Where to find a good 868MHz antenna

I am searching for a good 868MHz sma male antenna.
My NanoVNA-h just arrived and i tested my antennas but i a am not very glad about the results:

a longer antenna about 10cm
long

and a shorter one with about 5cm
short

the shorter one is better for the 868MHz range, but there must be a good cheap antenna out there.

please share your experience

Hi I normally modify Chinese Antennas if you have some photos I may be able to comment.I have failed to find many good ones at low cost and most on eBay /AliExpress are not very good.Here is an example had to remove part of the antenna and add a bit to the top to tune in to 868MHz. Simon

@Sivaelid
nice cats

i have these:

just opened both

just measured the long one again without plastic cover:

long2

Hi Sorry about the cats and other stuff sent ,message on phone after a beer !! .

The antennas you have are not great they with have arround -3db and have an impeadane of 25-35 ohms have no matching network to make then 50ohms, are helical so can have a weird radiation pattern, but small and can be good for short range. You can adjust a bit the resonant point altering the length by compressing or streching first . The first part of the coil act as a sort of matching/ counterpoise and the second part more the radiator.

You can can cut the lenght to trim but a once of activity. I have these antennas but only use for testing on the bench.

For installed applications I use the antenna I sent pictures of before like this https://www.ebay.co.uk/itm/5dBi-868MHz-Wireless-Antenna-Router-Antenna-RP-SMA-Female-to-IPX-1-13-Cable/112984385477?hash=item1a4e64e7c5:g:ZyUAAOSwKjha890C . These do not have 5dbI gain but more tlike 3dbi but can be made to match well if modified as picture. The Chineses antenas they makecover many bands e.g for GSM/ 868Mhz/ 4G and 915Mhz they suit none of these hence the need to modify . The black sheild BTW just pulls off. This type of antenna is call a sleaved diople , the coax runs up a metal tube, that acts a a balum for the antenna and it matche the low impeadance of the radiiating element . An alternative is a 1/4 wave diople mounted above 4 radial pointed down at 45degrees this matches the radiating antena to 50 ohms and hence a good performance. with a gain of 2.14.

The other antennas, I have used are https://connectedthings.store/gb/sirio-gp-868-c-lora-gateway-antenna.html very good., but pricy. I have used Sirio antennas professionally for years always very good .

Hope helps just ask for more info if you need it.

Simon

Thank you for explanation. Now these are a little bit clearer for me. I am new to the whole antenna thing and learning.

That groundpöane antenna is nice but too expensive and big for the normal nodes.

I will try the cheap ones and modify them.
But i dont like that you have a hinge.
Would like them better without it.

Will search for a cheap one without a hinge and that is easy to modify

flat

this one was special sold as a 868MHz antenna for LoRa

You cant trust a seller even with good recomendations

Yes you can’t trust them and they don’t ever test the antenna for they sell themselves. If you find anything else let me know and will let you have my comments. Have always been Radio Eng. and Ham Radio operator call sign G8HAM . Antennas are seen a as black art and wild claims are made a bit like lipo cell battery capacity.:grin: I practice you can get only limited antenna gain and that is at the expense of the radiation patten.

Simon

Out of interest, how are you finding the NanoVNA for testing 868Mhz antennas?

I was holding off getting one as I’d seen that were originally only specced for up to 300MHz, and the 900MHz software update meant that 868 was right at the upper bounds of what it’s capable of.

…I was holding out for a V2 when the price comes down a bit …which will supposedly go to 3Ghz so would also make it useful for testing 2.4Ghz kit as well. If the V1s are good enough for the job I’ll pick one up anyway. They’re certainly cheap enough.

i am using a nanovna-h.
i have tested it yesterday against an hp analyzer for several thousand euros.
and i can say if you dont go above about 920 MHz it is quiet accurate.

just found a fairly good antenna:

just found a fairly good antenna

Got a link to it by any chance?

I have a few different ones on order to try out but would be nice to have a couple of known good ones to compare against.

As you have the analyser, can’t you tune the bad ones and repot them ?

sizes for 868 helical antenna on this image https://www.google.com/url?sa=i&url=https%3A%2F%2Felectronics.stackexchange.com%2Fquestions%2F445415%2Fassembling-helical-antenna-in-production&psig=AOvVaw17rxSWF2ZdnZr9rOhn0tdo&ust=1586591189676000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCMDyiPSu3egCFQAAAAAdAAAAABAF

I could tune them that takes time for each antenna. I hope that it is cheaper to buy a good one