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Author Topic: Pickup Truck With Massive HAM Radio Antenna Clipping my Soun System!  (Read 904 times)

Douglas Cyr

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Alright, so I have an interesting situation.

The background:

I live in a small 2nd floor apartment in a downtown area, and there is a restaurant right across the street. From the window in my small "music studio" (aka an 8'x8'x8.5' bedroom), I can look right out to the restaurant's sidewalk seating. The sidewalk across the street is probably only about 40' from where I'm sitting now typing this in the "studio". Additionally, the only parking for the restaurant is on the street just outside the restaurant, which is no more than 40' from my desk. On my desk is a mixer (Soundcraft Signature 12MTK), which then leads to a BSS FDS-310 active crossover, which feeds an active subwoofer and an amplifier powering two monitors.

The situation is this:

Twice now, a big Ram 3500 pickup with a massive antenna I believe to be part of a HAM Radio system has parked just outside the restaurant. It looks something like this:
https://www.n1fd.org/wp-content/uploads/2016/08/Ant-Scorpion-medium.jpg

The first time I saw it, it was as I was walking back up to my apartment, I noticed the huge antenna and thought it was interesting, if not excessive. The truck was just parked outside the restaurant with no one inside it. About 40 minutes to an hour later, I was sitting in front of my monitors with my system powered on, with audio coming through my mixer at about -24dB (the lowest level on the meter). My blinds are also drawn, so I cant see out the window. Out of nowhere, an overpowering signal that sounds like an apocalypse comes through my system, scaring the hell out of me and spiking the meter to +16dB!

I frantically pull down faders and freak out until it stops, then look out the window and see the pickup truck is gone.

Fast forward to tonight, I notice the same pickup truck parked outside. Nearly as soon as I notice it, I see the owner get in and start it up, so I run over to the "studio" to see what happens and confirm that the pickup truck was related to my anomaly.

A few seconds after the truck starts driving away, the same thing: an apocalyptic distortion that sounds faintly like radio chatter blasts through my speakers, peaking the mixer. Pulling faders down didn't seem to do anything, I had to turn off the amplifier to stop it.

My questions are:

1) What is the legality of this radio system? My understanding is that it's legal as long as the driver of the truck has a license, but surely driving though a city with a system like that is causing issues for more people than just me?

2) Exactly what component of my system is picking up his transmission? What can I do to mitigate this?

The mysterious part to me is that the audio system in my studio picks this up, but my girlfriend didnt report experiencing anything similar from the sound system I have set up in the kitchen with the exact same model of amplifer I have in my studio powering some bookshelf speakers in there.

I've experienced amplifers picking up faint radio signals before any my friends house who lives several blocks from a local radio station, but nothing like this! And why didnt the amplifier in the kitchen pick anything up?!

Well if anyone has bothered to read this far down, thank you! I'd love some insight from anyone more knowledgeable about what's going on in more technical terms, I'm curious about this.

Thanks,
Doug
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Scott Holtzman

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Re: Pickup Truck With Massive HAM Radio Antenna Clipping my Soun System!
« Reply #1 on: April 08, 2021, 11:55:22 pm »

Alright, so I have an interesting situation.

The background:

I live in a small 2nd floor apartment in a downtown area, and there is a restaurant right across the street. From the window in my small "music studio" (aka an 8'x8'x8.5' bedroom), I can look right out to the restaurant's sidewalk seating. The sidewalk across the street is probably only about 40' from where I'm sitting now typing this in the "studio". Additionally, the only parking for the restaurant is on the street just outside the restaurant, which is no more than 40' from my desk. On my desk is a mixer (Soundcraft Signature 12MTK), which then leads to a BSS FDS-310 active crossover, which feeds an active subwoofer and an amplifier powering two monitors.

The situation is this:

Twice now, a big Ram 3500 pickup with a massive antenna I believe to be part of a HAM Radio system has parked just outside the restaurant. It looks something like this:
https://www.n1fd.org/wp-content/uploads/2016/08/Ant-Scorpion-medium.jpg

The first time I saw it, it was as I was walking back up to my apartment, I noticed the huge antenna and thought it was interesting, if not excessive. The truck was just parked outside the restaurant with no one inside it. About 40 minutes to an hour later, I was sitting in front of my monitors with my system powered on, with audio coming through my mixer at about -24dB (the lowest level on the meter). My blinds are also drawn, so I cant see out the window. Out of nowhere, an overpowering signal that sounds like an apocalypse comes through my system, scaring the hell out of me and spiking the meter to +16dB!

I frantically pull down faders and freak out until it stops, then look out the window and see the pickup truck is gone.

