TX Gain Calibration


K9MA
 

I hadn't run the TX gain calibration in almost 2 years on my K3. I was seeing some significant power overshoot when I changed bands, up to 126 W when set to 100 W. After the first transmission, it always settled down. The new TX Gain calibration resulted in significant changes in values, and that problem now seems to be gone. I'm not sure why the TX Gain calibration changed, but it seems to be a good idea to run it fairly frequently.

Does anyone have any idea why the TX Gain calibration changes?

73,
Scott K9MA


Wes Stewart
 

Drift in the BPF tuning.  It's a long story but my K3S had to go back for replacement of trimmer caps.

Wes  N7WS


On Wed, Nov 24, 2021 at 07:58 AM, K9MA wrote:
I hadn't run the TX gain calibration in almost 2 years on my K3. I was seeing some significant power overshoot when I changed bands, up to 126 W when set to 100 W. After the first transmission, it always settled down. The new TX Gain calibration resulted in significant changes in values, and that problem now seems to be gone. I'm not sure why the TX Gain calibration changed, but it seems to be a good idea to run it fairly frequently.

Does anyone have any idea why the TX Gain calibration changes?

73,
Scott K9MA


Jim McCook W6YA
 

The Elecraft guys say to never transmit at either 5 or 50 watts after doing the TX GAIN calibration because it may corrupt that calibration and cause this exact problem.   Jim W6YA


Ray Maxfield
 

Never had a Problem with running 5 or 50 Watts.

Sounds strange………….. Ray WA6VAB  K3

 

From: Jim McCook W6YA
Sent: Wednesday, November 24, 2021 11:32 AM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] TX Gain Calibration

 

The Elecraft guys say to never transmit at either 5 or 50 watts after doing the TX GAIN calibration because it may corrupt that calibration and cause this exact problem.   Jim W6YA

 


Bob McGraw - K4TAX
 

It was recommended to me to avoid the 12-watt to 15-watt power range.  Something about the KPA3a issues.  I've had 3 of them replaced.   Since then, I now have for some time avoided that range, and there have been no further issues.   My radio always drives either my KPA500 or KAT500 to any of the antenna systems.  

73
Bob, K4TAX


mikerodgerske5gbc
 

As far as the 5w thing, I’ve run 4.5 for several years into a modified als-600. 

73
Mike R

7!
Absolutely Awesome 

On Nov 25, 2021, at 10:40 AM, Bob McGraw - K4TAX <rmcgraw@...> wrote:

It was recommended to me to avoid the 12-watt to 15-watt power range.  Something about the KPA3a issues.  I've had 3 of them replaced.   Since then, I now have for some time avoided that range, and there have been no further issues.   My radio always drives either my KPA500 or KAT500 to any of the antenna systems.  

73
Bob, K4TAX


Keith_WE6R <keithtrinity@...>
 

Correct, never use 5.0 or 50 watts (or 1.0mw) -exactly- as it can cause an inadvertent manual TX gain calibration. 
If you think a cal is needed; You can manually run it on a single band and watch the config menu item TXGN number change.
Set config menu item "TUN PWR" to "nor", Go to your favorite freq, attach dummy load (or very flat load), set radio to exactly 5 watts, then long press XMIT to do a TUNE for several seconds. 
The number should change slightly. Repeat at 50W. The K3 Utility is best if you want to run all bands automatically. On wider bands like 10 & 6m, it is best to run it where you normally operate.
If you reset (EE INIT) the radio, you must run the tx gain cal on all bands (or load known good configuration).
Keith WE6R Elecraft K3/K4 Tech


Wes Stewart
 

Why hasn't this been fixed?

Wes N7WS


On Thu, Nov 25, 2021 at 11:22 AM, Keith_WE6R wrote:
Correct, never use 5.0 or 50 watts (or 1.0mw) -exactly- as it can cause an inadvertent manual TX gain calibration.


Brian K0DTJ
 

5w (QRP max) and 50w (CW rag chewing) are my go to operating powers and have never seen a problem. TUN PWR is set to 7w to keep the remote tuner happy. K3+KPA3 with current firmware. Been lucky I guess but I’ll mend my ways. 

73,
Brian, K0DTJ

On Nov 25, 2021, at 11:22, Keith_WE6R <keithtrinity@...> wrote:

Correct, never use 5.0 or 50 watts (or 1.0mw) -exactly- as it can cause an inadvertent manual TX gain calibration. 
If you think a cal is needed; You can manually run it on a single band and watch the config menu item TXGN number change.
Set config menu item "TUN PWR" to "nor", Go to your favorite freq, attach dummy load (or very flat load), set radio to exactly 5 watts, then long press XMIT to do a TUNE for several seconds. 
The number should change slightly. Repeat at 50W. The K3 Utility is best if you want to run all bands automatically. On wider bands like 10 & 6m, it is best to run it where you normally operate.
If you reset (EE INIT) the radio, you must run the tx gain cal on all bands (or load known good configuration).
Keith WE6R Elecraft K3/K4 Tech


Dave (NK7Z)
 

Keith,

Thank you for sharing, this sort of insight is like gold.

