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12 meter K3 RFI from nearby FM station

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Jon Zaimes AA1K

12 meter K3 RFI from nearby FM station

I had been noticing some RFI on 12 meters for some time that I initially had
thought was power line noise. My use of 12 meters is seldom so it wasn't
very high up on the list of things to track.

When I was reminded of it while listening for VP8STI recently, I did a
little more snooping and realized it was actually splatter from a BC signal
at the low edge or slightly below the 12 meter band, centered about 24.89
mHz but audible from 24.87-24.91 mHz.

The distorted splatter is audible as a BC station, all talk, no music, but
not clear enough to decipher any ID.

A few days ago I decided to try to pinpoint the source, so listened to the
RFI on one ear while scanning the AM and SW bands with the sub RX on the
other ear. But I could find no matches, though did find the splatter popped
up centered on these additional frequencies:

813 kHz
996 kHz
2.820 mHz
3.626 mHz
19.4 mHz

Figuring it must be an FM BC station, I started going through a list of
Delaware FM stations and on the third one, 91.1 mHz, matched the audio peaks
to my splatter. Further research determined this was a public radio station
with a transmitter on a commercial tower just a half mile west of my QTH!
While I of course was aware of the tower, which I knew to carry a couple of
cell sites and trunking radio, I hadn't been aware of the FM station, which
has apparently been there about 2 years. FCC data shows it has 2.1 KW ERP. I
had not had any previous issues with the site over the past 17 years.

Thinking that mixing or rectification might be produced either at the TX
site or on my own QTH, I decided to track with my mobile rig, an IC-706
MK2G. But there was NO evidence of the splatter on the 706.

Further debugging found that I was hearing the same splatter on BOTH of my
K3 radios (no. 3021 and 3057). Even when ALL cables are removed (only the
power lead connected). Grounding or ungrounding made no change. I tried the
radios on a battery but still had the RFI. Tried some ferrites on the power
lead but no change.

So I'm thinking now there's some internal mixing in the K3 going on, and
wondering if any others have had similar issues and found any solution.

73/Jon AA1K
Felton, Delaware
www.aa1k.us

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Vic Rosenthal

Re: 12 meter K3 RFI from nearby FM station

Jon,

I had a similar problem with a 50 kW AM BC station a few miles away. It
turned out to be strong enough to override the bias in the K3's T/R
switch. I built a high-pass filter which solved the problem.

You would need a low-pass filter in your case. Make sure it can handle
100w, because you must connect it in the main antenna path -- the RX
in/out path is before the T/R switch.

73,
Vic, 4X6GP/K2VCO
Rehovot, Israel
http://www.qsl.net/k2vco/

On 10 Feb 2016 16:58, Jon Zaimes wrote:

> I had been noticing some RFI on 12 meters for some time that I initially had
> thought was power line noise. My use of 12 meters is seldom so it wasn't
> very high up on the list of things to track.
>
> When I was reminded of it while listening for VP8STI recently, I did a
> little more snooping and realized it was actually splatter from a BC signal
> at the low edge or slightly below the 12 meter band, centered about 24.89
> mHz but audible from 24.87-24.91 mHz.
>
> The distorted splatter is audible as a BC station, all talk, no music, but
> not clear enough to decipher any ID.
>
> A few days ago I decided to try to pinpoint the source, so listened to the
> RFI on one ear while scanning the AM and SW bands with the sub RX on the
> other ear. But I could find no matches, though did find the splatter popped
> up centered on these additional frequencies:
>
> 813 kHz
> 996 kHz
> 2.820 mHz
> 3.626 mHz
> 19.4 mHz
>
> Figuring it must be an FM BC station, I started going through a list of
> Delaware FM stations and on the third one, 91.1 mHz, matched the audio peaks
> to my splatter. Further research determined this was a public radio station
> with a transmitter on a commercial tower just a half mile west of my QTH!
> While I of course was aware of the tower, which I knew to carry a couple of
> cell sites and trunking radio, I hadn't been aware of the FM station, which
> has apparently been there about 2 years. FCC data shows it has 2.1 KW ERP. I
> had not had any previous issues with the site over the past 17 years.
>
> Thinking that mixing or rectification might be produced either at the TX
> site or on my own QTH, I decided to track with my mobile rig, an IC-706
> MK2G. But there was NO evidence of the splatter on the 706.
>
> Further debugging found that I was hearing the same splatter on BOTH of my
> K3 radios (no. 3021 and 3057). Even when ALL cables are removed (only the
> power lead connected). Grounding or ungrounding made no change. I tried the
> radios on a battery but still had the RFI. Tried some ferrites on the power
> lead but no change.
>
>
> So I'm thinking now there's some internal mixing in the K3 going on, and
> wondering if any others have had similar issues and found any solution.
>
> 73/Jon AA1K
> Felton, Delaware
> www.aa1k.us
>
>
>
>
> ______________________________________________________________
> 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]
>

Jon Zaimes AA1K

Re: 12 meter K3 RFI from nearby FM station

Thanks for the tips.

Any filter likely would have to be inserted internally, since I am getting
this RFI without any antennas connected to the radios.Unless it is coming in
on the 12v power cord, which is still a possibility. I only tried a couple
ferrites and they may not have been the right one for choking out the FM
signal.

I did observe that I am only hearing it on the main receiver in my K3 that
has a sub RX, but not on the sub RX. Also, while checking for this, and then
going back to the main RX, the RFI signal on the main RX was greatly
reduced. Perhaps a relay contact issue. It is still just as strong as
previous on my other K3 (which has no sub RX). Toggling through PRE and ATT
did not eliminate it (though changed signal level as it would for any
signal).

