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K3 Ground Loop Issues using Ameritron ARB-704

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Alfred Frugoli

K3 Ground Loop Issues using Ameritron ARB-704

I've just gotten my K3 built and integrated into the shack about a week
ago. Operated WPX CW this weekend with GREAT success. Was very happy.

Tonight in setting up FSK, I was getting a lot of "AGN?" after my cq's.
Listening to my signal on a 2nd receiver, I realized that my signal had a
hum on it - basically sounded terrible. Tested in CW mode as well, and the
hum was also there (haven't dug out the mic yet for the dreaded SSB mode to
know if the hum was there as well, but I would suspect it would have been).
Tried changing a bunch of menu settings to no avail. Then I disconnected
everything from the back of the K3 except for the antenna, power and FSK
input. Beautiful clean signal. The hum reappeared when I connected the amp
keying line.

I've been using the Ameritron ARB-704 Amp Keying buffer, and even though
the K3 can handle the relay voltage on my AL-80 (the key voltage is not in
the AL-80 manual, but I believe it's 125v), I've kept in in line. However
this seems to be the item causing the hum. When I take it out of the line,
and connect the rig directly to the amp, no hum.

My shack is NOT well RF grounded, and things are not bonded together at this
point (that's a needed project - but the ARB-704 doesn't have a ground post
to connect to - I'd have to go directly under one of the case screws to
ground it).

Anybody else experience this? Am I correct in my deduction that the K3 key
out relay will handle the relay voltage on the AL-80? If so, I'll just
ditch the ARB-704 for now.

Thanks.

73 de Al, KE1FO

-----
Visit my amateur radio contesting blog at ke1fo.wordpress.com.
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Guy, K2AV

Re: K3 Ground Loop Issues using Ameritron ARB-704

>From the K3 manual:
KEY OUT (RCA/Phono) is the amplifier T-R relay keying output, capable of
keying up to +200VDC @ 5A.

You do not need the buffer for any Ameritron amplifier. In particular the
AL-80 schematic shows the Relay jack connected to the 12V bus.

Leave the K3 key out jack connected directly to the AL-80 relay jack, and
enjoy life : >)

73, Guy

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

From: "Alfred Frugoli" <[hidden email]>
To: <[hidden email]>
Sent: Tuesday, June 02, 2009 9:55 PM
Subject: [Elecraft] K3 Ground Loop Issues using Ameritron ARB-704

> I've just gotten my K3 built and integrated into the shack about a week
> ago. Operated WPX CW this weekend with GREAT success. Was very happy.
>
> Tonight in setting up FSK, I was getting a lot of "AGN?" after my cq's.
> Listening to my signal on a 2nd receiver, I realized that my signal had a
> hum on it - basically sounded terrible. Tested in CW mode as well, and the
> hum was also there (haven't dug out the mic yet for the dreaded SSB mode
> to
> know if the hum was there as well, but I would suspect it would have
> been).
> Tried changing a bunch of menu settings to no avail. Then I disconnected
> everything from the back of the K3 except for the antenna, power and FSK
> input. Beautiful clean signal. The hum reappeared when I connected the
> amp
> keying line.
>
> I've been using the Ameritron ARB-704 Amp Keying buffer, and even though
> the K3 can handle the relay voltage on my AL-80 (the key voltage is not in
> the AL-80 manual, but I believe it's 125v), I've kept in in line. However
> this seems to be the item causing the hum. When I take it out of the
> line,
> and connect the rig directly to the amp, no hum.
>
> My shack is NOT well RF grounded, and things are not bonded together at
> this
> point (that's a needed project - but the ARB-704 doesn't have a ground
> post
> to connect to - I'd have to go directly under one of the case screws to
> ground it).
>
> Anybody else experience this? Am I correct in my deduction that the K3
> key
> out relay will handle the relay voltage on the AL-80? If so, I'll just
> ditch the ARB-704 for now.
>
> Thanks.
>
> 73 de Al, KE1FO

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Clark L. Stewart

Re: K3 Ground Loop Issues using Ameritron ARB-704

In reply to this post by Alfred Frugoli

At 09:55 PM 6/2/2009 -0400, Alfred Frugoli wrote:

Elecrafters,

My friend, KC8UHE, just received his brand-new K-3 and in helping him
set it up, we encountered a similar problem. But, we are not using the
ARB-704. This K-3 is connected to a microHAM microKEYER II using the
microHAM DB37-EL-K3R cable set.