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources

On 11/25/21 11:22, Keith_WE6R wrote:
Correct, never use 5.0 or 50 watts (or 1.0mw) -exactly- as it can cause an inadvertent manual TX gain calibration.
If you think a cal is needed; You can manually run it on a single band and watch the config menu item TXGN number change.
Set config menu item "TUN PWR" to "nor", Go to your favorite freq, attach dummy load (or very flat load), set radio to exactly 5 watts, then long press XMIT to do a TUNE for several seconds.
The number should change slightly. Repeat at 50W. The K3 Utility is best if you want to run all bands automatically. On wider bands like 10 & 6m, it is best to run it where you normally operate.
If you reset (EE INIT) the radio, you must run the tx gain cal on all bands (or load known good configuration).
Keith WE6R Elecraft K3/K4 Tech


Kent Trimble, K9ZTV
 

Fourteen years digging it, apparently.

Kent K9ZTV

On Nov 25, 2021, at 2:59 PM, Dave (NK7Z) <dave@nk7z.net> wrote:

Keith,

Thank you for sharing, this sort of insight is like gold.



On 11/25/21 11:22, Keith_WE6R wrote:
Correct, never use 5.0 or 50 watts (or 1.0mw) -exactly- as it can cause an inadvertent manual TX gain calibration.


Bob NW8L
 

On pg. 67 of the current manual I see:

The gain constant is updated whenever the TUNE function is activated on a given band at one of three specific power levels: 5.0 W, 50 W, and 1.00 milliwatt.

However, I've set "TUN PWR" to 15 W in the config menu, so when I press TUNE the level is not 5 or 50 W. According the the above excerpt, there should be no inadvertent manual TX gain calibration. Do I misunderstand the manual? Or do you mean to say "never set TUN PWR to 5.0 or 50 watts"? If the statement in the manual is wrong, it should be corrected.

Bob NW8L


Keith_WE6R <keithtrinity@...>
 

Hi Bob NW8L;
Don't use 5 or 50 exactly ever, -especially- TUN PWR, then you should be safe from an accidental TX gain cal.
I know FW is "supposed" to keep this from happening  in several ways (not over certain SWR, only with deliberate TUNE etc), however radios have come in for Service with TUN PWR set to 5w, and their TX gain cal is out of whack. 
Keith 


Enno Korma
 

Hi all,

I also had issues with some power overshoot and slowly settling power levels after changing the output power with the PWR know. This can be quite annoying when driving - in my case - an SPE 1.3k (v3) linear which is very sensitive for even the slightest overdrive ...

So I did an automatic TX gain calibration with the K3 Utility. However, I found out that after running the calibration utility, the issue still remained. I have now done a fully manual calibration sequence on all bands. At each calibration level (5 and 50 W) I let the level settle for about 5 seconds. I could see that at the 50W point the reading sometimes changed after 3 seconds or so, meaning that the settling time can be quite long. The automatic utility does not wait that long.

After this I had no issues anymore.

--
Kind regards/73,

Enno Korma, PF5X


K9MA
 

On Sun, Dec 26, 2021 at 03:52 PM, Enno Korma wrote:
I also had issues with some power overshoot and slowly settling power levels after changing the output power with the PWR know. This can be quite annoying when driving - in my case - an SPE 1.3k (v3) linear which is very sensitive for even the slightest overdrive ...

So I did an automatic TX gain calibration with the K3 Utility. However, I found out that after running the calibration utility, the issue still remained. I have now done a fully manual calibration sequence on all bands. At each calibration level (5 and 50 W) I let the level settle for about 5 seconds. I could see that at the 50W point the reading sometimes changed after 3 seconds or so, meaning that the settling time can be quite long. The automatic utility does not wait that long.

After this I had no issues anymore.
I also just did the manual calibration. However, there doesn't appear to be a way to display the new calibration values. Even saving and restoring the configuration did not work, nor did cycling the power and re-starting the utility. Apparently, the utility will only display calibration values done automatically, so I can't tell if anything has actually changed. I have occasionally had the K3 initially overdrive the amplifier, so we'll see if that persists.

73,
Scott K9MA


John G4SWX
 

This is an issue that has troubled the K3 for over 6 years. I first noticed it on the 28MHz transverter output but I have found over twenty five(yes >25) K3 transceivers with similar issues over the years.
My view is that after any updates using the K3 Utility that a MANUAL re-calibration on all bands of all WMTR and gain values (50W 50W and 1mW transverter O/P) is required. The automatic calibration set-up is, as somebody else has pointed out, is simply not good enough!
It seems that either some actions of the K3 Utility or firmware updates resets all the values to some default setting. These have too much gain, cause overshoot and often unstable output with time.
It is certainly not drift of the tuning with time
It looks like Elecraft shelved my email................

John G4SWX


From: Elecraft Support <support@...>
Sent: 28 February 2017 18:10
To: Elecraft Support <support@...>
Cc: john.regnault@...
Subject: Re: FW: Unstable K3 Transverter Drive

 

Thanks John for the great sleuth work and the detailed email!