Fast forward to tonight, I notice the same pickup truck parked outside. Nearly as soon as I notice it, I see the owner get in and start it up, so I run over to the "studio" to see what happens and confirm that the pickup truck was related to my anomaly.

A few seconds after the truck starts driving away, the same thing: an apocalyptic distortion that sounds faintly like radio chatter blasts through my speakers, peaking the mixer. Pulling faders down didn't seem to do anything, I had to turn off the amplifier to stop it.

My questions are:

1) What is the legality of this radio system? My understanding is that it's legal as long as the driver of the truck has a license, but surely driving though a city with a system like that is causing issues for more people than just me?

2) Exactly what component of my system is picking up his transmission? What can I do to mitigate this?

The mysterious part to me is that the audio system in my studio picks this up, but my girlfriend didnt report experiencing anything similar from the sound system I have set up in the kitchen with the exact same model of amplifer I have in my studio powering some bookshelf speakers in there.

I've experienced amplifers picking up faint radio signals before any my friends house who lives several blocks from a local radio station, but nothing like this! And why didnt the amplifier in the kitchen pick anything up?!

Well if anyone has bothered to read this far down, thank you! I'd love some insight from anyone more knowledgeable about what's going on in more technical terms, I'm curious about this.

Thanks,
Doug


My guess is that's not a ham operator it's a CB person running a splattery linear amplifier.  Certainly that's illegal, getting the FCC to do anything about it, that's another thing.


Here's how you find out if it is a CB or a Ham.  Next time you see the truck stop by the restaurant and introduce yourself to the "operator" of the station.  Ham or CB they are both required to make sure their equipment is compliant and not interfering with other electronics.  If it's a ham operator they will be kind and have a discussion with you.  If it's a CB operator they will kick your ass and toss beer cans at you. 


What is it getting into?  My guess is it is illuminating anything that will act like an antenna, probably a couple kilowatts of power from DC to light. 



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Scott AKA "Skyking" Holtzman

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Douglas Cyr

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Re: Pickup Truck With Massive HAM Radio Antenna Clipping my Soun System!
« Reply #2 on: April 09, 2021, 12:43:34 am »

Interesting, is "CB" this Citizen's Band radio I found on wikipedia?: https://en.m.wikipedia.org/wiki/Citizens_band_radio

Any idea why my sound system in one room picked it up but the stripped down system in the kitchen wouldn't have picked it up?

Is there anything I could add to my signal path to to prevent it picking this up? I remember watching a video a while ago from a HAM radio operator who installed ferrite chokes onto almost every wire in his house to filter out his transmissions from his phone line and such.

Considering how powerful this signal was though, it's hard to imagine that would do anything in my situation.

Is there any risk of damage to any components in my mixer? For some reason this feels like a dumb question, but if whatever this signal is can cause my mixers meter to instantly clip and blast distortion through the speakers it can't be healthy. It only last for several seconds though, not minutes.

I guess the simplest solution is to talk to the driver and ask him to wait until he turns is system on and politely let him know the interference its causing?

Thanks for the response, this gives me some stuff to look into!
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Scott Holtzman

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Re: Pickup Truck With Massive HAM Radio Antenna Clipping my Soun System!
« Reply #3 on: April 09, 2021, 02:04:28 am »

Interesting, is "CB" this Citizen's Band radio I found on wikipedia?: https://en.m.wikipedia.org/wiki/Citizens_band_radio

Any idea why my sound system in one room picked it up but the stripped down system in the kitchen wouldn't have picked it up?

Is there anything I could add to my signal path to to prevent it picking this up? I remember watching a video a while ago from a HAM radio operator who installed ferrite chokes onto almost every wire in his house to filter out his transmissions from his phone line and such.

Considering how powerful this signal was though, it's hard to imagine that would do anything in my situation.

Is there any risk of damage to any components in my mixer? For some reason this feels like a dumb question, but if whatever this signal is can cause my mixers meter to instantly clip and blast distortion through the speakers it can't be healthy. It only last for several seconds though, not minutes.

I guess the simplest solution is to talk to the driver and ask him to wait until he turns is system on and politely let him know the interference its causing?

Thanks for the response, this gives me some stuff to look into!


Yes, I was only being 1/2 funny when I said ask him to stop the behavior, if he is a ham operator he more than likely will be polite and refrain from operating his system in this manner.


On the other hand if he is a CB user then I doubt you will get a courteous response.


Can it damage your gear, oh yes, most certainly.  The much RF illuminates almost anything it can get into and radio waves are very tiny.  Chokes can help under normal circumstances but not the kind of field it sounds like they are generatining.


