There is lots and lots to learn and lots of disinformation and outright bullshit to unlearn. Hardest thing when starting out is figuring out what is the bullshit because some things are repeated by so many people such as co-ax having to be a certain length, winding 18ft of coax into a coil makes a suitable RF choke etc etc etc. I was disabled and unable to work for a while which co-incided with me taking up amateur radio so I had plenty of time to go learn about antennas and put the theory into practice. When I started working again I did a lot of travelling so mobile ops was what I concentrated on.
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Cleaning up Interference Noise???
- Thread starter seagiant
- Start date
There is lots and lots to learn and lots of disinformation and outright bullshit to unlearn. Hardest thing when starting out is figuring out what is the bullshit because some things are repeated by so many people such as co-ax having to be a certain length, winding 18ft of coax into a coil makes a suitable RF choke etc etc etc. I was disabled and unable to work for a while which co-incided with me taking up amateur radio so I had plenty of time to go learn about antennas and put the theory into practice. When I started working again I did a lot of travelling so mobile ops was what I concentrated on.
Is it true that a 47 ohm antenna will magically appear to be 50 ohms at multiple frequencies with a random length cable without an antenna tuner or is that an old wives tale?
No noise with the antenna out means all of the noise you are hearing is radiated. If it was conducted you would hear it with the antenna out.
Radiated noise could be coming from any where. Have your radio running on a battery and turn all of your house power off. If the noise goes away you have a problem inside your house. If no change the power lines and or transformers in your neighborhood could be the culprit. Or you have a neighbor in the area growing with mercury vapor lights. Some times it can be an alarm panel, door bell transformer, or an iron bridge in the area picking up radio signals and redirecting them.
If you suspect the power lines the power company is obligated to clean up any electrical noise under FCC laws and regulations.
Radiated noise could be coming from any where. Have your radio running on a battery and turn all of your house power off. If the noise goes away you have a problem inside your house. If no change the power lines and or transformers in your neighborhood could be the culprit. Or you have a neighbor in the area growing with mercury vapor lights. Some times it can be an alarm panel, door bell transformer, or an iron bridge in the area picking up radio signals and redirecting them.
If you suspect the power lines the power company is obligated to clean up any electrical noise under FCC laws and regulations.
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Okay, all above still applies except the power lines, now it's your truck probably making all of the noise. HVAC fan motor, windshield wiper motor, radiator cooling fan, fuel pump, ignition system.
One thing you can do is pull fuse one by one until the noise stop and then you have a clue as to which circuit is the cause.
Now I will state the obvious do not be driving while testing and be in a safe location.
One thing you can do is pull fuse one by one until the noise stop and then you have a clue as to which circuit is the cause.
Now I will state the obvious do not be driving while testing and be in a safe location.
I never said an RF choke doesn't work. How you create the RF choke, its diameter, the number of turns, the ferrite material if you use a ferrite all affect the frequency that a RF choke works on because it is a tuned circuit.
Winding 18ft of coax into an air cored RF choke doesn't work on 27MHz because there is absolutely no combination of diameter or number of turns where it would. And given the very narrow bandwidth of an air cored choke the claims on amateur radio websites that it works from 160m to 10m are just outright wrong.
Testing is easy to do if you have a RF current meter. Hell you can even do a very rudimentary test using a flourescent tube as an indicator of the amount of common mode RFI on the feeder.
Winding 18ft of coax into an air cored RF choke doesn't work on 27MHz because there is absolutely no combination of diameter or number of turns where it would. And given the very narrow bandwidth of an air cored choke the claims on amateur radio websites that it works from 160m to 10m are just outright wrong.
Testing is easy to do if you have a RF current meter. Hell you can even do a very rudimentary test using a flourescent tube as an indicator of the amount of common mode RFI on the feeder.
No sorry M0GVZ that is incorrect. RF chokes are not tuned like a resonant circuit.
It is simply supposed to be an impedance to prevent the coax from radiating back down the line in side the radio room. There are TVI filters that are tuned to filter out harmonics to keep them from being radiated. If you put a choke on a line that is rich with harmonics it will radiate that as RF from the coax and any other place available but not down the coax after the choke..