73/Jon AA1K

-----Original Message-----
From: Elecraft [mailto:[hidden email]] On Behalf Of Vic
Rosenthal 4X6GP/K2VCO
Sent: Wednesday, February 10, 2016 10:20 AM
To: [hidden email]
Subject: Re: [Elecraft] 12 meter K3 RFI from nearby FM station

Jon,

I had a similar problem with a 50 kW AM BC station a few miles away. It
turned out to be strong enough to override the bias in the K3's T/R switch.
I built a high-pass filter which solved the problem.

You would need a low-pass filter in your case. Make sure it can handle 100w,
because you must connect it in the main antenna path -- the RX in/out path
is before the T/R switch.

73,
Vic, 4X6GP/K2VCO
Rehovot, Israel
http://www.qsl.net/k2vco/

On 10 Feb 2016 16:58, Jon Zaimes wrote:

> I had been noticing some RFI on 12 meters for some time that I
> initially had thought was power line noise. My use of 12 meters is
> seldom so it wasn't very high up on the list of things to track.
>
> When I was reminded of it while listening for VP8STI recently, I did a
> little more snooping and realized it was actually splatter from a BC
> signal at the low edge or slightly below the 12 meter band, centered
> about 24.89 mHz but audible from 24.87-24.91 mHz.
>
> The distorted splatter is audible as a BC station, all talk, no music,
> but not clear enough to decipher any ID.
>
> A few days ago I decided to try to pinpoint the source, so listened to
> the RFI on one ear while scanning the AM and SW bands with the sub RX
> on the other ear. But I could find no matches, though did find the
> splatter popped up centered on these additional frequencies:
>
> 813 kHz
> 996 kHz
> 2.820 mHz
> 3.626 mHz
> 19.4 mHz
>
> Figuring it must be an FM BC station, I started going through a list
> of Delaware FM stations and on the third one, 91.1 mHz, matched the
> audio peaks to my splatter. Further research determined this was a
> public radio station with a transmitter on a commercial tower just a half

mile west of my QTH!
> While I of course was aware of the tower, which I knew to carry a
> couple of cell sites and trunking radio, I hadn't been aware of the FM
> station, which has apparently been there about 2 years. FCC data shows
> it has 2.1 KW ERP. I had not had any previous issues with the site over
the past 17 years.

>
> Thinking that mixing or rectification might be produced either at the
> TX site or on my own QTH, I decided to track with my mobile rig, an
> IC-706 MK2G. But there was NO evidence of the splatter on the 706.
>
> Further debugging found that I was hearing the same splatter on BOTH
> of my
> K3 radios (no. 3021 and 3057). Even when ALL cables are removed (only
> the power lead connected). Grounding or ungrounding made no change. I
> tried the radios on a battery but still had the RFI. Tried some
> ferrites on the power lead but no change.
>
>
> So I'm thinking now there's some internal mixing in the K3 going on,
> and wondering if any others have had similar issues and found any

solution.

>
> 73/Jon AA1K
> Felton, Delaware
> www.aa1k.us
>
>
>
>
> ______________________________________________________________
> 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]
>

Bob McGraw - K4TAX

Re: 12 meter K3 RFI from nearby FM station

In reply to this post by Vic Rosenthal

An electrical 1/4 wavelength of coax as an open stub at the FM
frequency, connected using a T at the receiver input, will notch the FM
TX signal. It won't attenuate other frequencies across the ham bands
including 6M. Plus one can transmit with the stub arrangement in place.

73
Bob, K4TAX

On 2/10/2016 10:13 AM, Ron D'Eau Claire wrote:

> A single frequency issue like that also can be handled with a simple trap. A
> small coil with a capacitor across it tuned to the station's frequency at
> 91.1 MHz in series with the center conductor of your coax.
>
> 73, Ron AC7AC
>
> -----Original Message-----
>
>
> Jon,
>
> I had a similar problem with a 50 kW AM BC station a few miles away. It
> turned out to be strong enough to override the bias in the K3's T/R switch.
> I built a high-pass filter which solved the problem.
>
> You would need a low-pass filter in your case. Make sure it can handle 100w,
> because you must connect it in the main antenna path -- the RX in/out path
> is before the T/R switch.
>
> 73,
> Vic, 4X6GP/K2VCO
> Rehovot, Israel
> http://www.qsl.net/k2vco/
>
> On 10 Feb 2016 16:58, Jon Zaimes wrote:
>> I had been noticing some RFI on 12 meters for some time that I
>> initially had thought was power line noise. My use of 12 meters is
>> seldom so it wasn't very high up on the list of things to track.
>>
>> When I was reminded of it while listening for VP8STI recently, I did a
>> little more snooping and realized it was actually splatter from a BC
>> signal at the low edge or slightly below the 12 meter band, centered
>> about 24.89 mHz but audible from 24.87-24.91 mHz.
>>
>> The distorted splatter is audible as a BC station, all talk, no music,
>> but not clear enough to decipher any ID.
>>
>> A few days ago I decided to try to pinpoint the source, so listened to
>> the RFI on one ear while scanning the AM and SW bands with the sub RX
>> on the other ear. But I could find no matches, though did find the
>> splatter popped up centered on these additional frequencies:
>>
>> 813 kHz
>> 996 kHz
>> 2.820 mHz
>> 3.626 mHz
>> 19.4 mHz
>>
>> Figuring it must be an FM BC station, I started going through a list
>> of Delaware FM stations and on the third one, 91.1 mHz, matched the
>> audio peaks to my splatter. Further research determined this was a
>> public radio station with a transmitter on a commercial tower just a half
> mile west of my QTH!
>> While I of course was aware of the tower, which I knew to carry a
>> couple of cell sites and trunking radio, I hadn't been aware of the FM
>> station, which has apparently been there about 2 years. FCC data shows
>> it has 2.1 KW ERP. I had not had any previous issues with the site over
> the past 17 years.
>> Thinking that mixing or rectification might be produced either at the
>> TX site or on my own QTH, I decided to track with my mobile rig, an
>> IC-706 MK2G. But there was NO evidence of the splatter on the 706.
>>
>> Further debugging found that I was hearing the same splatter on BOTH
>> of my
>> K3 radios (no. 3021 and 3057). Even when ALL cables are removed (only
>> the power lead connected). Grounding or ungrounding made no change. I
>> tried the radios on a battery but still had the RFI. Tried some
>> ferrites on the power lead but no change.
>>
>>
>> So I'm thinking now there's some internal mixing in the K3 going on,
>> and wondering if any others have had similar issues and found any
> solution.
>> 73/Jon AA1K
>> Felton, Delaware
>> www.aa1k.us
> ______________________________________________________________
> 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]
>

