Brian Lloyd wrote:
On Fri, Dec 11, 2009 at 3:48 AM, roger <g6...@tiscali.co.uk> wrote:
I have noticed that with the RX preamps set to OFF, the Signal meter reads a
steady S3 with the antenna disconnected.
With Pre1, Pre2 or Att selected, the meter reads 0
Is this normal? or have I set something incorrctly or misunderstood something?
It is actually correct. It has to do with S9 being 50uV into a 50ohm
load and each S-unit below that being a 6dB reduction in signal
(voltage cut in half). At some point the noise voltage dominates and
that is where the S-meter will sit. That the S-meter drops when you
turn on the preamp tells you that the preamp is doing its job as the
effective noise floor is reduced.
While this may bother you what it is telling you is that your radio is
actually a calibrated RF power measuring instrument. S-meter readings
actually mean something with the Flex radios.
What Brian says is accurate, however there are a couple of wrinkles
regarding the original question.
On the FLEX 3000 there is only 1 preamp setting, so I have Pre, Off or
Att. There is no pre1 and pre2.
Also I don't see why the meter reading would drop when selecting Att. On
my F3K, on 75m to a dummy load with 2,7k BW, my S-reading is S3 in the
Off setting. With the Preamp on it drops to ~S1. With Att engaged it
rises to ~S5. This is just what I would expect.
As Brian says, this may be counterintuitive for folks used to the 'old'
way of doing things, but it is fundamentally correct.
73 Alf NU8I
Scottsdale AZ DM43an
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