Nate, the link you provided is for an antenna that is designed to transmit & receive 2-meter (144 MHz) and 70cm (450 MHz) radio waves. It will under-perform for the frequency band that the goTenna Mesh unit operates on, which is 900 MHz.
You should not expect good performance from that antenna because it is not properly matched to the frequency of your goTenna Mesh.
It would be better to search for a high gain antenna designed for 900 MHz if you want to add an aftermarket antenna for peak range and reception. Look for an “omnidirectional” design, so that the performance of your unit will be insensitive to the orientation of the antenna. (Unless you will know the distance & direction of other goTenna Mesh units that will hop your transmission onward, directionally-biased antennas won’t be a good choice.)
I don’t see a modified goTenna Mesh case holding up to the physical load exerted with an antenna like that. It’s a heavy antenna fior the Baofengs it is designed for and liklely clumsy to use with them. That would alll be magnified with the far lighter GTM form factor.
Here’s a high gain whip antenna optimized for the 900 MHz band, with an omnidirectional design. If you’re going to break open a goTenna Mesh unit and modify it to accept aftermarket antennas, this one would be an ideal candidate - the gain is 7dBi. (That’s excellent!) You may be able to find a better price at another website, so I’d conduct a few web searches at online sellers of radio equipment.
Thanks for the feedback! The idea for a whip antenna is really just to get a compact package. It would be cool to just throw it into a pouch, go and deploy when needed.
@ShootAnyAngle How are you making the connections for an external antenna? Do you have a few pictures to go off of? I am new to this whole project and have read a lot of the discussion on this site, but I haven’t seen any detailed photos or instructions for making that initial change to the unit.