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KPA1500 RFI on 10 Meters

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K9MA

KPA1500 RFI on 10 Meters

I guess it just shows how little I've been on 10, but I've had the
KPA1500 for over a year now, and I just noticed that when I turn it on,
my noise floor on 10 goes up about 3 dB. (And that's from an urban noise
floor.) It's pretty flat over much of the band, not typical switching
supply noise. Has anyone else experienced this and found a cure? (Other
than using the old amp tube.)

73,

Scott K9MA

--
Scott K9MA

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Alex Malyava

Re: KPA1500 RFI on 10 Meters

I had the same issue with homemade SS amp on 6m band... the noise, flat
uniform broadband white noise, was coming from no name chinese power
supply. The main one ( brandname 50V/50A) was no problem, but this one (
used for service voltages and CPU ) was generating RFI and its wires were
right next to the SWR bridge. The noise was getting into the receiver and
raised noise floor 5-6dB. No issue on HF, but 6m suffered really bad.

K2BB

On Sat, Dec 14, 2019 at 16:45 K9MA <[hidden email]> wrote:

> I guess it just shows how little I've been on 10, but I've had the
> KPA1500 for over a year now, and I just noticed that when I turn it on,
> my noise floor on 10 goes up about 3 dB. (And that's from an urban noise
> floor.) It's pretty flat over much of the band, not typical switching
> supply noise. Has anyone else experienced this and found a cure? (Other
> than using the old amp tube.)
>
> 73,
>
> Scott K9MA
>
> --
> Scott K9MA
>
> [hidden email]
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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N4ZR

Re: KPA1500 RFI on 10 Meters

In reply to this post by K9MA

I just tried that with my KPA-1500, Scott, and could not hear any
change. Another one of those RFI gremlins!

73, Pete N4ZR
Check out the Reverse Beacon Network
at <http://reversebeacon.net>, now
spotting RTTY activity worldwide.
For spots, please use your favorite
"retail" DX cluster.

On 12/14/2019 4:43 PM, K9MA wrote:

> I guess it just shows how little I've been on 10, but I've had the
> KPA1500 for over a year now, and I just noticed that when I turn it
> on, my noise floor on 10 goes up about 3 dB. (And that's from an urban
> noise floor.) It's pretty flat over much of the band, not typical
> switching supply noise. Has anyone else experienced this and found a
> cure? (Other than using the old amp tube.)
>
> 73,
>
> Scott K9MA
>

K9MA

Re: KPA1500 RFI on 10 Meters

Hi Pete,

It did help to put a couple ferrites on the PS control cable. It's now
barely perceptible, but that's with an urban noise level. It's
definitely coming in via the antenna, something over 100 ft away.

73,
Scott K9MA

On 12/14/2019 21:03, N4ZR wrote:

> I just tried that with my KPA-1500, Scott, and could not hear any
> change. Another one of those RFI gremlins!
>
> 73, Pete N4ZR
> Check out the Reverse Beacon Network
> at <http://reversebeacon.net>, now
> spotting RTTY activity worldwide.
> For spots, please use your favorite
> "retail" DX cluster.
>
> On 12/14/2019 4:43 PM, K9MA wrote:
>> I guess it just shows how little I've been on 10, but I've had the
>> KPA1500 for over a year now, and I just noticed that when I turn it
>> on, my noise floor on 10 goes up about 3 dB. (And that's from an
>> urban noise floor.) It's pretty flat over much of the band, not
>> typical switching supply noise. Has anyone else experienced this and
>> found a cure? (Other than using the old amp tube.)
>>
>> 73,
>>
>> Scott K9MA
>>
> ______________________________________________________________
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--
Scott K9MA

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Chris Codella, W2PA

Re: KPA1500 RFI on 10 Meters

In reply to this post by K9MA

Scott,

I noticed the same thing this last weekend, having not been on 10 much
since getting the amp. But I found the noise to be quite variable. It
doesn't always occur. When it does, it appears suddenly, out of the
blue while operating.

Sometimes I could make it go away by turning off the power, waiting a
while, then restarting. I also got it to stop a couple of times by
sending a single "dit" while in operate mode. Quite strange. I'm trying
to get more data but it does seem to be an intermittent thing and hard
to replicate.

This noise didn't affect any band below 10m but appeared very
broad-banded above, using an SDR receiver.

73,
Chris, W2PA

On 12/14/2019 4:43 PM, K9MA wrote:

Bob McGraw - K4TAX

Re: KPA1500 RFI on 10 Meters

I suggest one check the 240V wiring to confirm all connections are tight and solid all the way from the main breaker panel to the outlet for the amp. This includes L1, L2, Neut, and Ground. Also I would make sure there is a solid ground between the PS cabinet and amp cabinet.

