Rf in the shack distorting audio

classic Classic list List threaded Threaded
15 messages Options
Reply | Threaded
Open this post in threaded view
|

Rf in the shack distorting audio

Solosko, Robert B (Bob)
Hello All,

        Several month ago, after I finished my KPA100, I found that when
transmitting SSB on the higher bands (20, 17 & 15), the computer
speakers across the room, when turned on, would screech - adjusting the
speaker volume had no effect (but turning off the speakers quieted
them).  During a QSO a few weeks ago, it was commented that it sounded
like I was getting RF into my audio.

        To make a short story long, I don't have a very good ground
system, so there's a high level of RF in the shack - the shack is on the
2nd floor, about 18 ft above the ground rod. My primary antenna is a 100
ft multiband horizontal dipole feed with ladder line into a 9:1 balun,
which is connected to my KAT100 via 6' of RG8. While the antenna works
great on all bands (the KAT100 has no trouble tuning it), there's a
fairly high SWR on the feedline on the higher bands. I have two
different length wires connected the ground rod to the KAT100, and
adding counterpoises for 20, 17 & 15 meters hasn't change the high level
of RF in the shack on these bands.

        A week or two ago, I put up a second antenna, a vertical
parallel dipole for 20, 17 & 15 meters, fed with RG8 - this antenna has
very low SWR on these bands. When using this antenna, I have no problems
with the computer speakers screeching, so there's apparently not much RF
in the shack. This weekend, during the NA QSO party, when using the
ladder line fed dipole on the higher bands, several times, I was told
that my audio was distorted, and switching to the vertical coax fed
dipole immediately cured the problem.

        So, the question is, what can be done to fix the distorted audio
when there a high level of RF in the shack (besides getting a better
ground system - I plan to put in one or two more ground rods, but I
won't be able to do that until after the ground defrosts in the spring).
The mic I'm using is a RadioShack Electret replacement element in an old
mobile mic case - the case is plastic and not shielded, but the cable is
shielded, and I have grounded the mike jack in my K2.

        All suggestions about how I can eliminate the distortion will be
greatly welcomed,  as well as suggestions about how I can reduce the
high level of RF in the shack besides adding more ground rods.

        Thanks

Bob W1SRB
_______________________________________________
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

Reply | Threaded
Open this post in threaded view
|

Re: Rf in the shack distorting audio

R. Torsten Clay
> So, the question is, what can be done to fix the distorted audio
> when there a high level of RF in the shack (besides getting a better
> ground system - I plan to put in one or two more ground rods, but I
> won't be able to do that until after the ground defrosts in the spring).
> The mic I'm using is a RadioShack Electret replacement element in an old
> mobile mic case - the case is plastic and not shielded, but the cable is
> shielded, and I have grounded the mike jack in my K2.
>
> All suggestions about how I can eliminate the distortion will be
> greatly welcomed,  as well as suggestions about how I can reduce the
> high level of RF in the shack besides adding more ground rods.
>

I had similar problems, and they were cured by adding an RF choke to the
SSB module:

http://www.ac6rm.net/mailarchive/html/elecraft-list/2004-07/msg00453.html

Tor
N4OGW

_______________________________________________
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

Reply | Threaded
Open this post in threaded view
|

Re: Rf in the shack distorting audio

David A. Belsley
In reply to this post by Solosko, Robert B (Bob)
Robert:
   This problem is easily fixed.  Add a counterpoise for each band on  
which you operate.  The counterpoise is simply a 1/4 wave length of  
wire for the particular band.  Attach one end of the wire to your  
K2's ground, run the wire as inconspicuously as possible, keeping it  
out of reach of animals, children, etc.  Be sure the far end, which  
can have quite high rf voltages, is well insulated -- and the more  
isolated from other electronic items the better.  If you operate  
multibands, you may run your separate counterpoises together over  
part of their stretch, but separate the last several feet of each  
from the others, and insulate well.

best wishes,

david belsley, w1euy

On Jan 22, 2007, at 12:56 PM, Solosko, Robert B (Bob) wrote:

> Hello All,
>
> Several month ago, after I finished my KPA100, I found that when
> transmitting SSB on the higher bands (20, 17 & 15), the computer
> speakers across the room, when turned on, would screech - adjusting  
> the
> speaker volume had no effect (but turning off the speakers quieted
> them).  During a QSO a few weeks ago, it was commented that it sounded
> like I was getting RF into my audio.
>
> To make a short story long, I don't have a very good ground
> system, so there's a high level of RF in the shack - the shack is  
> on the
> 2nd floor, about 18 ft above the ground rod. My primary antenna is  
> a 100
> ft multiband horizontal dipole feed with ladder line into a 9:1 balun,
> which is connected to my KAT100 via 6' of RG8. While the antenna works
> great on all bands (the KAT100 has no trouble tuning it), there's a
> fairly high SWR on the feedline on the higher bands. I have two
> different length wires connected the ground rod to the KAT100, and
> adding counterpoises for 20, 17 & 15 meters hasn't change the high  
> level
> of RF in the shack on these bands.
>
> A week or two ago, I put up a second antenna, a vertical
> parallel dipole for 20, 17 & 15 meters, fed with RG8 - this antenna  
> has
> very low SWR on these bands. When using this antenna, I have no  
> problems
> with the computer speakers screeching, so there's apparently not  
> much RF
> in the shack. This weekend, during the NA QSO party, when using the
> ladder line fed dipole on the higher bands, several times, I was told
> that my audio was distorted, and switching to the vertical coax fed
> dipole immediately cured the problem.
>
> So, the question is, what can be done to fix the distorted audio
> when there a high level of RF in the shack (besides getting a better
> ground system - I plan to put in one or two more ground rods, but I
> won't be able to do that until after the ground defrosts in the  
> spring).
> The mic I'm using is a RadioShack Electret replacement element in  
> an old
> mobile mic case - the case is plastic and not shielded, but the  
> cable is
> shielded, and I have grounded the mike jack in my K2.
>
> All suggestions about how I can eliminate the distortion will be
> greatly welcomed,  as well as suggestions about how I can reduce the
> high level of RF in the shack besides adding more ground rods.
>
> Thanks
>
> Bob W1SRB
> _______________________________________________
> 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

--------------------------------------------
david a belsley
professor of economics
boston college


_______________________________________________
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

Reply | Threaded
Open this post in threaded view
|

RFI Tutorial

Jim Brown-10
In reply to this post by Solosko, Robert B (Bob)
>To make a short story long, I don't have a very good ground
>system, so there's a high level of RF in the shack

Hi Bob,

I've been working on a tutorial on RFI that is currently at the
advanced draft stage. It is posted on my website as a pdf.

The lack of, or quality of, a connection to mother earth is NOT the
cause of your problems.  

The REAL cause of most "RF in the shack" problems is a "pin 1
problem" in one or more pieces of equipment. Most ham gear
(including the K2), and most consumer products, are built with
designed-in pin 1 problems. See the tutorial for details.

http://audiosystemsgroup.com/RFI-Ham.pdf

73,

Jim Brown K9YC



_______________________________________________
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

Reply | Threaded
Open this post in threaded view
|

RE: Rf in the shack distorting audio

Don Wilhelm-3
In reply to this post by Solosko, Robert B (Bob)
Bob,

You counterpoises - are they 1/4 wave long at each of those bands?  Are the
far ends isolated?  Are the far ends seaprated for the various bands?  The
answer to each of these questions should be yes.

It is difficult to achieve a good RF Ground with a long run to a ground rod.
At frequencies where the length of wire to the ground rod is 1/4 wavelength,
there will be a high impedance to RF at those frequencies - a 16 foot run to
the ground rod would actually create a high impedance at 14 MHz in your
shack.  In that case, the counterpoise wires are a better solution.  You may
want to try connecting the counterpoise wires to the coax side of your
balun.

You could try inductors in series with the AF line in the K2 to get rid of
the distorted audio, but the real solution is to get the RF out of the
shack.

I wonder why you are using a 9:1 balun?  You may be better off using a 1:1
balun instead.  Yes, I know that 50 times 9 is 450, but that is only the
characteristic impedance of your feedline - the feedpoint impedance will be
quite different than 450 ohms, and may vary from very low to very high
depending on the frequency.  It just may be that your 9:1 balun is creating
more RF in the shack.  If you have no 1:1 balun available, try removing the
balun and connect the feeders to the center conductor and shield of your
coax - and connect your counterpoises to the shield at that point too - you
may find your RF in the shack will drop dramatically.

