For an odd reason, I happen to have a C8 without antennas, I've been debating incorporating it to handle devices I'm experimenting with before including them in my regular mesh. What antennas would be a good option for this?
I just migrated from my C7s with antenna mods to a C8 Pro and used those antennas:
Details from Lewis on recommended antennas: External Antenna:
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The cheapest option for a test hub would be any rp-sma 4G antenna.
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Yes. It should - based on the specs. You do not need the RP-SMA to SMA converter.
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This is working well for my Zigbee antenna https://a.co/d/8SLkrv9
I didn’t get good results with the L-Com Zigbee antenna.
YMMV
I have moved and tested my C7 antennae (hack) to my C8 and found no better results than the ones included with the C8.
A little worse in some cases as the L-Com has a better distance but looses vertical coverage due to the shallower toroidal shape of the radiation pattern.
In this particular instance the hub doesn’t have any antenna, so I am needing to get new antenna for it.
Yeah, just letting you know that the stock ones are fine if you can find a member who has removed them for whatever reason.
while it's tempting to "bigger is better" in terms of dBi, keep in mind the higher the dBi the more directional the antenna can be. My 2cents says for a ranch home,with a flat-ish type layout, a higher dBi antenna won't hurt, and may even help. But for an older 4 floor colonial you'll get better results with a lower dBi antenna as it can spread the signal better in the vertical direction.
I tend to stick with lower dBi antenna in most cases, as with a higher dBi antenna you can hit the sensor out at the mailbox, but the sensor with it's tiny antenna and low transmit power can never reach back to the hub.
Probably more important than dBi is VSWR, which correlates with the antenna's ability to better respond to weaker signals, the lower VSWR the better the antenna's ability. generally a rating of 2 or under is good.
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The stock antennas have poor vswr: over 2 for z wave with efficiency around 0.5. I got matching antennas: ANT-916-OC-LG-RPS for US z wave and ANT-2.4-OC-LG-RPS for zigbee. Very good efficiency, gain in the 2-3 range, and look alike except for a small colored band near the top that represents which frequency it is for.
Note that if your country (e.g. EU members) uses zwave frequencies in the 860s, you would get the ANT-868-OC-LG-RPS instead of the 916 version.
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Gain equals directionality times efficiency. Stock antenna for z wave has about 0.5 efficiency and 1 dB gain. So a 2 dB 1.0 efficiency antenna has the same directionality as the built in.
The follow-up question, is which post is which?
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FWIW, I upgraded to the C8-Pro from a C7 and could not get Zigbee devices to work in the same room as the hub with 15ft direct line of sight to the device. I replaced both antennas with these Amazon.com and they instantly started working. Hoping to get a little better z-wave range too to connect a few device too far out that I haven't been able to connect but haven't tried that yet. I am on a large ranch style so vertical directionality limiting is not a factor for me as there are no device above the antenna.
This indicates that the antennas themselves were bad. It. There have been several instances of this where a replacement oem antenna fixed the issue.,
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Rick - for future clarity's sake, you may want to fix the quote in your post above?... I thought I was going nuts with "Does Rick realize he has those same antennas", but then I realized it was supposed to be a quote 
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Anyone know what ant is what ? On aa C-8 ?
I was told the one closest to the usb is the zwave and the one near the green light is zigbee
is that true ? because on mine the little testing i did seems like this is untrue.
According to previous queries, Z-Wave is the one closest to the USB-C port.
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