There are antennas that will use a drop line coax as a portion of the antenna to resonate with a choke to use the drop line as a vertical radiator for certain frequencies.
Unless Rod Serling is in house, that is the truth.
I was having RF getting into the shack. My IMAX 2000 at 7' was most likely the culprit. I thought an ugly balun might help but I was getting so much different information on the way to wind one. 8 turns 6" diameter, 6 turns 8" diameter etc etc. I don't recall what I paid for it but no more than $40. The MFJ 915 with a double female connector putting it right up to my antennas so 239 and the problem of RF getting into the shack was gone. I hate mfj as I was taken for $230 when I purchased my 828. But this 915 works great and took the guess work out of how to correctly wind my coax for a correct choke.
Connect the antenna and power up the radio before you put the key in the ignition. Be sure the NB and ANL are both turned OFF.
See how much the noise increases when the key is turned form off to on, but don't start the motor.
Some electric fuel pumps will start briefly and shut off when fuel pressure is reached.
Other pumps just run all the time.
The brushes in the fuel-pump motor tend to generate a lot of RF hash noise. Brush noise tends to be a steady whine that changes pitch with the speed of the motor. Windshield wiper and blower motors will produce this sort of RF noise.
Most electric fuel pumps I have seen have a centrifugal speed regulator inside, as well. The contact points on the pump motor's regulator tend to generate even more noise, usually more random and raucous-sounding than motor-brush noise.
This assumes that the motor has fuel injection, which nearly always requires an electric fuel pump.
And if all is quiet until you start the motor, the noise source is elsewhere in the vehicle.
73
See how much the noise increases when the key is turned form off to on, but don't start the motor.
Some electric fuel pumps will start briefly and shut off when fuel pressure is reached.
Other pumps just run all the time.
The brushes in the fuel-pump motor tend to generate a lot of RF hash noise. Brush noise tends to be a steady whine that changes pitch with the speed of the motor. Windshield wiper and blower motors will produce this sort of RF noise.
Most electric fuel pumps I have seen have a centrifugal speed regulator inside, as well. The contact points on the pump motor's regulator tend to generate even more noise, usually more random and raucous-sounding than motor-brush noise.
This assumes that the motor has fuel injection, which nearly always requires an electric fuel pump.
And if all is quiet until you start the motor, the noise source is elsewhere in the vehicle.
73
There’s no end of mobile noise, ha!
This morning I got around to the experiment of using (3) on-hand 3/4” woven braid jumpers (with a lug at one end) to “ground” radio, tuner and amp cases. Used a copper split-bolt to bond them together at their unfinished ends to the fourth of these sister pieces, with that lug dropped over a machine screw holding the plastic overhead to its metal bracket. (Three reduced to One).
The Good News . . I can now hear alternator whine previously masked.
With RX cleaned up as hoped.
Tuner settings changed. Closer to what I’d have expected to see.
If I can maneuver the drill into that tight spot tomorrow morning, I’ll make that thick sheet-metal-end a far tighter bond with a #10 screw & star washer after some paint removal with the Dremel.
The rest of you all can stand up inside your vehicles to do this type work, right?
Older pic. Ancient. A week or three back.
DX99v2 now a DX86V.
KL203 atop radio (hidden).
MFJ-945e in the bin over the radio/amp.
Alternator whine be good news.
.
This morning I got around to the experiment of using (3) on-hand 3/4” woven braid jumpers (with a lug at one end) to “ground” radio, tuner and amp cases. Used a copper split-bolt to bond them together at their unfinished ends to the fourth of these sister pieces, with that lug dropped over a machine screw holding the plastic overhead to its metal bracket. (Three reduced to One).
The Good News . . I can now hear alternator whine previously masked.
With RX cleaned up as hoped.
Tuner settings changed. Closer to what I’d have expected to see.
If I can maneuver the drill into that tight spot tomorrow morning, I’ll make that thick sheet-metal-end a far tighter bond with a #10 screw & star washer after some paint removal with the Dremel.
The rest of you all can stand up inside your vehicles to do this type work, right?
Older pic. Ancient. A week or three back.
DX99v2 now a DX86V.
KL203 atop radio (hidden).
MFJ-945e in the bin over the radio/amp.
Alternator whine be good news.
.
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