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"Megamote" --> Mega Remote
(Sorry I am a nerd)
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This is a neat project I did which modifies my Lionel universal remote to make the bluetooth go really really really far, 10-100X further by calculation anyways. My prototype works at well over 1000 ft away and through walls. If you like electronics projects this is a fun one. The microwave parts are not super cheap (about 4-5X the remote itself!), and you need to be really good at soldering tiny things, but it is a very effective solution to the range limits of BLE on Lionel engines.
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First off some notes on FCC limitations
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1. This is not an illegal transmitter. 802.1 (Bluetooth/BLE) requires a transmit power of no more than 0dBm (1mW). That's the requirement to be a bluetooth compliant device and get a bluetooth sticker or logo on your product. This is also the power level your remote puts out when you buy it since it is a bluetooth product. The ISM band at 2.4 GHz has a much higher unlicensed transmit power limit. The literal FCC part 15 rule is "The maximum EIRP allowed is 53 dBm (30 dBm plus 23 dBi of antenna gain). In the 2.4 GHz band you can increase the antenna gain to get an EIRP above 36 dBm but for every 3dBi increase of antenna gain you must reduce the transmit power by 1 dB".
This tutorial shows you how to get to 15-20dBm out of a remote with a 3dBi antenna gain, which gets you up to 50-100mW, but not even close to the 30dBm (1000mW) limit. The Mega-mote is above board, it's just no longer officially 802.1 (BLE) compliant.
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The Basic Idea of the Megamote
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We disconnect the antenna inside the BLE module inside the Lionel remote, redirect it to a coax cable and put much much larger amplifiers to drive down the noise figure (improves Rx sensitivity) and increase the transmit power a lot.
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The slightly complicated part....
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Unfortunately in the cc2541 chip the Tx and Rx are already combined into a single antenna. If you just put an amplifier outside it can only point one way, so it will block either transmit or receive depending on which way the amplifier is pointing. So the only work around for this is to split the antenna port into two other ports, one for TX and one for RX, allowing signals to flow both ways. BLE is a TDD (Time division duplex) system meaning it doesn't transmit and receive at the same time, so you don't really need to worry about self coupling. Also since the modulation is GFSK (Gaussian Frequency Shift Keying) it's a phase modulation and you don't need to worry too much about getting the power levels just right to keep the amplifiers in the linear mode. Even if they start to gain compress a bit.... the effective SNR impact to a GFSK system is minimal.
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The shopping list
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The key things you need are a 2.4 GHz power splitter and some nice amplifiers for transmit and receive paths. I found the ZFRSC-123-S+ is a pretty low cost, good performance splitter from mini-circuits. Similarly for the amplifiers I went with two of the ZX60-v62 amp, also from mini-circuits. They run on 4V to 5V so they can tap the power supply from the remote directly without needing to add additional regulation or more battery or anything. Past those items the only other thing needed is a nice linear polarized 2.4 GHz antenna. I found this so so one on amazon (antenna).
The ZX60 amplifiers compress out of linear mode around 15dbm, so that's... you know... 50X more transmit power than the BLE module in the remote to begin with. You can put even bigger amplifiers, remember you can go up to 30dBm (1W) before the FCC knocks on your door, and that will go really really far, but it will also eat your battery life in the remote very quickly. I just picked out what was big enough for our club, mini-circuits, qorvo and others have lots of other choices if you like to do shopping for microwave components.
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Step 1
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So the BLE module in the universal remote right now has a folded F antenna, which has both a feed and ground connection on a section of microstrip lines that's 1/2-wave out-phased. You can just scratch the feeds away with a sharp hobby knife, but leave enough length to solder to on the chip side for the coax cable.
Soldering the coax can be a pain, I have a lot of practice but you may want to practice on something less expensive than the remote itself first if you're new to this. Once that's done you just need to drill a hole in the back of the remote to let the coax out, then you can mount all the microwave hardware on the back. A regular 2 part epoxy is fine unless you expect a lot of rough contact with the antennas.
For mine I just connected the amplifier DC power to the battery terminals. This is a lot easier than dealing with the on-off switch, but it means you have to take the batteries out to turn it off since the amps are always biased (even when the switch is in the off position). In the above photo I actually used a ZX60-43 which is a slightly older version of the ZX60-v62 that has a tiny bit less power. It really doesn't matter that much... going from 0dBm to 15dBm, or 0dBm to 14dBm is basically the same.
Anyways once you make those changes, that's it. The remote will go really really far. If you're more talented than me I'm sure you can think up a better mounting scheme or enclosure, but this is the basics of it. Technically you could also do the exact same thing at a train end but I wasn't brave enough to mess up a locomotive.
Enjoy!