 

We will save this info in case someone else has such issues.

 

-Gary

On Tuesday, February 28, 2017 at 6:04:53 AM UTC-7, John Regnault wrote:

I have been experiencing a few difficulties with a number of K3 transceivers.

I thought that I had emailed you an earlier version a few weeks ago after I had tested just two transceivers.

Now as you will read I have found quite a lot!

 

73

John G4SWX

 

From: John Regnault [mailto:john.regnault@...]
Sent: 28 February 2017 12:52
To: moon-net@...
Subject: Unstable K3 Transverter Drive

 

In an earlier thread Mike Willis writes:

 

  • The problem is many rigs have the same problem. Even the K3, which does not produce a power spike does not really control its power output tightly enough

 

After having experienced unstable transverter drive with the K3 transceiver that I use for SSB/CW (I use a TS2000 for digital modes (always on full power with a big attenuator)) I have now investigated ten others and have found that most have not got the power meter nor the TX gain per band calibrated!

 

My symptoms were that I was getting low transverter drive until I switched to FM, gave it a burst of full power and then it settled down. It remained that way until the transceiver was switched off/on again. At least 5 other amateurs that I know have commented on slow power build-up when using a transverter with the K3. My first test was to substitute the K3 transceiver with another which is used by the local HF contest group. Both were using the latest firmware, 5.50. It gave exactly the same behaviour with the transverter! Putting both K3 transceivers into a dummy load on 14MHz and setting the power to 100W showed 142W and 136W on a Bird Thruline. Clearly both were out of calibration, the WMTR calibration numbers were set at what I now believe is a default value!

 

I then went through the WMTR calibration procedure at 5W, 50W and 1mW as per the Elecraft handbook. Although both then ran 100W when set to do so on HF the transverter drive still showed abnormal behaviour. After recalibration of the TX gain at 5W, 50W and 1mW(transverter O/P) as per the Elecraft handbook both performed as one would have expected when driving the transverter.

 

I then tested six more from the HF contest group and two from local friends. The two local friends both use their K3 transceivers with transverters and had reported slow power build up and unrepeatable settings! seven out of eight contained the default setting for the WTMR calibration and gain settings, those with transverter outputs all showed abnormal behaviour! The score was now 9 out of 10!

 

I did think that it might be something to do with a loss of calibration after firmware upgrades. I then checked and subsequently recalibrated two transceivers and then upgraded from Firmware 4.85 to 5.50 but the WMTR and gain values were held OK! The two local friends now report that the transverter drive on the recalibrated K3 transceivers is well behaved.

I then performed a straw poll by phone/email of a few others and 4 out of 6 contained the same default values! In total twelve out of sixteen K3 (and K3S) transceivers checked have been out of TX calibration!

 

Whether this is a problem with resetting with firmware upgrades or what I just do not know. What I do know is that in this state the IMD performance on HF is pretty poor when the transceiver is set to 100W O/P and transverter drive and VHF emissions can be unpredictable!

 

The way to check if yours still has its basic calibration. With TECH MD enabled in Config. check the value of:

Config: WMTR- HP when you have the power set to 50W on HF – the default value seems to be 30

Config WMTR- LP when you have the power set to 5W on HF – the default value seems to be 70

Config WTMR -MW when you have the transverter set – the default value seems to be 120

 

If you discover these values I would strongly recommend that you recalibrated the TX  according to the Elecraft handbook!

 

73

John G4SWX


John G4SWX
 

My original posting on the subject, with some more details, which I reported to Electraft, was on the moon-bounce reflector in 2017.
http://mailman.pe1itr.com/pipermail/moon-net/2017-February/031244.html

73
John G4SWX


mikerodgerske5gbc
 

John must have meant 16 years not 6? LoL 

It’s always been said it wasn’t a problem, just a different way of doing things for cleaner output especially initially. 

I can see it being a issue with really low drive. 

My drive is 4-8 watts on HF bands only. 

73
Mike R

7!
Absolutely Awesome 

On Dec 27, 2021, at 1:52 PM, John G4SWX via groups.io <john.regnault@...> wrote:

My original posting on the subject, with some more details, which I reported to Electraft, was on the moon-bounce reflector in 2017.
http://mailman.pe1itr.com/pipermail/moon-net/2017-February/031244.html

73
John G4SWX


Bob McGraw - K4TAX
 

I typically do TX gain calibration a couple of times a year.  Things do change a wee bit and I'm a bit fussy about my operation.  Likewise, I do frequency calibration about once a month.   It is amazing by paying attention to details how it makes one's operation a real pleasure.   And the procedures are quite easy and only take a few minutes.  

I use 20 watts for TUNE and 20 watts +/- based on the band, to drive my KPA500.  Neve more than about 25 watts.  If one ever sees the yellow or red Power LED  flash on, you've hit it too hard, and for others on the band, that's not good!  And likely not good for the amp either.     And for barefoot operation, I run 100 watts from my K3S. 


73
Bob, K4TAX