Phil Kane-2

Re: 12 meter K3 RFI from nearby FM station

In reply to this post by Vic Rosenthal

On 2/10/2016 7:19 AM, Vic Rosenthal 4X6GP/K2VCO wrote:

> You would need a low-pass filter in your case. Make sure it can handle
> 100w, because you must connect it in the main antenna path -- the RX
> in/out path is before the T/R switch.

Using a low-pass filter on the output of an HF transmitter/transceiver
should be Job Number One - then again, I'm from the old school where
preventing Tennessee Valley Indians (TVI) was a real problem that hams
were concerned about.

73 de K2ASP - Phil Kane
Elecraft K2/100 s/n 5402

From a Clearing in the Silicon Forest
Beaverton (Washington County) Oregon
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Vic Rosenthal

Re: 12 meter K3 RFI from nearby FM station

In reply to this post by Jon Zaimes AA1K

I didn't notice that you said you get it with no antenna. That does make
it more complicated.

The fact that you get it on the main but not the sub points to the T/R
switch, since the sub receiver does not go through the T/R switch if the
sub is set to AUX to use either the non-transmit antenna or the BNC
input. If you don't know, turn on the sub and hold BSET -- you will see
either MAIN or AUX.

73,
Vic, 4X6GP/K2VCO
Rehovot, Israel
http://www.qsl.net/k2vco/

On 10 Feb 2016 19:10, Jon Zaimes wrote:

> Thanks for the tips.
>
> Any filter likely would have to be inserted internally, since I am getting
> this RFI without any antennas connected to the radios.Unless it is coming in
> on the 12v power cord, which is still a possibility. I only tried a couple
> ferrites and they may not have been the right one for choking out the FM
> signal.
>
> I did observe that I am only hearing it on the main receiver in my K3 that
> has a sub RX, but not on the sub RX. Also, while checking for this, and then
> going back to the main RX, the RFI signal on the main RX was greatly
> reduced. Perhaps a relay contact issue. It is still just as strong as
> previous on my other K3 (which has no sub RX). Toggling through PRE and ATT
> did not eliminate it (though changed signal level as it would for any
> signal).
>
> 73/Jon AA1K
>
> -----Original Message-----
> From: Elecraft [mailto:[hidden email]] On Behalf Of Vic
> Rosenthal 4X6GP/K2VCO
> Sent: Wednesday, February 10, 2016 10:20 AM
> To: [hidden email]
> Subject: Re: [Elecraft] 12 meter K3 RFI from nearby FM station
>
> Jon,
>
> I had a similar problem with a 50 kW AM BC station a few miles away. It
> turned out to be strong enough to override the bias in the K3's T/R switch.
> I built a high-pass filter which solved the problem.
>
> You would need a low-pass filter in your case. Make sure it can handle 100w,
> because you must connect it in the main antenna path -- the RX in/out path
> is before the T/R switch.
>
> 73,
> Vic, 4X6GP/K2VCO
> Rehovot, Israel
> http://www.qsl.net/k2vco/
>
> On 10 Feb 2016 16:58, Jon Zaimes wrote:
>> I had been noticing some RFI on 12 meters for some time that I
>> initially had thought was power line noise. My use of 12 meters is
>> seldom so it wasn't very high up on the list of things to track.
>>
>> When I was reminded of it while listening for VP8STI recently, I did a
>> little more snooping and realized it was actually splatter from a BC
>> signal at the low edge or slightly below the 12 meter band, centered
>> about 24.89 mHz but audible from 24.87-24.91 mHz.
>>
>> The distorted splatter is audible as a BC station, all talk, no music,
>> but not clear enough to decipher any ID.
>>
>> A few days ago I decided to try to pinpoint the source, so listened to
>> the RFI on one ear while scanning the AM and SW bands with the sub RX
>> on the other ear. But I could find no matches, though did find the
>> splatter popped up centered on these additional frequencies:
>>
>> 813 kHz
>> 996 kHz
>> 2.820 mHz
>> 3.626 mHz
>> 19.4 mHz
>>
>> Figuring it must be an FM BC station, I started going through a list
>> of Delaware FM stations and on the third one, 91.1 mHz, matched the
>> audio peaks to my splatter. Further research determined this was a
>> public radio station with a transmitter on a commercial tower just a half
> mile west of my QTH!
>> While I of course was aware of the tower, which I knew to carry a
>> couple of cell sites and trunking radio, I hadn't been aware of the FM
>> station, which has apparently been there about 2 years. FCC data shows
>> it has 2.1 KW ERP. I had not had any previous issues with the site over
> the past 17 years.
>>
>> Thinking that mixing or rectification might be produced either at the
>> TX site or on my own QTH, I decided to track with my mobile rig, an
>> IC-706 MK2G. But there was NO evidence of the splatter on the 706.
>>
>> Further debugging found that I was hearing the same splatter on BOTH
>> of my
>> K3 radios (no. 3021 and 3057). Even when ALL cables are removed (only
>> the power lead connected). Grounding or ungrounding made no change. I
>> tried the radios on a battery but still had the RFI. Tried some
>> ferrites on the power lead but no change.
>>
>>
>> So I'm thinking now there's some internal mixing in the K3 going on,
>> and wondering if any others have had similar issues and found any
> solution.
>>
>> 73/Jon AA1K
>> Felton, Delaware
>> www.aa1k.us
>>
>>
>>
>>
>> ______________________________________________________________
>> 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]
>>
> ______________________________________________________________
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> 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]
>

Russ Tobolic

Re: 12 meter K3 RFI from nearby FM station

In reply to this post by Jon Zaimes AA1K

What power are you running? Try an experiment by turning the power level down or up thereby switching between the LPA and the KPA3 to see if this changes the intermod level. This may narrow it down to the TR switch. I have had a similar problem with intermods between a couple of local AM stations. The level of intermod changed quite noticeably switching between the output amps. The KPA3 and LP are using different switching diodes for the TR switch.

