RFI after transmitting

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  • Updated 2 years ago
I have this issue that is driving me bonkers. Everytime after I unkey my mic I get three bursts of RFI each lasting approximately a second and about 5 - 6 seconds apart. 

My setup is a Flex 6700 connected to a LP-500 Station monitor, a SPE 1.3K-FA amp, and a Traffie Hex at 35 feet. I have taken the LP-500 and SPE out of the loop and connect the Hex directly to the radio and still get the same result.

Link below is a screenshot of what I am seeing. I am transmitting on 20m, but you can still see the noise on 17m and 15m (also on 10m). 

https://1drv.ms/i/s!ArkcCw0XzRtckzp6qxMTp4FmQld8

Any insights greatly appreciated!

73

Ross
W9TVX
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W9TVX

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Posted 2 years ago

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Doug Hall

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Ross,

Odd indeed. Does this happen even with your power output set to zero? In other words, is it the act of PTT on/off that causes it, or is it RF getting into some device in your home and possibly causing that device to reset/reboot?

Doug K4DSP
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W9TVX

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Doug, It doesn't do it at 0 power output. Some further observations:

- It is always 3 equal bursts of RFI evenly spaced apart. Sometimes a particular burst will be stronger than the others

- I can get it to start triggering at around 50W of power. Once I get it going, if I lower the power (e.g to 30W) and follow-up fairly quickly (~5 sec) after a transmission, I can get it to trigger. If I wait a while and then transmit at the lower power, the effect is not observed

It almost feels like a circuit with 'capacitance' is getting charged up and then discharging. I guess the next step is to power the down the circuit breakers and figure out what might be causing it

Oi!
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Lou

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Have you tried transmitting into a dummy load....nothing else hooked up ?

Lou N2TU
(Edited)
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Ned K1NJ

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   I love this stuff.  Reduce power close to the minimum that produces the effect and rotate the antenna. Maybe you'll see where the "target" is.

  Ned,  K1NJ
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W9TVX

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- Lou, Tried the dummy load no effect

- Ned, Tried rotating; unfortunately I'm getting the effect regardless of direction. The Antenna is on the roof of my house (my ham station is in the garage which is a separate building) so I'm guessing the house is getting RF regardless
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Doug Hall

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Yeah, it's almost for certain that RF is getting into some device in close proximity to you and causing that device to reset, and in the process of resetting/rebooting the device generates some broadband noise. Some possibilities, in no particular order, include wireless devices that have to link with something when they start, devices that have relays or motors (both can generate broadband noise when they start,) smart lighting controllers, or other "smart energy" devices. What you hope is that it's in your house (so you can unplug, or repair, or replace it) and not in a neighbor's house where you have no control over it.
Doug K4DSP
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Martin Ewing AA6E

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Maybe RF is overloading something in your house, like a smoke detector or whatever. You might try switching off all power circuits, except your shack, to see if that changes things.
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W9TVX

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I'm going to shutdown all the circuits in the house one day during the week (when the YL is out and about) and start narrowing it down. There are some other noise sources that have been irking me, so maybe I can kill two birds with one stone (unless of course the issue is with some electronics in one of my neighbours houses). 

I'll report back after I give it a go
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Al / NN4ZZ

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Ross,
Here is another hypothesis based on the reduced power scenario you described above:

- I can get it to start triggering at around 50W of power. Once I get it going, if I lower the power (e.g to 30W) and follow-up fairly quickly (~5 sec) after a transmission, I can get it to trigger. If I wait a while and then transmit at the lower power, the effect is not observed

Lower power means lower current draw,  And the fact you can trigger it again at a lower RF power setting if you do it quickly leads me to think there may be an issue in your power supply.   Maybe a part that is heating / cooling and intermittent.   

Do you have another power supply (or 12V battery) you could try?   At least this test could eliminate the power supply as a problem.

In addition since you noted that transmitting into a dummy load has no effect, that supports the idea of a power supply or other intermittent heating or connection issue rather than a transmitted RF triggered event.  It could also be the power cable connections or even a part in the radio.  But again, I'd start by trying a different power supply to eliminate that. 

Regards, Al / NN4ZZ  
al (at) nn4zz (dot) com
SSDR / DAX / CAT/ 6700 -  V 1.10.16
Win10
(Edited)
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Paul - K6HR

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I had the same problem here. In my case it turned out to be USB to Serial cables that were being reset due to RF. I put snap on ferrites at both ends of the cable and the problem disappeared completely.
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W9TVX

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Paul, I was so hopeful that you had my problem licked as I also have a couple of USB to serial cables. I slapped ferrites on mine with great hope, but alas to no avail. Back to plan A: Shut down the house and see if that cause is there or in the shack!
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Chris Tate - N6WM, Elmer

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Try removing the USB serial cables completely and see what happens...
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W9TVX

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Today, I spent some time diagnosing the issue and in the process cleaned up some other noise sources.

The root cause of the problem was RF resetting a netgear FS105 switch. In the process, I also discovered that several Axis PPOE cameras were the cause of substantial noise on 10 meters.

The process I used was to first shutdown the house, then bring up just my internet router to make sure it was not the source. Once I had ascertained this, I used SmartSDR on my iPad to watch what happened when I turned various circuits back on. Once I found the circuit that was the source of the trouble, I shut down all the devices on that circuit and started turning them on one by one until I sorted out which were causing problems.

I still have some noise problems, but I think they are caused by a transformer on a power pole not too far from the house butI can get around those with TNFs

Thank you everyone for helping me diagnose this problem

Ross
W9TVX
(Edited)
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Tim - W4TME, Customer Experience Manager

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 Once I had ascertained this, I used SmartSDR on my iPad to watch what happened when I turned various circuits back on. 

Excellent use of the iPad app!
(Edited)
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Pat - WH6HI

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It might be a good idea to measure the total run distance to your grounding point.  Anything over a 1⁄4 wave length can cause RF energy conducted and common mode to exits on your station and on your electrical system.  Even with filtered outlet devices/power strips.  The ground of the station can couple around these filters onto the electrical lines if strong enough.  
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Tim - W4TME, Customer Experience Manager

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Agreed.  Sometimes no ground is the best RF ground.  I've solved many a RFI issue by removing the RF ground connection; especially on shacks that are not really close to an earth grounding point.  

This article explains a lot.
https://helpdesk.flexradio.com/hc/en-us/articles/204779159-Grounding-Systems-in-the-Ham-Shack-Paradi...
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W9TVX

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I basically have short lengths of solid core wire (about max 4ft in length) running from the grounding lug of each piece of equipment to a ground bus (thats about a foot in length). That is connected to a grounding rod that is about 2 ft away.