50W Mobile GMRS Hidden Install - Midland MXT575 (full DIY build)

[ElGuano]

Here's the final piece:

I was having trouble finding a speaker/mic mount that would stick to the vinyl lower dash. Turns out it's some class of object know as "LSE" or "low surface energy" plastic. It's loaded with plasticizers to resist a decade of UV sun exposure, chemical release agents from the manufacturing process, etc. Long story short, nothing would stick to it, even VHB.

So I ended up 3D-printing a simple clip that mounts to the AC vents:

I used some adhesive-backed craft velvet to protect the dash finish, and lobotomized an old phone magnet mount (one of those you clip into the fins of the vents):

Here's the end result:

It seems pretty secure, and it's actually very easy to lift off and re-attach anywhere along that AC vent, kind of like a picatinny rail.

Here's the mic mounted centrally:

And I can any a whim slide it left or right instead:

Perfect. Hope it holds over time/bumps.

The last think I probably need is some form of tee nuts that fit in the Rivian's crossbars, so if I ever need to roof-mount the crossbars, I can easily move the antenna off the crossbar mounts onto the crossbars themselves (less because I need a radio 24/7 and more just to secure it out of the way while I'm using the crossbars, since the NMO mount can't be removed).

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[kallisti5]

Oh hell yes. Awesome write up! I've been trying to figure out a clean way to add an antenna without drilling into the body.. with the all Au body, even magnet mounts have been a no-go.

I'm no ham, but like to fiddle with the 900Mhz LoRA stuff. A NMO mount seems like just the ticket on my R1T.

 

[Zoidz]

Oh hell yes. Awesome write up! I've been trying to figure out a clean way to add an antenna without drilling into the body.. with the all Au body, even magnet mounts have been a no-go.

I'm no ham, but like to fiddle with the 900Mhz LoRA stuff. A NMO mount seems like just the ticket on my R1T.

"Au body" - that explains why Rivians are so damn expensive!

 

[kallisti5]

"Au body" - that explains why Rivians are so damn expensive!

LOL, my Chemist wife would murder me. Aluminum body

 

[ElGuano]

Oh hell yes. Awesome write up! I've been trying to figure out a clean way to add an antenna without drilling into the body.. with the all Au body, even magnet mounts have been a no-go.

I'm no ham, but like to fiddle with the 900Mhz LoRA stuff. A NMO mount seems like just the ticket on my R1T.

The RG58 that comes with the Midland radio is 5.5 mm diameter and can be squeezed into the panel gap between the huge rear fender/roofline and the rail for the cargo crossbars.

Since I installed the radio. I've actually swapped it out for a BTech 50w. Reasons include:

1) I couldn't use the fancy optional Midland handset because it just doesn't work with extension cat6.

2) the regular Midland handset has a bit of extra noise when using an extension. The BTech has none of these problems.

3) There are a few repeaters in my area on the same frequency, and the Midland's lack of programmable memory makes it impossible to switch between them while driving

The good news about the swap is that it was almost plug and play. Antenna mount? Same SO-239! Power? Same T-connector! Just take the Midland out, throw the Btech in, done. Other than changing the socket from an RJ45 to a GX16 8-pin for the handset unit.

The Btech chassis is about the same size, but it has a fan and lacks a built-in speaker.

It was easy to swap out the Midland and replace it with the BTech, as the antenna and power connectors are all the same.

I did have to custom print a mount for the GX16 aviation-style speaker/mic extension:

Shaved a few mm more off the RJ45 jack from the Midland, to the GX16 mount I printed for the BTech:

How it looks mounted to the lower dash:

With the speaker/mic connected:

All closed up, on the magnetic mount:

 

[zefram47]

The RG58 that comes with the Midland radio is 5.5 mm diameter and can be squeezed into the panel gap between the huge rear fender/roofline and the rail for the cargo crossbars.

Since I installed the radio. I've actually swapped it out for a BTech 50w. Reasons include:

1) I couldn't use the fancy optional Midland handset because it just doesn't work with extension cat6.

2) the regular Midland handset has a bit of extra noise when using an extension. The BTech has none of these problems.

3) There are a few repeaters in my area on the same frequency, and the Midland's lack of programmable memory makes it impossible to switch between them while driving

The good news about the swap is that it was almost plug and play. Antenna mount? Same SO-239! Power? Same T-connector! Just take the Midland out, throw the Btech in, done. Other than changing the socket from an RJ45 to a GX16 8-pin for the handset unit.

The Btech chassis is about the same size, but it has a fan and lacks a built-in speaker.

It was easy to swap out the Midland and replace it with the BTech, as the antenna and power connectors are all the same.

I did have to custom print a mount for the GX16 aviation-style speaker/mic extension:

Shaved a few mm more off the RJ45 jack from the Midland, to the GX16 mount I printed for the BTech:

How it looks mounted to the lower dash:

With the speaker/mic connected:

All closed up, on the magnetic mount:

If you're getting noise on the line, you can always try throwing some ferrite beads on the cables and see if it improves if you want to try the other speaker-mic again. When I had both a CB and a 2m/440 ham radio in my 4Runner I had to put a ton of ferrite on the antenna cabling at both ends to keep things quiet. I still haven't bothered installing any of my mobile rigs in the Rivian and just rely on handhelds when I need it. I may just toss a magmount on a pizza pan with a battery-operated mobile if I need long-distance comms while not moving. Luckily in Colorado we have a couple linked repeater networks with more or less statewide coverage in areas that I offroad. Especially when you're above treeline, it's impressive how far even an HT can reach.

 

[kallisti5]

Since those Cargo Crossbar adapters are now unobtainable, i've designed a 3d printable version here:

* https://cults3d.com/en/3d-model/tool/rivian-accessory-port-mount
* https://cults3d.com/en/3d-model/various/rivian-nmo-nmm-radio-mount

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