Elecraft

K2 and Feedback

Classic

List

Threaded

6 messages Options

David Fleming-3

K2 and Feedback

I have a significant feedback problem with my K2/KPA100. When
transmitting there feedback (sounds as clear and as loud as a PA system)
through an attached external speaker. The only partial solution I have
found is to use a sea rate power supply for the K2 and NOT connect the
power supply to ground. This makes a noticeable reduction in the
feedback. However, as soon as I attach the power supply to ground the
feedback returns. It seems there should be a solution other than not
connecting the power supply to ground.
Suggestions and help will be gratefully appreciated.

Dave Fleming KB3HCL
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

Larry-79

Re: K2 and Feedback

I have a Heil Clearspeech speaker and it specifically recommends a
separate power supply for the speaker, do not run off the same supply as
the rig.
I didn't see the reason for that, so I hooked the speaker up to the same
supply I used for the K2. It sounded pretty good a low volume, but when
I cranked up the K2, I heard feedback. Figured it was time to listen to
the manual and hooked up a separate 12vdc supply to the speaker, and
sure enough, plenty of volume and no feedback.
I didn't notice an issue with grounding.
I realize this doesn't specifically answer your question, but I think
you're on the right track using a separate supply.

73
Larry
WA2DGD

David Fleming wrote:

> I have a significant feedback problem with my K2/KPA100. When
> transmitting there feedback (sounds as clear and as loud as a PA system)
> through an attached external speaker. The only partial solution I have
> found is to use a sea rate power supply for the K2 and NOT connect the
> power supply to ground. This makes a noticeable reduction in the
> feedback. However, as soon as I attach the power supply to ground the
> feedback returns. It seems there should be a solution other than not
> connecting the power supply to ground. Suggestions and help will be
> gratefully appreciated.
>
> Dave Fleming KB3HCL
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

Don Wilhelm-3

RE: K2 and Feedback

In reply to this post by David Fleming-3

Dave,

I would believe you are experiencing ground loop problems rather than
feedback - yes, groundloops can introduce feedback of a type, but here in
ham corcles we usually relate feedback to the RF type. Check by operating
into a dummy load - if it persists, it is ground loop problems and not RF
feedback.

When you transmit (either keying or SSB speech), there is a varying load on
the power supply - that varying load translates into a small varying voltage
drop on the power supply leads which can couple into the external speaker
(which I figure is an amplified speaker).

Use a separate power supply for the speaker and things may tame down a bit.
Check the resistance of the entire power wiring to the KPA100 (including the
DC return (ground) lead) and make sure that resistance is very low (in the
milliohm range), and be certain the connections to the power supply are
tight and low resistance.

73,
Don W3FPR

> -----Original Message-----
>
> I have a significant feedback problem with my K2/KPA100. When
> transmitting there feedback (sounds as clear and as loud as a PA system)
> through an attached external speaker. The only partial solution I have
> found is to use a sea rate power supply for the K2 and NOT connect the
> power supply to ground. This makes a noticeable reduction in the
> feedback. However, as soon as I attach the power supply to ground the
> feedback returns. It seems there should be a solution other than not
> connecting the power supply to ground.
> Suggestions and help will be gratefully appreciated.
>
> Dave Fleming KB3HCL
>

--
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.5.441 / Virus Database: 268.18.2/692 - Release Date: 2/18/2007
4:35 PM

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

Jack Smith-6

Bypassing and Filtering Measurements

In reply to this post by David Fleming-3

I've added a new page to my web site presenting measurements of the
effectiveness of various capacitor and capacitor/ferrite bead bypassing
strategies. The page may be viewed at
http://www.cliftonlaboratories.com/bypassing.htm

Jack K8ZOA
K2 SN 5689
www.cliftonlaboratories.com
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

Craig Smith

RE: Bypassing and Filtering Measurements

A very nice piece of work Jack! Thanks for sharing it. I really like the
photos - kind of like I was right there.

I can confirm all of your conclusions based on my day job work. One
additional thing to mention that some might not be aware of is that it is
also good to parallel multiple capacitors of the same type/value. In a very
fortuitous way the capacitance adds while the equivalent series resistance
and inductance gets smaller and smaller ;>)

73
... Craig AC0DS

<> I've added a new page to my web site presenting measurements of the
<> effectiveness of various capacitor and capacitor/ferrite bead bypassing
<> strategies. The page may be viewed at
<> http://www.cliftonlaboratories.com/bypassing.htm
<>
<> Jack K8ZOA
<> K2 SN 5689
<> www.cliftonlaboratories.com

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

Jack Smith-6

Re: Bypassing and Filtering Measurements

Thanks for the nice words. Rereading the page this morning, I found a
couple small errors that are now fixed, and I added an image of the
Steward ferrite bead response curve from the data sheet.

The page is http://www.cliftonlaboratories.com/bypassing.htm

Jack K8ZOA
www.cliftonlaboratories.com

Craig D. Smith wrote:

> A very nice piece of work Jack! Thanks for sharing it. I really like the
> photos - kind of like I was right there.
>
> I can confirm all of your conclusions based on my day job work. One
> additional thing to mention that some might not be aware of is that it is
> also good to parallel multiple capacitors of the same type/value. In a very
> fortuitous way the capacitance adds while the equivalent series resistance
> and inductance gets smaller and smaller ;>)
>
> 73
> ... Craig AC0DS
>
> <> I've added a new page to my web site presenting measurements of the
> <> effectiveness of various capacitor and capacitor/ferrite bead bypassing
> <> strategies. The page may be viewed at
> <> http://www.cliftonlaboratories.com/bypassing.htm
> <>
> <> Jack K8ZOA
> <> K2 SN 5689
> <> www.cliftonlaboratories.com
>
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>