50kW commercial AM broadcast antenna < 1 mile away interferes with the daytime use of my 6500.

Justin Smith

The broadcast of KIXI 880 comes through on my speakers no matter to which  frequency I am tuned. I installed ferrite cores on all of my lines and I have installed a receive-only filter using RX A and loop A (FL1718RX DLW Associates). The interference is bad enough but to make it even more annoying is the station's playlist: elevator music meets the sort of music one hears when visiting a Medicare two-star nursing home. I have the ARRL book on minimizing RF interference but I would welcome any advice to help me mitigate this interference.
Thank you.
 

WA2SQQ

Its probably getting your speakers. I'm 1 mile from 770khz with no problems at all

Larry Loen WO7R

Check your panadapter.  It should show you if it is getting into your radio (as opposed to, say, the speakers).  If it is, maybe you can do something with a "deep null" cartoid pattern receive antenna, of which there are several designs.  That could throw some strong attenuation onto the direction of the offending signal.

Brian Morgan VK7RR

I suspect that your problem is rectification of the HF signal in the audio path of your system and almost certainly not inside your Flex. Are you using external speakers? Can you still hear the undesired "music" if you use your headphones rather than speakers? Are your speaker leads as short as you can make them? Have you tried winding excess speaker wire around circular toroids? It will need many turns to get rid of MF signals so don't be content with one or two turns.
If the phones are clean then you have a major clue that it is in your speaker system. If the phones are dirty then does the signal go when the antenna lead is removed? If not, it is coming in thru some other cabling so lots of toroids are called for.

If at first you don't succeed, try more decoupling and you will get there.

Jorgen

Hello Justin,

I guess you are using the consumer's loudspeaker set sold by a computer store? Some of these loudspeakers are of bad quality concerning RF interference from strong signals. Normally however, you can "****" the interference taking an iron powder (or ferrite) toroid core and pull the input cable (with the 1/8" plug) around the core making a toroid coil. The more windings the better. Do the same with the power supply cord and the interconnection cord between the L and R loudspeaker.

Vy 73 de OV6A Jorgen (Denmark)
 

Ken - NM9P

If there is nothing in your pan adapter display, you might need to get a ground loop isolator to put between your rig and powered speakers. This is usually a pair of 600 ohm transformers that go between the rig and speakers. (One for left and one for right channels). They can be purchased on Amazon for about $9.99.

Bill -VA3WTB

Or use twisted pair wires for the speaker wires.

Tim - W4TME

Justin - there are several different reasons this could be happening and it takes good troubleshooting techniques to figure out where is is coming from.

The first step is to see if the rectified signals are being generated the radio (it is possible) or in the RF signal path.  You can tell this by looking at the panadapter.  If you see images of the broadcast station on the panadapter when you hear it in the speakers and it goes away when you disconnect the antenna, the the rectification is in your RF signal path.  If not, then the rectification is in the audio signal path.

In regards to rectification in the RF signal path, I have worked with hams where the rectification came from a corroded bolt on a tower, a faulty lightning arrestor and a bad connector on a run of coax.  Your situation is compounded by a high aggregate signal level input into the SCU (ADC).  It is possible that the ESD protection diodes on the SCU/preslector module may be rectifying in the presence of such a strong signal.

If you do not get any relief from the suggestions made here on the Community, I recommend you submit a support ticket via our HelpDesk (https://helpdesk.flexradio.com/hc/en-us) so one of our Support Engineers can assign you a case number and investigate the issue.

Opening a HelpDesk support ticket will ensure our highest level of customer service we can provide.  For details on how to submit a HelpDesk support ticket, please refer to the following URL: http://helpdesk.flexradio.com/hc/en-us/articles/202118688-How-to-Submit-a-Request-for-Technical-Supp...

Once the support ticket is submitted, a support engineer will be in contact so we can work on the issue.

WA2SQQ

Make sure your preamp is set to 0, for testing. Also, decrease the span of the pan adapter so you are only looking at an amateur band for testing. This will insure you are using the band pass filters.

Justin Smith

To all of the members of this forum who so kindly offered such excellent and quick advice about how I can decrease or eliminate the interference from AM 880, I am grateful and once again impressed by the esprit de corps among amateur radio operators. I will try your suggestions over the next few days and by doing so, I am certain that I will be able to find a solution.

Regarding Jorgen's question about the source of the speakers that I am using, I use Bose Companion 5 Multimedia speakers. I have the  output of the PWR SPKR on the 6500 going to the line in input of a BHI Dual In-Line Noise Eliminating Module. The line out from the  BHI DSP goes to the accessory input goes the controller pod of the Bose system. The output of the pod is carried over a USB cable to the Bose integrated amplifier. I have placed ferrite cores on all of the cables mentioned above.

Justin Smith

Hi Jorgen:
Thank you for your insightful advice. Please see my reply below with regard to your question about the origin of my speakers.
Justin

Carl K5HK

I'm 1.5 miles from 50k. They have 3 very element ant being at me at night. No probls even on top band. I have 6500. All antennas resonant and plenty of grounding all station equipment. Check cables, connections and grounds.

KY6LA_Howard

According to FCC Data, I am 2,900' horizontal and -300' vertical from 18TV Transmit Antennas, 23 FM Transmit Antennas, numerous Public Safety transmit antennas and a bunch of "secret" US Navy things..  "Official" ERP is around 10MW...but realistically it is more due to the "secret" stuff... 

You can easily overload any RF field strength meter when you drive near them and the local joke is that you can light up a light bulb for free if you get near...

Needless to say, I live in RFI **** but the XYL loves our ocean view.

So I had to spend a lot of time and energy to clean up my station,   RFI is no longer a problem at my station. 

