LTE Gateway - the rebuild

Previously, we talked about building a LTE-WiFi gateway, and then we built a LTE-WiFi gateway.

There was just one major issue with it - the modem operates in serial mode, due to RouterOS v6 having no MBIM support (RouterOS v7 does but it’s still unreleased).

For a while now I was considering using another device to do the routing - like a Raspberry Pi, oDroid or Beaglebone. But I wanted one that booted quickly, isn’t SD card based (I have replaced so many cards at inconvenient times) and I wanted something that is less picky about power input.

On Twitter. I saw that @decryption bought a Mikrotik RBM11G to run ROOTer - an OpenWRT based firmware that is designed specifically to route a LTE modem.

The RBM11G looks nice - wide DC input, gigabit ethernet, miniPCIe slot. Running something that has a newer kernel than RouterOS v6 would give me MBIM support and might also stop the random dropouts that require power cycling the modem to make it seen again. I have a suspicion it’s either related to the unsupported PPP serial or maybe the RB2011’s USB hardware. Either way this fixes it.

So I ordered the RBM11G and a CA411-711 case from EuroDK.

Read on and we’ll put it all together then install it in the car.

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Building an End Fed Random Wire Antenna

I’ve previously covered building a multi-band linked dipole Inverted V antenna on here. This antenna has been a great performer - when and where you can set up the pole, get the angle on the V correct and keep other stuff out of its near field. Failing to do this will result in a VSWR that’s a little less than great.

And with the Codan 9323 running in addition to the Icom 7100 on some radio-based outings, a second HF antenna was needed.

I decided to build an end-fed random wire. It’s a compromise on performance but it’s much more versatile and easy to deploy.

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Gps Week Rollover - a further look

So I was going to go and take a look at Garmin’s support page for the eTrex H to see exactly when the last firmware update for the eTrex H was released… and I got a major surprise!

Turns out it was February 15, 2019!

Changes made from version 3.40 to 3.60:
Fix incorrect time date issue caused by GPS week number roll-over on ST BRAVO3H

Top marks to Garmin here - they actually released a firmware update for the device!

Read on and we’ll install it and see if it fixes the problem.

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GPS Week Rollover First Casualty

On the left: Garmin eTrex H (aka eTrex High Sensitivity), the 2007 update of the iconic yellow eTrex. (BTW - The screen is much more readable head on).

On the right: Garmin eTrex 10, released in 2011 (but purchased by me in 2018).

Why is the device on the left displaying a date in 1999? Because GPS just had a little Y2K style problem of its own. The 10 bit week number just rolled over to zero for the second time since the GPS system was switched on. Aside from the date being completely wrong, the device still finds a GPS position but it takes significantly longer to acquire satellites.

This has happened before in 1999 but back then GPS was much less of a consumer product (the first eTrex was still a year away) and most devices were programmed to cope with it. This time around though, there’s a lot of older, lower cost GPS devices still in use that may well have outlasted their manufacturers.

Fortunately the newer GPS signals have a 13 bit week number meaning this won’t be a problem again until 2137. For older devices still reading the 10 bit date/time, it’ll happen again on the 20th of November 2038 - 10 months after dealing with the other 2038 problem.

I bought the eTrex 10 to replace it because I don’t think there’s a firmware update coming for such an old device.

So I guess my eTrex H outlasted the 10 bit counter - now I guess we see if the eTrex 10 lasts until 2038…

Update: There’s a firmware update!

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Baofeng T1 Volume Mod

Previously we covered the Baofeng T1 Mini and there was one major complaint - it’s way too loud.

So let’s crack it open and fix it up.

First, remove the belt clip, the back panel, the battery and undo the four screws holding the radio together. Using a long instrument, lever the two halves apart through the bottom holes in the radio.

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Analyze All the Antennas

Now having purchased a low cost vector impedance analyzer, I feel like I have a hammer and everything looks like a nail.

I’ve complained about questionably genuine NA771s before in my SignalStick review but I thought it might be fun to stick them on the analyzer, sweep them out and see how they compare.

Here it is, the N1201SA by Accuracy Agility Instrument.

(bloom is because it’s still got the screen cover on)

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Codan 7727

For some reason I now have three HF radios. Picked up the Icom 7100 to start with as it’s one of those shack-in-a-box radios that does (nearly) everything. Managed to end up with a Codan 9323 while buying a Codan 9350 for a very good price (“local pickup only” in a location that is not what you’d call “convenient” but we happened to be going past on a massive road trip…)

But I found a Codan 7727 up for sale. According to the listing, the previous owner was a ham radio operator… but it’s also described as being a CB, which I don’t think I need to point out it’s not, so I’m not exactly sure what it’s set up for.

Here it is in all its glory, painted in a nice 70s green. It’s a little rusty. It’s clearly seen better days.

So let’s open it up and take a look at the dusty inside.

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Mashed Potato

Ordered two of the Baofeng T1 Mini, and they finally turned up…

… with a small problem.

A full refund from AliExpress was obtained without (much) argument in the dispute system.

Another two have been ordered from a different seller, and we’ll try again.

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