When the headset microphone is connected to the microKEYER and the
Amplifier is connected to the microKEYER, a serious amount of hum is
present on the mike audio. This is evident both in TX TEST mode and in
on-the-air reports.

If the microphone is connected directly to the rear MIKE input on the
K-3, there is no hum even with the amplifier connected. If the microphone
is run through the microKEYER and NO amplifier is connected to the
microKEYER relay output, there is no hum.

This hum is present when connecting the microKEYER relay output
directly to either the Ameritron AL-82 or the Heathkit SB-200 which has
been converted to 6-M. (Only one amp is connected at a time.) Both amps
are connected to 220 VAC.

The microKEYER has been modified with the RFI "fix" on the USB
cable. And, we swapped out KC8UHE's microKEYER with my own microKEYER and
the hum is present with either microKEYER in line.

Mike level on the K-3 was 20, CMP was Ø, and the internal pots of the
microKEYER as well as the Router software were adjusted as per the
manual. The headset is a Heil Pro Set Plus using the HC-4 element.

Does anyone have a suggestion to cure this as it is not possible for
KC8UHE to operate his K-3 with either amp on SSB while this hum is
present. Thanks.

Clark, W8TN

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Joe Subich, W4TV-4

Re: K3 Ground Loop Issues using Ameritron ARB-704

How are the amplifiers wired? Is the neutral connected to the
chassis (does not meet UL standards)?

If the neutral is connected to the chassis (ground) you will
place any unbalance in the input power on the chassis (ground)
and a portion of that current will inevitably find its way IN
SERIES with the microphone due to the choke in the mic return
(mic ground).

First, to be code compliant, any amplifier that has a neutral
REQUIRES a four wire power cord (hot-Neutral-hot plus ground).
The neutral must be isolated from the chassis (safety ground)
and must be returned to the source (breaker panel) separately.
The neutral may not be tied to the amplifier chassis.

In the K3, the mic ground jumper MUST be installed on the Audio
I/O board as shown in the Elecraft RF Immunity modification:
<www.elecraft.com/K3/mods/ELECRAFT_Application_Note_Improving_the_Immunity_of_
the_Rear-Panel_KIO3_RS232_and_Audio_Connectors_to_RF.pdf> (see the
second item on page 3). If the jumper is not installed and
every piece of equipment is not grounded separately to a common
station ground, any common mode hum (e.g., hum on the chassis of
an amplifier often due to neutral currents) flows from box to
box through the shields of interconnect cables. When it reaches
the K3 it appears across the RF choke between the shield of the
rear panel microphone cable and the chassis (in series with the
microphone signal).

