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CHASING MYSTERIOUS RF GREMLINS ARE A TON OF FUN


nokones
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Since, I finally got my repeater online and I am using my big stick antenna, I needed to come up with a better solution than using a mag-mount with a Phantom Stubby antenna sitting on the windowsill of my shop.  So, I decided to install a mobile antenna configuration in the attic above my shop since I only need to hit a few repeaters from my base station.  I used a Laird Base Coil Non-Ground Plane antenna with a Laird NMO Mount/Male N Adapter and a bracket affixed to wall near the top pitch of the roof and in front of the vent and ran about 25' of LMR400 cable to my radio on the bench that sits on top of the repeater. 

You would think that would be good-to-go for just hitting a few nearby mountain top repeaters that I can do with a 4 watt portable with no problem.  No, that wasn't good-to-go because the screen in front of the vent liked to reflect some RF back that I didn't like so I relocated the antenna further away from the screen.  Well that did take care of the reflection of RF and I kinda like the VSWR, under two so that seem to be good-to-go.  I ran a test with a radio repeater club member on the main repeater and everything sounded good and I was still liking the reflection and VSWRs so I decided to put everything back in its place.  I started tacking down the coax, reinstalling a metal grid type shelf that was in my way when I was installing the antenna in its original location and than relocating the antenna, put away all the tools and decided to check the reflection and RF out. 

Damn, I popped the GFI that I originally thought was the breaker.  I was wondering how can I pop 20 amp breaker with hardly a load on that circuit.  I didn't have that problem before so I went to the electrical panel and all the breakers were Ok.  I went to the outlet and saw the little itty bitty red light on the GFI reset so I reset and keyed the radio and damn it, the GFI popped again.  I ran an extension cord to another 20 amp dedicated circuit and I was still popping the same GFI outlet.

I decided to relocate the romex wire for the four-plex that I use for my radio stuff further away from the antenna.  I had to lower the metal grid type shelf again in order to relocate the romex wire further away. I also relocated the LMR400 further away from the romex wire and tacked it down on the roof/ceiling cross-members. After relocating the romex and retacking the coax. I went downstairs to the radios and fired everything up and walla, the GFI didn't popped alright.  So, I went back upstairs to put everything back in its place, take my tools back downstairs. Yes, I did key the base radio again and guess what, the GFI popped again.  Are you kidding me.  I went back upstairs and again relocated the coax LMR400 further away from the affected romex but, I didn't do anything with the metal grid type shelf, there was no reason to because the shelf wasn't in my way and I already replaced the three boxes what I had on the shelf which, were boxes full of Christmas decorations.

Went back downstairs and keyed the radio Pop goes-the GFI.  I go back up stairs and took the boxes off the shelf and checked again, and Pop.  Now, I'm trying to think what worked before and I know what is not working now.  The only thing I can think off is lower the metal grid type shelf and try again.  I'm thinking what in the hell does this shelf have to do with anything but, I did lower it.  I went back downstairs and keyed the radios and nothing popped, are you kidding me?  I went back upstairs and kinda popped up the shelf and went back downstairs and keyed the radio, Pop, goes-the-GFI.

Went back upstairs and lowered the shelf and rekeyed and nothing popped.  Wow, are you kidding me, so I left the shelf down.  I put everything away and I keyed the radio and nothing popped.  Unbelieveable, its fixed, I hope.

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Sounds like fun. 

 

Back in the day I used to have a Nextel phone which used iDEN that had a baked in radio service which would call a phone number and play music through the phone. Every time I used that service while in my bathroom the GFCI outlet would trip, despite the phone not being plugged in. Oddly enough that would never happen while on a call or using the ptt function, just while listening to packetstream radio.

My dad also had a ham rig which would set off our house alarm when he keyed up on a certain band, which long escapes memory.  

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9 hours ago, Sshannon said:

@nokones

Are your grounds (antenna and transceiver) bonded together and then bonded to the service ground?

They should be. 

The antenna and radio are only connected by the coax at this time. I do have a ground that is connected to the service ground up in the attic and nearby the radio. The ground up in the attic is for the lightning arrestor that I have on the big stick for the repeater. I intend to tap into that ground with this newly installed antenna.

I kinda figured that the cause of my problem could have been contributed to the lack of a grounding system on this antenna run.

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Some or all of my exterior motion lights come on when I key up on 462.700MHz.  The motion lights on my garage door openers in the unattached garage are triggered by 462.675MHz. Thankfully the doors don't roll open.

This occurs on those frequencies with either my 50 watt KG1000G with roof-mounted antenna or my 5 watt HTs...but I aint never popped a GFI 🤨.

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Some of the first smart meters PG&E rolled out were on a frequency that tripped early GFI breakers (Zinsco to be specific).  Also some of the first generation arc fault breakers were effected as well. I have seen two pump motors that were both grounded from the same source but not bonded together that created enough noise (magnetic field) to keep the flow meters on the water lines from working, once bonded together and all was good. It’s all PFM (pure fn magic).😀

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These comments point out an interesting issue if I understand things right. Most, if not all, electronic products are sold with FCC Part 15 compliance. A section in that part basically says the device accepts all interference even if it causes the device to malfunction. If it does then contact the manufacture.

Now try to explain that to your neighbor when they says it's YOUR problem to fix. Nope, so long as your radio meets all FCC certifications. Another reason to be sure your radio is Part 95 certified.

A case in point.

