P3 New LVL Cal Function (Beta 0.41)

[N5GE]

Where do I find the instructions for using this feature?  I think it's a great
enhancement!

Thanks,

Tom
Radio Amateur N5GE
QCWA Member 35102

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[Bill W4ZV]

Amateur Radio Operator N5GE wrote

Where do I find the instructions for using this feature?

Al must have forgotten to include the instructions.  The following is PRELIMINARY ONLY but should get you going:

Amplitude Calibration

The P3 comes with a default amplitude calibration that works well with a K3 transceiver that either was manufactured after approximately 9/1/2009 or, if an earlier unit, has the IF output buffer gain modification described in the application note on the Elecraft web site.  If you have an earlier unit without the modification, or you are using the P3 with a different model transceiver, or if you just wish to obtain better amplitude accuracy on the P3 display, you can do the following calibration.

The recommended test frequency is7040 kHz at a signal level of 50 microvolts (-73 dBm) using a calibrated signal generator such as the Elecraft XG2.  However, any frequency and power level within the range of the transceiver and P3 display will also work.

* Make sure the the P3 IF IN is connected to the transceiver IF output.  If the transceiver is a K3, connect the RS-232 cable as well.  Turn off the preamplifier and attenuator on the K3.  If you have the KRX3 installed, make sure SUB is disabled.

* Connect the signal generator to the transceiver antenna input.  If it is a K3 that includes the KXV3 or KXV3A option, it is best to use the RX ANT IN connector to eliminate the possibility of damaging the signal generator if the K3 transmits accidentally.

* Set the signal generator for 7040 kHz at a signal level of 50 mV (-73 dBm).

* Set the SPAN on the P3 to 100 kHz, and tune the transceiver to approximately 7015 kHz so that the signal is centered on the right half of the display.  Set the SCALE to maximum expansion (10 dB) and adjust the REF LVL to about -78 dBm, in order to place the peak of the signal about half way up the screen.  You may notice a slight variation (~1.5 dB) in the peak signal level with small adjustments in the transceiver frequency, as the signal is tuned from pixel to pixel across the display.  Adjust the frequency for a maximum reading.

* Tap MENU, select Lvl Cal, tap the knob, and adjust the level calibration until the signal is at -73 dBm on the display.

You can also calibrate a receiving or transceiving converter, either the K3's optional internal K144XV or an external device.  If you plan to do the above calibration on a standard frequency, do it first since that calibration is added to the converter calibration.

* Set up a signal generator, the transceiver and the P3 in a manner similar to the above to obtain a signal near the center of the right side of the display and approximately centered vertically, with the P3's SCAN at 100 kHz and the SCALE set to 10 dB.

* Tap MENU, select XV Gain, tap the knob, and adjust the knob to select the desired converter band, 1-9.  Tap the knob again and adjust the gain on the selected band so that the signal is at the the correct level on the display.

[N5GE]

Thanks, Bill!  I printed the instructions and will try it later today.

73,
Tom
Radio Amateur N5GE
QCWA Member 35102

On Thu, 11 Nov 2010 03:18:25 -0800 (PST), Bill W4ZV <[hidden email]>
wrote:

[snip]

