P3 Cal Question

[k6dgw]

I decided to do a K3 S-meter and P3 Lvl Cal, using my service monitor.
Everything seems to be OK, the P3 comes much closer to the S-meter now,
but the P3 Lvl Cal [transfer gain?] came out at -23.7 ... it was -7.6
when I put it together.  I'm sure the difference between the P3 and
S-meter is just averaging, with the service mon it is right on -73 dBm
for 50 uV.  Is -23 normal?  K3 S/N = 642, it's been in Aptos two years
ago however.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2012 Cal QSO Party 6-7 Oct 2012
- www.cqp.org

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[Alan Bloom]

Fred,

It could be that the IF output mod was never done on your K3.  I'm
pretty sure S/N 642 was before the change was made in production.

http://www.elecraft.com/K3/mods/IF_Output_Buffer_Gain_Mod_Rev_A.pdf

Another possibility:  Were you using a CW or a modulated signal for
calibration?  Modulation spreads the signal out over several pixels of
the P3 screen, making it look lower in amplitude than on the K3 S-meter,
which measures the complete signal within its filter bandwidth.

Another possibility:  If the K3's CONFIG:SMTR MD is set to NOR (normal)
then the K3 S meter reading is affected by the on/off state of its
preamplifier and attenuator, which does not affect the P3 reading.

Both of those last two issues are explained in the "How to Set Up and
Interpret the P3 Display" section of the P3 manual, under "Spectrum
Display".

Alan


On Sat, 2012-03-24 at 13:57 -0700, Fred Jensen wrote:

> I decided to do a K3 S-meter and P3 Lvl Cal, using my service monitor.
> Everything seems to be OK, the P3 comes much closer to the S-meter now,
> but the P3 Lvl Cal [transfer gain?] came out at -23.7 ... it was -7.6
> when I put it together.  I'm sure the difference between the P3 and
> S-meter is just averaging, with the service mon it is right on -73 dBm
> for 50 uV.  Is -23 normal?  K3 S/N = 642, it's been in Aptos two years
> ago however.
>
> 73,
>
> Fred K6DGW
> - Northern California Contest Club
> - CU in the 2012 Cal QSO Party 6-7 Oct 2012
> - www.cqp.org
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html
>

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[k6dgw]

On 4/1/2012 9:05 PM, Alan Bloom wrote:

> It could be that the IF output mod was never done on your K3.  I'm
> pretty sure S/N 642 was before the change was made in production.

I'm thinking that's it.

> Another possibility:  Were you using a CW or a modulated signal for
> calibration?

Just a CW signal from the service monitor.

> Another possibility:  If the K3's CONFIG:SMTR MD is set to NOR (normal)

It's set to ABS

Not going to worry about it, I was just curious.  The P3 matches the
S-meter now, that's all I cared about.  Thanks

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2012 Cal QSO Party 6-7 Oct 2012
- www.cqp.org

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[Alan Bloom]

On Mon, 2012-04-02 at 09:21 -0700, Fred Jensen wrote:
> On 4/1/2012 9:05 PM, Alan Bloom wrote:
>
> > It could be that the IF output mod was never done on your K3.  I'm
> > pretty sure S/N 642 was before the change was made in production.
>
> I'm thinking that's it.

You might want to go ahead and do the modification next time you have
the front bottom cover off the K3.  It's a very easy mod (one resistor
change) and improves the P3's sensitivity, which is noticeable on the
high bands at times when atmospheric noise levels are low.

Alan N1AL


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