Looks to me like you got it OK Jim. I have always used the
relationships you derived there for voltage to db conversion,
Namely, 0.5/2 X voltage = 6db power change. 0.1/10 X
voltage = 20db power change.
For power to power conversions I use 0.5/2 X power = 3db
power change and 0.1/10 X power = 10db power change.
BTW, these will work for any resistance as long as it is held
constant for the comparison.
-73-
-Lee-
On 30 Jul 2002 at 10:47, Jim Reid wrote:
> Hi,
>
> I am learning to use a new propagation predicting program,
> called ACE-HF (see, http://home.att.net/~acehf/da1.htm ).
> Program uses the VOACAP prediction "engine".
>
> One of the predicted parameters is the rcvd signal strength
> at a DX station selected about the globe vs. my xmit output
> power, my antenna sort, and the rcv antenna type. However,
> the signal is given in dB microvolts, dBuv ! I don't speak that
> well, hi. So, I did the following arithmetic attempting to translate
> that figure into dBm, and from there into S units, as follows (this is
> what I would like you to check for correctness/error):
>
> 1 uv standing across a 50 ohm resistor, dissipates a power
> of 2 X 10 to the minus 14 watts, or -107 dBm.
>
> So 0.5uv would be -113 dBm. Then 0.1uv, or -10dBuv is
> equal to -127 dBm ? So 10 microvolts, or +10 dBuv is -87 dBm ?
> That's very nearly an S6 signal (at S9 equals a 50uv signal, and
> 6dB delta per S unit change).
>
> Or a 10X's change in dBuv causes a 20 dB change in dBm.
>
> dBm is of interest to me, since my RX-340 S meter is
> calibrated in dBm, down to -140 dBm and up to +80 dBm !
>
> Been a long time since I did such figuring, hi.
>
> 73, Jim KH7M
>
>
>
>
>
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