Russ, N3CO

From: Jon Zaimes <[hidden email]>
To: 'Vic Rosenthal 4X6GP/K2VCO' <[hidden email]>; [hidden email]
Sent: Wednesday, February 10, 2016 12:10 PM
Subject: Re: [Elecraft] 12 meter K3 RFI from nearby FM station

Thanks for the tips.

Any filter likely would have to be inserted internally, since I am getting
this RFI without any antennas connected to the radios.Unless it is coming in
on the 12v power cord, which is still a possibility. I only tried a couple
ferrites and they may not have been the right one for choking out the FM
signal.

I did observe that I am only hearing it on the main receiver in my K3 that
has a sub RX, but not on the sub RX. Also, while checking for this, and then
going back to the main RX, the RFI signal on the main RX was greatly
reduced. Perhaps a relay contact issue. It is still just as strong as
previous on my other K3 (which has no sub RX). Toggling through PRE and ATT
did not eliminate it (though changed signal level as it would for any
signal).

73/Jon AA1K

-----Original Message-----
From: Elecraft [mailto:[hidden email]] On Behalf Of Vic
Rosenthal 4X6GP/K2VCO
Sent: Wednesday, February 10, 2016 10:20 AM
To: [hidden email]
Subject: Re: [Elecraft] 12 meter K3 RFI from nearby FM station

Jon,

I had a similar problem with a 50 kW AM BC station a few miles away. It
turned out to be strong enough to override the bias in the K3's T/R switch.
I built a high-pass filter which solved the problem.

You would need a low-pass filter in your case. Make sure it can handle 100w,
because you must connect it in the main antenna path -- the RX in/out path
is before the T/R switch.

73,
Vic, 4X6GP/K2VCO
Rehovot, Israel
http://www.qsl.net/k2vco/

On 10 Feb 2016 16:58, Jon Zaimes wrote:

solution.

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pa4la

Re: 12 meter K3 RFI from nearby FM station

In reply to this post by Jon Zaimes AA1K

Hi Jon,

What you experience is mixing of the FM BC frequency with the 3th, 5th, 7th etc. harmonic(s) of the K3's VCO.
If the mix product result is 8,215 Mhz you can hear it.

I'm 3 km away from a BC tower hosting 10 station with >20kw each.
Used SDR-radio on the K3-IF at 8,215 Mhz to identify the FM stations.
That was easy, stereo and even RDS could be decoded via the K3-IF.
the "mixing" frequencies could quickly be found.

You can calculate where 91,1 pops up

For the 3th VCO harmonic
((BCfreq-8,215)/3)-8,215 and
((BCfreq+8,215)/3)-8,215

That is 19,413 Mhz and 24,890 Mhz (you already knew :) )

For the 5th 8,362 Mhz and 11,648 Mhz
For the 7th 3,626 Mhz and 5,973 Mhz
And so on,
With a strong enough signal from a generator, mixing of the 11th harmonic could be detected.

I have only seen the BC mix phenomena when using the RX-in with MainRx and the SubRX on separate (wideband) antenna.
When using the RX-in, the K3 LPF is bypassed and with the Subrx, there is no LPF in the KRX3 !
The LPF in the main antenna circuit has enough attenuation to stop BC FM leakage to the K3 mixer in my situation.

Since you have such a strong signal on 91.1 Mhz
Check if the products can be heard with the suggested external LPF connect to a dummy load on Ant1 (K3 LPF is inline too)
If that is still the case, the antenne input(s) is probably not the route the BC signal makes to the mixer.
Hope you find a solution.

73 Hugo pa4la

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k6dgw

Re: 12 meter K3 RFI from nearby FM station

In reply to this post by Bob McGraw - K4TAX

I easily could have misread the original emailed problem, but he
included the note that this RFI occurred with all antennas [and I guess
other cables] disconnected which is very strange indeed. If that is so,
then I doubt stubs/filters on the antenna circuits would cure the problem.

His list of frequencies might suggest some sort of intermod between
constant signals, one being the FM carrier, and possibly their
harmonics. Very strange problem at any rate. FWIW, and Phil can
correct me, but US FM/TV stations are usually authorized in EIRP, I
think ... we referred to KSBY-TV, where I worked while in college, as
"Full-power television for the Central coast, one hundred thousand watts
on Channel 6 in San Luis Obispo" on ID's. That was EIRP, 10 KW to a 10
dB turnstile. If that's still true, it would seem a 2 KW EIRP FM
station 2 miles away shouldn't be a big deal.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the Cal QSO Party 1-2 Oct 2016
- www.cqp.org

On 2/10/2016 2:04 PM, Ron D'Eau Claire wrote:

> I agree. Even better.
>
> 73, Ron AC7AC
>
> -----Original Message-----
> From: Elecraft [mailto:[hidden email]] On Behalf Of Bob
> McGraw K4TAX
> Sent: Wednesday, February 10, 2016 9:18 AM
> To: [hidden email]
> Subject: Re: [Elecraft] 12 meter K3 RFI from nearby FM station
>
> An electrical 1/4 wavelength of coax as an open stub at the FM frequency,
> connected using a T at the receiver input, will notch the FM TX signal. It
> won't attenuate other frequencies across the ham bands including 6M. Plus
> one can transmit with the stub arrangement in place.
>
> 73
> Bob, K4TAX

Jim Brown-10

Re: 12 meter K3 RFI from nearby FM station

Yes, this hit me between the eyes as well. The K3 has Pin One Problems
at many (most?) connectors, so RF current flowing on shields of cables
plugged into those connectors will couple into the K3. I've been
preaching to Wayne about Pin One Problems since 2004, when we met in
Dayton.

