Right now the C8 ships with antenna connectors that are 90 degrees for placing the Hubitat on a table top or shelf. I usually mount on particleboard on the wall with the antenna side up with the C7's . Is there any option to have straight out antennas for C8 say aftermarket options? In the picture below is one install I did the top Hubitat has the radios on the bottom one has the radios off.
There are no "official" option besides the ones they come in the box. However, any RP-SMA antennas you can find that work in the 2.4 GHz (Zigbee) and 900-ish MHz (Z-Wave) bands should work. You could find "dual band" antennas like you have in box or one that works for each frequency (in which case you'll need to know that Z-Wave is the one closer to the USB-C port).
This is probably way overkill for you (I wanted this so I could put the hub in a rack and the antennas outside it), but here are two I'm using on a hub now: https://www.amazon.com/gp/product/B09CDJ66K2/. Z-Wave appears to be working about the same as it did with the internal antennas, but Zigbee is still on my other hub, and I haven't tested that. However, there are many others, some closer to the size and appearance of the stock options, that have flexible connectors and should also work.
L-com or another reputable vendor is more likely to have clearer sprecs ans or also better products, but for the price I can't complain about these. 
Others might have recommendations for things they've tried.
And the logo is right side up!!!
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The basic rule of monopole passive antennas is that the higher the dBi, the further the signal can travel. However there is a trade off as the sphere of coverage shrinks with higher dBi. So using a higher gain antenna may actually cause gain to go down.
Every added connector has a power loss.
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Depends on how you want the radiation patterns to propagate. But it's good to have options. In one location the hubs are located deep in a concrete basement within close proximity to a repeating Z-Wave and ZibBee device(s). In another in a open woodshop in their data closet that is sealed and filtered to keep out the dust and other debris. At least the antenna's are not glued to the terminals like the FCC mandates for GRMS radios.
Since one of my other hobby is SDR and microsecond clock pulse accuracy I have lots of options to build antennas that are frequency compatible with Z-Wave (900 MHz) and ZigBee (2.4 GHz). I may just have to play around if / when I get to the C8.