When I was a kid I had a dynamometer and a 500w tube linear in my car.  Keying that bad boy up in the drive through line would generally shutdown the headsets and reboot the registers.  One time one of the techs I worked with had a 150w VHF low band 6 meter GE Mastr II in his Bronco.  I had a 10kva Lorain UPS in the service bay that fed specialized computers that controlled paging and mobile telephone transmitter and other land mobile gear.  The UPS had a couple of huge SCR (or triacs I forgot now) that chopped the DC from the batteries into AC.  The thing was so load it was unreal.  He pulled in to the bay and wanted to see if he could still hit the 6 meter repeater.  The RF got into the UPS and turned on both SCR's at the same time (probably TTL input lines so didn't take much) and crowbarred about 2000 amps of DC.  Giant fiberball came out of the UPS, it was impressive.  Think of what the low power computers in your studio gear that probably operate at 1/2 of CMOS voltages (or lower).  That much RF will turn on every gate, buffer and what not and certainly could fry something along with just directly overload it. 
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Scott AKA "Skyking" Holtzman

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Russell Ault

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Re: Pickup Truck With Massive HAM Radio Antenna Clipping my Soun System!
« Reply #4 on: April 09, 2021, 02:10:35 am »

If you can (safely) photograph the antenna we might be able to tell you a bit more.

Judging by what you're describing (both antenna and experience) I'm with Scott that it's much more likely to be CB than Ham. Most mobile stations in the amateur service these days are VHF or UHF (so the antennas aren't typically very large) and FM or digital (which rarely decodes accidentally in a way that would allow you to identify the contents of the signal). Some amateur license holders do maintain mobile SSB HF rigs, but those would be the exception, rather than the rule.

As Scott mentioned, if it is a licensed amateur causing this interference, they'll likely be glad to know that there's a problem and will want to take steps to solve it, while if it's a CBer (who isn't required to hold a license anymore)...I wouldn't bother raising the issue.

As far as steps you can take, judging by what you've described (peaking metres on the console unaffected by fader moves) I'm at least 85% sure that it's the output-stage line amplifiers on the Soundcraft that are "receiving" the transmissions. (Fun aside: not sure about the Signature, but I did once accidentally feed phantom power into the main L-R out on a Soundcraft Spirit, which had no audible effect before or after but did express its displeasure by pinning the meters.) It's possible that this might cause damage to the console (although it's somewhat unlikely, since any damage would be heat-relate, and that should require quite a bit of heat), but I'd be more worried about possible damage to your speakers.

I'd start by checking to make sure all your cables and devices are grounded properly (since cable shields quickly turn into antennas if they aren't). Installing ferrite chokes on all the cables that are plugged into the console (including the power cable it it doesn't already have one) certainly wouldn't hurt anything (chokes act as low-pass filters, which means even modestly-sized ferrite beads can still produce significant attenuation at higher frequencies).

Since the BSS crossover has a grounded electrical connection (and therefore should be supplying a proper signal ground reference), something else you can try is lifting the ground from the console end of the those cables, which will hopefully discourage any RF transduced by the cable shields from heading towards the console.

Finally, if you're feeling adventurous, you can try swapping the mic cables in your system for unshielded twisted pair cables (e.g. Cat5e). This is unorthodox, but in situations where you have a combination of differential audio connections and equipment grounds that can't cope with the RF they're taking on (assuming that is, in fact, the problem), eliminating the cable shielding can drastically reduce the overall RF being sent to ground.

-Russ
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Jeff Bankston

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Re: Pickup Truck With Massive HAM Radio Antenna Clipping my Soun System!
« Reply #5 on: April 09, 2021, 02:42:46 am »

Thats a CB radio antenna on the truck. My dad was a big time Ham operator and involved in emergency communications. Ham radio is low power and does not interfere with AV stuff. CB radios with cheap lineir amps can interfere but your audio equipment is also part of the problem. You do not need a license to operate a CB anymore. I had a license in the 70's but the FCC did away with the requirements. You need a license to operate a ham radio. I have a top of the line CB radio and a kicker for use on the open road when needed. You can buy a lenier amp just about anywhere and they are legal to sell. Good luck complaining to the FCC. About 20 years someone near the interstate hid a CB radio jammer. "We" reported it to the FCC and were told do to a limited staff it could take a year or more to investigate it. Most people like me with CB radio use it when traveling for immediate weather and traffic info the all the modern internet stuff doesnt have. And there are places on I-10 in Texas and other places that do not have cell service and a CB radio will get you help. Nothing will ever be able to replace the CB radio not even a computer in your vehicle. 
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Douglas Cyr

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Re: Pickup Truck With Massive HAM Radio Antenna Clipping my Soun System!
« Reply #6 on: April 09, 2021, 02:50:28 am »

This is very interesting information and definitely above my head in terms of electrical circuit knowledge, I appreciate all the help. I just got a bread board and started messing around with recreating circuits from schematics and learning about RC and LR circuits, simple filters, decoupling capacitors, etc so I'm very interested in this as as learning experience.

