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RF feedback? only when using KXPA100

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David F. Reed-2

RF feedback? only when using KXPA100

This did not used to happen; it is new to my set-up, nothing I am aware
of has changed...

When trying to operate JT65, if I set the power to 10 watts, everything
is fine (KXPA100 is not active).
If I set to anything above 10 watts (yeah, like 11 watts or more), I get
bad RF feedback (sounds like motor boating in monitor).
SWR via tune looks good, all cables have been taken out, checked and
re-inserted.

I am stumped and looking for hints as to what I ought to look at next,
or re-check or try.

Thanks & 73 de Dave, W5SV
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David F. Reed-2

Re: RF feedback? only when using KXPA100

Mike, it is clean on a dummy load; I guess I need to track down if I
have lost my ground somewhere, or find the feedback path...

73 de Dave, W5SV

On 8/6/17 00:13, Mike Flowers wrote:

> Hi Dave,
>
> Have you tried this using a dummy load? May be useful to eliminate RFI as a cause.
>
> -- Mike Flowers, K6MKF, NCDXC - "It's about DX!"
>
>> On Aug 5, 2017, at 9:26 PM, David F. Reed <[hidden email]> wrote:
>>
>>
>> This did not used to happen; it is new to my set-up, nothing I am aware of has changed...
>>
>> When trying to operate JT65, if I set the power to 10 watts, everything is fine (KXPA100 is not active).
>> If I set to anything above 10 watts (yeah, like 11 watts or more), I get bad RF feedback (sounds like motor boating in monitor).
>> SWR via tune looks good, all cables have been taken out, checked and re-inserted.
>>
>> I am stumped and looking for hints as to what I ought to look at next, or re-check or try.
>>
>> Thanks & 73 de Dave, W5SV
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
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>>
>> This list hosted by: http://www.qsl.net
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>> Message delivered to [hidden email]

--
שָׁלום עֲלֵיכֶם - עֲלֵיכֶם שָׁלום
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Bob N3MNT

Re: RF feedback? only when using KXPA100

In reply to this post by David F. Reed-2

Make sure you have not accidentally enabled Ant 2 on the KXPA100.

David F. Reed-2

Re: RF feedback? only when using KXPA100

In reply to this post by David F. Reed-2

Great news; found it!

It was a connection to my coax switch; take it out of line, it goes
away. re-connected, it comes back. Cleaned the connections and
reconnected, it is gone.
Hurrah!

73 de Dave, W5SV

On 8/6/17 12:12, Mike Flowers wrote:

> Good to find the root cause. Fix will be an easy one.
>
> -- Mike Flowers, K6MKF, NCDXC - "It's about DX!"
>
>> On Aug 6, 2017, at 10:07 AM, David F. Reed <[hidden email]> wrote:
>>
>> Mike, it is clean on a dummy load; I guess I need to track down if I have lost my ground somewhere, or find the feedback path...
>>
>> 73 de Dave, W5SV
>>
>>
>>> On 8/6/17 00:13, Mike Flowers wrote:
>>> Hi Dave,
>>>
>>> Have you tried this using a dummy load? May be useful to eliminate RFI as a cause.
>>>
>>> -- Mike Flowers, K6MKF, NCDXC - "It's about DX!"
>>>
>>>> On Aug 5, 2017, at 9:26 PM, David F. Reed <[hidden email]> wrote:
>>>>
>>>>
>>>> This did not used to happen; it is new to my set-up, nothing I am aware of has changed...
>>>>
>>>> When trying to operate JT65, if I set the power to 10 watts, everything is fine (KXPA100 is not active).
>>>> If I set to anything above 10 watts (yeah, like 11 watts or more), I get bad RF feedback (sounds like motor boating in monitor).
>>>> SWR via tune looks good, all cables have been taken out, checked and re-inserted.
>>>>
>>>> I am stumped and looking for hints as to what I ought to look at next, or re-check or try.
>>>>
>>>> Thanks & 73 de Dave, W5SV

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Jim Brown-10

Re: RF feedback? only when using KXPA100

On 8/6/2017 5:25 PM, David F. Reed wrote:
> It was a connection to my coax switch; take it out of line, it goes
> away. re-connected, it comes back. Cleaned the connections and
> reconnected, it is gone.

Many years ago, a very smart guy said something it the effect that with
any problems with TX or RX, ALWAYS check for bad coax FIRST. From lots
of experience, I've learned the value of that. First things to check are
the SHIELD connections, any junk connectors and adapters (if it doesn't
say Amphenol, it's probably junk).

If you "cleaned the connections" and fixed it, there's a good chance
that the problem is still there, lurking as an intermittent shield
connection that will return. Or maybe the switch is poor.

