Hum/buzz Noise In My Radio

[KennyD]

He y'all. I have an RHF-618 (same board as a 2950dx). It recently developed a humming/buzzing type of noise in my transmit audio. My first thought was a bad power supply as it is a base radio so I switched it from 110vac source to 12vdc and it still does it. Could this be a bad filter cap? Any help would be appreciated. I have tools including as well as access to a scope and I am comfortable poking around with guidance.

 

[Captain Kilowatt]

There are no such filter caps in a 12 volt radio. Filter caps are in power supplies which the 2950DX does not have. Check the microphone cord or try a different microphone. The shield wire may be broken.

 

[KennyD]

I have tried the stock mic as well as another mic from a known working radio with the same results.

 

[Captain Kilowatt]

Have you tried loosening and re tightening the screws that hold the circuit board to the chassis Sometimes one will loosen a bit and cause that issue.

 

[mechanic]

This radio has a large LCD display, could be a feed-back from the display driver getting into the mic circuits, does it happen in all modes? Check the wires from the mic input, inside the radio, repositioning may change the level of hum/buzz. Is it possible to post this audio when you transmit?

73 mechanic

 

[KennyD]

I have been hesitant to open it up because it just came back from a certified ranger repair center about 6 months ago. But since I can't get them to answer me maybe I will break the seal. They replaced the processor in it last time because of this noise and an SWR problem.

Yes I can hear it in all modes, altho loudest in AM.

 

[Captain Kilowatt]

I have been hesitant to open it up because it just came back from a certified ranger repair center about 6 months ago. But since I can't get them to answer me maybe I will break the seal. They replaced the processor in it last time because of this noise and an SWR problem.

Yes I can hear it in all modes, altho loudest in AM.

Ummmmm......OK..........Unless I missed it you didn't tell us that before. My guess is it needs to go back to them again. If it was doing it before and then fixed by replacing the processor and now it is acting up again then it would be logical to assume it has to be replaced again............maybe. If the processor was bad the radio should have other problems. Perhaps the processor is generating RF noise for some reason.

 

[222DBFL]

Agree with capt. Kilowatt here, if there was a similar issue before it maybe the same issue. Do you have all your equipment grounded well and also your antenna system? Often overlooked, good grounding helps a bunch. I have roughly 6-8 grounds of #2awg solid going to 4 ground rods and then a separate ground rod for my equipment with a #10awg solid wire going to the other ground rod. But seems like you have other issues that may need to be addres by the repair shop.

 

[GnG8d]

Often overlooked, good grounding helps a bunch. I have roughly 6-8 grounds of #2awg solid going to 4 ground rods and then a separate ground rod for my equipment with a #10awg solid wire going to the other ground rod.

And you don't have issues? You've certainly set your self up for some in just about anything microprocessor controlled, plus RF equipment and audio equipment. Not to mention lightning.

 

[222DBFL]

Actually I have zero rf issues. Don't come through anything. Guess I am doing it all wrong. Next I will install a poly phaser surge arrestor in line and ground it as well. Then it will be totally wrong! God bless.

 

[KennyD]

I finally got in touch with the shop that worked on it, they are shipping me another processor board.

 

[GnG8d]

Actually I have zero rf issues. Don't come through anything. Guess I am doing it all wrong. Next I will install a poly phaser surge arrestor in line and ground it as well. Then it will be totally wrong! God bless.

You've made a perfect ground loop, it's hard to believe you've not experienced any issues.

 

[Captain Kilowatt]

You've made a perfect ground loop, it's hard to believe you've not experienced any issues.

Not necessarily. if all the grounds are connected together there is no ground loop. You can have more than one ground point in the ground and as long as they are connected together at one AND ONLY ONE point then all is good. in fact better than good. this is the proper way to do it.I have three ground rods at my tower base each with it's own connection to a leg. the three legs are bonded together at the bottom on all three sides. There is a main ground cable running from the tower towards the house where it encircles the entire house. there are multiple ground rods along the length. At the opposite side of the house where my electrical service entrance is located this perimeter ground that is connected to my tower is bonded to the main electrical service ground. Any cables entering the house have the shields bonded to this ground at point of entry. There is one ground wire coming into the shack to the equipment desk. Although I have multiple points to ground all these points are connected to one common point and thus no ground loops are possible. This is also the proper way to install a lightning ground.

 

[GnG8d]

Not necessarily. if all the grounds are connected together there is no ground loop. You can have more than one ground point in the ground and as long as they are connected together at one AND ONLY ONE point then all is good. in fact better than good. this is the proper way to do it.I have three ground rods at my tower base each with it's own connection to a leg. the three legs are bonded together at the bottom on all three sides. There is a main ground cable running from the tower towards the house where it encircles the entire house. there are multiple ground rods along the length. At the opposite side of the house where my electrical service entrance is located this perimeter ground that is connected to my tower is bonded to the main electrical service ground. Any cables entering the house have the shields bonded to this ground at point of entry. There is one ground wire coming into the shack to the equipment desk. Although I have multiple points to ground all these points are connected to one common point and thus no ground loops are possible. This is also the proper way to install a lightning ground.

If I'm understanding, all of your grounds are external of your house wiring and are then bonded to the service ground? You don't have equipment separately grounded to 6 or 7 different ground points.

EDIT___
You have 3 ground rods at the tower base to try and dissipate as much of a hit that you can there. What doesn't go to ground goes to the house via a ground cable and coax shield but doesn't enter the house, it is then diverted to the service ground. I'll buy that.

 

[Captain Kilowatt]

Correct. I have several ground rods at the tower base and all along the perimeter ground which is tied to my electrical service entrance. From this point I have ONE piece of heavy copper cable running into the shack where I have a ground buss with ground leads going to various pieces of gear. I'm not sure exactly how 222dbfl has his configured however I just wanted to mention that multiple ground points does not necessarily mean ground loops. A lot of people think that just because there is more than one ground rod than there will be ground loops present. Not so as long as they are all connected together at one point and not multiple points.