[time-nuts] Now For Something Completely Different...GPS Security

Brian Lloyd brian at lloyd.com
Fri Feb 14 09:58:08 EST 2014


On Fri, Feb 14, 2014 at 7:45 AM, J. Forster <jfor at quikus.com> wrote:

> You should not denigrate PhotoMultiplier tubes.
>
> They are virtually perfect, almost noiseless, detectors. With the right
> photocathode, they are capable of QEs >50%, spectral response from the VUV
> to near IR, and dark counts <1 PPS, with maximum count rates >10 MPPS.
> Thay can easily have current gains of >10E+6
>

Really? I used to work on photon-counting systems for photometric
astronomy. As I recall, the best quantum efficiency I had ever seen was
around 21%. Which cathode material are you talking about?

Conversely I remember working on current amps for photodiodes. The
photodiodes I was playing with had QEs of 90% but, of course, they had no
current gain. Detecting individual photoelectrons is a challenge.

Yeah, PM tubes are very cool devices, especially if you cool them to reduce
the emission of thermal electrons. ;-)

-- 
Brian Lloyd, WB6RQN/J79BPL
706 Flightline Drive
Spring Branch, TX 78070
brian at lloyd.com
+1.916.877.5067


More information about the time-nuts mailing list