[Elecraft] P3 Questions

[Alan Bloom]

A noise level of -140 dBm is reasonable with no antenna connected or a
quiet band.  It also depends on the span and how you have the K3 set up.
On mine, the noise level is around -160 dBm with no antenna connected to
the K3, the K3 preamp turned on, and the span set to 2 kHz.  If I turn
off the preamp, turn on the attenuator, and set the span to 200 kHz, the
noise level is a little below -120 dBm.  With an antenna connected it is
higher than that.

You can get an idea if everything is working right by comparing the K3
S-meter reading of a signal within the receive passband.  S9 should show
as roughly -73 dBm on the P3 display and change by 6 dB per S-unit below
that.  There's a table of dBm levels versus S-units in the latest P3
manual.

Alan N1AL


On Fri, 2010-10-29 at 11:38 -0700, David Yarnes wrote:
> I may need some assistance on how my P3 should act.  My P3 
> arrived while I was away on an extended trip to the 
> Northwest.  I now have it up and running, but I have some 
> questions.  I've perused the manual, including the newer 
> version on the website.  It seems that my levels may be 
> wrong, but not sure.
> 
> Here's what I have done--I updated my K3 firmware to the 
> latest version on the website.  I also updated the P3 
> firmware.  I also had to make the mod to my K3 (#96) for the 
> I.F. output gain.  Prior to making that modification, the 
> noise level seemed to be around -110 dbm, but that was also 
> before I updated my K3 firmware also.
> 
> Now, I seem to have a reference level way down to 
> around -140 dbm.  I do see signal spikes, but it seems to 
> take an S8 or S9 signal to really show on my screen (to 
> differentiate them from just noise), which I assume is 
> indicative of my noise floor.  None of the illustrations in 
> the manual show something starting that low.  It makes me 
> wonder if I did the K3 mod properly.  I did replace the SMT 
> part with the supplied SMT device (or think I did!). 
> Hopefully I didn't screw that up.
> 
> All of this scaling varies from band to band somewhat, but 
> it's always -120 dbm or lower.  I see nice spikes from 
> stronger signals, but some that are quite copiable on the K3 
> don't seem to make much of a spike at all.  The waterfall 
> does seem to show the signal better in those cases.  I'm 
> assuming it's just because those signals are right at the 
> noise level, but I was primarily concerned about the fact 
> that my setting has to be so much lower (higher numberical 
> value of "minus" dbm) than anything shown in the manual.
> 
> Dave W7AQK
> 
> 
> 
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