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Radio noise/interference

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9 replies to this topic

#1
DHappel

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Here's one for you - what's the best way to combat a noisy radio?

 

I got to actually use the Kenwood 281A in my D1 last week on it's first 'real' trip.  While the radio seemed to work well enough, when I turned on my fridge I got all sorts of noise.  Nothing the squelch would dampen.  While this isn't the fridge that's going to live full-time in this truck, there's a fair chance the new one will cause the same once installed.  And anyway, it's generally a good topic of discussion.

 

I haven't made any attempts on this yet and I'm not on any radio forums to discuss so I'm coming here for wisdom, insight, and general know-how.  Don't fail me oh Rover people!

 


Don
'07 LR3 HSE/HD - slightly non-stock

'96 D1 - even more non-stock


#2
GraemeWare

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Don,

What did your interference sound like?

First you have to establish whether it is airborne or electrical. I'd guess airborne, and that normally leads towards antenna grounding problems.

Graeme

Graeme Ware -- San Carlos, CA

1990 Range Rover Classic - LT230 Transfer box, Warn winch, 2" lift, 235/85-16 Dunlop MUD Rovers, "Blue Submarine"
1996 Discovery 1 (R380 Manual Transmission, Ashcroft under-drive, RoverWare rear bumper, 33x12.5-15 BFG ATs) -- we call her "Katrina" -- Fordyce 7.5 mile survivor
1999 Discovery 2 (D1 CDL Linkage, 265/75-16 BFG A/T KO, RoverWare front and rear bumper)
1993 Jaguar XJS convertible; 1971 Triumph GT6; 1959 Morris Minor convertible
other assorted British pot metal ...


#3
DHappel

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Basically it sounds like static breaking the squelch, but turning up the squelch has no noticeable effect.

 

Playing with it today, I'm not so sure it's the fridge doing it after all.  Seems almost random.  Sometimes it's nothing, other times bursts of noise, other times full-time noise. 

 

Sorta like this:

https://goo.gl/photo...uBJ6CWccLUQU2VA


Don
'07 LR3 HSE/HD - slightly non-stock

'96 D1 - even more non-stock


#4
DHappel

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Wait - it's your welder, isn't it?


Don
'07 LR3 HSE/HD - slightly non-stock

'96 D1 - even more non-stock


#5
GraemeWare

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Basically it sounds like static breaking the squelch, but turning up the squelch has no noticeable effect.

 

Playing with it today, I'm not so sure it's the fridge doing it after all.  Seems almost random.  Sometimes it's nothing, other times bursts of noise, other times full-time noise. 

 

Sorta like this:

https://goo.gl/photo...uBJ6CWccLUQU2VA

 

 

Don,

 

That sounds like single side band transmissions being picked up on an FM receiver.  Got any local long-distance amateur guys near you?

 

Regards,

 

Graeme


Edited by GraemeWare, 24 June 2017 - 11:22 PM.

Graeme Ware -- San Carlos, CA

1990 Range Rover Classic - LT230 Transfer box, Warn winch, 2" lift, 235/85-16 Dunlop MUD Rovers, "Blue Submarine"
1996 Discovery 1 (R380 Manual Transmission, Ashcroft under-drive, RoverWare rear bumper, 33x12.5-15 BFG ATs) -- we call her "Katrina" -- Fordyce 7.5 mile survivor
1999 Discovery 2 (D1 CDL Linkage, 265/75-16 BFG A/T KO, RoverWare front and rear bumper)
1993 Jaguar XJS convertible; 1971 Triumph GT6; 1959 Morris Minor convertible
other assorted British pot metal ...


#6
DHappel

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No idea, but I had the noise all the way up to and back from the Rubicon so not a local transmitter.

 

Actually not 'all the way'.  Sometimes it would stop for a while but it always came back. 

 

I do have a number of high powered comercial transmitters a few miles away; TV and microwave, not sure what else.  But I don't really think they have anything to do with it.


Don
'07 LR3 HSE/HD - slightly non-stock

'96 D1 - even more non-stock


#7
GraemeWare

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No idea, but I had the noise all the way up to and back from the Rubicon so not a local transmitter.

