[Elecraft] K3S Audio buzz on transmit, especially AM

Sat Apr 27 19:18:50 EDT 2019

Hi Nick, 

You've done a good job organizing your tests and test results. 

One more question: how far is your transmitting antenna from 
your ham shack and other nearby homes? 

Very telling is this comment at the end of your email: 
"Transmitting into a dummy load *while* turning off all nearby power 
supplies and lights with the KX3 immediately adjacent the dummy load: nice, 
pristine signal" 

That certainly points to EMC issues in your environment. When you're 
ready for additional tests, first go back to your pristine signal case. 
Then -- one by one -- turn additional radio accessories and household 
on and reconnect them. Repeat your test each time you change 
something. 

I strongly suspect that you have a common EMI condition in your 
ham shack, probably elsewhere in your home and possibly in adjacent 
homes known as "RF FLOODING." 

What the heck is RF Flooding? When a strong RF signal enters a 
non-linear device (semiconductors most commonly, but also ferrites 
near saturation) that also carries other signals (most commonly AC 
power, but also computer related signals such as Ethernet), the 
non-linear device will mix the two signals together and reradiate 
them (including harmonics of the RF signal) on the wires connected 
to the non-linear device. 

Multi-operator and SO2R operator contest stations have experienced 
RF Flooding interference for decades, but the problem has become 
much worse as semiconductor devices have proliferated. Switching 
power supplies are among the worst offenders, especially wall-warts. 

If you have a RF flooding problem it will be especially apparent on 
the second and third harmonic of your transmitted signal. On the 
harmonic frequencies the buzz sidebands may be stronger than the 
transmitted harmonic. 

So what to do about it? If you don't intend to operate multi-operator 
or SO2R contests from your QTH, there's no reason to fix the problem 
at all. The buzz sidebands probably don't radiate more than a few 
hundred feet from your QTH. In that case its simply been an EMC 
learning experience about the consequences of introducing a strong 
RF field into a houseful of electronics. 

73 
Frank 
W3LPL 

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

From: "Nicklas Johnson" <nick at n6ol.us> 
To: "elecraft" <elecraft at mailman.qth.net> 
Sent: Saturday, April 27, 2019 6:31:53 PM 
Subject: Re: [Elecraft] K3S Audio buzz on transmit, especially AM 

I don't think that "collecting data" and "process of elimination" are 
particularly ANTI-methodical either. But the fact is that most people will 
never encounter this kind of problem and don't spend their days practicing 
how to troubleshoot it, so they seek advice from people who do have 
experience. Thus this email thread, which began with my thinking I'd 
developed an audio fault in the rig and seeking advice, but successive 
tests have pointed in other directions. 

To answer Jim's earlier question, yes, it does appear that transmitting an 
unmodulated AM carrier from the K3S into anything resembling an antenna 
yields a buzz on the KX3 receiver (and vice-versa). The buzz is NOT 
audible when listening to the K3S's own TX monitor. 

And to answer Frank's question, the PG&E transformer in our front yard for 
the underground utilities is approximately 30 horizontal feet over and 6 
vertical feet down from the station. The distance to the utilities that 
run through the back of our lot is approximately 60 feet. 

I spent the morning reviewing (again) materials on grounding and bonding 
over my morning coffee to see if there's something important I missed, and 
I also found by repeating it that an earlier test I'd done had given me a 
misleading/contradictory result-- transmitting into a dummy load 
immediately adjacent the KX3 receiving it produces a nice, clean signal. I 
was misled before by the KX3 picking up a different buzz (probably off a 
wall wart) in the shack when performing this test earlier. (It also helped 
in this case to put the KX3 into CW mode to detect the unmodulated AM 
carrier.) 

FWIW, this morning I also disconnected the bonding between the station's 
ground rod and the house's utility power and also disconnected the DTV 
antenna run into the house (which shares the same coax grounding/surge 
protection bus outside, but of course could find another path to ground 
over the coax shield via either one of the TV receivers). Doing so 
eliminated any *direct * connection with the utility power, as I'm still 
running purely on battery power. This had NO effect on the received buzz. 

At this point I'm pretty sure this is an environmental issue and not a 
problem with either rig, so it's probably not appropriate for me to 
continue to pester the list about it. Thank you again to everyone who 
offered suggestions and advice. 

But for posterity, and in case anyone comes along searching the list while 
debugging a similar problem, here's a list of all the other things that I 
tried to isolate the problem, none of which had any effect: 

- Complete disconnection of all other inputs and outputs on the K3S 
other than the antenna. 
- Turning off all nearby power supplies. 
- Setting the input to any other selection (front panel, rear panel, 
line in) 
- Setting the line input level to 0, verifying that front and rear panel 
gains were set to "low" 
- Running solely on battery power without the solar charge controller 
- TX EQ settings- cutting the low end completely 
- Taking the receiver outdoors, away from power supplies 
- Trying a different transmit antenna (ie, making sure I wasn't having 
problems with a damaged dipole having the house neutral wiring as one leg) 
- Temporarily disconnecting the station ground 
- Temporarily disconnecting the utility bonding from the station's 
ground rod 
- Reversing the direction: transmitting with the KX3 into a portable 
antenna and receiving with the K3S also produced a much more significant 
buzz 

What DID yield some useful data: 

- Transmitting into a dummy load *while* turning off all nearby power 
supplies and lights with the KX3 immediately adjacent the dummy load: nice, 
pristine signal 
- Checking the TX monitor on the K3S: only white noise with the line 
input and the monitor output turned to maximum while transmitting. 

What I have yet to do, and will require some more time and effort to 
organize and implement: 

- Going portable or to another QTH to test again 
- Getting a signal report from a distant station to see if this is a 
local reception problem, or something actually getting into the transmitted 
signal. 

Nick 

On Sat, 27 Apr 2019 at 01:19, Jim Brown <jim at audiosystemsgroup.com> wrote: 

> On 4/26/2019 10:44 PM, donovanf at starpower.net wrote: 
> > Y our emails leave the impression that your approach 
> > isn't very methodical. 
> 
> Yes, but that lack of methodical troubleshooting is the result of most 
> hams being weak on the fundamentals of fields and passive IM, instead 
> seeing problems in the light of RFI and mythical concepts like "ground 
> loops." 
> 
> The two causes I've come around to smelling in this problem are passive 
> IM (which Frank reminded me of) and power-related fields. And Frank's 
> advice is right on. 
> 
> 73, Jim K9YC 
> 
> 
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-- 
*N6OL* 
Saying something doesn't make it true. Belief in something doesn't make it 
real. And if you have to lie to support a position, that position is not 
worth supporting. 
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