Adding an external antenna jack


#1

I was wanting to check the feasibility of adding an external antenna jack. Based on the rf switch data sheet I see that vrx1, vrx2, vtx1, vtx2 using logic control changes the Rx and tx antenna used. If I could swap the logic I could attach an external jack but I would still be able to use the original onboard antenna. Sounds straight forward right?

Now here’s the issue. I used the data sheet and found pins 21, 22, 25, & 26 on the board. My issue is that all the pins were low using a 10k-ohm resistor. This is not a listed configuration on the data sheet.

In addition vrx1 and vrx2 on the back side of the board don’t seem to be connected via traces to the switch.

So now here I am wondering if I am just seeing things wrong or there is a missconfiguration with the board. If there is a intended fraction antenna may not be selected properly.

Can anyone else confirm what I am seeing?

My board version is v1.0 2017 Gt-175-00003.


Warning about ESD (when hardware-modding)
#2

I have not removed the RF shield on my “experimental” unit (send solderwick !) so I have only looked at the photos that I have found on line. I have not probed it yet. Thanks for the info that everything looks to be pulled low.
And I need to get some hot air gear. This is my first real venture into SMT. I started with tubes so it looks like I am retooling. Again.


#3

Here are a few images that I was able to take. Please excuse the vignetting as I was putting the camera up to the microscope eyepiece.

You can see VTX1 & VTX2 (xfer switch pin 21 & 22 respectively). Both pass through a 10 KOhm to ground. (R40 & R3)

You can see VRX1 & VRX2 (xfer switch pin 25 & 26 respectively) Both are also passed directly to a 10KOhm and then ground. (I am unsure what the R label is)

And lastly you can see the inverse of the board. The two arrowed locations are the VRX1 & VRX2 feeds from the topside of the board. (I drew the sharpie on there so I could remember where they where.) There is no connection to the rest of the bottom side of the board.


#4

On the topside of the board the arrows I drew are the locations where the signal passes thorough the board.


#5

Dogshoes posted in MOAN 2017/10/14 that he had put an MMCX on. How’s that going, dogshoes ?


#6

It has been linked before but here is the Xfer switch datasheet. On the 3rd page you can see the connected Path logic setup required to have the switch transfer from ANT1 or ANT2. Non of the configurations show low for all the inputs. :confused:


#7

Calling/tagging @dogshoes


#8

Yeah. I posted that info and what I could see in my thread “1st step to hdwr mod”


#9

You may not need to use solderwick to remove the shield. I didn’t use my solderwick when removing the shield from mine. Just extended heat and a small spugger to lift the shield. Then worked to the next solder joint to repeat. It got easier over time as the shield dissipated the localized heat across the entire body of the shield.


#10

SMT continues to frighten me. I am considering this. It seems about minimum entry level.


I worry about unsoldering everything else.
I need some waldos.


#11

I’m coming to borrow that. lol I currently use a cheap microscope that plugs into my computer / phone / tablet and a cheap soldering iron. You will have to let us know if you pull the trigger on that unit. I’ve seen some pretty sweet setups at the HAM fests. I’ve been tinkering with the idea of attaching my microscope and webcam to a VR viewer.

I’m not planning to mess with an external connector attached directly to the board. I think it would be better to add a short run of cable to the Gotenna. That creates 1 less point of failure and 1 less impedance mismatch that may increase SWR. I’m thinking ~1 foot of cable with the connector I need.


#12

Sounds good (short cable to antenna). The whole lot could go into 1 pc 1 1/2 thinwall PVC with a power cord hanging out the bottom.
My headlamp binocs go up to 25x, but then I have to get so close that my nose is in danger.


#13

That’s why I use the USB microscope. I love PVC. My weatherproof test box consist of PVC and some end caps. PVC is also good because it can be bent with a heat gun for odd shaped pieces. I used it as a trailer hitch for my bike and a skeg for my kayak. It’s good for testing.


#14

I was having kinking problems with a “fancy bend” project and used the hot-sand-poured-inside method, and it was the bomb. But, yeah, it is great. Radio transparent, & there are all those fittings that have nothing to do with plumbing.
But I am getting of topic. I will be back after I have tortured some electrons. Until then I really have nothing to add to this thread.


#15

I’ve done a bit of a minimalist intervention approach in opening up the mesh v1.0 2017 - GT0175-00003 0.6 . Aim is to add ext. antenna jack at top, but waiting for those parts to arrive. Now I may have gotten lucky with my unit because the RF shield isn’t soldered all the way around the top, so this approach has been viable so far… it still works fine.

I used a razor saw to cut only part of the upper cover, to expose the RF Shield. Across the top face, cut from just above the switch by a millimetre or two (about 26 mm from top), and diagonally across face to other side, about 34 millimetres from top. Also cut seam between front and back plastic components to meet the top diagonal cut. Because seam is below motherboard, it is pretty safe to cut. Cut along top may have saw brush up against aluminum RF shield. Best to be sensitive about when saw has broken through the 2mm casing.

The last move is to score the rf shield along the top with a razor blade a few times to create a fold line (not penetrating the shield). Also to score either end where it slopes down to meet the motherboard, but in this case, score enough - say 10x, a little pivot motion with blade in control - to actually cut through the ends. Last move is to lift the aluminum shielding up via a small screwdriver in thumb+forefinger, braced against top housing cut, so aluminum hinges upwards, thus exposing C50 where the antenna should be seated.

Some pics. Note my first cut was straight across, but I changed it to an angle cut to get more access to the RF shield. I’ll post an update when antenna mount is in place.

Cheers!

Damion


#16

P.s. I’m assuming that the whole fractal antenna part can be chopped away to make way for SMA female plug, right?


#17

Damion,
Nice work on opening that up. :+1: I like your approach, at least in comparison to using a Land Cruiser, which is how I accessed this one originally (and unintentionally.)

That’s one side of the top end. This is the best view of the other side.

Looking forward to how you finish this.


Vancouver, Canada
#18

Thanks Mike. Lets just say those model railroading skills can come in handy (I’ve done a number of LaBelle etc. kits in past). The razor saw is perfect for opening the case up along the seam though it takes some time. Glad to see all your mesh / solar work in Urbana.


#19

Aw, you’ve got some of those special skills! Anyone who can knock out a Labelle kit is well-qualified for this sort of hack.

That’s not actually a LaBelle kit hovering back there (of which I’ve built and bashed about a dozen passenger cars), but one of those relatively rare 1968 Westwood Sumpter Valley (makes any two of five different) passenger car kits. In this case, I shortened the coach plan to better fit my needs. You can see some of them amongst this album of my layout pics: https://imageshack.com/a/0Apl/1


#20

Another question for antenna people: electrostatic issues with antenna & pole. Although there are a lot of other juicy trees around that are much higher, should I be considering only a fibreglass pole say, for extending 10’ above 2 story roof gable top? If I use aluminum, should it have full-strength grounding? Is there a chance a GTM would get fried if connected directly to a Laird FG9023 (https://www.arcantenna.com/laird-fg9023-25-inch-outdoor-rated-900mhz-fiberglass-omni-antenna-with-fixed-n-female-connector.html). I ask, knowing that the center lead of the antenna is going to be soldered directly to both ends of that c50 capacitor on the motherboard.