Years back people were experiencing car alarm failures around the I-75 and 14 Mile intersection close to where I work. The FCC was notified. The issue was traced to a Ham ATV transmitter on top of a tall senior apartment building a couple of miles west of the location above. The FCC shut the site down while they did their investigation. They found everything complied with all technical requirements and allowed the site to resume normal operations. The ding-dongs had put the alarm system on the 70cm band. I believe there is a provision in the rules for this were the equipment manufactures can use 433MHz.

https://www.edn.com/using-433-mhz-for-wireless-connectivity-in-the-internet-of-things/

The head guy at the alarm company asked one of the site's equipment owners in for a talk. He asked how much power they were running. The answer was about 100 watts. Then he asked the second one. How much CAN they run. The answer was 1500 watts. The owner I was talking to telling me this story said the alarm company guy almost crapped his shorts.

Then he proceeded to tell me another story about how Chrysler, as it was known at the time, had their tire pressure sensors malfunction. They were running tests on them and had the problem again in about the same area. In their case they figured out the cause and understood it was their problem to fix.

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Thanks for sharing that info Lscott!  This will the fourth or fifth time I have heard mention of tire pressure management system interference...and not always the same auto manufacturer..

I am compelled to ask, regarding the car alarm failures, do you know if this was this a permanent failure or a temporary condition?

In either case I can see how people could be a little miffed that their car alarms could be so easily and anonymously defeated.

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21 minutes ago, Sab02r said:

Thanks for sharing that info Lscott!  This will the fourth or fifth time I have heard mention of tire pressure management system interference...and not always the same auto manufacturer..

I am compelled to ask, regarding the car alarm failures, do you know if this was this a permanent failure or a temporary condition?

In either case I can see how people could be a little miffed that their car alarms could be so easily and anonymously defeated.

My understanding was it only occurred in the vicinity of the ATV site. Once the affected systems were far enough away they were OK. 

I guess what it came down to the designers didn't do enough research when selecting what frequency, band, to use for their product. The radio spectrum is very complex with the same band being used for different purposes, shared, and sometimes they don't play together very well.

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More gremlins came and visited this morning.  My repeater decided that it didn't want to unkey when a transmitting radio unkeyed.  The repeater stayed key because there was a signal present to the receiver.  This problem cropped up this morning.  It appeared like a distant open carrier with a little intermod signal mixing in.  When I removed the receiver cable from the duplexer, of course the signal quit and the repeater unkeyed.

My big stick antenna that I use for the repeater will see very far.  I can even communicate with a 4 watt portable little over 10 miles to the repeater.  That is why at first I thought it was a distant signal.  I connected the repeater to my secondary antenna, you know, the one that was popping my GFI, and put my base radio on the big stick.  The GFIs are fine and after the swap, the repeater operated as designed, no problem at all.  I put the repeater back on the big stick and the problem was still present.

Just for giggles, I checked the RF out and reflected between the duplexer antenna output port and the big stick antenna and the needle on my Bird barely moved on the reflected so I put the 10W slug in and checked the reflected again and I saw a tad over a watt reflected.  The RF power from the duplexer was about 26-27 watts on 462.625 MHz.

So, in case that someone decided to communicate through my repeater I decided it was best to put the repeater on my secondary antenna, for the interim, so it will function properly and not stay keyed up forever.  Anyways, I already had another project to occupy my time for the day.

Today, my plans were to install my additional grounds to the repeater station and the secondary antenna system that I use for the base radio.  I completed the job and I decided to reconnect the big stick antenna system to the repeater and the secondary antenna system to the base radio.  The repeater unkeys as designed and the problem appears to be eliminated.

I elected to leave the metal grid shelf lowered up in the attic that was causing the GFI to pop because I didn't want to push my luck but, my curiosity will no doubt get the best of me and I more than likely put the shelf back in place to see if the grounds eliminated the popping GFI.  Anyways, I don't use the shelf and it just gets in my way.

I think the newly installed "Green" wires scared and chased the gremlins away.  At the moment, everything is just peachy. 

I must have been creating my own intermod problem without the secondary antenna system and the repeater station not being grounded.

Grounding the Repeater station.

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Grounding the Secondary Antenna System for my base radio.

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Connecting to the ground system at the Lightning Arrestor that is used on the LMR400 Cable run from the Big Stick to the Repeater Station.

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Grounding is good!  Glad you got the problem solved. 

I would never have thought to move the shelf to solve the GFCI problem, though after reading your excellent writeup it does make some sense.  Perhaps we should keep a long-running thread (some forums allow stickies - not sure if MYGMRS does) on this forum of odd things that can interfere with radios and repeaters, and also devices that our radios occasionally interfere with...as a reference for others who run into gremlins in their systems.

Since it was your experience, I'll leave it up to you to decide if you want to start that thread.

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I forgot to mention that the GFI would only pop on the 462 Meg freqs and not the 467 Meg freqs. To be on the safe side for the future, I'm going to either replace it with a GFI dialed-in on a HAM band freq since, I'm not a HAM, or a non-GFI outlet.

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55 minutes ago, Sab02r said:

Grounding is good!  Glad you got the problem solved. 

I would never have thought to move the shelf to solve the GFCI problem, though after reading your excellent writeup it does make some sense.  Perhaps we should keep a long-running thread (some forums allow stickies - not sure if MYGMRS does) on this forum of odd things that can interfere with radios and repeaters, and also devices that our radios occasionally interfere with...as a reference for others who run into gremlins in their systems.

Since it was your experience, I'll leave it up to you to decide if you want to start that thread.

A Sticky is a good idea for people to add their experiences. I have a few odd balls that I could that I have learned over the years such as pouring oil down a tower guy-wire once a month and oil and torque tower joint bolts to eliminate intermod interference.

I don't have a clue on how to start a Sticky. I think a Forum God would have to do that.

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