 

Actually not 'all the way'.  Sometimes it would stop for a while but it always came back. 

 

I do have a number of high powered comercial transmitters a few miles away; TV and microwave, not sure what else.  But I don't really think they have anything to do with it.

 

I would put a reflected power meter into the antenna line to at least see what the radio thinks it has for an antenna.  The crazy thing is, very few people ever tune their antennas or ensure adequate grounding.  "It works" so they think that is good.  People put 75 Watt transmitters onto antennas that aren't going to radiate more than a fraction of the power.  If you try that on the 10M band, or the 20M or 40M with an older radio, you'll burn up the output transistors within minutes.  Modern radios with FET output stages "fold back" when they get hot, so prevent serious damage to themselves.

 

If the interference is 'local' to the truck, I'd say it can only be a capacitive grounding issue due to the sporadic nature of the noise.  Does it change with engine on to engine off?

 

Edit:

I just listened to your recording again, and the fact that it stops on certain frequencies infers that it is external interference which 'beats' with one of the oscillator frequencies.  I'm not sure that you can cure this.  The front end of the radio might just be too sensitive for whatever that interference is.  Is there a "distant/local" setting on the radio?  That might de-sense the receiver and would at least isolate that potential problem.

 

Graeme


Edited by GraemeWare, 25 June 2017 - 09:11 AM.

Graeme Ware -- San Carlos, CA

1990 Range Rover Classic - LT230 Transfer box, Warn winch, 2" lift, 235/85-16 Dunlop MUD Rovers, "Blue Submarine"
1996 Discovery 1 (R380 Manual Transmission, Ashcroft under-drive, RoverWare rear bumper, 33x12.5-15 BFG ATs) -- we call her "Katrina" -- Fordyce 7.5 mile survivor
1999 Discovery 2 (D1 CDL Linkage, 265/75-16 BFG A/T KO, RoverWare front and rear bumper)
1993 Jaguar XJS convertible; 1971 Triumph GT6; 1959 Morris Minor convertible
other assorted British pot metal ...


#8
DHappel

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I did cut the antenna for 146.460.  SWR was about 2.0 at that freq; less lower and more higher.  Not going to win any awards with that but not terrible.

 

I did realize one issue with my current antenna location though - when off-road it sways side to side and bounces off the roll cage.  Boing Boing Boing...  I'm thinking I may put a mounting plate at the back center of the cage near the 3rd brake like and mount a 1/4 wave on a spring mount there.  That would also give me a chance to try a differnt mount that will let me use RG8 instead of the smaller stuff I have now.


Edited by DHappel, 25 June 2017 - 11:53 AM.

Don
'07 LR3 HSE/HD - slightly non-stock

'96 D1 - even more non-stock


#9
RedRover

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Were you able to clear up the noise?  If so, what was the fix?


Jared (KJ6MQI)
1992 Range Rover Classic - Portofino Red
2012 Range Rover HSE - Santorini Black

 


#10
DHappel

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The fix was putting a cheapo 1/4 wave mag mount on top of the roll cage.  :)

 

Actually I also changed out from my Dometic fridge which normally lives in the LR3 to the Overland Pros fridge I bought from Nick and Ted, but I really doubt that was the issue.

 

I don't know if the trouble was related to grounding on the NMO mount, a cabling issue, or (and I suspect this for some reason) reflections due to the antenna running along-side the vertical tubework of the roll cage. 

 

Regardless, I discovered that the antenna was swaying when off-road and would prang off the roll cage constantly.  boing! boing! boing!  Very annoying.  I picked up an Amazon special $20 Tramm mag mount complete with 12' of RG-8 and welded a 6" wide 1/4" plate above the 3rd brake light.  Works pretty well based on the last trip.  I did knock it off on a tree and bent the whip a bit but I just bent it back.  The magnet is very strong so the whip takes a lot of bend before it lets go.  We then realized for trail work I can just turn it upside down and not worry about trees.  Probably doesn't do much for reception/transmission but works fine for talking to the guy 1/4 mile behind you on the trail.  It does look a little funny though. 


Don
'07 LR3 HSE/HD - slightly non-stock

'96 D1 - even more non-stock





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