If the problem is around 90 MHz, I'd use multiple one-turn and two turn
chokes with #43 material on every cable except the SO239 output, which
IS actually bonded to the chassis. Also choke the power cable.

73, Jim K9YC

On Wed,2/10/2016 2:53 PM, Fred Jensen wrote:
> I easily could have misread the original emailed problem, but he
> included the note that this RFI occurred with all antennas [and I
> guess other cables] disconnected which is very strange indeed. If
> that is so, then I doubt stubs/filters on the antenna circuits would
> cure the problem.

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Don Wilhelm-4

Re: 12 meter K3 RFI from nearby FM station

Since the problem occurs without an antenna connected, it is a version
of the "RF in the shack" problem, although the RF field is coming from
the nearby FM station rather than the classic situation where the
transmitted signal is the source of the RF.

Jim makes some very good suggestions for 'taming' that problem.

It would be very difficult to cure the K3 of the "pin 1" problems.

For those who are not familiar with the "pin 1" problem, that is a
situation where the shields of interconnecting cables are connected to
the circuit boards rather than directly to the outside of the
transceiver enclosure. That allows any pickup on attached cables to be
imposed into the boards of the transceivers. In days of old when we
mounted all connectors to the enclosure rather than to the circuit
boards, the enclosure itself provided a shield for whatever trash was
picked up by the external wiring - because those trash signals would
flow on the 'outside' of the enclosure and not affect the circuits
inside. With modern transceivers where cable jacks are connected to the
ground plane of the circuit boards rather than to the enclosure, the
external signals are coupled to the ground plane of the internal boards,
and will couple the offending signals into the transceiver.

In other words, "board ground plane" does not equal "ground" -
variations in the ground plane reference will cause "funny happenings"
within the interior circuits. In other words, the enclosure does not
offer a sufficient shielding effect for the circuits inside the enclosure.

The K3 is not alone in this problem, it is shared by any transceiver
that does not ground the connectors directly to the enclosure.

73,
Don W3FPR

73,
Don W3FPR

73,
Don W3FPR

On 2/10/2016 6:57 PM, Jim Brown wrote:

> Yes, this hit me between the eyes as well. The K3 has Pin One Problems
> at many (most?) connectors, so RF current flowing on shields of cables
> plugged into those connectors will couple into the K3. I've been
> preaching to Wayne about Pin One Problems since 2004, when we met in
> Dayton.
>
> If the problem is around 90 MHz, I'd use multiple one-turn and two
> turn chokes with #43 material on every cable except the SO239 output,
> which IS actually bonded to the chassis. Also choke the power cable.
>
> 73, Jim K9YC
>
> On Wed,2/10/2016 2:53 PM, Fred Jensen wrote:
>> I easily could have misread the original emailed problem, but he
>> included the note that this RFI occurred with all antennas [and I
>> guess other cables] disconnected which is very strange indeed. If
>> that is so, then I doubt stubs/filters on the antenna circuits would
>> cure the problem.
>

Jim Miller

Re: 12 meter K3 RFI from nearby FM station

Open antenna connectors are like baby antennas. Terminate the antenna port in question before proceeding.

Jim ab3cv

On Feb 10, 2016, at 7:25 PM, Don Wilhelm <[hidden email]> wrote:

Since the problem occurs without an antenna connected, it is a version of the "RF in the shack" problem, although the RF field is coming from the nearby FM station rather than the classic situation where the transmitted signal is the source of the RF.

Jim makes some very good suggestions for 'taming' that problem.

It would be very difficult to cure the K3 of the "pin 1" problems.

For those who are not familiar with the "pin 1" problem, that is a situation where the shields of interconnecting cables are connected to the circuit boards rather than directly to the outside of the transceiver enclosure. That allows any pickup on attached cables to be imposed into the boards of the transceivers. In days of old when we mounted all connectors to the enclosure rather than to the circuit boards, the enclosure itself provided a shield for whatever trash was picked up by the external wiring - because those trash signals would flow on the 'outside' of the enclosure and not affect the circuits inside. With modern transceivers where cable jacks are connected to the ground plane of the circuit boards rather than to the enclosure, the external signals are coupled to the ground plane of the internal boards, and will couple the offending signals into the transceiver.

In other words, "board ground plane" does not equal "ground" - variations in the ground plane reference will cause "funny happenings" within the interior circuits. In other words, the enclosure does not offer a sufficient shielding effect for the circuits inside the enclosure.

The K3 is not alone in this problem, it is shared by any transceiver that does not ground the connectors directly to the enclosure.

73,
Don W3FPR

73,
Don W3FPR

73,
Don W3FPR

> On 2/10/2016 6:57 PM, Jim Brown wrote:
> Yes, this hit me between the eyes as well. The K3 has Pin One Problems at many (most?) connectors, so RF current flowing on shields of cables plugged into those connectors will couple into the K3. I've been preaching to Wayne about Pin One Problems since 2004, when we met in Dayton.
>
> If the problem is around 90 MHz, I'd use multiple one-turn and two turn chokes with #43 material on every cable except the SO239 output, which IS actually bonded to the chassis. Also choke the power cable.
>
> 73, Jim K9YC
>
>> On Wed,2/10/2016 2:53 PM, Fred Jensen wrote:
>> I easily could have misread the original emailed problem, but he included the note that this RFI occurred with all antennas [and I guess other cables] disconnected which is very strange indeed. If that is so, then I doubt stubs/filters on the antenna circuits would cure the problem.
>

Alan Bloom

Re: 12 meter K3 RFI from nearby FM station

In reply to this post by Jim Brown-10

On 02/10/2016 03:57 PM, Jim Brown wrote:
> Yes, this hit me between the eyes as well. The K3 has Pin One Problems
> at many (most?) connectors, so RF current flowing on shields of cables
> plugged into those connectors will couple into the K3. I've been
> preaching to Wayne about Pin One Problems since 2004, when we met in
> Dayton.
>
> If the problem is around 90 MHz, I'd use multiple one-turn and two turn
> chokes with #43 material on every cable except the SO239 output, which
> IS actually bonded to the chassis. Also choke the power cable.