73,
Don W3FPR

> -----Original Message-----
>
> To make a short story long, I don't have a very good ground
> system, so there's a high level of RF in the shack - the shack is on the
> 2nd floor, about 18 ft above the ground rod. My primary antenna is a 100
> ft multiband horizontal dipole feed with ladder line into a 9:1 balun,
> which is connected to my KAT100 via 6' of RG8. While the antenna works
> great on all bands (the KAT100 has no trouble tuning it), there's a
> fairly high SWR on the feedline on the higher bands. I have two
> different length wires connected the ground rod to the KAT100, and
> adding counterpoises for 20, 17 & 15 meters hasn't change the high level
> of RF in the shack on these bands.
>
> A week or two ago, I put up a second antenna, a vertical
> parallel dipole for 20, 17 & 15 meters, fed with RG8 - this antenna has
> very low SWR on these bands. When using this antenna, I have no problems
> with the computer speakers screeching, so there's apparently not much RF
> in the shack. This weekend, during the NA QSO party, when using the
> ladder line fed dipole on the higher bands, several times, I was told
> that my audio was distorted, and switching to the vertical coax fed
> dipole immediately cured the problem.
>
> So, the question is, what can be done to fix the distorted audio
> when there a high level of RF in the shack (besides getting a better
> ground system - I plan to put in one or two more ground rods, but I
> won't be able to do that until after the ground defrosts in the spring).
> The mic I'm using is a RadioShack Electret replacement element in an old
> mobile mic case - the case is plastic and not shielded, but the cable is
> shielded, and I have grounded the mike jack in my K2.
>
> All suggestions about how I can eliminate the distortion will be
> greatly welcomed,  as well as suggestions about how I can reduce the
> high level of RF in the shack besides adding more ground rods.
>
> Thanks
>
> Bob W1SRB
>
--
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.5.432 / Virus Database: 268.17.4/644 - Release Date: 1/22/2007
7:30 AM

_______________________________________________
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

Reply | Threaded
Open this post in threaded view
|

Re: Rf in the shack distorting audio

Stuart Rohre
In reply to this post by Solosko, Robert B (Bob)
Bob, you need quarter wave insulated radials in the shack right at the rig
ground post to eliminate the hot rf problem on each high band.   Connected
at the ground rod, they do no good, since that is 18 feet ? away from the RF
source, (Rig).  Also, how close is your antenna to the rig?  Making that
maximum distance separation helps.

Stuart
K5KVH


_______________________________________________
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

Reply | Threaded
Open this post in threaded view
|

RE: Rf in the shack distorting audio

Ron D'Eau Claire-2
In reply to this post by Don Wilhelm-3
Don, W3FPR wrote:

I wonder why you are using a 9:1 balun?  You may be better off using a 1:1
balun instead.  Yes, I know that 50 times 9 is 450, but that is only the
characteristic impedance of your feedline - the feedpoint impedance will be
quite different than 450 ohms, and may vary from very low to very high
depending on the frequency.  It just may be that your 9:1 balun is creating
more RF in the shack.  If you have no 1:1 balun available, try removing the
balun and connect the feeders to the center conductor and shield of your
coax - and connect your counterpoises to the shield at that point too - you
may find your RF in the shack will drop dramatically.

------------------------------------

To follow up Don's comments, I've fed open wire line from a so-called
"unbalanced" output with *no* balun and RF ammeters in each leg of the
feeders showed that the currents were still balanced. The currents *inside*
a coax line are balanced. The current flowing inside the shield is equal and
opposite the current on the outer surface of the center conductor. Where
things go awry is where the coax shield ends and RF can flow around the end
onto the outside. Now there's two loads on those currents: one is the
antenna and the other is whatever is connected to the outside of the coax
shield, including the rig.

If that sounds confusing, remember that RF does not flow *in* a conductor,
but only along the surface. So the RF currents flowing along the inside of
the coax (or inside your rig near the antenna connector) are totally
independent of any RF currents flowing on the outside of the coax (or on the
outside surface of the rig). It's those outside currents that tend to cause
most of the problems. It's those outside currents you upset when you touch
the rig and so detune the system or give yourself an RF "bite" (Ouch!). It's
those outside currents that get inductively coupled into things like speaker
wires, telephones, microphones, etc., and cause mischief.  

A balun is just a length of transmission line, sufficiently long that any
unbalance at one end is "smoothed out" by the interaction between the RF
fields around the wires before RF currents get to the other end. Years ago,
we made a balun by winding up transmission line in a big coil. Sometimes we
wound each leg into its own coil and sometimes both legs were wound next to
each other in one huge 'bifilar' coil. For HF an open wire balun might be 4
to 6 inches in diameter and a foot or two long. (It was common to mount them
on standoff insulators on a large board and screw it to the wall!) Nowadays
we use ferrite cores that give us the inductance needed in a much smaller
space, but the operation is the same. If you look at a 1:1 balun schematic,
it's easy to see how it's a coiled-up two-wire transmission line. Other
baluns, offering various impedance conversions, are also simply coiled-up
transmission lines; usually two or three interconnected to provide the
impedance conversion wanted. You could achieve the same impedance
conversions with sections of open wire stretched out and interconnected. It
would work exactly the same way, but take up a fair bit of space!

