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P3 Understanding the REF LVL Settings and Signal Level in General

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Phil Hystad-3

P3 Understanding the REF LVL Settings and Signal Level in General

I am trying to get a better understanding of the P3 signal level scale (left vertical scale) with respect to absolute signal levels and the S meter readings.

I have my REF LVL set to -132 dBm. My first question is: what is a reasonable setting? I merely am guessing at the value of -132 dBm and also I am not quite sure how accurate this is. According to the P3 manual, this is essentially the signal strength at the antenna terminal of my K3 (taking into account the pre amplifier which I happen to have Off).

Also, I was monitoring a signal using the PEAK reading capability of the P3 and noticed that this particular SSB signal on 17 meter band this morning read peak about -100 dBm or about a 32 dBm strength over the minimum reading on the scale. I would like to equate this to a rough idea of an S meter reading. By my calculations, this should be a little bit above an S4 reading. Can someone confirm that I am in the right ball park?

Thanks for the help.
73, phil, K7PEH

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Alan Bloom-2

Re: P3 Understanding the REF LVL Settings and Signal Level in General

> My first question is: what is a reasonable setting?

It's kind of a "season to taste" -- whatever gives a pleasing display to
your eyes. When the waterfall is turned on, I find that it's best to
adjust the REF LVL so that the noise level is right at the bottom of the
spectrum screen. That seems to make weak signals easiest to spot on the
waterfall.

> I am not quite sure how accurate this is.

I would guess that typically it should be within a few dB. Let's say
within one S-unit (6 dB). I plan to add a feature so you can calibrate
it against an accurate signal source.

> ...and noticed that this particular SSB signal on 17 meter band this morning read peak about -100 dBm or about a 32 dBm strength over the minimum reading on the scale. I would like to equate this to a rough idea of an S meter reading. By my calculations, this should be a little bit above an S4 reading. Can someone confirm that I am in the right ball park?

What I do is to remember that S9 is -73 dBm (an easy number for a ham to
remember) and there's 6 dB per S-unit. So -100 dBm is (100-73)/6 = 4.5
S-units below S9. So between S4 and S5.

Another item on my "to-do" list is a MENU option to change the scale
from dBm to S-units and dB over S9. It's not all that hard to do, I
just need to clear some higher-priority tasks off the list first.

Alan N1AL

On Sat, 2010-09-04 at 09:12 -0700, Phil Hystad wrote:

> I am trying to get a better understanding of the P3 signal level scale (left vertical scale) with respect to absolute signal levels and the S meter readings.
>
> I have my REF LVL set to -132 dBm. My first question is: what is a reasonable setting? I merely am guessing at the value of -132 dBm and also I am not quite sure how accurate this is. According to the P3 manual, this is essentially the signal strength at the antenna terminal of my K3 (taking into account the pre amplifier which I happen to have Off).
>
> Also, I was monitoring a signal using the PEAK reading capability of the P3 and noticed that this particular SSB signal on 17 meter band this morning read peak about -100 dBm or about a 32 dBm strength over the minimum reading on the scale. I would like to equate this to a rough idea of an S meter reading. By my calculations, this should be a little bit above an S4 reading. Can someone confirm that I am in the right ball park?
>
> Thanks for the help.
> 73, phil, K7PEH
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

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Phil Hystad-3

Re: P3 Understanding the REF LVL Settings and Signal Level in General

Alan,

Thanks for the excellent answers. So, if you created a signal level calibration
would the Elecraft XG2 be a bitting and accurate signal source? Or, would some
lab equipment be needed. Actually, I don't really know how the XG2 compares
to some lab quality equipment, it may be just as accurate.

PEH

On Sep 4, 2010, at 11:42 AM, Alan Bloom wrote:

>> My first question is: what is a reasonable setting?
>
> It's kind of a "season to taste" -- whatever gives a pleasing display to
> your eyes. When the waterfall is turned on, I find that it's best to
> adjust the REF LVL so that the noise level is right at the bottom of the
> spectrum screen. That seems to make weak signals easiest to spot on the
> waterfall.
>
>> I am not quite sure how accurate this is.
>
> I would guess that typically it should be within a few dB. Let's say
> within one S-unit (6 dB). I plan to add a feature so you can calibrate
> it against an accurate signal source.
>
>> ...and noticed that this particular SSB signal on 17 meter band this morning read peak about -100 dBm or about a 32 dBm strength over the minimum reading on the scale. I would like to equate this to a rough idea of an S meter reading. By my calculations, this should be a little bit above an S4 reading. Can someone confirm that I am in the right ball park?
>
> What I do is to remember that S9 is -73 dBm (an easy number for a ham to
> remember) and there's 6 dB per S-unit. So -100 dBm is (100-73)/6 = 4.5
> S-units below S9. So between S4 and S5.
>
> Another item on my "to-do" list is a MENU option to change the scale
> from dBm to S-units and dB over S9. It's not all that hard to do, I
> just need to clear some higher-priority tasks off the list first.
>
> Alan N1AL
>
>
> On Sat, 2010-09-04 at 09:12 -0700, Phil Hystad wrote:
>> I am trying to get a better understanding of the P3 signal level scale (left vertical scale) with respect to absolute signal levels and the S meter readings.
>>
>> I have my REF LVL set to -132 dBm. My first question is: what is a reasonable setting? I merely am guessing at the value of -132 dBm and also I am not quite sure how accurate this is. According to the P3 manual, this is essentially the signal strength at the antenna terminal of my K3 (taking into account the pre amplifier which I happen to have Off).
>>
>> Also, I was monitoring a signal using the PEAK reading capability of the P3 and noticed that this particular SSB signal on 17 meter band this morning read peak about -100 dBm or about a 32 dBm strength over the minimum reading on the scale. I would like to equate this to a rough idea of an S meter reading. By my calculations, this should be a little bit above an S4 reading. Can someone confirm that I am in the right ball park?
>>
>> Thanks for the help.
>> 73, phil, K7PEH
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>
>

