Which coax is better?

I never remember the numbers, so i will just describe it.

CB and low power ham radios use one type. TV antennas use the other.

Both coax is about the same diameter and looks alike on the outside.

I have a police scanner. It has an ext. antenna connector on the rear that is one of those "Motorola jacks" (same as the ant. connectors on car radios).

I used to use a CB (car type) antenna on my roof, for the scanner. It used the CB coax with them big connectors on the end. When I moved, that antenna got left behind.

I recently dug out that scanner again, and have it connected to my homemade weather radio outside antenna. But this weather antenna has the TV style coax with F connectors.

I dont yet have an adaptor for F connector to the Motorola jack, but found one on ebay and am waiting for it to arrive.

My question is whether it matters which coax is used? My weather radio works fine as it is. I did try the scanner using alligator clips to connect the antenna and i do get a signal.

I dont know how well that antenna, made specifically for 162.xx mhz will work on the UHF scanner bands, but I have gotten 155.xx VHF signals well, even with the alligator clip mess.....

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50 & 75 ohm. Each is optimised for its own job. Loss & power handling diffe r, and there's impedance matching to what you're using. There's also wide v ariation in frequency response with co-ax, some is only good for baseband. Some is well screened, some less so.


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The cable must match the impedances at both ends and these impedances must be the same. Personally, I recommend shielded cable (signal+alu shield+ground return).

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Communication radios tend to use 50 ohm coax. RG-58 1/4", RG-8X 5/16" and RG-8 RG-213 1/2" (Roughly)

TV and most CCTV stuff use 75 ohm coax. RG-59 and RG-6 5/16" and RG-11 1/2"

The 75 ohm is noticeably thicker.

It doesn't make much if any difference. Don't let people wind you up about impedance matching on receive antennas.

Generally, UHF is 3 times the VHF frequencies. What looks like a

1/4 wave whip antenna (16-18")on VHF will look like 3/4 wave on UHF. And will work just fine.
"I am a river to my people." 
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Fox's Mercantile

For receiving the impedance will not make any difference as the receiver impedance varies all over the place over a wide range of frequencies. Just as Jeff says.

I would use the RG-6 TV type as the losses are usually lower for coax around 1/4 inch in diameter and the cost is very low. Some have even gotten short ( 50 to 100 feet) pieces for free from the cable TV companies. The main problem will be getting a good connection. You need the proper crimp connectors and tool as the shield is aluminum.

For me, the next best would be some RG-8X. It is 50 ohm, but the shield and center conductor is copper so you can solder to it with no problem. The rg-8X is about the same size as the rg-6 TV coax. Uhnless the distance is less than about 25 feet I would stay away from the rg-58 that is slightly smaller in diameter.

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Ralph Mowery


RG-6/u (usually good stuff) RG-59a/u (which is garbage)

I use RG-6/u with F-connectors for EVERYTHING, whether it's 50 or 75 ohms. I also have a fair collection of Type-F to BNC or PL-259. The mismatch loss is negligible:

Please note that there are variations in RG-6/u quality varying from Radio Shack junk to "satellite TV" grade with lower losses at >1GHz frequencies. Some variations are more flexible than others, some have a UV resistant jacket, and some use CCA (copper clad alumunium) which is cheap junk. Caveat emptor.

Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Jeff Liebermann

Co-ax impedance is not critical, but choosing rf rather than baseband co-ax is.

Try it & see.


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