Also , since recent issues are reported as new for 10M, make sure the station ground ( if one is used) is not near 1/4 wavelength on 10M. That’s about 8’ or so.

73
Bob, K4TAX

Sent from my iPhone

> On Dec 16, 2019, at 4:28 PM, Chris Codella, W2PA <[hidden email]> wrote:
>
> Scott,
>
> I noticed the same thing this last weekend, having not been on 10 much since getting the amp. But I found the noise to be quite variable. It doesn't always occur. When it does, it appears suddenly, out of the blue while operating.
>
> Sometimes I could make it go away by turning off the power, waiting a while, then restarting. I also got it to stop a couple of times by sending a single "dit" while in operate mode. Quite strange. I'm trying to get more data but it does seem to be an intermittent thing and hard to replicate.
>
> This noise didn't affect any band below 10m but appeared very broad-banded above, using an SDR receiver.
>
> 73,
> Chris, W2PA
>
>> On 12/14/2019 4:43 PM, K9MA wrote:
>> I guess it just shows how little I've been on 10, but I've had the KPA1500 for over a year now, and I just noticed that when I turn it on, my noise floor on 10 goes up about 3 dB. (And that's from an urban noise floor.) It's pretty flat over much of the band, not typical switching supply noise. Has anyone else experienced this and found a cure? (Other than using the old amp tube.)
>>
>> 73,
>>
>> Scott K9MA
>>
>
> ______________________________________________________________
> Elecraft mailing list
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> Post: mailto:[hidden email]
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K9MA

Re: KPA1500 RFI on 10 Meters

In reply to this post by Chris Codella, W2PA

Chris,

In my case, the noise is present any time the KPA1500 is turn on. Its
effect depends only on the direction my beam is pointed, as both my
noise level and the amplifier noise vary with direction. In the worst
case, I'm seeing about a 5 dB increase from my high urban noise floor. I
think the effect would be far more dramatic in a quiet location. (My
antenna is about 100 feet from the amplifier, which is in the basement.)

73,
Scott K9MA

On 12/16/2019 16:16, Chris Codella, W2PA wrote:

> Scott,
>
> I noticed the same thing this last weekend, having not been on 10 much
> since getting the amp. But I found the noise to be quite variable.
> It doesn't always occur. When it does, it appears suddenly, out of
> the blue while operating.
>
> Sometimes I could make it go away by turning off the power, waiting a
> while, then restarting. I also got it to stop a couple of times by
> sending a single "dit" while in operate mode. Quite strange. I'm
> trying to get more data but it does seem to be an intermittent thing
> and hard to replicate.
>
> This noise didn't affect any band below 10m but appeared very
> broad-banded above, using an SDR receiver.
>
> 73,
> Chris, W2PA
>
> On 12/14/2019 4:43 PM, K9MA wrote:
>> I guess it just shows how little I've been on 10, but I've had the
>> KPA1500 for over a year now, and I just noticed that when I turn it
>> on, my noise floor on 10 goes up about 3 dB. (And that's from an
>> urban noise floor.) It's pretty flat over much of the band, not
>> typical switching supply noise. Has anyone else experienced this and
>> found a cure? (Other than using the old amp tube.)
>>
>> 73,
>>
>> Scott K9MA
>>
>

Elecraft mailing list

Re: KPA1500 RFI on 10 Meters

I see no difference whatsoever on 10M with the KPA1500 powered on or off, or with the TH7DX tribander pointed at the station or pointed at some other azimuth. My resting noise level on 10M is approx -125 dBM on the P3. The tower is about 60 feet from the station.

73, Charles, K4ZRJ

> On Dec 17, 2019, at 14:07, K9MA <[hidden email]> wrote:
>
> Chris,
>
> In my case, the noise is present any time the KPA1500 is turn on. Its effect depends only on the direction my beam is pointed, as both my noise level and the amplifier noise vary with direction. In the worst case, I'm seeing about a 5 dB increase from my high urban noise floor. I think the effect would be far more dramatic in a quiet location. (My antenna is about 100 feet from the amplifier, which is in the basement.)
>
> 73,
> Scott K9MA
>
> On 12/16/2019 16:16, Chris Codella, W2PA wrote:
>> Scott,
>>
>> I noticed the same thing this last weekend, having not been on 10 much since getting the amp. But I found the noise to be quite variable. It doesn't always occur. When it does, it appears suddenly, out of the blue while operating.
>>
>> Sometimes I could make it go away by turning off the power, waiting a while, then restarting. I also got it to stop a couple of times by sending a single "dit" while in operate mode. Quite strange. I'm trying to get more data but it does seem to be an intermittent thing and hard to replicate.
>>
>> This noise didn't affect any band below 10m but appeared very broad-banded above, using an SDR receiver.
>>
>> 73,
>> Chris, W2PA
>>
>> On 12/14/2019 4:43 PM, K9MA wrote:
>>> I guess it just shows how little I've been on 10, but I've had the KPA1500 for over a year now, and I just noticed that when I turn it on, my noise floor on 10 goes up about 3 dB. (And that's from an urban noise floor.) It's pretty flat over much of the band, not typical switching supply noise. Has anyone else experienced this and found a cure? (Other than using the old amp tube.)
>>>
>>> 73,
>>>
>>> Scott K9MA
>>>
>>
>
> --
> Scott K9MA
>
> [hidden email]
>
> ______________________________________________________________
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Eric Swartz - WA6HHQ