But it sounds like he was still getting the problem with no cables
connected to the K3:

On 02/10/2016 06:58 AM, Jon Zaimes wrote:
...
> Even when ALL cables are removed (only the power lead connected).
> Grounding or ungrounding made no change. I tried the radios on a
> battery but still had the RFI. Tried some ferrites on the power
> lead but no change.

I suppose it could be a "pin 1" problem on the power leads. It's kind
of hard to avoid that with an Anderson PowerPole connector. Probably
additional low-pass filtering on the DC input would help.

Alan N1AL

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Bob McGraw - K4TAX

Re: 12 meter K3 RFI from nearby FM station

I can't imagine 2 KW ERP FM directly causing that issue. In reading
the original post, he was getting splatter on 12M which would indicate
the antenna was connected. Nothing mentioned about the Preamp being on
or off. Normally for 12M it is on, maybe PRE II is on as well. There
are precautions stated n the manual in this regard. As a result of any
reactive input termination, it could be oscillating. If so, all bets
are off. Birdies abound!

Then disconnecting "all cables" and I don't take this to mean antenna
disconnected as well, but powering from a battery still show evidence of
the problem. I could see with the antenna connected, corrosion on the
antenna element(s) or feed line connectors acting as a diode or even a
metal gutter, downspout and etc. and being excited by the FM carrier
plus subcarrier/pilot making it appearance as multiple birdies modulated
by the FM audio. However, with "everything" disconnected except for
power cable and the problem remain, very strange. The K3S is built
better and shielded better than this.

73
Bob, K4TAX

On 2/11/2016 11:03 AM, Alan wrote:

> On 02/10/2016 03:57 PM, Jim Brown wrote:
>> Yes, this hit me between the eyes as well. The K3 has Pin One Problems
>> at many (most?) connectors, so RF current flowing on shields of cables
>> plugged into those connectors will couple into the K3. I've been
>> preaching to Wayne about Pin One Problems since 2004, when we met in
>> Dayton.
>>
>> If the problem is around 90 MHz, I'd use multiple one-turn and two turn
>> chokes with #43 material on every cable except the SO239 output, which
>> IS actually bonded to the chassis. Also choke the power cable.
>
> But it sounds like he was still getting the problem with no cables
> connected to the K3:
>
> On 02/10/2016 06:58 AM, Jon Zaimes wrote:
> ...
> > Even when ALL cables are removed (only the power lead connected).
> > Grounding or ungrounding made no change. I tried the radios on a
> > battery but still had the RFI. Tried some ferrites on the power
> > lead but no change.
>
> I suppose it could be a "pin 1" problem on the power leads. It's kind
> of hard to avoid that with an Anderson PowerPole connector. Probably
> additional low-pass filtering on the DC input would help.
>
> Alan N1AL
>
> ______________________________________________________________
> 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]
>

Chris Hallinan

Re: 12 meter K3 RFI from nearby FM station

In reply to this post by k6dgw

I have a similar problem. I have a 1KW AM station about 1/2 mile away
(1100W by day, 110W by night). With nothing connected to the radio, and
even with a 50-ohm terminator on RX Ant in, I can clearly hear the signal
at several places, most prominently at 14.220 MHz. Nothing I've tried,
including expensive filters, shielded cables, etc. has helped. I get some
relief using a RX Loop antenna basically nulled (broadside) to the tower,
but that antenna is not always the best one for band and/or conditions. :(
Some frequencies are simply unusable, and it overloads a front end
protector I purchased to try to kill the COR relay clicking when I
transmit, making it unusable.

Chris
K1AY

On Wed, Feb 10, 2016 at 5:53 PM, Fred Jensen <[hidden email]> wrote:

> I easily could have misread the original emailed problem, but he included
> the note that this RFI occurred with all antennas [and I guess other
> cables] disconnected which is very strange indeed. If that is so, then I
> doubt stubs/filters on the antenna circuits would cure the problem.
>
> His list of frequencies might suggest some sort of intermod between
> constant signals, one being the FM carrier, and possibly their harmonics.
> Very strange problem at any rate. FWIW, and Phil can correct me, but US
> FM/TV stations are usually authorized in EIRP, I think ... we referred to
> KSBY-TV, where I worked while in college, as "Full-power television for the
> Central coast, one hundred thousand watts on Channel 6 in San Luis Obispo"
> on ID's. That was EIRP, 10 KW to a 10 dB turnstile. If that's still true,
> it would seem a 2 KW EIRP FM station 2 miles away shouldn't be a big deal.
>
> 73,
>
> Fred K6DGW
> - Northern California Contest Club
> - CU in the Cal QSO Party 1-2 Oct 2016
> - www.cqp.org
>
>
> On 2/10/2016 2:04 PM, Ron D'Eau Claire wrote:
>
>> I agree. Even better.
>>
>> 73, Ron AC7AC
>>
>> -----Original Message-----
>> From: Elecraft [mailto:[hidden email]] On Behalf Of Bob
>> McGraw K4TAX
>> Sent: Wednesday, February 10, 2016 9:18 AM
>> To: [hidden email]
>> Subject: Re: [Elecraft] 12 meter K3 RFI from nearby FM station
>>
>> An electrical 1/4 wavelength of coax as an open stub at the FM frequency,
>> connected using a T at the receiver input, will notch the FM TX signal.
>> It
>> won't attenuate other frequencies across the ham bands including 6M. Plus
>> one can transmit with the stub arrangement in place.
>>
>> 73
>> Bob, K4TAX
>>
>
> ______________________________________________________________
> 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]
>

--
Life is like Linux - it never stands still.
______________________________________________________________
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Post: mailto:[hidden email]

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Jon Zaimes AA1K

Re: 12 meter K3 RFI from nearby FM station

In reply to this post by Alan Bloom

Yes, that is the case. Hearing it on both of my K3 transceivers with only
the 12v power cable connected, nothing else (listening on speaker).

