Right, Tom - many references and a lot of confusion when people start mixing
them.
I notice on my 606A that while the 0 dB scale on the *attenuator* is linked
to the 0-0.3 volt *meter* scale, when the meter is set with the vernier to
indicate 0 dBm with the switch on the 0 dB scale, the meter voltage reading
is 0.2236 such that a power of one milliwatt is being dissipated in a 50 ohm
load. (No, I can't read the meter that close, but that is what it must be
indicating! <:} )
So, the 606A is really not using 0.3 volts across 50 ohms as a 0 dB
reference if that was your point. It is using 0.2236 volts approximately as
a 0 dB reference which is the value which yields one milliwatt or 0 dBm in a
50 ohm load..
Or maybe I misunderstood you.
You are certainly right about the load sensitivity of the 606A - as well as
the frequency stability with load. Could stand much improvement which is why
we buy them so cheap these days! <:}
73/72, George
Amateur Radio W5YR - the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13QE
"In the 57th year and it just keeps getting better!"
<mailto:w5yr@att.net>
----- Original Message -----
From: "Tom North" <tomnorth@airmail.net>
To: <tentec@contesting.com>
Sent: Wednesday, July 30, 2003 12:32 PM
Subject: [TenTec] dbm and VU units of audio measurement
> Lots of confusion abt how the dB standard has been applied and used over
the
> years. My HP-606A SG uses the DBM range referencing 0db=10 dB below 1V
(.3V)
> into a 50 Ohm load. This has been a standard for some years, but impedance
> can throw a curve.
>
> dBm referenced to 1 mV as a unit of power is pretty well spelled out, both
> in reason and formula, in the ARRL Handbook; page 17.2 in the 1999
edition.
> Used as a reference, for reasons discussed in the handbook, for very low
> power levels. Ran across it in use most recently with a MMIC device
> associated with TT's little RF preamp kit.
>
> GL & 73'
>
> Tom N5OZQ
>
>
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
|