Source of RFI in console?

[NCFire11]

This may be a question no one can help me with without actually going hands on but here it is anyway..

I have an old M1225 VHF radio that I use to scan the local county while I'm at work. The local county simulcasts to simplex VHF for paging(which i monitor), and they have their own P25 VHF system. I use the statewide 800mhz system.

The M1225 is mounted in the console along with a 05 remote head and Whelen controller. I have noticed that I have pretty bad signal degradation on this unit while it is installed in the console. I can take it out of the console and it works fine, pretty evident on a NOAA weather channel, for instance. VHF 1/4 wave mounted on the trunk with an NMO lip mount.

Is there anything I can check to fix this issue? Or is it simply too much electronics in the console causing interference? Wired to the console box using blocks that are wired directly to the battery, positive and negative.

TL/DR: Console mounted VHF radio has poor receive, what can I do to fix it?

 

[prcguy]

The M1225 should be well shielded and the coax is somewhat shielded from nearby interference leaking in. If something in the console is generating RFI I would think its getting onto the coax shield and riding up to the antenna where its being picked up.

You might put a dummy load on the radio to see if its picking up the interference, that will show if its really strong in the console and possibly coming through the radio case. You could add a string of #43 snap on ferrite cores around the coax after it exits the console, which will attenuate RFI riding on the shield to the antenna. Bottom line is you need to find the method of RFI ingress before you can treat it.

 

[SteveC0625]

Your primary wiring grounds at the battery terminal? Not a good practice. Ground the console to the chassis at or near the chassis. If the radio is powered by a fuse block In the console, it’s ground also needs to go to vehicle chassis preferably at a factory ground point. If the radio is powered direct to the battery, move its ground from the battery post to a factory chassis ground near the battery.

These are not just my recommendations but are Motorola's preferred install instructions. I always use Motorola power cables, hot to the battery hot with the inline fuse near the battery, and ground to a factory grounding point near the battery. Connecting ground to the battery ground post may interfere with battery monitor and other computer Systems in the car or truck.

 

[NCFire11]

I will mention that the coax is terminated with a BNC connector so Im using a BNC to Mini UHF to connect to the M1225. I should probably address that first. Ordering another run of NMO/mini UHF coax tonight so I'll try that.

 

[NCFire11]

Your primary wiring grounds at the battery terminal? Not a good practice. Ground the console to the chassis at or near the chassis. If the radio is powered by a fuse block In the console, it’s ground also needs to go to vehicle chassis preferably at a factory ground point. If the radio is powered direct to the battery, move its ground from the battery post to a factory chassis ground near the battery.

These are not just my recommendations but are Motorola's preferred install instructions. I always use Motorola power cables, hot to the battery hot with the inline fuse near the battery, and ground to a factory grounding point near the battery. Connecting ground to the battery ground post may interfere with battery monitor and other computer Systems in the car or truck.

I probably worded that wrong. I wired it to the terminals that are already in the console as installed by the upfitter. Three blocks are provided, 12+ hot, 12+ switched and ground, so I wired into those. Past the console I am not sure how the vehicle is wired.

 

[mmckenna]

I will mention that the coax is terminated with a BNC connector so Im using a BNC to Mini UHF to connect to the M1225. I should probably address that first. Ordering another run of NMO/mini UHF coax tonight so I'll try that.

Adapters can put a lot of strain on the mini-UHF connectors, so it's a good idea to replace it with the right one. But unlikely an adapter is causing your issue.

I probably worded that wrong. I wired it to the terminals that are already in the console as installed by the upfitter. Three blocks are provided, 12+ hot, 12+ switched and ground, so I wired into those. Past the console I am not sure how the vehicle is wired.

It would be a good idea to figure that out. I've seen some upfitters do really crappy install jobs, cut corners, fail to connect things, etc.


I agree with PRC guy, try disconnecting the antenna at the radio and see if the noise goes away.
Other thing you can try is to power the radio off a separate 12volt source, not connected to the vehicle. The interference is getting in the radio somehow, and that's usually via the power or antenna connection. Work on ruling those out.

 

[NCFire11]

Adapters can put a lot of strain on the mini-UHF connectors, so it's a good idea to replace it with the right one. But unlikely an adapter is causing your issue.