Thanks to all for the tips. Still absorbing the advice before proceeding.

73/Jon AA1K
Felton, Delaware
www.aa1k.us

-----Original Message-----
From: Elecraft [mailto:[hidden email]] On Behalf Of Alan
Sent: Thursday, February 11, 2016 12:04 PM
To: [hidden email]
Subject: Re: [Elecraft] 12 meter K3 RFI from nearby FM station

On 02/10/2016 03:57 PM, Jim Brown wrote:
> Yes, this hit me between the eyes as well. The K3 has Pin One Problems
> at many (most?) connectors, so RF current flowing on shields of cables
> plugged into those connectors will couple into the K3. I've been
> preaching to Wayne about Pin One Problems since 2004, when we met in
> Dayton.
>
> If the problem is around 90 MHz, I'd use multiple one-turn and two
> turn chokes with #43 material on every cable except the SO239 output,
> which IS actually bonded to the chassis. Also choke the power cable.

But it sounds like he was still getting the problem with no cables connected
to the K3:

On 02/10/2016 06:58 AM, Jon Zaimes wrote:
...
> Even when ALL cables are removed (only the power lead connected).
> Grounding or ungrounding made no change. I tried the radios on a >
battery but still had the RFI. Tried some ferrites on the power > lead but
no change.

I suppose it could be a "pin 1" problem on the power leads. It's kind of
hard to avoid that with an Anderson PowerPole connector. Probably
additional low-pass filtering on the DC input would help.

Alan N1AL

______________________________________________________________
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]

______________________________________________________________
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Message delivered to [hidden email]

Bob McGraw - K4TAX

Re: 12 meter K3 RFI from nearby FM station

In reply to this post by Chris Hallinan

Very interesting. I would not expect the integral shielding of the K3
radio to be that poor. Most of the box is metal and most connectors are
mounted on the metal box. For an AM BC station, I would not think
anything related to the carrier frequency, harmonics or parasitic , to
have anything near 14 MHz existing. So, it seems there are issues
internal to the radio which contribute to the spurious reception.

The worst thing causing spurious is near field dis-similar metals, in
effect diodes, excited by the RF. I've found in more than one case, the
metal fence around the BC tower and guy anchor points to be a
contributor. Better defined as poor site maintenance. In another case,
poor lighting conduit bond to the BC tower and also metal gutters and
downspouts around any build in the near field causing the same effect.
These will radiate like crazy at the resonant point. For example, a 8
ft downspout attached to a 33 ft metal gutter makes a nice 20M inverted
L. That 1100 watt station wouldn't just happen to be on 890 kHz or
close by would it?

If one is experiencing activation of the front end protector, then a
coax stub at the offending frequency should be of great assistance. The
only issue is the length of coax required to make the stub. {about 125
ft or so depending on BC frequency and velocity factor of the coax} As
to insertion of filters, unless attention is paid to negate the common
mode current, i.e current induced on the feed line from the BC station,
then the current simply flows around the outside of the expensive
filters and they are not effective.

The problem is solvable, identifying it is the challenge. That will
take some detective work.

73
Bob, K4TAX

On 2/11/2016 11:33 AM, Chris Hallinan wrote:

> I have a similar problem. I have a 1KW AM station about 1/2 mile away
> (1100W by day, 110W by night). With nothing connected to the radio, and
> even with a 50-ohm terminator on RX Ant in, I can clearly hear the signal
> at several places, most prominently at 14.220 MHz. Nothing I've tried,
> including expensive filters, shielded cables, etc. has helped. I get some
> relief using a RX Loop antenna basically nulled (broadside) to the tower,
> but that antenna is not always the best one for band and/or conditions. :(
> Some frequencies are simply unusable, and it overloads a front end
> protector I purchased to try to kill the COR relay clicking when I
> transmit, making it unusable.
>
> Chris
> K1AY
>
> On Wed, Feb 10, 2016 at 5:53 PM, Fred Jensen <[hidden email]> wrote:
>
>> I easily could have misread the original emailed problem, but he included
>> the note that this RFI occurred with all antennas [and I guess other
>> cables] disconnected which is very strange indeed. If that is so, then I
>> doubt stubs/filters on the antenna circuits would cure the problem.
>>
>> His list of frequencies might suggest some sort of intermod between
>> constant signals, one being the FM carrier, and possibly their harmonics.
>> Very strange problem at any rate. FWIW, and Phil can correct me, but US
>> FM/TV stations are usually authorized in EIRP, I think ... we referred to
>> KSBY-TV, where I worked while in college, as "Full-power television for the
>> Central coast, one hundred thousand watts on Channel 6 in San Luis Obispo"
>> on ID's. That was EIRP, 10 KW to a 10 dB turnstile. If that's still true,
>> it would seem a 2 KW EIRP FM station 2 miles away shouldn't be a big deal.
>>
>> 73,
>>
>> Fred K6DGW
>> - Northern California Contest Club
>> - CU in the Cal QSO Party 1-2 Oct 2016
>> - www.cqp.org
>>
>>
>> On 2/10/2016 2:04 PM, Ron D'Eau Claire wrote:
>>
>>> I agree. Even better.
>>>
>>> 73, Ron AC7AC
>>>
>>> -----Original Message-----
>>> From: Elecraft [mailto:[hidden email]] On Behalf Of Bob
>>> McGraw K4TAX
>>> Sent: Wednesday, February 10, 2016 9:18 AM
>>> To: [hidden email]
>>> Subject: Re: [Elecraft] 12 meter K3 RFI from nearby FM station
>>>
>>> An electrical 1/4 wavelength of coax as an open stub at the FM frequency,
>>> connected using a T at the receiver input, will notch the FM TX signal.
>>> It
>>> won't attenuate other frequencies across the ham bands including 6M. Plus
>>> one can transmit with the stub arrangement in place.
>>>
>>> 73
>>> Bob, K4TAX
>>>
>> ______________________________________________________________
>> 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]
>>
>
>

