Why am I picking up a 'machine gun' - type sound?

[Alex1041]

When my son and I are waiting on the trains to pass through town while sitting in the car I will randomly get a machine-gun type sound. It randomly cycles through the programmed channels and will come and go.

The vehicle can be running or off and it happens.....when I exit it does it less frequently.

Do I have something programmed incorrectly?
I hope this turns out right:


Display Frequency L/O Tone Tone LO Att Pri Step Mod NAC AudioType Alt Tone Alt Level Alt Color Alt Pat Vol Adj Num Tag Rec Out Comment
Dispat-Tpa/Bone 160.23000 False None False False False AUTO FM SRCH All 0 0 Off On 0 NONE True CSX - Uceta Yard/ Tampa Terminal (Tampa)
CSX - Tpa Yard 160.29000 False None False False False AUTO FM SRCH All 0 0 Off On 0 NONE True Tampa yard & Baldwin
Dispat-Jax 160.32000 False None False False False AUTO FM SRCH All 0 0 Off On 0 NONE True Jacksonville Terminal Subdivision - Dispatcher
Moncreif - B 160.48500 False None False False False AUTO FM SRCH All 0 0 Off On 0 NONE False
CSX A-Line Rd-32 160.59000 False None False False False AUTO FM SRCH All 0 0 Off On 0 NONE True Callahan Subdivision (The ''A'' Line) - Ro
CSX 45 160.78500 False None False False False AUTO FM SRCH All 0 0 Off On 0 NONE True P&A Sub. Maintenance of Way (MOW)
CSX - Jax Yard 160.86000 False None False False False AUTO FM SRCH All 0 0 Off On 0 NONE True
Dispat A&S Line 160.92000 False None False False False AUTO FM SRCH All 0 0 Off On 0 NONE True Wildwood Subdivision (The ''S'' Line) - Dispatcher (South of Stark #54
CSX 62 161.04000 False None False False False AUTO FM SRCH All 0 0 Off On 0 NONE True Police
CSX S-Line Rd 66 161.10000 False None False False False AUTO FM SRCH All 0 0 Off On 0 NONE True Wildwood Subdivision (The ''S'' Line) - Ro
Rkpor/Mon -Yard 161.34000 False None False False False AUTO FM SRCH All 0 0 Off On 0 NONE True
Bone Valley 161.37000 False None False False False AUTO FM SRCH All 0 0 Off On 0 NONE True P&A Sub. Road Channel
Winston Yard 161.40000 False None False False False AUTO FM SRCH All 0 0 Off On 0 NONE True
Dispat-Auburndal 161.52000 False None False False False AUTO FM SRCH All 0 0 Off On 0 NONE True Dispatcher - Auburndale. Miami subs

 

[KD0LDK]

How are you getting power for your scanner? Do you usually park in the same spot or does where you park affect it?

 

[Alex1041]

Where I park does not affect it. It happens while I'm driving, sitting still, engine on or off.

I'm using a BCD396XT on the OEM batteries and a Watson 801 antenna. It also does it regardless of the antennas...

 

[KD0LDK]

Interesting, does it happen with any other frequencies or have you checked that?

I was going to suggest some form static build up since you mentioned it seems to go down when you're out of your vehicle, but if you're not getting power from your vehicle that pretty well rules that out.

 

[Alex1041]

Interesting, does it happen with any other frequencies or have you checked that?

I was going to suggest some form static build up since you mentioned it seems to go down when you're out of your vehicle, but if you're not getting power from your vehicle that pretty well rules that out.

No, only on the railroad frequencies in the 160's.

 

[KD0LDK]

Ok, well a couple things I'd start with. Try a few other area frequencies in the similar frequency range, weather will probably be your closest. Be sure to give it a shot in similar locations you listen from.

Another would be to try another scanner, if you haven't already to see if you get the same results.

 

[Alex1041]

What could be causing the noise?

Forgot to mention I'm in a 2011 Tahoe

 

[KD0LDK]

Its anybody's guess to be honest. I have noticed in some newer vehicles the machine gun noise you describe can be caused by the ignition coil packs firing, in your case if it continues outside the vehicle I'd rule that out. The radios in my truck pickup random spurious emissions as well, and it's pretty hard to narrow down. There are certain spots here in town I get the same interference consistently and sometimes I just get random interference with my squelch's cranked all the way up.

It could be a number of things but unfortunately most of the time you can't narrow it down since what's making the interference isn't something you can turn off. What you can do is at least make sure your equipment is working properly by checking the frequencies on another receiver.