So all you're doing when you add a balun to the end of a piece of coax (or
at the "unbalanced" output of a rig) is you're isolating one end from the
other  by imposing a long section of transmission line between them. The
simple fact is that, if it's long enough, the open wire transmission line
itself will do the same thing *if* the antenna is balanced. If it's an off
center fed doublet or other inherently unbalanced antenna, the feeder
currents won't be balanced no matter what you do. That doesn't make the
feeder inherently lossy. The worst is that the feeders will tend to radiate
a bit, depending upon the degree of unbalance.  

The solution to unwanted RF on the outside of the rig is to stop the
currents from flowing on the outside of the coax shield and the rig. Usually
they get there by flowing out of the open end of the coax at the transition
to the open wire line and around the edge right onto the outer surface.
Sometimes a balun will provide enough isolation that the surface currents
don't cause trouble, but sometimes not. Another way to reduce those currents
is to put some ferrite beads over the coax. A number of companies sell
ferrite beads for just that purpose. Some even provide a complete cable
assembly with the beads installed. Those beads show a very high impedance to
any RF currents on the outside of the shield, stopping or reducing them
drastically. Your rig still is not "grounded" for RF, but you don't care.
There's no RF to cause trouble on the rig anyway.

Another approach many installations use is to have a long section of coax
coiled up to act as an effective balun because the currents on the outside
experience the coil as an inductor with reactance that stops them while the
currents on the inside of the coax only "see" the transmission line and are
unaffected by the fact it's wound up in a coil. (It's important the coil be
solenoidal and single-layer so the input end is well isolated from the
output end. A jumble of coax is not very effective). That's *not* a good
idea for you because you're operating the coax at a high SWR, so you have
significant losses for every foot of coax you have in the system. Keep the
coax as short as possible!

Ron AC7AC

_______________________________________________
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

Reply | Threaded
Open this post in threaded view
|

RE: Rf in the shack distorting audio

Solosko, Robert B (Bob)
In reply to this post by Solosko, Robert B (Bob)
Thanks for all of the very good information and suggestions. My
counterpoise had been several wires running together - I wasn't aware of
the need to separate the ends. So, I removed the counterpoise that I had
and made 3 new separate ones, 1/4 wave for 15, 17 & 20 meters, cut for
the middle of the phone band on each. These are attached to the
grounding screw on my KAT100 and run in 3 different directions... and
guess what? The problem is still there. Measuring with my field strength
meter, there appears to be no appreciable difference in the level of RF
in the shack on these bands.

On to the next things to try, which will have to wait until the weekend
when I can hang out of my window during daylight. The next things I'll
try are 1) attach the counterpoises directly to the coax ground on the
balun, 2) replace the 9:1 voltage balun with a 4:1/1:1 current balun, 3)
running more, and different lengths of wire from the KAT100 to the
ground rod (although if the counterpoises have little affect, would this
have any different affect?) 4) changing the length of ladder line to the
balun and the length of coax from the balun to the KAT100 (I don't have
a lot of room for flexibility here). I'll let you know the results.

Thanks again for all of the information and suggestion.

Bob W1SRB

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Solosko, Robert B
(Bob)
Sent: Monday, January 22, 2007 12:57 PM
To: [hidden email]
Subject: [Elecraft] Rf in the shack distorting audio

Hello All,

        Several month ago, after I finished my KPA100, I found that when
transmitting SSB on the higher bands (20, 17 & 15), the computer
speakers across the room, when turned on, would screech - adjusting the
speaker volume had no effect (but turning off the speakers quieted
them).  During a QSO a few weeks ago, it was commented that it sounded
like I was getting RF into my audio.

        To make a short story long, I don't have a very good ground
system, so there's a high level of RF in the shack - the shack is on the
2nd floor, about 18 ft above the ground rod. My primary antenna is a 100
ft multiband horizontal dipole feed with ladder line into a 9:1 balun,
which is connected to my KAT100 via 6' of RG8. While the antenna works
great on all bands (the KAT100 has no trouble tuning it), there's a
fairly high SWR on the feedline on the higher bands. I have two
different length wires connected the ground rod to the KAT100, and
adding counterpoises for 20, 17 & 15 meters hasn't change the high level
of RF in the shack on these bands.

        A week or two ago, I put up a second antenna, a vertical
parallel dipole for 20, 17 & 15 meters, fed with RG8 - this antenna has
very low SWR on these bands. When using this antenna, I have no problems
with the computer speakers screeching, so there's apparently not much RF
in the shack. This weekend, during the NA QSO party, when using the
ladder line fed dipole on the higher bands, several times, I was told
that my audio was distorted, and switching to the vertical coax fed
dipole immediately cured the problem.

        So, the question is, what can be done to fix the distorted audio
when there a high level of RF in the shack (besides getting a better
ground system - I plan to put in one or two more ground rods, but I
won't be able to do that until after the ground defrosts in the spring).
The mic I'm using is a RadioShack Electret replacement element in an old
mobile mic case - the case is plastic and not shielded, but the cable is
shielded, and I have grounded the mike jack in my K2.

