Spurs on 6 meters on FT8

[cbscholl]

I am having a problem only on 6 meters with spurs being generated while using
FT8. I have the audio level turned down so no alc reading appears or even
lower and that does not eliminate them. The other point that I noticed is
that only on 6 meters the 100 final turns on above 8 watts rather than 12
watts on other bands. Does anyone have any ideas or what else I can check?
Barney K3LA



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[donovanf]

Hi Barney,


Please share some details about the nature of the spurious signals you're
trying to solve


Thanks


73
Frank
W3LPL

----- Original Message -----

From: "cbscholl" <[hidden email]>
To: [hidden email]
Sent: Friday, June 12, 2020 3:25:12 PM
Subject: [Elecraft] Spurs on 6 meters on FT8

I am having a problem only on 6 meters with spurs being generated while using
FT8. I have the audio level turned down so no alc reading appears or even
lower and that does not eliminate them. The other point that I noticed is
that only on 6 meters the 100 final turns on above 8 watts rather than 12
watts on other bands. Does anyone have any ideas or what else I can check?
Barney K3LA



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[Don Wilhelm]

Barney,

I assume you are talking about a K3/K3S or KX3.
For those you need to increase the audio drive so you have 4 bars solid
showing on the ALC meter with the 5th flashing.  That is the NO ALC
point on those radios.  It is required for proper power control.
See the article on my website www.w3fpr.com for more detail.

I don't know if that will help with the spurs, but it will help with
your power output and keep the radio from Power Hunting.

73,
Don W3FPR

On 6/12/2020 11:25 AM, cbscholl wrote:
> I am having a problem only on 6 meters with spurs being generated while using
> FT8. I have the audio level turned down so no alc reading appears or even
> lower and that does not eliminate them. The other point that I noticed is
> that only on 6 meters the 100 final turns on above 8 watts rather than 12
> watts on other bands. Does anyone have any ideas or what else I can check?
> Barney K3LA
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[cbscholl]

This is a picture of my signal on a 7851 about 6 miles away.
<http://elecraft.365791.n2.nabble.com/file/t317357/IMG_9900.jpg>
At another point I had the KPA500 and it looked like this.
<http://elecraft.365791.n2.nabble.com/file/t317357/IMG_9901.jpg>
I also saw a similar view on a 7300 in the shack but did not take a picture.
Barney



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[cbscholl]

Yes this was a K3. I had been running the audio gain at about that point. But
when the pictures were taken I had backed off to try to help the situation.
Barney



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[KeithWE6R]

If you have a K3S (or late K3, with the KPA3A type 100w amp).
Please see the recent FW notes in the K3 Utility about setting the 6m
Atn6 attenuator switch to prevent 6m oscillations.
Also, what rev of KLPA3A and KPA3A are you at? There have been improvements.
Keith WE6R, Elecraft K3 Tech.

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[cbscholl]

I have an older K3 ( under 3000) so I do not have the newer KPA3A. Several
yeas ago I had to replace at least one of the driver transistors. At that
time I also changed some transformers either on the driver or final board. I
do not remember without looking but the nature of the wire change was either
to or from enameled. I also recently installed gold pins because the pins
leading from the main board to the interface board to the KPA3 had
tarnished. Those are the only changes that I have made to the TX side since
it had been sent back to the factory by the prior owner. Barney K3LA



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[KeithWE6R]

Did you re-set the Bias after changing finals and working on the KPA3
and LPA?
1. The 8W vs 12W switch-over point on 6m is normal.
2. If the 6 pins for KPA3 DC power were darkened and you replaced with
gold, you *MUST* also replace the corresponding KPAIO3 Riser-Board SOCKET!!
The socket gets cooked internally. Sometimes you can see blueing and
heat damage, but not always.
3. Check C28 & C52 capacitors marked "M2" near the Finals output. Some
older revs KPA3 they were mounted right between the Final tabs near C50
& C51, they get cracked from thermal cycles and should be replaced and
moved out away from the finals and mounted in-between the legs of
C50&51. (If cracked, they usually cause spurs on 20m). Elecraft part #
E530321
4. Make sure your WM HP cal number is good, typically 25-55, so the
radio is not struggling to make more power than it should, then;
I recommend do a manual TX gain Cal at 50W on your main operating
frequency because 6m is 4megs wide;
IE; "TECH MD" to "on",  TUN PWR" to "nor". Then make note of the number
of "TXGN HP", Then set power to 50W exactly, set to your favorite
frequency, then long press XMIT to do a TUNE for several seconds. Unkey
and check the TXGN HP number. It may or may not change, but should be
reasonable, typical numbers are 9 thru 60.
(You can do a 5.0w exactly if you like for the "LP" calibration)
*** Then never, ever, set to 5 or 50w exactly as you may do an
inadvertent TX Gain Cal and mess up the numbers.
5. Try the internal 2-tone generator and look at the spectrum using
that, maybe you are over-driving with the FT8 audio.
Keith WE6R Elecraft K3 Tech

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[cbscholl]

After further thought at lunch I realize that I did replace both sockets. I still remember getting them unsoldered. My other unrelated comment is that I hope the lessons learned from the K3 will make it into the K4 and that the K4 whenever it appears. Barney K3LA

-----Original Message-----
From: Keith Trinity WE6R [mailto:[hidden email]]
Sent: Wednesday, June 17, 2020 11:15 AM
To: [hidden email]; [hidden email]
Subject: Re: [Elecraft] Spurs on 6 meters on FT8 Barney K3LA

Did you re-set the Bias after changing finals and working on the KPA3 and LPA?
1. The 8W vs 12W switch-over point on 6m is normal.
2. If the 6 pins for KPA3 DC power were darkened and you replaced with gold, you *MUST* also replace the corresponding KPAIO3 Riser-Board SOCKET!!
The socket gets cooked internally. Sometimes you can see blueing and heat damage, but not always.
3. Check C28 & C52 capacitors marked "M2" near the Finals output. Some older revs KPA3 they were mounted right between the Final tabs near C50 & C51, they get cracked from thermal cycles and should be replaced and moved out away from the finals and mounted in-between the legs of C50&51. (If cracked, they usually cause spurs on 20m). Elecraft part #
E530321
4. Make sure your WM HP cal number is good, typically 25-55, so the radio is not struggling to make more power than it should, then; I recommend do a manual TX gain Cal at 50W on your main operating frequency because 6m is 4megs wide; IE; "TECH MD" to "on",  TUN PWR" to "nor". Then make note of the number of "TXGN HP", Then set power to 50W exactly, set to your favorite frequency, then long press XMIT to do a TUNE for several seconds. Unkey and check the TXGN HP number. It may or may not change, but should be reasonable, typical numbers are 9 thru 60.
(You can do a 5.0w exactly if you like for the "LP" calibration)
*** Then never, ever, set to 5 or 50w exactly as you may do an inadvertent TX Gain Cal and mess up the numbers.
5. Try the internal 2-tone generator and look at the spectrum using that, maybe you are over-driving with the FT8 audio.
Keith WE6R Elecraft K3 Tech


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