Finally got my scanner re-installed in my truck with a new antenna, getting a good amount of static when picking up transmissions in the 33MHz area. I put the clamp-on ferrite core i got a while back around the coax and dc power cord. It seems to help some, however i was hoping someone here had a more effective measure i could take.
VHF Low-Band static
- Thread starter JCairsoft
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Try attaching some wire to a good ground point on the vehicle body and touch the other end to the outside of the antenna connector on the scanner. If the static is reduced or eliminated, then the static is coming through the coax shield.
Do you have a 12V USB cellphone charger in the truck? You could be experiencing this interference:
http://forums.radioreference.com/ra...-forum/299421-scanner-phone-car-chargers.html
http://forums.radioreference.com/ra...-forum/299421-scanner-phone-car-chargers.html
Have not had an issue with my charger that i have noticed. I did program in the PL tones of the frequencies i monitor, if that would make a difference. i will try grounding the plug on the coax today, if i can find a transmission that is compromised.
The first thing to check is to see if you still get the static with the antenna cable unplugged. If so, it's coming in through the power cord, and you'll need to install a better RF-blocking common-mode filter on the power cord near the scanner.
Next thing to check is whether the interference is present when the vehicle engine and all accessories are turned off. Computers create a lot of RF hash below 250MHz and could be causing your problem. If you can make it go away, turn things back on one at a time until you get the static again. Depending on what is causing the static, the solution may be as simple as putting a capacitor across the offending device power leads, or there may not be any feasible solution other than relocating the antenna farther from the source of the interference.
If you're still getting the static with the engine and everything else shut off, try moving to a different location to see if the static level changes. If so, there's not much you can do unless it's coming from inside your house somewhere.
Make sure your antenna is properly grounded, and putting a common-mode choke near the antenna (this can be as simple as several turns of coax zip-tied into a 3-4" diameter coil next to the antenna connector) is a good idea to ensure you're not getting stray RF on the coax shield. It's also a way to make use of excess coax if you have a prefabricated cable.
Next thing to check is whether the interference is present when the vehicle engine and all accessories are turned off. Computers create a lot of RF hash below 250MHz and could be causing your problem. If you can make it go away, turn things back on one at a time until you get the static again. Depending on what is causing the static, the solution may be as simple as putting a capacitor across the offending device power leads, or there may not be any feasible solution other than relocating the antenna farther from the source of the interference.
If you're still getting the static with the engine and everything else shut off, try moving to a different location to see if the static level changes. If so, there's not much you can do unless it's coming from inside your house somewhere.
Make sure your antenna is properly grounded, and putting a common-mode choke near the antenna (this can be as simple as several turns of coax zip-tied into a 3-4" diameter coil next to the antenna connector) is a good idea to ensure you're not getting stray RF on the coax shield. It's also a way to make use of excess coax if you have a prefabricated cable.
Thanks for the info, I am fairly confident it is not the power leads, however would you still recommend the filter? The static has nothing to do with the vehicle, i am sure of that. How would you recommend grounding the antenna? I will be taking some of the excess coax and making the choke, how many turns do you think?
The problem with all scanners and VHF LOW BAND is that none of the scanners have a noise blanker.
As a result I stopped monitoring LOW BAND with scanners and for the past 10 years I have been using commercial radios, GE Orion low band models and Motorola Maxtracs.
The GE Orions have a better noise blanker but even my Maxtracs noise blankers are suitable and these radios are orders of magnitude above any scanner for mobile low band scanning.
As a result I stopped monitoring LOW BAND with scanners and for the past 10 years I have been using commercial radios, GE Orion low band models and Motorola Maxtracs.
The GE Orions have a better noise blanker but even my Maxtracs noise blankers are suitable and these radios are orders of magnitude above any scanner for mobile low band scanning.
Jon gave some good advice to try.
I think one of the big problems today is the fact that almost everything electronic these days is using oscillators that operate in the low band range.
Computers are bad with low band and that applies to in car computers and navigation system.
Same goes for switching type power supplies that may plug into a cig lighter socket.
There are literally tons of devices that can and will mess with low band.
Try what Jon suggested and see if you can determine where the noise is getting in and then work from that point and try different filtering devices and grounding or even floating the ground.
I did one once where powering the radio from its own battery that was disconnected from the cars power during use cured the problem in the portion of the low band that I was interested in.
It did not clean up the entire band but did clean up the 42 MHz range which is what I was after.
I'd used something like an 8 amp SLA battery as it would run the radio for days before I'd need to flip the switch so it would charge from the cars system. I had to use an ungrounded antenna and speaker also. I think that one was a lot of luck more than anything.
That was also back in the days before electronic ignition so that helped.
Missouri State Patrol always placed the low band whips on the rear side fender away from the engine compartment.
I never knew if that was to minimize engine noise or simply because the high power radios were also mounted in the trunk.
I think one of the big problems today is the fact that almost everything electronic these days is using oscillators that operate in the low band range.
Computers are bad with low band and that applies to in car computers and navigation system.
Same goes for switching type power supplies that may plug into a cig lighter socket.
There are literally tons of devices that can and will mess with low band.
Try what Jon suggested and see if you can determine where the noise is getting in and then work from that point and try different filtering devices and grounding or even floating the ground.
I did one once where powering the radio from its own battery that was disconnected from the cars power during use cured the problem in the portion of the low band that I was interested in.
It did not clean up the entire band but did clean up the 42 MHz range which is what I was after.
I'd used something like an 8 amp SLA battery as it would run the radio for days before I'd need to flip the switch so it would charge from the cars system. I had to use an ungrounded antenna and speaker also. I think that one was a lot of luck more than anything.
That was also back in the days before electronic ignition so that helped.
Missouri State Patrol always placed the low band whips on the rear side fender away from the engine compartment.
I never knew if that was to minimize engine noise or simply because the high power radios were also mounted in the trunk.
The answer to that question is Yes. For both reasons.
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