        All suggestions about how I can eliminate the distortion will be
greatly welcomed,  as well as suggestions about how I can reduce the
high level of RF in the shack besides adding more ground rods.

        Thanks

Bob W1SRB
_______________________________________________
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

Reply | Threaded
Open this post in threaded view
|

Re: Rf in the shack distorting audio

Stuart Rohre
Bob,
The length of conductor from the rig chassis to the eventual ground rod,
including the length of the rod to the physical dirt, all makes a resonant
system.  If such a "ground" lead is 1/4 wave or a substantial length at a
given band, you will have a poor RF ground.

As someone said, you need to find out if your antenna is causing the RF to
appear in your shack.
First is the antenna a dipole, and therefore balanced?

Next, is the antenna remote from the shack, not just over the roof just over
the shack?

Are both legs of the dipole, if it is, equally spaced from nearby metal and
conductors, including foliage, trees, buildings, etc.?

What are you feeding the antenna with?  Are you feeding with coax to a
balanced antenna?

These are all thought questions to get you thinking in terms of what is
resonating to cause this RF to appear?  How is it getting from the antenna,
feeder, or rig to the undesired places?  The fact that adding quarter wave
elements did not change it, says the point at which you added quarter waves
was not the point where the RF was strongest.

Don't forget the effect of your AC wiring, it can function as an antenna if
its legs make quarter wave resonant lengths on ham bands.

Simplify your set up to just the rig, tuner and antenna, and work backwards
to add in any computer, jumper cables, other cabling, like phone, or
lighting, and see if there are complex paths the RF is taking.

The ARRL publishes a book on tracking RFI problems and eliminating them.

Make sure any grounding screws holding chassis boxes and cases onto the
radio are really conductors by loosening them slightly, then retightening
them, to break any buildup of oxides.

Make sure you have proper connections of low impedance on the mike cable and
its plug.  Is the mike cable shielded?  Sometimes there is a press to talk
pair in a mike, and separately, the audio line shield and those should not
be bonded together in some cases.  Have you tried another mike and its
cable?

Well, that is a start at some diagnostics.

GL and 73,
Stuart
K5KVH


_______________________________________________
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

Reply | Threaded
Open this post in threaded view
|

RE: Rf in the shack distorting audio - the results

Solosko, Robert B (Bob)
In reply to this post by Solosko, Robert B (Bob)
 Hello All,

        Several weeks ago, I posted the attached e-mail describing my
problems with RF in the shack distorting the audio when transmitting. I
received many responses with good suggestions about how the cure the
problem -- thank you to all of you who responded, and especially thank
you to Don, the "Friendly, Patient Radioman", with whom I subsequently
had an e-mail dialog about the design of by balun and the materials
used.

        The results: problem cured!

        The first thing I did was move the counterpoises from the ground
on the KAT100 to the ground side of the coax where it connects to the
balun. That had the most effect, significantly reducing the level of RF
in the shack, as measured by my field strength meter, and mostly
eliminated the RF getting into the computer speakers.

        The next thing was to use the 4:1 taps on my voltage balun
instead of the 9:1 taps - that reduced the RF level a little more, at
the expense of the KAT100 not being able to get down to a 1:1 SWR on
15m; the lowest SWR achieved was about 2:1 (I was using the 9:1 taps
because the KAT100 could get down to essentially 1:1 on all bands).

        Next, AA1SB gave me a few toroid cores of unknown type that were
just large enough to fit over a PN-259 connector- I slipped them over
the coax where it connects to the balun. That made a slight difference
in the RF level on 10m, but had no other affect on any other bands.

        The final step was to replace my 9:1/4:1 voltage balun, made
using a T300A-1 core, with a 4:1/1:1 current balun made using a pair of
FT-240-43 baluns. Don, W3FPR, had suggested that the FT material in a
current balun would be much more effective at eliminating the RF
problem. I finally got this current balun made and installed this
weekend, and just as Don predicted, the RF in the shack is essentially
completely eliminated. Also, the KAT100 now can achieve a 1:1 SWR on
15m. However, you don't get something for nothing - with this balun, I
lost the upper 40 kHz of 160m... The KAT100 doesn't get the SWR down
below 9:1 and just gives up. But, below that, there is about a 10kHz
range over which the minimum SWR that the KAT100 can achieve goes from
1:1 to 9:1. This is not quite surprising since my antenna is a 100'
shortened multi-band dipole which by design has a very narrow bandwidth
on 160M. Furthermore, the inductance of the 4:1 current balun made with
the FT material is about 50 times greater than the 9:1 voltage balun I
made. On 160m the balun impedance was likely less that the impedance at
the balun end or the ladder line (the rule of thumb is that the balun
impedance should be at least 4 times the impedance at the balun
input)... So, it's likely that the KAT100 was really tuning to the balun
impedance and not the antenna impedance. However, with the new 4:1
current balun, the balun impedance shouldn't be much of a factor and the
KAT100 is probably seeing more of the actual characteristics of the
antenna... And, now that I think of it, all of the few QSOs that I've
had on 160m have been below the upper 50kHz or so.