73, Jim K9YC

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David Bunte

Re: RF feedback? only when using KXPA100

Jim -

I recently sent my K3 to the 'Mother Ship' for some upgrades while my wife
and I took a 3 week road trip. I hooked up the returned rig over the
weekend. Much to my chagrin, I was extremely high SWR. I verified that I
had the RF path correct from the K3 through assorted other devices and to
the antenna. While doing so I noticed one coax connector that was about 1/4
to 1/2 turn loose. I tightened it, and all was fine... for about 30
seconds.

Remembering what a wise man once said I suspected a bad piece of coax. I
checked the same connection again... it was loose... as I tightened it, all
of a sudden it became loose again. This was a 1 foot jumper, from a company
that advertises heavily. I had been using it for several years from the
output of my KPA500 to the sensor for my LP-100A. The threads did not
appear to be stripped, although it felt like it. I looked like the threads
were cur very shallow. I replaced it with a jumper I made many years ago,
using
Amphenol connectors, and all is now working as it should.

Well... not quite all... I have made some nice CW QSOs, but decided to
check SSB operation. It is not working on that mode (which I almost never
use), but I will tackle it to see what is not set correctly.

Dave - K9FN

On Mon, Aug 7, 2017 at 5:28 PM, Jim Brown <[hidden email]> wrote:

> On 8/6/2017 5:25 PM, David F. Reed wrote:
>
>> It was a connection to my coax switch; take it out of line, it goes away.
>> re-connected, it comes back. Cleaned the connections and reconnected, it
>> is gone.
>>
>
> Many years ago, a very smart guy said something it the effect that with
> any problems with TX or RX, ALWAYS check for bad coax FIRST. From lots of
> experience, I've learned the value of that. First things to check are the
> SHIELD connections, any junk connectors and adapters (if it doesn't say
> Amphenol, it's probably junk).
>
> If you "cleaned the connections" and fixed it, there's a good chance that
> the problem is still there, lurking as an intermittent shield connection
> that will return. Or maybe the switch is poor.
>
> 73, Jim K9YC
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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> Message delivered to [hidden email]
>

Bob McGraw - K4TAX

Re: RF feedback? only when using KXPA100

Just as a comment. PL-259 connectors are all created equal. Some are
great looking connectors and are just pure crap! The plating makes for
good looks but poor performance.

To that end, I always and every time snug my PL-259 connectors with a
pair of 4" Channel Lock pliers. Finger tight is never good enough!
You'd be surprised at the number of RFI issues I've corrected with this
approach.

73

Bob, K4TAX

On 8/7/2017 4:59 PM, David Bunte wrote:

> Jim -
>
> I recently sent my K3 to the 'Mother Ship' for some upgrades while my wife
> and I took a 3 week road trip. I hooked up the returned rig over the
> weekend. Much to my chagrin, I was extremely high SWR. I verified that I
> had the RF path correct from the K3 through assorted other devices and to
> the antenna. While doing so I noticed one coax connector that was about 1/4
> to 1/2 turn loose. I tightened it, and all was fine... for about 30
> seconds.
>
> Remembering what a wise man once said I suspected a bad piece of coax. I
> checked the same connection again... it was loose... as I tightened it, all
> of a sudden it became loose again. This was a 1 foot jumper, from a company
> that advertises heavily. I had been using it for several years from the
> output of my KPA500 to the sensor for my LP-100A. The threads did not
> appear to be stripped, although it felt like it. I looked like the threads
> were cur very shallow. I replaced it with a jumper I made many years ago,
> using
> Amphenol connectors, and all is now working as it should.
>
> Well... not quite all... I have made some nice CW QSOs, but decided to
> check SSB operation. It is not working on that mode (which I almost never
> use), but I will tackle it to see what is not set correctly.
>
> Dave - K9FN
>
> On Mon, Aug 7, 2017 at 5:28 PM, Jim Brown <[hidden email]> wrote:
>
>> On 8/6/2017 5:25 PM, David F. Reed wrote:
>>
>>> It was a connection to my coax switch; take it out of line, it goes away.
>>> re-connected, it comes back. Cleaned the connections and reconnected, it
>>> is gone.
>>>
>> Many years ago, a very smart guy said something it the effect that with
>> any problems with TX or RX, ALWAYS check for bad coax FIRST. From lots of
>> experience, I've learned the value of that. First things to check are the
>> SHIELD connections, any junk connectors and adapters (if it doesn't say
>> Amphenol, it's probably junk).
>>
>> If you "cleaned the connections" and fixed it, there's a good chance that
>> the problem is still there, lurking as an intermittent shield connection
>> that will return. Or maybe the switch is poor.
>>
>> 73, Jim K9YC
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
>>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

Edward R Cole

Re: RF feedback? only when using KXPA100

In reply to this post by David F. Reed-2

Concur on suspecting cables as first step for most problems. Also
suspect the meter that measures the signal/voltage/current/etc. Or
other items in the line.