It would be a good idea to figure that out. I've seen some upfitters do really crappy install jobs, cut corners, fail to connect things, etc.


I agree with PRC guy, try disconnecting the antenna at the radio and see if the noise goes away.
Other thing you can try is to power the radio off a separate 12volt source, not connected to the vehicle. The interference is getting in the radio somehow, and that's usually via the power or antenna connection. Work on ruling those out.

The correct cable will be here Tuesday. As far as the wiring on the box, its done in house by the agency so I'm not going to touch it either way. If that's the source of my problems I will be out of luck on that front. From what I can tell there is plenty of wiring to the positive terminal in the trunk but only one small wire to the negative. Wire is too small to be a main ground(hopefully).

A CDM1250 also has the issue. Picks up well if I hold it outside of the box but as soon as I drop it in it becomes static or even totally cuts out.

I will try powering it from a jump box while its mounted in the console.

 

[popnokick]

With the mobile installer expertise that has responded in this thread I'm surprised this hasn't been brought up, but.... Does the light controller control LED lights? I've read in other places (maybe even here on RR) that LED lights and electronic controllers are infamous for gobs of RFI / EMI emissions if not properly installed.... or sometimes even IF properly installed. Some of the mfr's even have special optional RFI shielding / adapters for their controllers.

 

[prcguy]

It would be nice if you have a spectrum analyzer to sniff with, set that up to see the same VHF frequency range as the radio being interfered with and sniff the console area with a VHF rubber duck on the end of some coax. That will usually find the source of RFI or the wires its traveling on.

You have to choose a narrow enough resolution BW to get the analyzer noise floor down as much as possible to see really weak signals. Might have to use 1KHz or less RBW with no internal attenuation. When the noise floor trace gets down below -100dBm you should be able to see weak interfering signals.

 

[RFI-EMI-GUY]

Are there any 12V to USB power plugs in the console or wired nearby.?

 

[NCFire11]

Are there any 12V to USB power plugs in the console or wired nearby.?

WOW. I have two of them to power phone chargers, GPS, flashlight charger etc. As soon as I unplugged them the problem went right away.

Thank you!

 

[mmckenna]

WOW. I have two of them to power phone chargers, GPS, flashlight charger etc. As soon as I unplugged them the problem went right away.

Thank you!

Cool.

Yeah, my son has one for his Nintendo Switch. When he uses it in my wife's car, the tire pressure monitoring system goes nuts.

 

[NCFire11]

Oddly enough one of them completely wipes out signal when plugged in while the other seems to have no effect. Either way, the culprit will be finding a new home.

 

[RFI-EMI-GUY]

Those things seem to be proliferating like weeds and most seem to have no FCC certification.

 

[NCFire11]

I can’t help but wonder what kind of wicked RF this thing is blasting to desensitize a radio like that. I wonder what else will work better now that that’s gone

 

[nd5y]

You don't need a lot of power to cause interference when the receive antenna and interference source are that close.

 

[NCFire11]

It was about 15 inches away from the radio, the antenna is on the trunk. To be that small blasting that much dirty RF makes you wonder how they are allowed to come off the line in that bad of shape.

 

[SteveC0625]

I have Blue Sea brand USB outlets in my truck, RV, and there’s at least three of them in our new ambulance. There is no RFI interference in any vehicle

They cost more than the cheapie look-alikes, but quality is readily apparent.

 

[NCFire11]

I have Blue Sea brand USB outlets in my truck, RV, and there’s at least three of them in our new ambulance. There is no RFI interference in any vehicle

They cost more than the cheapie look-alikes, but quality is readily apparent.

The bad one is made by Griffin, the good one is provided by Verizon wireless so I’m not sure of the manufacturer. I may look into Blue Sea for a replacement, seems like it will be well worth it.

for reference:

 

[DJ11DLN]

I have a small collection of those that I would like to launch out of a potato gun or something similar, or maybe provide to a precision shooter as targets. Oddly some of the cheapest convenience-store-next-to-the-checkout ones are the best behaved and the ones that are noisy are mostly more expensive ones, several are name-brand.