S meter question

[Ken Bessler-2]

I found the XG2 manual and the K2 manual a bit ambiguous on the
issue of weather to do CAL S-Lo and S-Hi with the preamp on
or off.

I guess that it's a bit of YMMV but I've found if I set the S meter
with the preamp on, then I get no background signal above 20m.

OTOH, If I do it with the preamp off, then the S meter seems too
"hot" below 30m. I suppose that is a hint not to run the preamp
below 30m?

Help?


73's de Ken KG0WX - Kadiddlehopper #11808,
       Flying Pigs #-1055, Grid EM17io,
Elecraft K2 #4913, XG2, 4SQRP Tenna Dipper,
Heath GD-1B, MP-1(X)antenna & HLA-150 amp.

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[Ron D'Eau Claire-2]

Ken, KG0WX asked:

I found the XG2 manual and the K2 manual a bit ambiguous on the issue of
weather to do CAL S-Lo and S-Hi with the preamp on
or off.

I guess that it's a bit of YMMV but I've found if I set the S meter with the
preamp on, then I get no background signal above 20m.

OTOH, If I do it with the preamp off, then the S meter seems too "hot" below
30m. I suppose that is a hint not to run the preamp below 30m?

Help?

-----------------------------

The preamp is only needed only under certain circumstances. It is there to
ensure you have adequate input to the receiver to overcome the internal
noise so your weak signal capability isn't limited by the K2.

Tune to a spot where there's no signals, just normal background QRN. Set
your filters for the narrowest bandwidth you ever use. Turn off the preamp
and adjust the volume to hear the background QRN. Remove the antenna. If the
noise level dropped when your removed the antenna, the weak-signal
capability of your K2 is limited entirely by external noise, not internal
receiver noise. The preamplifier is not needed.

Using the preamplifier on bands where it is not needed increases the volume
of signals but it also compromises the dynamic range of the K2. The K2 has
excellent dynamic range, so you can generally get away with using it and
never suffer any negative consequences, but it's not needed. Still, it's
best to use the AF gain to control the volume in your phones or speaker.

With normal Ham antennas you'll likely never need the preamp below 20
meters, and even 20 may not benefit from it. Very low gain antennas such as
small loops, etc., that you might use for a separate receive antenna may
benefit from using the preamplifier on lower frequencies while some
excellent antennas may eliminate the need for the preamp even on bands above
20 meters. At the other extreme, you may be better off with the attenuator
switched in on the nosier, lower frequency bands such as 160 or 80 meters.  

The "S-Meter" gives you a visual display of relative variations in signal
strength. Trying to use it to measure a specific voltage at your antenna is
an exercise in futility. It can do that under specific circumstances if you
adjust your S-meter using something like the XG signal generators, but
that's not its main purpose and, as you've discovered, it can be
frustrating.

If you hear a faint, just barely perceptible signal, it's S-1. If you hear a
signal you judge to be extremely strong, it's S-9. If the S-meter doesn't
agree, it's the S-meter that's out of calibration <G>.

When a company manufactures something like a receiver, it's necessary to run
a series of tests before the finished product is shipped to be sure
everything is adjusted and working as expected. For "communications
receivers" having an S-meter, that meant that some sort of simple, "go,
no-go" alignment and test was required. Various companies adopted an
arbitrary standard signal level to feed into the receiver which the
technician would use to set the S-meter to a reading of S-9. Collins, among
others, adopted 50 uV for this signal level. It's a purely arbitrary level
and is essentially meaningless in general use.

The XG2 and XG3 generators let you do the same with your K2. It doesn't
really matter if the preamplifier is on or off. It only matters that the
meter agrees with your ears <G>.

Ron AC7AC




-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Ken Bessler
Sent: Wednesday, March 29, 2006 7:44 AM
To: Elecraft
Subject: [Elecraft] S meter question


I found the XG2 manual and the K2 manual a bit ambiguous on the issue of
weather to do CAL S-Lo and S-Hi with the preamp on
or off.

I guess that it's a bit of YMMV but I've found if I set the S meter with the
preamp on, then I get no background signal above 20m.

OTOH, If I do it with the preamp off, then the S meter seems too "hot" below
30m. I suppose that is a hint not to run the preamp below 30m?

Help?


73's de Ken KG0WX - Kadiddlehopper #11808,
       Flying Pigs #-1055, Grid EM17io,
Elecraft K2 #4913, XG2, 4SQRP Tenna Dipper,
Heath GD-1B, MP-1(X)antenna & HLA-150 amp.

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[Don Wilhelm-3]

Ken,

I usully use the XG1 and check the S-meter with the preamp off on 40
meters - if the AGC Threshold is set for optimum receiver performance, and
CAL S Hi and Lo are set the S-meter usually comes right in at S-9 with the
preamp off.

Yes, the manual is non-committal on this point, so I take that as an
indication that either way may be right, the S-meter is not an absolute
device, the point for S-9 varies all over the place from one receiver
manufacturer to another anyway, so other than being useful as a relative
measurement, I personally don't worry about the absolute calibration, but I
set it as close as possible for other's K2s that I work on.  In other words,
do what suits you best.

73,
Don W3FPR

> -----Original Message-----
>
> I found the XG2 manual and the K2 manual a bit ambiguous on the
> issue of weather to do CAL S-Lo and S-Hi with the preamp on
> or off.
>
> I guess that it's a bit of YMMV but I've found if I set the S meter
> with the preamp on, then I get no background signal above 20m.
>
> OTOH, If I do it with the preamp off, then the S meter seems too
> "hot" below 30m. I suppose that is a hint not to run the preamp
> below 30m?
>
> Help?
>
>

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