 

[mm]

What you are describing sure sounds like squelch motor-boating.

I find this pretty common on my Uniden scanner and also have it on an Alinco radio from time to time when scanning.

I have found that the cause is from internally generated spurs from the radios processor getting back into the receiver resulting in the squelch opening and closingm sometimes it even occurs with the antenna disconnected on certain channels.

If you tighten the receivers squelch or briefly enable the attenuator on the channel causing the noise does this fix the problem ?


The reason I suggest this is because sometime these will fix it but at other times I have to move the receive frequency slightly a few KHz to make the squelch stay closed.


Mike

 

[majoco]

Ah ha. The old cellphone noise. Your cellphones may not sound the same but here, they all seem to make the same noise when checking in the the base station. It's a sort of 'tick - tickety - tick - tickety - tick' repeated about four or five times - then it goes away for a while. If you get an incoming call you'll get the signal beforee the phone rings. Blasts hell out of a broadcast band radio and comes through the car radio if listening to a weak station.

 

[Alex1041]

Ah ha. The old cellphone noise. Your cellphones may not sound the same but here, they all seem to make the same noise when checking in the the base station. It's a sort of 'tick - tickety - tick - tickety - tick' repeated about four or five times - then it goes away for a while. If you get an incoming call you'll get the signal beforee the phone rings. Blasts hell out of a broadcast band radio and comes through the car radio if listening to a weak station.

The scanner ticks when I have my work nextel nearby. Does the same with the speakers in the car..........

 

[KD0LDK]

Ah ha. The old cellphone noise. Your cellphones may not sound the same but here, they all seem to make the same noise when checking in the the base station. It's a sort of 'tick - tickety - tick - tickety - tick' repeated about four or five times - then it goes away for a while. If you get an incoming call you'll get the signal beforee the phone rings. Blasts hell out of a broadcast band radio and comes through the car radio if listening to a weak station.

I've heard this as well, it's REALLY bad with my computer speakers. I know I'm getting a phone call before my phone even rings.. hadn't even thought of that.

 

[aps_ak]

Whats the possibility of him hitting a control channel for some system? Is that even possible on 160mhz? Motorola control channels make the motorboat/machine gun noise when they are tuned in to.

 

[Rt169Radio]

Maybe its some data that the scanner cannot decode?

 

[radioman2001]

Or is there some NXDN rail yard repeaters nearby. We are running 18 NXD repeater pairs now. They are for yard operations except for train movement. Some are really close to our existing channels, with scanner receivers being wide-band, who knows?

 

[myspacebarisbroken]

I had the same problem

Hi. May I ask the general area where you are trying to receive? I had similar results last week listening to marine and coast guard here in Delaware. The marine and railroad bands are both very similar and in the 160 MHz range.
What I heard sounded like a very weak control channel to an EDACS or other similar system and I would hear it for about five seconds, then it would dissappear and my Uniden would continue scanning.

 

[ducksoup65]

Could it be the trains themselves? The AAR (Association of American Railroads) has adopted NXDN as its destination for narrowbanding and the official platform for the industry. Many companies are skipping narrow and going ultra narrow at this juncture.

Are you hearing NXDN from the trains?

 

[myspacebarisbroken]

Could it be the trains themselves? The AAR (Association of American Railroads) has adopted NXDN as its destination for narrowbanding and the official platform for the industry. Many companies are skipping narrow and going ultra narrow at this juncture.

Are you hearing NXDN from the trains?

I'm not exactly sure what NXDN is, but I have only heard the "noise" on marine frequencies. Cecil County nearby has a VHF EDACS system in the mid 150MHz range and it's possible that I am hearing an Image of these frequencies. This could possibly be your problem too.

 

[Drake69]

Has anyone mentioned that he might be picking up a masked or jamming signal? I was talking with local law enforcement one day about those "hyperactive woodpecker" sounds that come through the radio at certain frequencies, and they told me that a lot of those are masked broadcasts that they don't want Joe Shmoe to listen in on. Usually they are used for DEA, FED, or ATF broadcasts, and are meant for local LEOs in the area only. I tested this with a cop when he turned down his squelch on a broadcast I was trunking to on my scanner, and we both heard the operator on his handheld and "machinegun fire" on mine.

Just curious.

 

[Alarms50]

Try listening through the audio samples of various radio formats, etc. at Digital Modes Samples.