This is a question for the PLB experts on here. If I were to attach a SOLAS marked/approved zenon strobe light to the belt of a lifejacket and also attached a PLB to the webbing, should one find oneself adrift at sea is the flashing circuitry likely to render the GPS receiver within a PLB non-functional?
I am aware that many lifejackets have a small lithium powered flashing incandescent bulb, but my questions related specifically to strobes. Yes, one might be unlikely to end up in the water but if the strobe unknowingly prevented rescue this would be a disaster! Thanks.

The PLB manufacturer might have the best answer for you.

It's a very real possibility (from theory) but would be difficult to test for yourself whether it actually does have an effect.

Definitely consult the PLB manufacturer.

You might be able to figure it out yourself by firing up your strobe. If you tune a radio to 406 MHz and don't hear any strobe-related interference, you're probably good to go. Test a GPS receiver with the strobe as well. If a cold start takes the same amount of time with and without the strobe, that would tell you a lot.

I suspect that if you put the strobe on one side of your body and the PLB on the other (for example, opposite shoulders) that both would function properly.

Here's a response from one of my PLB experts who had this to say:

As with most of these things there is no black and white yes / no answer, it depends on the PLB, the strobe being used and how close they are.

As you rightly state, there is no issue with a normal lifejacket light or for that matter a new LED strobe light as neither of these use high frequency inverters or generate hundreds / thousands of volts pulses which is what causes the potential problems.

Obviously if you design things correctly there is no problem either, as a number of 406 MHz EPIRBs include xenon strobe lights and GPS receivers within the same EPIRB housing running off the same battery and they worked ok, but due to the use of the common power supply and very close proximity they did need some careful design.

The biggest problem with strobes is conducted interference, but this isn’t an issue in this scenario as there are no electrical connections between the PLB and the strobe, thus we only have to worry about radiated interference. The problem here is that there are many different strobe light circuits that work in different ways and at many different frequencies with different wiring arrangements, some of which can act as antennas. However most operate in the tens to hundreds of kilohertz region and while they can generate lots of harmonics, by the time you get up to GPS frequencies of around one and a half gigahertz these should be well down. This then leaves the effects of the xenon strobe tube discharge which are difficult to assess, however a bit of distance between the strobe light and the PLB will help a lot.

It's worth noting that in most life vest installations the strobe should not be in line with the GPS receiver in the PLB which is pointing up to the sky, rather it should be off to one side and thus not in the main GPS beam which will also help a lot.

In summary I would not recommend mounting a strobe right next to a PLB, it might be OK but without testing it you would not know. Ideally it would be best to mount them on opposite sides of the life vest to try and get several inches of separation between them, in which case I am sure there would be no interference, however a few inches of separation is probably fine as well.