October 2013 Archives

Plantronics Headset Quick Overview

I suppose part of growing older is re-experiencing some memories for the sake of sating some feelings of nostalgia. Growing up in Rocket City, USA, for me these are things I ran into around Marshall Space Flight Center (MSFC). Things like telephone headsets with push-to-talk buttons, seen the world around as mission controllers talked to each other on television, and the Motorola Saber (III), a solid chunk of a two-way radio that could be carried and talked on for an entire eight hour shift. Back to those headsets....

The standard series of headset that I'm familiar with -- mostly by touch, recognition, and use, not intimately familiar with -- is the H-series, particularly the H41 and the H51. Both use the same clear "speaking tube", however the H41 does not have a "headset" feel where the outside of the earphone rests on the ear. The H41 has a plastic support below which the earphone pivots to direct sound at the ear. Both headsets have the standard Plantronics headset plug, which also functions as a strain-relief point for the wearer. The H-series is designed to be used with an external interface/amplifier box in the case of telephony use. The amplifier box may have a name like "Vista" or a letter/number code like "M10" or "M22". The P-series is designed to be terminated into a RJ-22 plug and connected directly to a telephone featuring an internal amplifier. The H51 is the "standard" single headphone variety; the H61 has two earpieces, but is monophonic.The "N" suffixed models (i.e.: H51N, H61N, P51N, P61N) do not have the clear "speaking tube"; those models have a noise-cancelling microphone at the end of a tiny flexible metal tube.

A standard feature of the H-series combined with the M-series amplifier is that of a noise gate on transmitted audio. In the era before cell phones, the loss of "sidetone" -- sound echoed back to the user as a reference for how loud the person was -- was indicative of a disconnected circuit. Likewise, if there is little noise at the transmitting point, the headset interface will turn off the microphone input, causing the circuit to go completely silent. In situations where several users may be communicating together over the same conference bridge (or conference call), the lack of additive noise was greatly appreciated. This was equipment designed by people who thought about the problem and fixed it the right way.

The M22 Vista is the current model of amplifier/adapter box for telephones. For PTT use, the CA12CD provides cordless connectivity with a standard QD / dual Bantam jack interface. For wired PTT use, the SSP1051-xx may be used for 4-wire connectivity; it has a QD connector for the headset and for the connected device (telephone, etc.).  The SHS1890-xx provides the dual Bantam plug (WE-425 or PJ-7) interface used in 6-wire connectivity or dispatch environments. The -xx denotes the length of cable in feet; -10, -15, and -25 are typical for the SHS, but the SSP suffix of -03 indicates a ten foot cord.

The console interface port of the CA12CD is a standard RJ11 six-position plug: 68331-01 - CA12CD Console Interface Cable

Trivia: The MS50 headset was the type used during Apollo-era NASA; it was the same headset type that transmitted Neil Armstrong's words: "It's one small step for man, but one giant leap for mankind." Judging from the pictures, it was a somewhat modified type. Also, the MS50 doesn't have an earpiece (unlike the MS30).


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