73,

... Joe, W4TV

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Clark
> L. Stewart
> Sent: Thursday, June 04, 2009 12:51 PM
> To: [hidden email]
> Subject: Re: [Elecraft] K3 Ground Loop Issues using Ameritron ARB-704
>
>
> At 09:55 PM 6/2/2009 -0400, Alfred Frugoli wrote:
> >I've just gotten my K3 built and integrated into the shack
> about a week
> >ago. Operated WPX CW this weekend with GREAT success. Was
> very happy.
> >
> >Tonight in setting up FSK, I was getting a lot of "AGN?"
> after my cq's.
> >Listening to my signal on a 2nd receiver, I realized that my
> signal had
> >a hum on it - basically sounded terrible. Tested in CW mode as well,
> >and the hum was also there (haven't dug out the mic yet for
> the dreaded
> >SSB mode to know if the hum was there as well, but I would
> suspect it
> >would have been). Tried changing a bunch of menu settings to
> no avail.
> >Then I disconnected everything from the back of the K3
> except for the
> >antenna, power and FSK input. Beautiful clean signal. The hum
> >reappeared when I connected the amp keying line.
> >
> ><<<< SNIP >>>>>
> >
> >Thanks.
> >
> >73 de Al, KE1FO
>
>
> Elecrafters,
>
> My friend, KC8UHE, just received his brand-new K-3 and
> in helping him
> set it up, we encountered a similar problem. But, we are not
> using the
> ARB-704. This K-3 is connected to a microHAM microKEYER II using the
> microHAM DB37-EL-K3R cable set.
>
> When the headset microphone is connected to the
> microKEYER and the
> Amplifier is connected to the microKEYER, a serious amount of hum is
> present on the mike audio. This is evident both in TX TEST
> mode and in
> on-the-air reports.
>
> If the microphone is connected directly to the rear
> MIKE input on the
> K-3, there is no hum even with the amplifier connected. If
> the microphone
> is run through the microKEYER and NO amplifier is connected to the
> microKEYER relay output, there is no hum.
>
> This hum is present when connecting the microKEYER relay output
> directly to either the Ameritron AL-82 or the Heathkit SB-200
> which has
> been converted to 6-M. (Only one amp is connected at a
> time.) Both amps
> are connected to 220 VAC.
>
> The microKEYER has been modified with the RFI "fix" on the USB
> cable. And, we swapped out KC8UHE's microKEYER with my own
> microKEYER and
> the hum is present with either microKEYER in line.
>
> Mike level on the K-3 was 20, CMP was Ø, and the
> internal pots of the
> microKEYER as well as the Router software were adjusted as per the
> manual. The headset is a Heil Pro Set Plus using the HC-4 element.
>
> Does anyone have a suggestion to cure this as it is not
> possible for
> KC8UHE to operate his K-3 with either amp on SSB while this hum is
> present. Thanks.
>
>
> Clark, W8TN
>
> ______________________________________________________________
> 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

W8ZN

Re: K3 Ground Loop Issues using Ameritron ARB-704

Haven't followed this too close until I saw Ameritron. W3ZZ had almost the exact issue very early after receiving his K3 when they first were released. For him the issue only showed hum on 160m but the problem turned out to be the QSK mod factory installed on his amp caused there to be a DC voltage on the RF coax between the K3 and the amp. Since there is no DC blocking cap between the antenna jack and the SWR bridge in the K3 (or at least then there wasn't) this caused the DC voltage to be grounded and caused the hum. I added a .01 HV ceramic disc right at the input jack of the amp.

Disconnect the amp completely from the K3. Measure the DC voltage from the center conductor of the coax coming from the amp to ground and key the amp. If there is any DC voltage there, you need to add a blocking cap.

YMMV - This is only what I found and it worked for him.

Terry
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P.B. Christensen

Re: K3 Ground Loop Issues using Ameritron ARB-704

In reply to this post by Joe Subich, W4TV-4

> "First, to be code compliant, any amplifier that has a neutral
REQUIRES a four wire power cord (hot-Neutral-hot plus ground).
The neutral must be isolated from the chassis (safety ground)
and must be returned to the source (breaker panel) separately.
The neutral may not be tied to the amplifier chassis."

The schematics for both the Ameritron AL-82 and Heathkit SB-200 amplifiers
show that no neutral is used, regardless of primary voltage setting. Amps
that utilize a neutral (e.g., ETO/Alpha 77 series & older Henry) make use of
a neutral only to power the 120 VAC blower. These amps require 4-wire
electrical service as W4TV states. They were designed and manufactured at a
time when little attention was paid to the ground v. neutral wiring
structure. A fault as a result of a neutral loss between the amp and
service panel causes the chassis to carry the full blower current. Anything
on the amp chassis that's grounded (e.g., SO-239, BNC, RCA) including a
grounded operator touching the amp will complete the current path.

Most amps do not utilize a neutral and use a jumpered center-tap transformer
primary to ensure that the amp's blower or fan works correctly on both 120
VAC and 240 VAC circuits.

Paul, W9AC

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Joe Subich, W4TV-4

Re: K3 Ground Loop Issues using Ameritron ARB-704

> The schematics for both the Ameritron AL-82 and Heathkit
> SB-200 amplifiers show that no neutral is used, regardless
> of primary voltage setting.

Unfortunately, the AL-82 and SB-200 both create a pseudo-neutral
by placing high voltage bypass capacitors from each line to the
chassis/ground. Unless the chassis is properly grounded to the
station common point ground along with every other piece of
equipment in the shack, the noise (hum) s still going to appear
in common mode on the shields/cases.

