Tiny micro transmitters

[Howardlong]

I came across this article in Nature a few days ago where they have tied tiny VHF transmitters to hornets for tracking purposes.

https://www.nature.com/articles/s42003-018-0092-9



The article claims a range of "up to 800m". These micro transmitters used a 100mm antenna.

http://www.biotrack.co.uk/pdf/pip_picopip.pdf
http://www.biotrack.co.uk/pdf/pip.19.pdf

They're using tiny 1.5v silver oxide coin cells. One uses the "AG337" appears to be the same as SR416SW, 8.3mAh in 4.8mm dia by 1.6mm thick. There is another device Pip.19 (12mm x 5mm x 2mm, http://www.biotrack.co.uk/pdf/pip.19.pdf) that uses an "AG190" cell, but I haven't been able to find any specifications on that one.

The AG337 lifespan is quoted as 12 days days, with a 0.7Hz RF pulse, 20ms pulse width, so a duty cycle of 1.4%. With 8mAh, that suggests about 27uA average current, or at most 2mA when the pulse is active. So output power is ITRO 1mW.

I'm not clear if the pulse is modulated for identification, let's assume not.

So how would you generate 1mW at a reasonably stable frequency at ~150MHz given a 1.5V cell source?

[philpem]

Given the size and power constraints? Probably a transistor oscillator ringing a tuned circuit?

[NivagSwerdna]

The 'Pip' is a 'two-stage' transmitter circuit board with separate oscillator and amplifier/antenna matching
circuits. It has an independent pulse-forming circuit (a stable multivibrator) and is built from some of the
smallest surface mount components available, including a surface mount crystal. The inclusion of this
small crystal is the main advance in the Pip, and enables 0.3g to be shaved off the weight of our small
tags. For the very smallest tag, this represents a weight reduction of nearly 60%. The transmitter is
named after Britain's smallest species of bat (Pipistrelle). The frequency bands that these Pip tags are
currently available on are listed below.

[iMo]

Each tag operated at a specific frequency within the band designated for wildlife telemetry within that country (in France = 150.xxx MHz; in UK including Jersey = 173.xxx MHz). Tags of different frequencies were used to ensure activated tags could be distinguished in the field. The frequencies were preprogrammed into a Sika radio tracking receiver (138–174 MHz band width; Biotrack Ltd, UK), fine-tuned to each individual tag, and signal detection confirmed with a suitable Yagi antenna (Biotrack Ltd, UK) before release of a tagged individual.

A complete PLL tuned transmitter (ie. 6.25/12.5kHz channel spacing @140-170MHz) could be placed on a 1x1mm WCSP chip (9pins) easily (except the crystal). When using the 01005 smd R,L,C it may fit on a 2x3mm board.. I wonder what crystal size they used..

[Howardlong]

Each tag operated at a specific frequency within the band designated for wildlife telemetry within that country (in France = 150.xxx MHz; in UK including Jersey = 173.xxx MHz). Tags of different frequencies were used to ensure activated tags could be distinguished in the field. The frequencies were preprogrammed into a Sika radio tracking receiver (138–174 MHz band width; Biotrack Ltd, UK), fine-tuned to each individual tag, and signal detection confirmed with a suitable Yagi antenna (Biotrack Ltd, UK) before release of a tagged individual.

A complete PLL tuned transmitter (ie. 6.25/12.5kHz channel spacing @140-170MHz) could be placed on a 1x1mm WCSP chip (9pins) easily (except the crystal). When using the 01005 smd R,L,C it may fit on a 2x3mm board.. I wonder what crystal size they used..

I don't doubt the size is eminently achievable, I'm more interested in how to achieve this given the power constraints (voltage and current). A PLL is going to be quite power hungry in my view.

It is possible to find miniature crystals with fundamentals up to 300MHz (2mm x 1.6mm). https://www.golledge.com/products/gsx-228-ultra-miniature-high-frequency-fundamental-crystal-with-inverted-mesa-technology/c-26/p-155

[hagster]

The old school way to do this was with a single diode and a very short antenna. When lit up with a radar the non-linear diode creates 3rd order harmonics that can be detected.