Bob McGraw - K4TAX

Re: 12 meter K3 RFI from nearby FM station

In reply to this post by Jon Zaimes AA1K

One other item, if available, try another brand/model radio using the
same power supply, location, antenna and such. If it is present on
that radio, most likely it is radiated. If it is not present, then most
likely it is generated in the K3. {To which that is an entirely
different can of worms.}

73
Bob, K4TAX

On 2/11/2016 12:55 PM, Jon Zaimes wrote:

> Yes, that is the case. Hearing it on both of my K3 transceivers with only
> the 12v power cable connected, nothing else (listening on speaker).
>
> Thanks to all for the tips. Still absorbing the advice before proceeding.
>
> 73/Jon AA1K
> Felton, Delaware
> www.aa1k.us
>
> -----Original Message-----
> From: Elecraft [mailto:[hidden email]] On Behalf Of Alan
> Sent: Thursday, February 11, 2016 12:04 PM
> To: [hidden email]
> Subject: Re: [Elecraft] 12 meter K3 RFI from nearby FM station
>
> On 02/10/2016 03:57 PM, Jim Brown wrote:
>> Yes, this hit me between the eyes as well. The K3 has Pin One Problems
>> at many (most?) connectors, so RF current flowing on shields of cables
>> plugged into those connectors will couple into the K3. I've been
>> preaching to Wayne about Pin One Problems since 2004, when we met in
>> Dayton.
>>
>> If the problem is around 90 MHz, I'd use multiple one-turn and two
>> turn chokes with #43 material on every cable except the SO239 output,
>> which IS actually bonded to the chassis. Also choke the power cable.
> But it sounds like he was still getting the problem with no cables connected
> to the K3:
>
> On 02/10/2016 06:58 AM, Jon Zaimes wrote:
> ...
> > Even when ALL cables are removed (only the power lead connected).
> > Grounding or ungrounding made no change. I tried the radios on a >
> battery but still had the RFI. Tried some ferrites on the power > lead but
> no change.
>
> I suppose it could be a "pin 1" problem on the power leads. It's kind of
> hard to avoid that with an Anderson PowerPole connector. Probably
> additional low-pass filtering on the DC input would help.
>
> Alan N1AL
>
> ______________________________________________________________
> 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]
>

Vic Rosenthal

Re: 12 meter K3 RFI from nearby FM station

In reply to this post by Jon Zaimes AA1K

I doubt that it is being picked up directly on the boards of the K3. I
would try ferrite on the power leads as well as a line filter on the AC
line to the power supply. Have you tried listening with battery power?

73,
Vic, 4X6GP/K2VCO
Rehovot, Israel
http://www.qsl.net/k2vco/

On 11 Feb 2016 20:55, Jon Zaimes wrote:

> Yes, that is the case. Hearing it on both of my K3 transceivers with only
> the 12v power cable connected, nothing else (listening on speaker).
>
> Thanks to all for the tips. Still absorbing the advice before proceeding.
>
> 73/Jon AA1K
> Felton, Delaware
> www.aa1k.us
>
> -----Original Message-----
> From: Elecraft [mailto:[hidden email]] On Behalf Of Alan
> Sent: Thursday, February 11, 2016 12:04 PM
> To: [hidden email]
> Subject: Re: [Elecraft] 12 meter K3 RFI from nearby FM station
>
> On 02/10/2016 03:57 PM, Jim Brown wrote:
>> Yes, this hit me between the eyes as well. The K3 has Pin One Problems
>> at many (most?) connectors, so RF current flowing on shields of cables
>> plugged into those connectors will couple into the K3. I've been
>> preaching to Wayne about Pin One Problems since 2004, when we met in
>> Dayton.
>>
>> If the problem is around 90 MHz, I'd use multiple one-turn and two
>> turn chokes with #43 material on every cable except the SO239 output,
>> which IS actually bonded to the chassis. Also choke the power cable.
>
> But it sounds like he was still getting the problem with no cables connected
> to the K3:
>
> On 02/10/2016 06:58 AM, Jon Zaimes wrote:
> ...
> > Even when ALL cables are removed (only the power lead connected).
> > Grounding or ungrounding made no change. I tried the radios on a >
> battery but still had the RFI. Tried some ferrites on the power > lead but
> no change.
>
> I suppose it could be a "pin 1" problem on the power leads. It's kind of
> hard to avoid that with an Anderson PowerPole connector. Probably
> additional low-pass filtering on the DC input would help.
>
> Alan N1AL
>
> ______________________________________________________________
> 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
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Bill Frantz

Re: 12 meter K3 RFI from nearby FM station

In reply to this post by Jon Zaimes AA1K

Just a thought: Are all the screws on the K3 case tight? there
are a lot of them, and good contact between the case pieces is
needed for shielding.

Also, I remember being told to remove some insulator tape during
assembly. Was this properly done?

Grasping at straws - 73 Bill AE6JV

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Bill Frantz | When it comes to the world | Periwinkle
(408)356-8506 | around us, is there any choice | 16345
Englewood Ave
www.pwpconsult.com | but to explore? - Lisa Randall | Los Gatos,
CA 95032

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