        So, thank you all again - I'm very satisfied with the results.

Bob W1SRB

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Solosko, Robert B
(Bob)
Sent: Monday, January 22, 2007 12:57 PM
To: [hidden email]
Subject: [Elecraft] Rf in the shack distorting audio

Hello All,

        Several month ago, after I finished my KPA100, I found that when
transmitting SSB on the higher bands (20, 17 & 15), the computer
speakers across the room, when turned on, would screech - adjusting the
speaker volume had no effect (but turning off the speakers quieted
them).  During a QSO a few weeks ago, it was commented that it sounded
like I was getting RF into my audio.

        To make a short story long, I don't have a very good ground
system, so there's a high level of RF in the shack - the shack is on the
2nd floor, about 18 ft above the ground rod. My primary antenna is a 100
ft multiband horizontal dipole feed with ladder line into a 9:1 balun,
which is connected to my KAT100 via 6' of RG8. While the antenna works
great on all bands (the KAT100 has no trouble tuning it), there's a
fairly high SWR on the feedline on the higher bands. I have two
different length wires connected the ground rod to the KAT100, and
adding counterpoises for 20, 17 & 15 meters hasn't change the high level
of RF in the shack on these bands.

        A week or two ago, I put up a second antenna, a vertical
parallel dipole for 20, 17 & 15 meters, fed with RG8 - this antenna has
very low SWR on these bands. When using this antenna, I have no problems
with the computer speakers screeching, so there's apparently not much RF
in the shack. This weekend, during the NA QSO party, when using the
ladder line fed dipole on the higher bands, several times, I was told
that my audio was distorted, and switching to the vertical coax fed
dipole immediately cured the problem.

        So, the question is, what can be done to fix the distorted audio
when there a high level of RF in the shack (besides getting a better
ground system - I plan to put in one or two more ground rods, but I
won't be able to do that until after the ground defrosts in the spring).
The mic I'm using is a RadioShack Electret replacement element in an old
mobile mic case - the case is plastic and not shielded, but the cable is
shielded, and I have grounded the mike jack in my K2.

        All suggestions about how I can eliminate the distortion will be
greatly welcomed,  as well as suggestions about how I can reduce the
high level of RF in the shack besides adding more ground rods.

        Thanks

Bob W1SRB
_______________________________________________
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

Reply | Threaded
Open this post in threaded view
|

Re: Rf in the shack distorting audio - the results

Lowell-8
I found your solutions to curing RF in the shack very interesting.  I have a
similiar problem to yours and would appreciate info on the 4:1/1:1 Current
balun.  Thanks
                         Lowell, W5FH
----- Original Message -----
From: "Solosko, Robert B (Bob)" <[hidden email]>
To: "Solosko, Robert B (Bob)" <[hidden email]>;
<[hidden email]>
Sent: Wednesday, February 21, 2007 11:57 AM
Subject: RE: [Elecraft] Rf in the shack distorting audio - the results


Hello All,

Several weeks ago, I posted the attached e-mail describing my
problems with RF in the shack distorting the audio when transmitting. I
received many responses with good suggestions about how the cure the
problem -- thank you to all of you who responded, and especially thank
you to Don, the "Friendly, Patient Radioman", with whom I subsequently
had an e-mail dialog about the design of by balun and the materials
used.

The results: problem cured!

The first thing I did was move the counterpoises from the ground
on the KAT100 to the ground side of the coax where it connects to the
balun. That had the most effect, significantly reducing the level of RF
in the shack, as measured by my field strength meter, and mostly
eliminated the RF getting into the computer speakers.

The next thing was to use the 4:1 taps on my voltage balun
instead of the 9:1 taps - that reduced the RF level a little more, at
the expense of the KAT100 not being able to get down to a 1:1 SWR on
15m; the lowest SWR achieved was about 2:1 (I was using the 9:1 taps
because the KAT100 could get down to essentially 1:1 on all bands).

Next, AA1SB gave me a few toroid cores of unknown type that were
just large enough to fit over a PN-259 connector- I slipped them over
the coax where it connects to the balun. That made a slight difference
in the RF level on 10m, but had no other affect on any other bands.

