accurate [µV], [dBµV] or [dBm] signal amplitude readout in
an amateur receiver, that is frequency and bandwith indepen-
dent, is one of the challenges, that directly leads to the
development of something similar to a measurement-class-
receiver...and this measurement stuff, if seriously made,
is expensive like hell (appr. 40.000,-- US$ for a brandnew
approbriate and accurate HF-model from a German manufacturer
with worldwide reputation is not a remarkable price i.e.).
73 from
Herbert, DG7MCC
Pietro Lapiana schrieb:
Tnx to everybody for the explanations that give to the S meter a real
relative value and function. Much more correct it could be just to read the
microvolts indication for signal intensity instead of a S meter settled
following different standards among different receivers. 2 signals with
amplitude S9+20 can have a huge difference in terms of real signal at the
antenna of 2 receivers even if the sound at the speaker "looks good". My
question was mainly a doubt coming from my engineer background where numbers
are not just an indication.
Tnx to everybody for the interesting considerations.
73
De
IOKPL, Pietro-----Messaggio originale-----
Da: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]] Per conto di [EMAIL PROTECTED]
Inviato: martedì 23 marzo 2004 15.59
A: Robert Schenck
Cc: [EMAIL PROTECTED]
Oggetto: Re: [drakelist] RIF: S meter to be or not to beGreat explaination Bob,
Yes to all. I have only once in my life seen a receiver that had any
"standard" and that was a receiver from South Africa. I don't now remember
who made it, but it was designed for their equivilent of our FCC. I was
calibrated in microvolts and not "S" units. As I recall, it read up to 1000
microvolts (why I don't know) and was designed to RDF erant transmitters,
and not as a standard. It had a switch to move between "Average" and "Peak".
But, it had no S-Meter at all. I think we sometimes make too much of the
meter. I generally use terms such as "Arm Chair Copy" or "Patch Quality"
with to most older hams, means a great deal more than an S-Meter reading.
Add to this, that in a contest, everyone is S-9. In fact, give any other
report than S-9 to a contest station, and you actually confuse them,
specially if they are not very fluent in English. I find that most times,
the only time I even look at my S-Meter is when someone actually asks what
their relative signal strength is, !
or when "peaking" up the heading of my yagi.So, this all being said, my advice is to do our calibration via the manual,
and not worry about the "absolutes".73,
Mike - K7OV
>
> When signal strength meters were added to receivers they were set up
> measure the reduction in plate current flow, typically in an AGC
> controlled IF stage. The AGC voltage was a high impedance circuit and
> could hardly drive a milliamp meter. Since plate current was typically
> several milliamps, it was fairly easy to come up with a cheap circuit
> to add to deflect a meter. Some receivers had the meter directly in
> the cathode leg, but these required special reverse deflecting meters so
that maximum current drove the meter leftwards to zero.
> Others, like the R4 have a bridge circuit in the plate circuit
> comparing current drian of stages with AGC control to those without.
> All depend upon a logarithmic relation between AGC and stage gain.
> Manufacturers arbitrarily set S9 at half scale and determined the 10 dB
marks above mid scale by tests on the prototype.
> The lower half was just arbitrarily divided into S units. Eventualy
> the 50 uV for S9 "standard" was set to try and settle the a!
> rgument. As to the actual values of S1 to S9 it basically absurd on a
> radio as it was totally subjective in the first place. The S units
> from original CW work were totally subjective in the first place.
>
> As to the value of a S unit, 6 dB makesd most sense to me, but what
> the heck do I know. Drake deicded on 5 dB. this is probably because
> the prototypes worked out that way....nothing else. As a matter of
> personal perception, what is the difference between S1 and S2? Or, for
> that matter S8 and S9? If S1 originally mean "barely peceptable,"
> doesn't that mean just above the noise floor? Wouldn't that imply
> something like 10 dB S+N / N ???? For my R4, 10 dB S=N / N for SSB is at
.18 uV. That is about 9 dB below .5 uV or S-1 if S1 is .5 uV.
>
> Whatever the left hand scale edge may have printed on it, S1 or S0, it
> is really the point of AGC threshold. That is, the signal level for
> which the AGC just starts to reduce gain, as determined by some stage
> having its bias current start to fall. This is actually somewhere
> around what used to thgouht of as S3...or was that S4....S2?
>
> As a final thought, I had thought about changing the S meter circuit
> by adding a FET meter drive circuit to actually measure the AGC
> voltage itself. Another consideration was to also add a PIC
> microcontroller to not only measure the voltage but also correct it
> and drive the meter movement and calibrate the thing.
>
> rob - K2CU
>
>
> >Herbert Schulz <[EMAIL PROTECTED]> wrote:
>
> >Months ago, i have read in a publication, that "S9" in the US
> >corresponds to 50[µV] into 50[Ohms] and that one S-unit is 5[dB]. In
> >Europe, "S9" is equal to 100[µV] into 50[Ohms] and one S-unit
> >corresponds to 6[dB]. I have to double check, if my remembrance
> >according this article is right, but i think so.
> >
> >Now, assume three cases (let's assume, that the S-meters are
> >displaying a perfect log scale, which is almost never the case in
> >reality; furthermore let's assume, that Drake's "S9 = 30[µV] into
> >50[Ohms]" statement is based on the "5[dB] per S-unit"
> >definition):
> >
> >- S9 = 100[µV] into 50[Ohms] / 6[dB]: S1 then equals to 0.39[µV]
> >- S9 = 50[µV] into 50[Ohms] / 5[dB]: S1 then equalt to 0.50[µV]
> >- S9 = 30[µV] into 50[Ohms] / 5[dB]: S1 then equals to 0.30[µV]
> >
> >The manual of my R-4C states a sensivity of better than 0.25[µV] at a
> >noise ratio (S+N)/N = 10[dB] in the ham bands and better than
> >0.50[µV] at noise ratio (S+N)/N = 10[dB] on other frequencies.
> >
> >As S1 normally is a indication of the receivers sensivity at its
> >noise limit, and this readout should be given at the receivers worst-
> >case sensivity value (which is "0.50[µV] on other frequencies" accor-
> >ding to the R-4C specification), i would suggest to use the
> >US-defini- tion "S9 = 50[µV] into 50[Ohms] at a 5[dB] per S-unit scale"
here.
> >
> >Regards and 73 from
> >
> >
> >Herbert, DG7MCC
> >
> >
> >
> >
> >mailbox55122 schrieb:
> >
> >> Hi friends,
> >> on the R4C manual is stated that S9 on the S meter means 30
> >> microvolts of RF
> signal at the antenna input. It looks that the standard S9 signal are
> 100 microvolts of RF signal (on 50 ohm).....
> >>
> >> Where is the true? Or better, what is the real S9 value?
> >>
> >> 73
> >> de
> >> IOKPL, Pietro
> >>
> >>
> >>
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