>Al must have forgotten to include the instructions.  The following is
>PRELIMINARY ONLY but should get you going:
>
>Amplitude Calibration
>
>The P3 comes with a default amplitude calibration that works well with a K3
>transceiver that either was manufactured after approximately 9/1/2009 or, if
>an earlier unit, has the IF output buffer gain modification described in the
>application note on the Elecraft web site.  If you have an earlier unit
>without the modification, or you are using the P3 with a different model
>transceiver, or if you just wish to obtain better amplitude accuracy on the
>P3 display, you can do the following calibration.
>
>The recommended test frequency is7040 kHz at a signal level of 50 microvolts
>(-73 dBm) using a calibrated signal generator such as the Elecraft XG2.
>However, any frequency and power level within the range of the transceiver
>and P3 display will also work.
>
>* Make sure the the P3 IF IN is connected to the transceiver IF output.  If
>the transceiver is a K3, connect the RS-232 cable as well.  Turn off the
>preamplifier and attenuator on the K3.  If you have the KRX3 installed, make
>sure SUB is disabled.
>
>* Connect the signal generator to the transceiver antenna input.  If it is a
>K3 that includes the KXV3 or KXV3A option, it is best to use the RX ANT IN
>connector to eliminate the possibility of damaging the signal generator if
>the K3 transmits accidentally.
>
>* Set the signal generator for 7040 kHz at a signal level of 50 mV (-73
>dBm).
>
>* Set the SPAN on the P3 to 100 kHz, and tune the transceiver to
>approximately 7015 kHz so that the signal is centered on the right half of
>the display.  Set the SCALE to maximum expansion (10 dB) and adjust the REF
>LVL to about -78 dBm, in order to place the peak of the signal about half
>way up the screen.  You may notice a slight variation (~1.5 dB) in the peak
>signal level with small adjustments in the transceiver frequency, as the
>signal is tuned from pixel to pixel across the display.  Adjust the
>frequency for a maximum reading.
>
>* Tap MENU, select Lvl Cal, tap the knob, and adjust the level calibration
>until the signal is at -73 dBm on the display.
>
>You can also calibrate a receiving or transceiving converter, either the
>K3's optional internal K144XV or an external device.  If you plan to do the
>above calibration on a standard frequency, do it first since that
>calibration is added to the converter calibration.
>
>* Set up a signal generator, the transceiver and the P3 in a manner similar
>to the above to obtain a signal near the center of the right side of the
>display and approximately centered vertically, with the P3's SCAN at 100 kHz
>and the SCALE set to 10 dB.
>
>* Tap MENU, select XV Gain, tap the knob, and adjust the knob to select the
>desired converter band, 1-9.  Tap the knob again and adjust the gain on the
>selected band so that the signal is at the the correct level on the display.

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[Stan Gibbs, KR7C]

The calibration procedure is very easy to do, and went as described.  My XG2 signal is right on the money at -73 dbm now.

I'm curious what the nominal range of transfer gain is that we might expect to see.  Mine is around -18 db.  What does this number mean, anyway?

The release notes for this firmware says: "Added many new RS-232 commands".  Are these documented anywhere; in a P3 Programmer's Reference perhaps?

Thanks, Alan!

[Bill W4ZV]

Stan Gibbs wrote

I'm curious what the nominal range of transfer gain is that we might expect to see.  Mine is around -18 db.  What does this number mean, anyway?

Transfer loss is loss from the K3 ANT input to the KXV3 IF OUT.  -18 dB sounds high...as though you may have an older unit which has not been modified (easy to check by removing the bottom front panel and inspecting R8):

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

I have two K3s (#2183 and #4717).  The first was modified by me (R8 = 13k SMD) and the latter came from the factory with the change implemented in production.  Both of mine measured -7.3 dB but other Field Testers reported as much as -14 dB.  BE SURE you follow the instructions below exactly since these can affect the measurement:

1.  Turn off PRE, ATT and SUB.
2.  Carefully tune the VFO for the signal peak (which may vary by ~1.5 dB depending on VFO setting).

73,  Bill

[Stan Gibbs, KR7C]

Thanks, Bill, for the response.

My K3 is #4181, so the mod is not necessary.  Yes, -18 dB does sound excessive.  However, I really can't be sure whether the issue is an XG2 that doesn't output 50uV, or excessive loss in the RX input stages.  I don't have the test equipment to determine which is correct, unfortunately.

Bill W4ZV wrote

I have two K3s (#2183 and #4717).  The first was modified by me (R8 = 13k SMD) and the latter came from the factory with the change implemented in production.  Both of mine measured -7.3 dB but other Field Testers reported as much as -14 dB.  BE SURE you follow the instructions below exactly since these can affect the measurement:

[John_N1JM]

Mine turned out to be -10db and I have the IF mod.

[Stan Gibbs, KR7C]

I did an EEINIT on the advice of Gary at Elecraft and now my transfer gain is -12.3 dB.  Don't know exactly what to make of that, or why the EEINIT should have made a difference, but at least my result isn't so extreme compared to others noted in this thread.

What is really interesting to me, however, is that after doing the EEINIT, I did a fresh RF Gain calibration using my XG2 and found that the non-linearity in the RF Gain calibration that I reported recently is gone!

Thanks, Gary!