The final step was to replace my 9:1/4:1 voltage balun, made
using a T300A-1 core, with a 4:1/1:1 current balun made using a pair of
FT-240-43 baluns. Don, W3FPR, had suggested that the FT material in a
current balun would be much more effective at eliminating the RF
problem. I finally got this current balun made and installed this
weekend, and just as Don predicted, the RF in the shack is essentially
completely eliminated. Also, the KAT100 now can achieve a 1:1 SWR on
15m. However, you don't get something for nothing - with this balun, I
lost the upper 40 kHz of 160m... The KAT100 doesn't get the SWR down
below 9:1 and just gives up. But, below that, there is about a 10kHz
range over which the minimum SWR that the KAT100 can achieve goes from
1:1 to 9:1. This is not quite surprising since my antenna is a 100'
shortened multi-band dipole which by design has a very narrow bandwidth
on 160M. Furthermore, the inductance of the 4:1 current balun made with
the FT material is about 50 times greater than the 9:1 voltage balun I
made. On 160m the balun impedance was likely less that the impedance at
the balun end or the ladder line (the rule of thumb is that the balun
impedance should be at least 4 times the impedance at the balun
input)... So, it's likely that the KAT100 was really tuning to the balun
impedance and not the antenna impedance. However, with the new 4:1
current balun, the balun impedance shouldn't be much of a factor and the
KAT100 is probably seeing more of the actual characteristics of the
antenna... And, now that I think of it, all of the few QSOs that I've
had on 160m have been below the upper 50kHz or so.

So, thank you all again - I'm very satisfied with the results.

Bob W1SRB

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Solosko, Robert B
(Bob)
Sent: Monday, January 22, 2007 12:57 PM
To: [hidden email]
Subject: [Elecraft] Rf in the shack distorting audio

Hello All,

Several month ago, after I finished my KPA100, I found that when
transmitting SSB on the higher bands (20, 17 & 15), the computer
speakers across the room, when turned on, would screech - adjusting the
speaker volume had no effect (but turning off the speakers quieted
them).  During a QSO a few weeks ago, it was commented that it sounded
like I was getting RF into my audio.

To make a short story long, I don't have a very good ground
system, so there's a high level of RF in the shack - the shack is on the
2nd floor, about 18 ft above the ground rod. My primary antenna is a 100
ft multiband horizontal dipole feed with ladder line into a 9:1 balun,
which is connected to my KAT100 via 6' of RG8. While the antenna works
great on all bands (the KAT100 has no trouble tuning it), there's a
fairly high SWR on the feedline on the higher bands. I have two
different length wires connected the ground rod to the KAT100, and
adding counterpoises for 20, 17 & 15 meters hasn't change the high level
of RF in the shack on these bands.

A week or two ago, I put up a second antenna, a vertical
parallel dipole for 20, 17 & 15 meters, fed with RG8 - this antenna has
very low SWR on these bands. When using this antenna, I have no problems
with the computer speakers screeching, so there's apparently not much RF
in the shack. This weekend, during the NA QSO party, when using the
ladder line fed dipole on the higher bands, several times, I was told
that my audio was distorted, and switching to the vertical coax fed
dipole immediately cured the problem.

So, the question is, what can be done to fix the distorted audio
when there a high level of RF in the shack (besides getting a better
ground system - I plan to put in one or two more ground rods, but I
won't be able to do that until after the ground defrosts in the spring).
The mic I'm using is a RadioShack Electret replacement element in an old
mobile mic case - the case is plastic and not shielded, but the cable is
shielded, and I have grounded the mike jack in my K2.

All suggestions about how I can eliminate the distortion will be
greatly welcomed,  as well as suggestions about how I can reduce the
high level of RF in the shack besides adding more ground rods.

Thanks

Bob W1SRB
_______________________________________________
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


--
No virus found in this incoming message.
Checked by AVG Free Edition.
Version: 7.5.441 / Virus Database: 268.18.3/694 - Release Date: 2/20/2007
1:44 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

Reply | Threaded
Open this post in threaded view
|

RE: Rf in the shack distorting audio - the results

Don Wilhelm-3
Lowell,

Look at the Elecraft BL2 for a switchable 1:1/4:1 balun, it will handle up
to 250 watts.  If you do not need the switchable arrangement, the BL1 can be
constructed for either a 1:1 or a 4:1 configuration and its power rating is
150 watts.  A convenient ground lug is located on the balun output side.

Look on the Elecraft website - click Our Products, and from there click on
Mini-module kits.