Suggest you read my presentation on "How to Build a Quiet Station"  https://db.tt/xG8SOiRI

I have included a number of hints that worked well for my RFI ****....

Justin Smith

Hi Carl and Howard:

Thank you for your advice. I particularly appreciate the link to download “How to Build a Quiet Station”, a presentation filled with hard to come by but eminently useful information intended to help amateur radio operators obtain the clearest possible signals.

My "ham shack" is less than one month old and I have not yet installed either an outdoor copper RF ground or purchased an artificial ground such as the model offered by MFJ Enterprises. I was pleased however to find that the artificial ground has received favorable reviews and is certainly a less expensive proposition than hiring an electrician to install an RF ground that is up to code. 

KY6LA_Howard

Justin

I don't know your physical layout but you really do not need an electrician to drive in a couple of 8' ground rods outside your shack.. Copper clad ground rods are standard at Home Depot.. you could borrow or rent an fence post driver.. and **** them into the ground nearest your shack... they will work better than the artificial ground because they do not need to be constantly retuned...

Justin Smith

I appreciate your advice on this, Howard; I could easily install the outdoor RF ground myself were it not for one salient fact: I promised a member of my family that if she agreed to let me put my antenna over her garden, I would promise to have any outdoor radio electrical work done by professionals. Thank you just the same.
Justin

KY6LA_Howard

Justin

You could always argue that A RF ground rod is NOT electrical work but is part of your antenna system....

Anyways you could drive in the rod into the ground, bury it and the cables leading to it all the way until it enters your house.. hence nothing shows and it would not need a professional...

WA2SQQ

From my experience most electricians would not have a clue as to what makes a proper RF ground. It's your money, but if I were you I'd do it myself.

Dan -- KC4GO

Don't think RF Grounding has a place in the NEC (National Electrical Code)
It's for us to do and separate from the safety ground for electrical systems.

Justin Smith

Thank you all for the outpouring of advice that made it possible for me to systematically approach this problem of AM interference. With a wealth of information that you have so generously shared with me, I was able to create a "lite" root cause analysis for the cause of the RF interference.

The problem was not the lack of RF grounding, undesired reception by the speaker wires, or by interference within the 6500 itself. To appreciate the cause of the interference, I should tell you that the PWR SPKR output of the 6500 goes to a dual channel DSP made by BHI, and the line output from the DSP goes to the input pod of Bose Companion 5 multimedia speakers. Remove the DSP unit from the audio circuit, connect the output of the 6500 directly to the input pod of the Bose System and the interference disappears. The interference is caused by the presence of the DSP unit in the audio circuit.

This leads to a follow-up question: I can certainly Live without the DSP unit but I like the degree to which it reduces the background noise and improves the intelligibility of faint or noisy speech. If there is a way of keeping it in the circuit and avoiding the RF interference, I would like to do so. Do you have any suggestions about how to shield the DSP unit to prevent it from picking up the local AM station. Would it be helpful to wrap the DSP unit in copper mesh?

With appreciation,

Justin

WA2SQQ

Obviously the DSP unit has an input and an output cable, right? OK, so if you connect it to the Bose speakers, and disconnect the  input cable, is the interference heard? If not, that would suggest that the input cable is introducing the BCB RF, acting as your "antenna". That would be where I would start. I'd replace the standard audio cable with a piece of home made balanced audio cable. Take a short length of coax, like RG-58. Remove one twisted pair from a length of network cable. Use the center conductor of the coax to pull the twisted pair through the shield. Now you've got double nise immunity, a shielded twisted pair. Use the two twisted wires to feed audio and ground the shield. She if that keeps the RF out. Keep cable as short as possible.

Ken - NM9P

Sometimes you can get a ground loop between you rig, the DSP unit, and the powered speakers. Ground loop isolators between one or both pieces of equipment can often relieve the problem. The first step is to determine which junction is the offending piece and isolate that one. Also, do you have a second audio input connected to your Bose, or the DSP unit? With the Bose Companion 2 series 3 that I have, I started getting ground loop RF interference when I connected a second rig (my 1500) to the second audio input. When I unplugged the cable from the 1500, the interference went away. So I put the ground loop isolator between the 1500 and the Bose Companions, and that ended the problem. It only cost me abou $10 at Amazon. Now I can transmit on the 6500 and even listen to myself on the 1500 with no "RF interference." Ken - NM9P

KY6LA_Howard

@Justin

1.Have you installed the latest SSDR Release V1.4.11??
 - it has a vastly improved Noise Reduction Feature which may be good enough for you to totally eliminate the outboard DSP Unit

2.  If  the internal NR is not good enough for you then I would suggest you install Type 31 Ferrites on the input and output leads to the DSP Box.

Justin Smith

Friends: 

 I have read all of your suggestions and tested nearly all of them in a stepwise fashion so that I would be able to arrive at as specific a solution as possible. The undesirable intrusion of AM 880 KIXI was caused by two ground loops: one involving the line from the 6500 PWR SPKR output to the line input of the BHI Dual-channel DSP, and the other involved the cable from the line out of the DSP to the line input of the Bose Companion 5 pod. As Ken suggested, I bought two Pyle PLGI35T 3.5 mm/1/8-Inch Stereo Audio Ground Loop Isolators     for $10.24 each. I installed these on the input and the output audio cables to and from the DSP.  At  maximum volume there is now no hint of the formerly interfering signal. 

The problem has been eliminated completely and inexpensively. Once again, my great thanks to each of you for your generous consideration of what was a vexing problem. A side benefit is that I can still use the BHI-DSP to nearly eliminate the background noise from even the faintest incoming voice signal .

With appreciation,
Justin Smith

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