Let me say that I calculate path losses the same way I did as an
engineer at the phone co when calculating the losses in fiber optic
systems - the path loss includes all losses between the TX and RX.
This is the path the signal takes, hence this is the path loss. We
must deliver a certain amount of energy to the RX. If it is in the
path and it has loss, it becomes part of the path loss.
As best I can tell this is the same approach employed in VOACAP. There
they call it system loss instead of path loss. But I believe it is the
same quantity.
If you chose to define it differently that is fine.
And keep in mind that this does not include the gain of an amp or a
beam. If you put those into the mix the RX noise level increases by
several dB.
You can call the level by whatever term you prefer. -27 dBm, 2
microwatts, S9+45. They are all the same. S9 is a reference point, so
many dBm.
TX/RX makes no difference. It is a signal level we are talking about.
A level of S9 is something many hams are familiar with. They can
relate to S9+45 better than they can relate to 2 uW.
This is just like SWR = 2, return loss = 9.5 dB, voltage reflection
coefficient = .33, power reflection coefficient = .11, they are all
different ways of expressing the same thing. But far more hams know
what SWR = 2 means than know what RL = 9.5 dB means.
And, yes, the wideband noise emitted by any of the Flex TX is excessive.
73 de dave
ab9ca/4
On 12/31/13 5:50 PM, Bruce Beford wrote:
Dave, I agree with your math, except...
Having a noise level of -27dBm delivered by the transmitter to the antenna
system, does not mean the antenna has 100% radiation efficiency, yes?
So -27dBm is 2 microwatts in transmitted noise to the antenna system, at
this particular spacing, in a 500Hz bandwidth.
You must make some allowances for not only path loss, but antenna efficiency
on each end, yes?
As I said, I am not trying to defend these performance (or lack thereof)
claims. I just disagreed with the statement that the "Flex is transmitting
wideband S9+45 noise"
"S9+45dB" is a receive measurement, not a transmitter measurement. The Flex
is sending 2 microwatts to the antenna at the frequency in question.
Admittedly, that's too much, in many situations.
Peace,
Bruce N1RX
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