Okay; I’ve done some tests with the two long-range LF readers I received yesterday. The first one is the ACM08Y, and the second one is the ACM26C - both from Goldbridge Industrial in China.
This is gonna be a mini-review of those devices, with an emphasis on performances with implants.
First of all, they’re unbelievably heavy. That’s because they’re big plastic half-clamshells with the coil and the electronics put inside, then filled up to the brim with epoxy. All that epoxy ain’t light.
Secondly, they don’t come with a plug. I can understand if you order the Wiegand versions, since those things are usually connected to an alarm system with screw connectors. But I ordered the RS232 versions. A DB9 and a power socket would have been nice. But cheap Chinese products are cheap for a reason 
Thirdly, they’re friggin’ loud - and I mean LOUD. They both have a tiny buzzer embedded in the epoxy, and they make a terrible racket when they self-calibrate after powering up. Then they emit a powerful beep each time they scan something. I covered up the buzzers with 5 or 6 layers of paper labels, but they’re still annoying. I’ll have to see about filling them up with epoxy or something, to shut them up permanently, as there’s no way to access the leads underneath without destroying the potting. Ironically, both have a line out labeled “buzzer”, so the manufacturer made provisions to make them even louder.
As far as I can tell, they only read EM4xxx chips. I’ve tried a few different other chips, but they don’t register. Fair enough, I didn’t ask for more.
Annoying, they’re single-shot readers. The distributor assured me they were repeating readers, but they’re not. When they read something, they send the UID once, until you remove the transponder from the EM field and present another one.
There is an RS232 RX line, and I seem to remember seeing a video from the Chinese manufacturer on Youtube in which the device was beeping continuously. So there’s a possibility that you can send them a command to put them on autorepeat, or poll them. But they don’t seem to react to anything I send them. So if they do support commands, I’ll probably need the command set from the manufacturer- that is, from a Chinese manufacturer… good luck with that…
Re range: the ACM26C has a square coil, while the ACM08Y has a round coil. But both have pretty similar performances. They both put out a torus-shaped EM field around their coil. Being a torus, there’s a hole in the middle where the field is weaker.
Transponders that have a decent antenna (full-size cards and tags) “see” a horn torus and get picked up in the hole. Not so with implants: they “see” a much slimmer ring torus. If you approach your hand dead-center above the devices and get closer, nothing happens right up to the surface of the device.
The torus an implant “sees” has a circle radius of about 4" if the implant is oriented correctly, meaning if you approach your hand anywhere around the coil within 4" of the coil, the implant will register. When I say “oriented correctly”, I mean that the implant should be perpendicular to the plane of the coil for best performances, as expected with Ampere’s law. If the implant is coplanar with the coil, the range is greatly reduced - 1" at the most.
So all in all, as far as implants are concerned, think of the two ACM devices as oversized desktop readers: they work exactly the same way with the same limitations, only with a longer range, and the added bonus that you also get a solid read if you present your implant edgewise - something desktop readers and their flat PCB coils don’t do.
Even with a limited range, an implant under the skin can be picked up reliably at close range within a 6 to 8" band strip around the coil provided it’s oriented correctly. That’s not half bad, and it’s probably suitable for my butt implant project. I’ll have to give some thought on implant placement (probably just under one of my cheeks, oriented along the leg). More importantly, I’ll have to get the devices to autorepeat for the project to make any sense. But at least as far as detecting an approximately-placed implant is concerned, the devices seem to fit the bill.
Of course, they would work even better with a : the FlexEM-sized tag I tried is picked up anywhere over the device, and a good 20" off the surface. That would make placement even easier. But somehow I don’t see myself sitting on that thing all day Maybe implanted behind my back just above one my cheeks or something, where I don’t sit… Amal, any thought?