[bars] WRKO RFI on 14.280 MHz

Sat Feb 11 22:06:44 EST 2023

 Interesting Chris,
Sounds like one or more of the WRKO harmonics snuck past the low pass filter and was aliased into the spectrum when in direct conversion mode. Would be interesting to see what kind of power you are seeing at their 5th and 7th harmonics. Not sure what sample rate they are running at when you tune that low.

-Craig K1CWD
    On Saturday, February 11, 2023 at 09:41:46 PM EST, Christopher Lennon <kwaj.speedo at gmail.com> wrote:  

The radio I have is a SDRPlay RSPdx.  It is a receive only SDR but it has good coverage even below the AM band.  I occasionally look at 60 kHz to see if I can see WWVB.  When I go down that low the radio displays a two sided spectrum.  This evening I could not see WWVB, but at 0 Hz there was a signal that looked like AM.   So I clicked on that using AM to demod and I heard an intelligible voice.  I tuned to 680 kHz.  Hmmm was it the same?  Back and forth a few times and, yes, what I was hearing at 680 kHz I was also hearing at baseband on the SDR.

I don't see it at 14280 kHz.  But I that radio station is sneaking into my radio at baseband.  I haven't studied up on the SDRPlay to understand the frequency plan.  I have mostly been using the ham bands laid out in the software.  I think if select a low enough frequency you get a direct digital sampling.  The SDRPlay RSP dx is supposed to have a low pass filter to take out the AM Broadcast bands when you select a lower frequency.  I don't see a switch to turn that on.  But it was clearly not on when I went to 60 kHz because I could see the AM broadcast band in the two sided spectrum.

I guess I will have to RTFM.

Chris W2BPL

 On 2/11/2023 7:32 PM, Craig Davidson via bars wrote:

  Wow - thanks Art - great field work haha. 
  Simonds park is close to my QTH. I'll bet the sensitivity on my rigs might be better than the Grundig, but can't be sure by how much. 
  As power falls off I believe as a function of distance squared, the probability of  seeing the harmonics after a few miles is pretty low. 
  Appreciate you taking the time to capture this data - will have to think about this some more. 
  -Craig 
      On Saturday, February 11, 2023 at 06:27:25 PM EST, apizer at comcast.net <apizer at comcast.net> wrote:  

And here is the data form Simmonds park overlooking the common.  No issues there, I was able to copy some dx even on 14280 ssb.

-Art

NF1A

From: bars <bars-bounces at w1hh.org> On Behalf Of apizer at comcast.net
 Sent: Saturday, February 11, 2023 5:19 PM
 To: 'wo1n' <wo1n at comcast.net>; 'Craig Davidson' <cwdavidson1 at yahoo.com>; 'BARS Reflector' <bars at w1hh.org>
 Subject: Re: [bars] WRKO RFI on 14.280 MHz

Got the data before sunset.  Will send something out later.

-Art

From: bars <bars-bounces at w1hh.org> On Behalf Of wo1n
 Sent: Saturday, February 11, 2023 4:52 PM
 To: apizer at comcast.net; 'Craig Davidson' <cwdavidson1 at yahoo.com>; 'BARS Reflector' <bars at w1hh.org>
 Subject: Re: [bars] WRKO RFI on 14.280 MHz

Don’t forget they reduce power and change the pattern on the array precisely at local sunset.

Ken

From: bars <bars-bounces at w1hh.org> On Behalf Of apizer at comcast.net
 Sent: Saturday, February 11, 2023 3:46 PM
 To: 'Craig Davidson' <cwdavidson1 at yahoo.com>; 'BARS Reflector' <bars at w1hh.org>
 Subject: Re: [bars] WRKO RFI on 14.280 MHz

OK you guys really got me going . . .literally  . . . I am heading out now with my Grundig to the Network Drive/ Middlesex Pike construction site.

Art

NF1A

From: bars <bars-bounces at w1hh.org> On Behalf Of Craig Davidson via bars
 Sent: Saturday, February 11, 2023 1:03 PM
 To: 'BARS Reflector' <bars at w1hh.org>
 Subject: Re: [bars] WRKO RFI on 14.280 MHz

Thanks Tom,

I first assumed an overload case, but using the input attenuators, or using a terrible antenna (a two foot piece of coax) I think would eliminate the cause as being a front end overload.

The other concerning clue is this just started happening a few days ago. It could be that WRKO increased transmitter power at that point, but not being familiar with broadcast operations I'm not sure it that's even reasonable to consider.  

I do see this on two receivers, and both receivers are direct conversion front ends (IC-7300 and ANAN 7000 DLE), so don't know if that is a factor.

If this was ongoing from when I first set up my shack a few months ago I would be less suspicious of some change at WRKO.

I did see that they have a night antenna pattern, so that's a good reminder to check out the interference level tonight.   

