Another antenna question

[k8jd]

I have been considering running more coax to get my AM/FM 36 " auto antenna away from the house and noise on AM. Currently it uses the incorperated high Z (maybe 90+ Ohms) Shieded fine wire coax and a 12 ft extension coax made for the auto radio design..
I was thinking of using some Cable TV grade RG59 , 75 ohm coax for a longer run.
My guess is it will work OK for FM but I am afraid it will have enough extra capacitance to swamp out the AM freq signals and negate all the purpose of moving it.
Any tech oriented folks have any views on this project ?

I think the noise across the AM band comes from the incoming power line and TV cable leakage. The outside BC antenna is curently within 15-20 ft of those.

[Round Six]

What orientation is your antenna?
If it's vertical, the first thing I'd try is a dipole on the flat side. Horizontals are less induced by power lines.

[Ben Zonia]

Things were different then, but I did something similar about 45 years ago. It was electrically quiet then, and I had no TVs for a mile across a farm on one side. I didn't have a TV, because I had to study all the time. I used the 25 foot twin lead from the TV antenna, twisted the leads together, and fed it into a modified Tom Kneitel one transistor tuned preamp, and coupled the ferrite loop output inductively to the ferrite rod in a Sony Portable. Where I lived in Mecosta County, where there was only AM daytime station, all the other signals were 250 uV/m or less, the strongest other than the local station being WMAQ 670 Chicago. Inside, I could get probably sixty AM stations listenable well in the daytime. The Delco radio in my car was much better than most radios, but still didn't receive non local stations that well. I ran 300 ohm twin lead to a ferrite loopstick, and coupled it inductively to the windshield antenna. It worked very well, but there weren't nearly as many electrical noisemakers then.

[k8jd]

I hear the AM pretty well on my Amateur radio recievers with a 250 ft Dipole but I was looking for some FMHD reception as welll with a JVC aftermarket auto radio . Just hoping to get away from the noise on AM.
The high Z input for a car radio, on the AM side, is a problem.
50 or 75 Ohm coax feedline will become a big loss factor.

[km1125]

Have you tried to isolate the noise sources in the band? I doubt you're getting much from the cable lines, as they're using 5MHz and above. All their switched supplies are inside amplifier housings and they'd have bigger problems if that was leaking out.

I also have a 12 ft extension section with the male/female motorola plugs that you can have if it helps with the distance. It's still in the original Radio Shack pack.

[Round Six]

... I doubt you're getting much from the cable lines, as they're using 5MHz and above. All their switched supplies are inside amplifier housings and they'd have bigger problems if that was leaking out ...

I dunno. I know a ham who had a high noise floor for years. Went away when Xfinity swapped out a pole amplifier.

[km1125]

... I doubt you're getting much from the cable lines, as they're using 5MHz and above. All their switched supplies are inside amplifier housings and they'd have bigger problems if that was leaking out ...

I dunno. I know a ham who had a high noise floor for years. Went away when Xfinity swapped out a pole amplifier.

The 10 meter band can be decimated by cable leakage, as that's one of the busiest areas in cable return (frequency-wise) and some of the highest levels at the amplifiers. They can affect all the way down to the 60 meter band but that's not a common usage in the cable plant. AM radio is below the band the amplifiers even operate, so any interference there would have to be from other causes (like a bad power supply).