73,
Don W3FPR


> -----Original Message-----
>
> I found your solutions to curing RF in the shack very
> interesting.  I have a
> similiar problem to yours and would appreciate info on the
> 4:1/1:1 Current
> balun.  Thanks
>                          Lowell, W5FH
>
--
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.5.441 / Virus Database: 268.18.3/697 - Release Date: 2/22/2007
11:55 AM

_______________________________________________
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

Reply | Threaded
Open this post in threaded view
|

RE: Rf in the shack distorting audio - the results

Solosko, Robert B (Bob)
 Lowell,
       
        Don is giving some good advice here, as usual. The circuit of
balun that I built is essentially identical to the BL2. I made mine
using two FT-240-43 toroid cores - I needed a balun in a watertight box
since it located outside in the rain and snow. I also wanted a balun
that can handle more power than the BL2, since I aspire to higher power
when I grow up. The one I made uses 12 bifilar turns of #12 wire, and
should easily handle a kW. A diagram of this two core balun is found on
page 26-24 of the ARRL antenna book (the same diagram is also in the
transmission line section of my 1999 edition of the ARRL handbook). I
mounted the two toroids in a plastic box from Radio Shack, with a coax
connector on one side and screw terminals for the ladder line on the
another side, plus a screw terminal for the ground connection for the
counterpoises. If you look at the schematic on the BL2, several of the
toroid leads go the switch. In place of the switch, I brought those
leads out to screw terminals and use one external jumper between screw
terminal for the 4:1 configuration, and two external jumpers between
from the other screw terminals for the 1:1 configuration. With wing nuts
on these jumper screw terminals, I can quickly switch between the 1:1
and 4:1 configurations (for my home setup, I just keep the balun in the
4:1 configuration - the quick change ability I use when I take the K2 on
the road with antennas that the characteristics will change depending on
the trees they're attached to) - of course, you can put the BL2 in a
watertight box, but then you don't have easy access to the 1:1/4:1
switch, which in a fix setup you probable don't need to change often
anyway.

73

Bob W1SRB

-----Original Message-----
From: Don Wilhelm [mailto:[hidden email]]
Sent: Thursday, February 22, 2007 12:44 PM
To: Lowell; Solosko, Robert B (Bob); [hidden email]
Subject: RE: [Elecraft] Rf in the shack distorting audio - the results

Lowell,

Look at the Elecraft BL2 for a switchable 1:1/4:1 balun, it will handle
up to 250 watts.  If you do not need the switchable arrangement, the BL1
can be constructed for either a 1:1 or a 4:1 configuration and its power
rating is 150 watts.  A convenient ground lug is located on the balun
output side.

Look on the Elecraft website - click Our Products, and from there click
on Mini-module kits.

73,
Don W3FPR


> -----Original Message-----
>
> I found your solutions to curing RF in the shack very interesting.  I
> have a similiar problem to yours and would appreciate info on the
> 4:1/1:1 Current
> balun.  Thanks
>                          Lowell, W5FH
>
--
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.5.441 / Virus Database: 268.18.3/697 - Release Date:
2/22/2007
11:55 AM

_______________________________________________
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

Reply | Threaded
Open this post in threaded view
|

Re: Rf in the shack distorting audio - the results

Darrell Bellerive-2
In reply to this post by Don Wilhelm-3
On February 22, 2007 09:44 am, Don Wilhelm wrote:
> Look at the Elecraft BL2 for a switchable 1:1/4:1 balun, it will handle up
> to 250 watts.  If you do not need the switchable arrangement, the BL1 can
> be constructed for either a 1:1 or a 4:1 configuration and its power rating
> is 150 watts.  A convenient ground lug is located on the balun output side.

How can a balun be switchable from 1:1 or 4:1? Surely the characteristic
impedance of the windings will be missmatched at one of the settings.

--
Darrell Bellerive
Amateur Radio Stations VA7TO and VE7CLA
Grand Forks, British Columbia, Canada
_______________________________________________
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

Reply | Threaded
Open this post in threaded view
|

Re: Rf in the shack distorting audio - the results

Bob Nielsen

On Feb 23, 2007, at 9:29 AM, Darrell Bellerive wrote:

> On February 22, 2007 09:44 am, Don Wilhelm wrote:
>> Look at the Elecraft BL2 for a switchable 1:1/4:1 balun, it will  
>> handle up
>> to 250 watts.  If you do not need the switchable arrangement, the  
>> BL1 can
>> be constructed for either a 1:1 or a 4:1 configuration and its  
>> power rating
>> is 150 watts.  A convenient ground lug is located on the balun  
>> output side.
>
> How can a balun be switchable from 1:1 or 4:1? Surely the  
> characteristic
> impedance of the windings will be missmatched at one of the settings.

Actually the characteristic impedance of the windings will ideally be  
2*Z0.  For a 1:1 balun they will appear in parallel, while for 4:1  
they will appear to be in parallel at one port and in series at the  
other.

Bob, N7XY

_______________________________________________
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