Re: KPA1500 RFI on 10 Meters

Administrator

In reply to this post by K9MA

Hi Scott,

We have seen this in rare cases on a few 1500s. It appears to be caused by the
ground connection between the rear RF INPUT SO-239 flange and the chassis.

Very slightly loosening (not too far!) and then firmly re-tightening all four
screws on this SO-239 connector will insure a good ground connection between
this connector and the rear panel. (There are lock washers between the nuts and
the SO-239 inside.)

If the screws are loosened too far, you may have to remove the bottom cover of
the amp to hold the interior nuts in place while you re-tighten the four
screws. (Make sure the 50V power and control cables are disconnected when you
remove any covers on the amp.)

73,
Eric
/elecraft.com/

On 12/14/2019 1:43 PM, K9MA wrote:

> I guess it just shows how little I've been on 10, but I've had the KPA1500 for
> over a year now, and I just noticed that when I turn it on, my noise floor on
> 10 goes up about 3 dB. (And that's from an urban noise floor.) It's pretty
> flat over much of the band, not typical switching supply noise. Has anyone
> else experienced this and found a cure? (Other than using the old amp tube.)
>
> 73,
>
> Scott K9MA
>

Jim Brown-10

Re: KPA1500 RFI on 10 Meters

In reply to this post by K9MA

On 12/17/2019 11:07 AM, K9MA wrote:
>
> In my case, the noise is present any time the KPA1500 is turn on. Its
> effect depends only on the direction my beam is pointed, as both my
> noise level and the amplifier noise vary with direction. In the worst
> case, I'm seeing about a 5 dB increase from my high urban noise floor. I
> think the effect would be far more dramatic in a quiet location. (My
> antenna is about 100 feet from the amplifier, which is in the basement.)

Scott,

Your result suggests a problem with bonding in your station. Study this
tutorial, http://k9yc.com/GroundingAndAudio.pdf and/or N0AX's recent
ARRL book on the topic, to which I contributed extensively.

73, Jim K9YC
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Jim Brown-10

Re: KPA1500 RFI on 10 Meters

In reply to this post by Eric Swartz - WA6HHQ

On 12/17/2019 11:44 AM, Eric Swartz - WA6HHQ, Elecraft wrote:
> We have seen this in rare cases on a few 1500s. It appears to be caused
> by the ground connection between the rear RF INPUT SO-239 flange and the
> chassis.

Or, if the station is not properly bonded. Or coax with a poor shield
connection to a connector.

73, Jim K9YC
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Michael Walker

Re: KPA1500 RFI on 10 Meters

Hi Jim

How many slides are in that deck?

Mike

On Tue, Dec 17, 2019 at 3:08 PM Jim Brown <[hidden email]> wrote:

> On 12/17/2019 11:44 AM, Eric Swartz - WA6HHQ, Elecraft wrote:
> > We have seen this in rare cases on a few 1500s. It appears to be caused
> > by the ground connection between the rear RF INPUT SO-239 flange and the
> > chassis.
>
> Or, if the station is not properly bonded. Or coax with a poor shield
> connection to a connector.
>
> 73, Jim K9YC
> ______________________________________________________________
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Jim Brown-10

Re: KPA1500 RFI on 10 Meters

On 12/17/2019 12:16 PM, Michael Walker wrote:
> How many slides are in that deck?

Lots. It's a pdf for a talk that runs about 90 minutes. Lots of detail
on the slides.

73, Jim

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K9MA

Re: KPA1500 RFI on 10 Meters

In reply to this post by Eric Swartz - WA6HHQ

Hi Eric,

I was able to tighten those screws a little, but it made no difference.
Adding ferrites to the control cable near the PS helped slightly,
suggesting that that is the source. The RF is definitely being received
by the antenna, about 100 feet away: its strength depends on the antenna
direction, and it is at least 7 dB weaker with a dummy load.

