-Meter-140MHz-2-7GHZ/182592795913?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
« Last Edit: May 29, 2018, 03:16:26 PM by Felix »

mgrooms

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #42 on: May 30, 2018, 08:35:37 PM »
Felix,

Thanks for the info on the eBay seller you used to purchase your N1201SA antenna analyzer. I just placed my order with the same eBay seller, with expected delivery to Texas on 4/5 June.

On the PCBs.io circuit board fab-house non-delivery of my order of Chem-E's 915MHz v2 dipole antennas. . .  I checked my stack of recently received goodies and didn't find a package from them. Looks like another strike against them for non-delivery. If I do find them lying around I'll post a correction here.

I looked again and found the delivered order from PCBs.io. The post mark date on the package matched the promised 'delivery' date [4 April] provided in the order history. USPS made the physical delivery to my door some days after that. To PCBs.io's credit they included an extra board in my order. [ordered 4 / received 5]. I just now placed an order for eight more.

Could someone make them available on OSHPark? [not familiar with the process...]. Would gladly pay more for them there, in return for more rapid, reliable delivery.

-Matt, San Antonio, TX.
« Last Edit: May 31, 2018, 08:25:59 PM by mgrooms »

LukaQ

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #43 on: June 04, 2018, 03:43:30 AM »
you guys are spoiled  ;D
Many places in the world have to wait weeks (for free shipping postage) for delivery, in EU from China and even US takes time to get something delivered. Free is not free but = more time, almost everything is not free, you do pay in some way or the other. Take that into calculation ;)

Sergegsx

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #44 on: June 16, 2018, 03:48:28 AM »
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.