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I have a Lora radio device that runs at 868mhz, it came with a tiny stubby antenna.

I want to use the device out and about so wanted to know if it will be OK connected to a magnetic/car antenna I got for 2m use?

As antenna seem to be listed as 2m/70cm -- and 868 is 34.5cm (about half of 70cm) -- I was thinking it would be fine.

The actual antenna is around 45cm long.

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    $\begingroup$ Most antennas aren't made to work on second harmonics. You'll note that 70cm is (approximately) the third harmonic of 2m. $\endgroup$ Nov 26 '21 at 3:05
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    $\begingroup$ I think the correct monopole for 868MHz would be 8cm long? Maybe your "stubby" is actually perfect. A correct much longer antenna might be a colinear. $\endgroup$
    – user10489
    Nov 26 '21 at 12:41
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We tried it out- in parallel with devices with stubby antenna and with a device with a proper high quality antenna.

It is quite a hilly area around here and it seemed clear that even low power stubbies were plenty to cover 'line of sight' - the other antenna didn't seem to add much (if anything). We'll be doing more trials and I'll update if there is some significant difference.

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    $\begingroup$ Hello and welcome to ham.stackexchange.com! Please do explain how you managed to transmit on 868 MHz with an antenna designed for 144–148 MHz and 420–450 MHz. I can't imagine that the transmitter was very happy with such a mismatched load. $\endgroup$
    – rclocher3
    Dec 3 '21 at 0:38
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    $\begingroup$ I just plugged it in... a Lora Heltek (v2.1) and the magnetic antenna on top of the car. And sent messages over bluetooth to the Heltek and it sucessfully Lora'd them to another board back home. The landscape (hilly) meant we didn't get more than 1.5Km away before hills blocked the signal, but it was OK upto there -- I don't know how reliable the reading is - but testing with a second lora device in the car reported a signal strength of 98% from the antenna on top of the car; $\endgroup$
    – pperrin
    Dec 4 '21 at 12:26

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