73,

... Joe, W4TV

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Paul
> Christensen
> Sent: Thursday, June 04, 2009 3:06 PM
> To: [hidden email]
> Subject: Re: [Elecraft] K3 Ground Loop Issues using Ameritron ARB-704
>
>
> > "First, to be code compliant, any amplifier that has a neutral
> REQUIRES a four wire power cord (hot-Neutral-hot plus
> ground). The neutral must be isolated from the chassis
> (safety ground) and must be returned to the source (breaker
> panel) separately. The neutral may not be tied to the
> amplifier chassis."
>
> The schematics for both the Ameritron AL-82 and Heathkit
> SB-200 amplifiers
> show that no neutral is used, regardless of primary voltage
> setting. Amps
> that utilize a neutral (e.g., ETO/Alpha 77 series & older
> Henry) make use of
> a neutral only to power the 120 VAC blower. These amps
> require 4-wire
> electrical service as W4TV states. They were designed and
> manufactured at a
> time when little attention was paid to the ground v. neutral wiring
> structure. A fault as a result of a neutral loss between
> the amp and
> service panel causes the chassis to carry the full blower
> current. Anything
> on the amp chassis that's grounded (e.g., SO-239, BNC, RCA)
> including a
> grounded operator touching the amp will complete the current path.
>
> Most amps do not utilize a neutral and use a jumpered
> center-tap transformer
> primary to ensure that the amp's blower or fan works
> correctly on both 120
> VAC and 240 VAC circuits.
>
> Paul, W9AC
>
>
>
>
>
>
>
> ______________________________________________________________
> 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

P.B. Christensen

Re: K3 Ground Loop Issues using Ameritron ARB-704

> Unfortunately, the AL-82 and SB-200 both create a pseudo-neutral
> by placing high voltage bypass capacitors from each line to the
> chassis/ground.

Right. The problem has been around at least since the early '30s. For the
caps used in the AL-82, that works out to about 0.5 mA of current per leg
diverted to ground. Possibly enough to cause audio problems, depending on
shack grounding configurations.

Somewhat surprising, commercial RFI/EMI AC line filters (e.g., Corcom) use
modular CM chokes, but also contain multiple HV bypass caps from line to
ground. I just checked Corcom's website and typical AC leakage from line
to ground for their 10A series filters is ~ 1.5 mA @ 250VAC and these
devices are routinely used in lab-grade instrumentation and audio
equipment.<g>

Paul, W9AC

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Jim Brown-10

Re: K3 Ground Loop Issues using Ameritron ARB-704

In reply to this post by Joe Subich, W4TV-4

On Thu, 4 Jun 2009 19:43:30 -0400, Joe Subich, W4TV wrote:

>Unfortunately, the AL-82 and SB-200 both create a pseudo-neutral
>by placing high voltage bypass capacitors from each line to the
>chassis/ground. Unless the chassis is properly grounded to the
>station common point ground along with every other piece of
>equipment in the shack, the noise (hum) s still going to appear
>in common mode on the shields/cases.

Actually, nearly ALL equipment powered from the AC line has
capacitance between phase and ground, thanks both to stray
capacitance in the power transformer and bypass capacitors that
are part of line filters. This capacitance couples leakage current
to the green wire (the equipment ground). The return path for this
current is to the power system ground via the breaker panel, so
there will be IR drop in the green wire. Because the coupling is
capacitive, most of this current consists of the harmonics of 60
Hz, and is what we commonly call "ground buzz."

As Joe and Paul have noted, some older power amps improperly
connect 120V fans between one side of 120V and the green wire. In
addition to the IR drop issues, there this current generates a 60
Hz hum field that can magnetically couple into the rig and/or
interconnect wiring. This field tends to be pure 60 Hz, so is
heard as HUM, not buzz.

For a more detailed analysis of both mechanisms, see

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

http://HamInterfacing.pdf

Another source of HUM is the magnetic field produced by the
transformers in big power supplies. The unshielded audio
transformers used in the K3 make it susceptible to strong magnetic
fields. The above tutorials show how to reliably interconnect ham
gear, computers, and other audio gear without transformers.

73,

Jim Brown K9YC

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