Alan Bloom-2

Re: P3 Understanding the REF LVL Settings and Signal Level in General

I just looked it up. The XG2 has a specified level accuracy of 2 dB,
and 1 dB typical. A professional lab-quality RF signal generator would
typically be about twice that good (hard spec in the 1 dB range):

http://www.home.agilent.com/agilent/redirector.jspx?action=ref&cname=AGILENT_EDITORIAL&ckey=843957&lc=eng&cc=US&nfr=-536906709.536910813.00

So if you have access to a calibrated lab-quality signal generator, then
use it. But the XG2 isn't bad and is about 100 times cheaper. :=)

Alan N1AL

On Sat, 2010-09-04 at 11:55 -0700, Phil Hystad wrote:

> Alan,
>
> Thanks for the excellent answers. So, if you created a signal level calibration
> would the Elecraft XG2 be a bitting and accurate signal source? Or, would some
> lab equipment be needed. Actually, I don't really know how the XG2 compares
> to some lab quality equipment, it may be just as accurate.
>
> PEH
>
>
> On Sep 4, 2010, at 11:42 AM, Alan Bloom wrote:
>
> >> My first question is: what is a reasonable setting?
> >
> > It's kind of a "season to taste" -- whatever gives a pleasing display to
> > your eyes. When the waterfall is turned on, I find that it's best to
> > adjust the REF LVL so that the noise level is right at the bottom of the
> > spectrum screen. That seems to make weak signals easiest to spot on the
> > waterfall.
> >
> >> I am not quite sure how accurate this is.
> >
> > I would guess that typically it should be within a few dB. Let's say
> > within one S-unit (6 dB). I plan to add a feature so you can calibrate
> > it against an accurate signal source.
> >
> >> ...and noticed that this particular SSB signal on 17 meter band this morning read peak about -100 dBm or about a 32 dBm strength over the minimum reading on the scale. I would like to equate this to a rough idea of an S meter reading. By my calculations, this should be a little bit above an S4 reading. Can someone confirm that I am in the right ball park?
> >
> > What I do is to remember that S9 is -73 dBm (an easy number for a ham to
> > remember) and there's 6 dB per S-unit. So -100 dBm is (100-73)/6 = 4.5
> > S-units below S9. So between S4 and S5.
> >
> > Another item on my "to-do" list is a MENU option to change the scale
> > from dBm to S-units and dB over S9. It's not all that hard to do, I
> > just need to clear some higher-priority tasks off the list first.
> >
> > Alan N1AL
> >
> >
> > On Sat, 2010-09-04 at 09:12 -0700, Phil Hystad wrote:
> >> I am trying to get a better understanding of the P3 signal level scale (left vertical scale) with respect to absolute signal levels and the S meter readings.
> >>
> >> I have my REF LVL set to -132 dBm. My first question is: what is a reasonable setting? I merely am guessing at the value of -132 dBm and also I am not quite sure how accurate this is. According to the P3 manual, this is essentially the signal strength at the antenna terminal of my K3 (taking into account the pre amplifier which I happen to have Off).
> >>
> >> Also, I was monitoring a signal using the PEAK reading capability of the P3 and noticed that this particular SSB signal on 17 meter band this morning read peak about -100 dBm or about a 32 dBm strength over the minimum reading on the scale. I would like to equate this to a rough idea of an S meter reading. By my calculations, this should be a little bit above an S4 reading. Can someone confirm that I am in the right ball park?
> >>
> >> Thanks for the help.
> >> 73, phil, K7PEH
> >>
> >> ______________________________________________________________
> >> Elecraft mailing list
> >> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> >> Help: http://mailman.qth.net/mmfaq.htm
> >> Post: mailto:[hidden email]
> >>
> >> This list hosted by: http://www.qsl.net
> >> Please help support this email list: http://www.qsl.net/donate.html
> >
> >