I have attached a video of the interference while using a two foot piece of unterminated coax. The signal level is at around a S5-S7

73, Craig 

On Saturday, February 11, 2023 at 12:40:46 PM EST, Tom Walsh <k1tw at comcast.net> wrote: 

Hi Folks,

I am a mere 2-3 miles from WRKO’s transmitter site and there is no detectable signal at my QTH on 14.280 even with my beam pointed at their transmitter site.  I will try listening again after dark when they shift to a night antenna pattern.

Craig, if you are an ARRL member, you can also reach out to their Lab folks in Newington for advice.

Please look at this web page from ARRL http://www.arrl.org/broadcast-station.  

This may explain what is probably occurring at Craig’s QTH which is very close to the WRKO transmitter site in Burlington.  It also suggest remedies such as reducing the receiver input sensitivity.  

>From the ARRL page and I quote:

“In ARRL’s experience, however, the majority of broadcast interference reports arise because the fundamental signal overloads sensitive amateur receivers. In that case, the additional filtering or attenuation necessary to protect the receiver must be installed by the amateur operator.”

73,

Tom K1TW

From: bars <bars-bounces at w1hh.org> On Behalf Of Craig Davidson via bars
 Sent: Saturday, February 11, 2023 10:48 AM
 To: Christopher Lennon <kwaj.speedo at gmail.com>; ARTHUR PIZER <apizer at comcast.net>; n1hts at comcast.net
 Cc: Craig Davidson via bars <bars at w1hh.org>
 Subject: Re: [bars] WRKO RFI on 14.280 MHz

Hi Jim,

I think If it's actually a spur from the station then a filter wont help.

This morning, I am able to see the 680 KHz station at 21.280 MHz using *NO* antenna, but just a short two foot piece of coax connected to the rig. I see it on both of my receivers.

>From Art - NF1A

"I could not hear it at my home station on 14280 tried 4 antennas various polarizations including hex beam at 40 ft pointed south. I live just north of the Billerica Country Club golf course.  Let me know if it still persists.  I may throw my Grundig G6 in the car and drive around and monitor the next time I run errands in Burlington.

Art

NF1A"

Thanks for your report Art.

Since I have the signal with a terrible antenna (short piece of coax), and it responds like a normal signal to attenuation, can I assume my digital front-ends are not overloaded? Is it more likely I'm seeing the 21'st harmonic spur from a station a few miles away? Also - this just started a few days ago - no real change to my setup.

-Craig, K1CWD

On Saturday, February 11, 2023 at 10:32:06 AM EST, n1hts at comcast.net <n1hts at comcast.net> wrote: 

If AM stations are bleeding in, buy a filter. 

Morgan Filters (kf7p.com) 

jim 

On 02/10/2023 7:19 PM Christopher Lennon <kwaj.speedo at gmail.com> wrote: 

I live in Bedford.  I hear 680kHz loud and clear, but that is WBEZ. 

I only have an SDR receiver with a simple wire antenna set up at the moment.  I didn't hear anything on 14.280. 

Chris W2BPL 

On Fri, Feb 10, 2023, 12:32 PM ARTHUR PIZER <apizer at comcast.net> wrote: 

Hi all I’ve been sending these replies from my iPhone voice to text feature from my cafeteria during lunch at work so I apologize for any typographical errors or that is to say transcription errors when I get home I will give a listen for my shack tonight 73 Art 

On 02/10/2023 12:27 PM Craig Davidson via bars <bars at w1hh.org> wrote: 

Thanks for all the replies from everyone. I'm not sure if everyone sees the replies through the reflector, but wanted to add some additional info: 

I have two rigs, an ANAN 7000 and an IC-7300. Both rigs see the AM signal at 14.280. 

I can tell it's WRKO because I switch to the AM band and hear the same dialog on their station. Of course, their station is booming because I'm only a few miles away. 

There is no overload condition on the front-ends of either receiver that I can tell. I can reduce the input attenuation and the signal is still there, although reduced somewhat with the attenuation, which is to be expected I think if it's actually interference being picked up by the antenna, as opposed to an RFI path after the front-end. 

I have two wire antennas with two separate feedlines, and have the interference on both antenna's.  

This just started recently, and can't correlate it to any change I made in my station. 

Thanks, 

Craig 

On Friday, February 10, 2023 at 11:32:10 AM EST, Craig Davidson via bars <bars at w1hh.org> wrote: 

Good Morning, 

Has anybody else noticed interference at 14.280 from the WRKO station broadcasting at 680 KHz? 

This seems to have started a few days ago. 

I'm pretty sure it's not receiver overload on my end, but actual out-of-band stuff generated by the station (granted that my QTH is very close to the transmitter in Burlington). 

I tried calling the station numbers I had available but just get voicemail. 

Anybody deal with this before, or have good contact info for the station engineer? 

Thanks, 

Craig, K1CWD 

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