[time-nuts] Question.....

[Robert LaJeunesse]

If memory serves me correct that unit of measure was chosen by the Institute for 
High Fidelity (IHF) roughly 40 years ago as the unit to rate FM tuner 
sensitivity. The dBf unit was to replace the more common (at the time) microvolt 
since the dBf was a true power measument in positive whole numbers, while 
the microvolt rating was typically not "whole" and had an implied impedance that 
was not always stated, or met in practice. For example the Outlaw RR2150 is 
specified to have a "Usable Sensitivity IHF: 12dBf" (see: 
http://www.outlawaudio.com/products/rr2150.html). Other than for better FM 
tuners I've not ever seen the dBf unit used.

Bob LaJeunesse

________________________________
From: "Brian, WA1ZMS" <wa1zms at att.net>
To: Time-Nuts <time-nuts at febo.com>
Sent: Wed, December 14, 2011 10:10:13 PM
Subject: [time-nuts] Question.....

OK......here's a question I never found a solid answer to:

On the HP-8656A signal generators, one of the amplitude scale buttons is in
dBf.

dB relative to a femptowatt.  (ie: -120dBm)



What drove that requirement?  I have yet to see a later vintage sig gen use
that scale.





-Brian, WA1ZMS



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