I have submitted a request to tech support.

73,
Scott K9MA

On 12/17/2019 13:44, Eric Swartz - WA6HHQ, Elecraft wrote:

> Hi Scott,
>
> We have seen this in rare cases on a few 1500s. It appears to be
> caused by the ground connection between the rear RF INPUT SO-239
> flange and the chassis.
>
> Very slightly loosening (not too far!) and then firmly re-tightening
> all four screws on this SO-239 connector will insure a good ground
> connection between this connector and the rear panel. (There are lock
> washers between the nuts and the SO-239 inside.)
>
> If the screws are loosened too far, you may have to remove the bottom
> cover of the amp to hold the interior nuts in place while you
> re-tighten the four screws. (Make sure the 50V power and control
> cables are disconnected when you remove any covers on the amp.)
>
> 73,
> Eric
> /elecraft.com/
>
> On 12/14/2019 1:43 PM, K9MA wrote:
>> I guess it just shows how little I've been on 10, but I've had the
>> KPA1500 for over a year now, and I just noticed that when I turn it
>> on, my noise floor on 10 goes up about 3 dB. (And that's from an
>> urban noise floor.) It's pretty flat over much of the band, not
>> typical switching supply noise. Has anyone else experienced this and
>> found a cure? (Other than using the old amp tube.)
>>
>> 73,
>>
>> Scott K9MA
>>
>

Eric Swartz - WA6HHQ

Re: KPA1500 RFI on 10 Meters

Administrator

Scott - what is your 1500 s/n?
Eric
/elecraft.com/

On 12/17/2019 1:04 PM, K9MA wrote:

> Hi Eric,
>
> I was able to tighten those screws a little, but it made no difference. Adding
> ferrites to the control cable near the PS helped slightly, suggesting that
> that is the source. The RF is definitely being received by the antenna, about
> 100 feet away: its strength depends on the antenna direction, and it is at
> least 7 dB weaker with a dummy load.
>
> I have submitted a request to tech support.
>
> 73,
> Scott K9MA
>
>
>
> On 12/17/2019 13:44, Eric Swartz - WA6HHQ, Elecraft wrote:
>> Hi Scott,
>>
>> We have seen this in rare cases on a few 1500s. It appears to be caused by
>> the ground connection between the rear RF INPUT SO-239 flange and the chassis.
>>
>> Very slightly loosening (not too far!) and then firmly re-tightening all four
>> screws on this SO-239 connector will insure a good ground connection between
>> this connector and the rear panel. (There are lock washers between the nuts
>> and the SO-239 inside.)
>>
>> If the screws are loosened too far, you may have to remove the bottom cover
>> of the amp to hold the interior nuts in place while you re-tighten the four
>> screws. (Make sure the 50V power and control cables are disconnected when
>> you remove any covers on the amp.)
>>
>> 73,
>> Eric
>> /elecraft.com/
>>
>> On 12/14/2019 1:43 PM, K9MA wrote:
>>> I guess it just shows how little I've been on 10, but I've had the KPA1500
>>> for over a year now, and I just noticed that when I turn it on, my noise
>>> floor on 10 goes up about 3 dB. (And that's from an urban noise floor.) It's
>>> pretty flat over much of the band, not typical switching supply noise. Has
>>> anyone else experienced this and found a cure? (Other than using the old amp
>>> tube.)
>>>
>>> 73,
>>>
>>> Scott K9MA
>>>
>>
>
> --
> Scott K9MA
>
> [hidden email]

K8TE

Re: KPA1500 RFI on 10 Meters

In reply to this post by K9MA

My finding was similar to Scott's. I noticed between one and two S-units
increase in noise on a 10m dipole located within 40 ft. of the shack. I
also noticed the same on 15m with a 40m dipole at the same distance. I
added type 31 ferrite snap-on cores to the 240 VAC, the "high" DC voltage,
and control lines at the power supply. Now, the noise is back to the
ambient level which is still too high.

Now I can copy another level or two of signals I couldn't copy as well prior
to adding the ferrite cores. BTW, that previous level of noise disappeared
when I powered the amplifier down and not the PSU.

73, Bill, K8TE

--
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Jim Brown-10

Re: KPA1500 RFI on 10 Meters

On 5/26/2020 10:22 AM, K8TE wrote:
> I
> added type 31 ferrite snap-on cores to the 240 VAC, the "high" DC voltage,
> and control lines at the power supply.

Hi Bill,

For 10M, I suggest three turns through a #31 clamp-on that's large
enough to hold the turns. Two turns is about right for 6M.

73, Jim K9YC
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