[Elecraft] K3: Strange SWR reading

Wed Jan 6 17:23:48 EST 2010

Tnx Dick,

Then I guess it is the K3 MCU firmware code that is "ramping up the power" because I see it doing it on the K3 front panel display as the Calibrate routine is running.  It approaches 5 Watts from below, takes a fraction of a second to get there.  Until it gets there, the SWR reading on the K3 screen is 1.1.  When it does get there (e.g., to 5 Watts), the SWR reading changes to 1.0.  Then the K3 stays in transmit for about a second or two before moving on to the next frequency.  At 50 Watts, the ramp-up time (if any) is so quick that it doesn't have time to show up on the K3 front panel display.

I guess I was thinking that the K3 Utility was doing more than it was doing.  Thanks for the description.

It must be a gas to write this stuff and have it work so well.  Wish the code were public so we could admire it.

73,
Oliver Johns
W6ODJ

On 6 Jan 2010, at 1:16 PM, Dick Dievendorff wrote:

> The K3 Utility doesn't "ramp up the power" during the Tx Gain calibration.
> It sets the power to exactly 5 watts, and the K3 MCU firmware code performs
> calibration at that power level (and also at exactly 50 watts).
> 
> Tx Calibration also sets TUN PWR to "Normal" and restores your setting
> afterward.
> 
> Glad it's working for you now!
> 
> 73 d Dick, K6KR
> 
> 
> -----Original Message-----
> From: O. Johns [mailto:ojohns at metacosmos.org] 
> Sent: Wednesday, January 06, 2010 12:04 PM
> To: Dick Dievendorff
> Cc: Elecraft; Gary Surrency
> Subject: Re: [Elecraft] K3: Strange SWR reading
> 
> Gents,
> 
> Problem solved, or at least worked around.
> 
> I had the TUNE PWR set to 4 Watts.  But my K3 SWR reading is inaccurate
> below 5 Watts.  I set TUNE PWR to 7 Watts and now the problem is solved.
> With the DL1 connected to Ant 1, and KAT3 on BYPASS, pressing TUNE now gives
> 1.0 on all bands.
> 
> Here are the readings at various powers with my K3 in the 40 meter band:
> 1 Watt --->  no reading
> 2 Watt --->  1.2
> 3 Watt --->  1.1
> 4 Watt --->  1.1
> 5 Watt ---> 1.0
> 6 Watt and above ---> 1.0
> 
> 73,
> 
> Oliver Johns
> W6ODJ
> 
> P.S.  The reason the Elecraft K3 Utility seemed to be adjusting the SWR
> reading was that it was ramping up the power to 5 Watts.  As it passed 3 and
> 4 Watts, it showed 1.1;  when it reached 5 Watts it showed 1.0.
> 
> 
> On 5 Jan 2010, at 5:23 PM, O. Johns wrote:
> 
>> Dear Dick,
>> 
>> I posted this problem on the reflector some time back, but noone picked up
> on it, so I'll try again.  This is a before and after story and has me
> puzzled.
>> 
>> BEFORE:  I connected DL1 dummy load to Ant 1 using only a BNC-MtoM and a
> PL259-FtoF (no coax at all, just small straight-through adapters).  I set
> the KAT3 to BYPASS.  I pressed TUNE and saw 1.0, on all bands.  Fine, this
> is what I expect.  Also, using my link-coupled external tuner with the
> antenna connected (I seldom use the KAT3), I was able to adjust to 1.0 on
> all bands (except 6 meters).
>> 
>> AFTER:  After the first time I ran the "Calibrate Transmitter Gain"
> routine from the Elecraft K3 Utility, I pressed TUNE with the DL1 still
> connected and saw a SWR reading of 1.1 on all bands, not 1.0 as before.
> Also, when I use my external tuner, the lowest SWR I can obtain now is 1.1,
> not 1.0 as before.  
>> 
>> WHY?
>> 
>> I just upgraded the K3 (#1741) with all current mods and the new DSP
> board.  So, I re-calibrated everything.  Same result re the 1.1 SWR reading.
> 
>> 
>> Here is what happens:
>> 
>> I attach the DL1 and set KAT3 to BYPASS as per the instructions.  I run
> through the steps and click on Calibrate in the 5 Watt page.  The
> calibration routine runs to completion successfully.  At every frequency I
> see on the K3 front panel readout the following two-step sequence:
>> - The frequency to be used
>> - The numbers 1.1 which quickly change to 1.0
>> It seems as if the software is adjusting something to get to 1.0 for the
> SWR.  What?  I don't hear any clicks so doubt it is adjusting any toroids or
> capacitors the ATU.  Maybe it is adjusting the final transistor bias?  
>> 
>> After this calibration, pressing TUNE with the DL1 still connected and the
> KAT3 still in BYPASS, I see 1.1 SWR.
>> 
>> I then did the routine again, but this time doing the 5 watt and then the
> 50 Watt Calibration (the DL1 doesn't get very hot due to the short duty
> cycle).  At 5 Watts, the result is the same as above.  At 50 Watts, I see
> the following for each frequency step:
>> - The frequency to be used
>> - The number 1.0
>> This time it doesn't seem to be adjusting anything.  Maybe that was
> already done at 5 Watts?  It just starts out at 1.0 and stays there.
>> 
>> After this calibration, pressing TUNE with the DL1 still connected and the
> KAT3 still in BYPASS, I see 1.1 SWR.
>> 
>> So, what is going on?  It seems to me that if I adjust the transmitter
> using DL1 as the reference for 1.0 SWR, then pressing TUNE with the DL1
> attached and KAT3 still in BYPASS should also give 1.0.
>> 
>> So, two question:
>> (1)  What is the software adjusting that affects the SWR shown on the K3
> front panel display?
>> (2)  Why is the end result a lowest SWR of 1.1 instead of 1.0?
>> 
>> Thanks for any information.
>> 
>> Oliver Johns
>> W6ODJ
>> 
>> PS:  Configuration information:
>> K3 #1741, KPA3, KAT3, KBPF3, KTCXO3-1, KXV3, K3DSPUPGD upgrade, REMIOUPGD
> upgrade, all Elecraft-recommended user mods up to 1 Jan 2010 done, and no
> other mods done.  No KRX3.  No KXV3A upgrade.
>> 
>> 
>> 
>> 
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