Regarding the ferrite chokes: it's my understanding the ferrite density and number of wraps around the choke need to be calculated somehow, but in this situation throwing anything on there would help?

What really confused me is that it did seem like the signal was being picked up inside the mixer rather than in the amplifier powering the speakers which is what I would have expected. The only cables running into the mixer at the time if the most recent occurence were all unbalanced. The AC power cable going into the mixer does not currently have a ferrite choke.

What makes the amplifiers at the end of the mixers internal signal path most susceptible to the RF transmission?

The antenna looked like this (with loose coils at the base and straight up after that), except it extended closer to 10' from the truck bed: https://ae01.alicdn.com/kf/HTB111E5n4uTBuNkHFNRq6A9qpXat/OSHINVOY-CB-radio-whip-antenna-26-28MHz-CB-27MHz-magnet-mount-antenna-26-28MHz-car-roof.jpg
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Jeff Bankston

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Re: Pickup Truck With Massive HAM Radio Antenna Clipping my Soun System!
« Reply #7 on: April 09, 2021, 02:54:49 am »



The antenna looked like this (with loose coils at the base and straight up after that), except it extended closer to 10' from the truck bed: https://ae01.alicdn.com/kf/HTB111E5n4uTBuNkHFNRq6A9qpXat/OSHINVOY-CB-radio-whip-antenna-26-28MHz-CB-27MHz-magnet-mount-antenna-26-28MHz-car-roof.jpg
Thats a base load antenna. My Wilson cell antenna and mobile internet antennas look just like that one and have base load coils. The old classic non coil CB antenna is a 102" stainless whip.
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Scott Holtzman

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Re: Pickup Truck With Massive HAM Radio Antenna Clipping my Soun System!
« Reply #8 on: April 09, 2021, 04:09:51 am »

Thats a CB radio antenna on the truck. My dad was a big time Ham operator and involved in emergency communications. Ham radio is low power and does not interfere with AV stuff. CB radios with cheap lineir amps can interfere but your audio equipment is also part of the problem. You do not need a license to operate a CB anymore. I had a license in the 70's but the FCC did away with the requirements. You need a license to operate a ham radio. I have a top of the line CB radio and a kicker for use on the open road when needed. You can buy a lenier amp just about anywhere and they are legal to sell. Good luck complaining to the FCC. About 20 years someone near the interstate hid a CB radio jammer. "We" reported it to the FCC and were told do to a limited staff it could take a year or more to investigate it. Most people like me with CB radio use it when traveling for immediate weather and traffic info the all the modern internet stuff doesnt have. And there are places on I-10 in Texas and other places that do not have cell service and a CB radio will get you help. Nothing will ever be able to replace the CB radio not even a computer in your vehicle.


Jeff, it is not legal to sell an amplifier for Citizens Band per Part 95 of FCC regulations.  You are limited to 4 watts AM or 12 watts SSB.  It is also illegal to connect a 10 meter amateur linear amplifier retuned for 11 meter CB operation.


Amateur HF operations with a General license are allowed high powered operation 1500 Watts IIRC.
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Scott AKA "Skyking" Holtzman

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Jeff Bankston

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Re: Pickup Truck With Massive HAM Radio Antenna Clipping my Soun System!
« Reply #9 on: April 09, 2021, 04:26:53 am »


Jeff, it is not legal to sell an amplifier for Citizens Band per Part 95 of FCC regulations.  You are limited to 4 watts AM or 12 watts SSB.  It is also illegal to connect a 10 meter amateur linear amplifier retuned for 11 meter CB operation.


Amateur HF operations with a General license are allowed high powered operation 1500 Watts IIRC.
As far as i have been informed its legal to sell amps. You can buy them online, i have seen them in CB section in truck stops, a CB radio shop here in socal sells them. If they are still illegal the feds are not inforcing the law. In the 70's many CB radio guys in south mississippi had tall antennas in their yard with tube amps connected to their CB. I never knew of anyone to get busted.
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ProSoundWeb Community

Re: Pickup Truck With Massive HAM Radio Antenna Clipping my Soun System!
« Reply #9 on: April 09, 2021, 04:26:53 am »


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