Radio transmits but barely recieves

Sounds like you have a noise problem. If your truck has an inverter, shut it off and see if the noise level drops. If you can shut down the truck completely (not on ACC) and run the radio off of a battery, try that. If the noise level drops, then turn things back on until the noise comes back.

Alternators and fuel pumps are notorious noise generators.

 

I agree with MsJamie. If the radio has been fine for a while, and just started acting up, I'd suspect a ground worked it's way loose, and it doesn't have to be on the radio..

It can be a fun and frustrating hunt..

 

I bet the inverter is it. The one i use for my microwave really creates noise on the cb. I leave it off unless i need to use the microwave.
I have another little 500 watt inverter that stays on all the time for my TV,phone charger,ect.
It does not cause a problem but it is about 20 years old.

I think the new inverters are the worst unless you buy a good Pure Sine wave inverter.It will not create "white noise" on other electronics.
They are more expensive than the regular inverters.

 

Well unless the inverter is one of the very expensive ones like a Pure Sinewave Xantrex or something similar grounding probably won't cure the issue. If you need the inverter to run 24/7 it wil be an issue, if you don't then I would suggest that you put a remote switch on it and only run it when needed. Something else to look for is in the newer trucks they sometimes have inverter/converter circuits to power led dome lights ETC...these will also generate noise as well as keyboard interfaces for SAT links to COMM Links.. There a number of issues now in trucks that can gen noise even control heads for some of the other Two Way FM radios that some companies use and the list goes on and on !!!

Here are some things I have done over the years and most of the time these things will work but require some effort..

Basic rules:

1) Keep the DC leads from the battery to the inverter as short as practicable.

2) Twist the DC leads together if possible. If not possible, keep them as close together as you can. The goal is to have the RFI magnetic energy from each lead cancel the RFI magnetic energy in the other. As was also pointed out, it may be helpful to run each DC leg in metal conduit or good copper shield like in large coax you can purchase this at good CB shops and then GROUND the conduit/Copper shield to an earth ground at more than on point - the shorter the better. Failure to ground the conduit will simply turn the conduit into another antenna. An RFI ground is separate from the earth "protective" ground. If you use the AC "ground", it too becomes an antenna unless it's kept short, and you've got a good connection to the grounding electrode conductor with highly conductive earth. It's tough to achieve all three together, but it can be done in some locations.

Someone suggested a "filter capacitor" be connected across the DC leads. This won't hurt, but isn't likely to be effective given the very low impedance of inverter input circuits.

3) Ferrite cores may be slipped over the length of each cable, and placed at the point where the cables exit the inverter. Toroid cores or similar may be of help, but you'll need many of them, and they'll need to extend at least two to three feet starting at the inverter. More is better, and keep in mind .. when many are used .. they're heavy.

Do not install them at the battery end. Installing at the battery end, and leaving some cable exposed at the inverter allows the exposed conductors at the inverter to act as antennas.

Select the proper type of ferrite. Surprisingly, various formulations of ferrite react differently depending on the frequency range in which they're used. For example, some ferrites are good for 100-500 Mhz, and would not do a good job blocking RFI that interferes with AM radio. For AM radio RFI, select ferrite that's rated to work from 250 kHz up to 2 Mhz or more.

4) AC EMI/RFI filters are also available, and may be installed on the AC output circuit at the inverter. These are made by Corcom, Tyco, and others. Select a unit rated for the output voltage AND current of the inverter. RFI filters will be UL/ETL/CSA recognized. If you find some that aren't .. don't buy them.

5) As was suggested, a radio with external antenna may help, especially if the antenna is fed with coaxial cable, which can act as a shield until the cable is well away from the house and/or inverter. Keep the radio antenna as far from the inverter and house wiring as you can.

6) A battery-operated radio is also an option. This too was mentioned earlier in this thread. Even well-filtered inverter AC output always carries with it some level of interference. A weak radio signal will still be affected by a weak source of interference.

7) Ground the inverter housing in accordance with the manufacturer's instructions. All inverters today are required to meet certain levels of FCC interference criteria. Actions of internal RFI filtering circuits may be improved if the inverter is properly grounded.

8) Ever drive into a parking garage while listening to the radio, and the radio station gets very weak or disappears altogether?? Same thing happens when we drive through long highway tunnels.

We can make use of that trait. It's caused by the reinforcing steel bars ("re-bar") acting to block the radio signals from getting to the antenna on your vehicle. The same characteristic that keeps signals from getting to your radio, also works to keep interference IN.

In addition to all the above, you may have to construct a screen around the entire inverter, then connect the screen itself to earth ground. This screen should NOT come into contact with the inverter housing. To do so would defeat the purpose of the screen. However, properly filtered DC and AC leads may pass through it.

In this case, you'll be constructing a "Faraday shield", which will keep interference inside. Surprisingly, this can be ferrous or non-ferrous metal. I'd recommend ferrous (such as chicken wire with small openings), for ease of soldering. Build a "box" around the inverter, including the back of the inverter. To do this, you'll need a board or other means to keep the inverter enclosure from contacting the wire.

Once you've constructed the box .. connect the box to its own "RFI" earth ground. This will be similar to a standard protective ground.

Next, add a bond wire from the RFI ground to the system protective earth for the system. This RFI-ground to safety ground bond wire should be outside if you can .. and buried in the soil if at all possible. Adding this bond wire avoids opportunity for AC ground loops or other issues. Keeping it in the soil also slightly reduces the opportunity it will become an antenna for the interference. If all the above are done properly, they won't impact the effectiveness of the box you've just constructed.


Reducing radio frequency interference is, at best, a snipe hunt. The strength of the radio/TV station signal itself can and will vary, and is dependant on a variety of variables. This can give the impression something you've done had an effect on the interference level from the inverter, where in fact you didn't change a thing. The weaker the radio signal, the more difficult it will be to reduce the interference from the inverter to make the radio signal listenable.


The best thing to do is keep the inverter and all of its wiring as far from the radios as you can. If this simply isn't possible .. see steps 1-8.

I wish you well.

 

I'd bet the inverter. They're notoriously noisy. The one I have kills the cb receive when it's on.


No bits were harmed in the posting of this message.

 

Well it could be a combination of all. One thing is most likely the power leads to the battery will act as an antenna and Unfortunately the Cobra inverters are the worst. If you can do the things outlined in the info I posted for you, It may just be the ticket. I have been troubleshooting noise issues for a long time and it's a 50/50 prospect that you will be able to calm it down. But like everything in life nothing ventured nothing gained.