I ran into a similar issue using an antenna tuner on 2m. I had just
put up a 11-element yagi (not real high but equivalent to the
vertical previously used). I could hardly hear my neighbor on 2m-SSB
only 15 miles away. More interestingly he reported my signal as
low...hmm. I switched back to the vertical and signals in both
direction jumped up in strength...double hmm!

OK the yagi had not been in service for a couple years and I was
unable to make any tests before it was put up on another tower. SWR
was close to marginal so I inserted my 2m antenna tuner and that
fixed the SWR. I checked power on each side of the tuner and it was
about the same ( a little lower on output). Soooo I removed the
tuner and power indicated went from 110w to 100w but the signal
jumped in both directions. Note to self: "leave this tuner on the
dusty shelf".

The SWR is about 1.8 without and tuner but the 100w amplifier is
happy (no fold back) and signal are much better on both ends of the
circuit (S0 jumped to S3). Guess that tuner is very lossy
(MFJ-921). Of course MFJ means "mighty fine junk" <smile>

73, Ed - KL7UW
http://www.kl7uw.com
Dubus-NA Business mail:
[hidden email]

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Bob McGraw - K4TAX

Re: RF feedback? only when using KXPA100

A comment on tuners. The SWR and associated increased loss remains the same on the feed line regardless of the action of the tuner. When using a tuner, the load only looks better to the transmitter and the tuner presents added overall loss.

Reflected power is not totally lost power. Only the loss of the feed-line contributes to lost power.

Bob, K4TAX

Sent from my iPhone

> On Aug 7, 2017, at 8:19 PM, Edward R Cole <[hidden email]> wrote:
>
> Concur on suspecting cables as first step for most problems. Also suspect the meter that measures the signal/voltage/current/etc. Or other items in the line.
>
> I ran into a similar issue using an antenna tuner on 2m. I had just put up a 11-element yagi (not real high but equivalent to the vertical previously used). I could hardly hear my neighbor on 2m-SSB only 15 miles away. More interestingly he reported my signal as low...hmm. I switched back to the vertical and signals in both direction jumped up in strength...double hmm!
>
> OK the yagi had not been in service for a couple years and I was unable to make any tests before it was put up on another tower. SWR was close to marginal so I inserted my 2m antenna tuner and that fixed the SWR. I checked power on each side of the tuner and it was about the same ( a little lower on output). Soooo I removed the tuner and power indicated went from 110w to 100w but the signal jumped in both directions. Note to self: "leave this tuner on the dusty shelf".
>
> The SWR is about 1.8 without and tuner but the 100w amplifier is happy (no fold back) and signal are much better on both ends of the circuit (S0 jumped to S3). Guess that tuner is very lossy (MFJ-921). Of course MFJ means "mighty fine junk" <smile>
>
> 73, Ed - KL7UW
> http://www.kl7uw.com
> Dubus-NA Business mail:
> [hidden email]
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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>

Jim Brown-10

Re: RF feedback? only when using KXPA100

In reply to this post by Bob McGraw - K4TAX

On 8/7/2017 3:06 PM, Bob McGraw K4TAX wrote:
> PL-259 connectors are all created equal.

This is definitely NOT true. There are as many cheap knock-offs as there
are cheap factories and cheap vendors. There are tolerances on diameters
of the center pin and center receptacle, there are poor/cheap choices of
metals, dielectric that melts when you solder to it, metals that don't
take solder, even dissimilar metal issues when mated with another
connector. I've also seen threads that are too short, and outer rings
that are too short. And that's just PL259s.

What IS entirely right about Bob's post is the importance of making
connectors wrench-tight.

73, Jim K9YC

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Bob McGraw - K4TAX

Re: RF feedback? only when using KXPA100

In looking back at my original post..........I omitted the word NOT.
Thus "all PL-259 connectors are not all created equal".

Sorry folks, and thanks Jim for catching the over site.

73

Bob, K4TAX

On 8/8/2017 12:42 AM, Jim Brown wrote:

> On 8/7/2017 3:06 PM, Bob McGraw K4TAX wrote:
>> PL-259 connectors are all created equal.
>
> This is definitely NOT true. There are as many cheap knock-offs as
> there are cheap factories and cheap vendors. There are tolerances on
> diameters of the center pin and center receptacle, there are
> poor/cheap choices of metals, dielectric that melts when you solder to
> it, metals that don't take solder, even dissimilar metal issues when
> mated with another connector. I've also seen threads that are too
> short, and outer rings that are too short. And that's just PL259s.
>
> What IS entirely right about Bob's post is the importance of making
> connectors wrench-tight.
>
> 73, Jim K9YC
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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> Message delivered to [hidden email]
>