TheRadioBoard

Hello
I have a large amount of coax cable, can it be used for antenna, any suggestions welcomed, btw i'm a newbie. Thanks

Welcome to The RadioBoard! There should be markings on the cable giving the type number, such as RG-58, RG-59, etc. Coax is used to connect a receiver or transmitter to an antenna. Before we can advise whether you can use it we need to know the type. Here's more info on coax: http://en.wikipedia.org/wiki/Coaxial_cable

73,

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KR1S
Thanks for responding, I have a good bit of both types

Okay! The characteristic impedance of RG-58 is 52 ohms, and the characteristic impedance of RG-59 is 72 ohms. It just so happens that a half-wavelenght dipole antenna has a characteristic impedance of 72 ohms, so RG-59 is good for that. You calculate the total length of a dipole by

468/F (MHz)

For receiving, obtaining an exact match isn't critical, so you could use the RG-58 if you have more of it.

There are other types of antennas with different impedances. Most listeners use a random length of wire and try to arrange some form of ground system, either a rod in the ground or wires laid out on or just below the surface, connected to the radio's ground terminal. If the end point of a random-length wire is some distance from your receiver, you can use either coaxial cable to connect to it. Ground the shield at the receiver end, but not at the antenna end, and connect the antenna to the center conductor. This can help reduce noise pickup from the line between radio and antenna.

So the next questions are

What frequencies do you plan to listen to?
What type of receiver?
What type of antenna can you install?

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/

So the next questions are

What frequencies do you plan to listen to?
What type of receiver?
What type of antenna can you install?

Have been away from this stuff for over 50 years and recently became wheelchair bound I ordered 3 crystalradio kits and 1 crystal SW kit. I have an old Philco AM SW radio. One 20 ft standing mast antenna was used for TV (now on DirecTV satellite) . Plenty of room in back yard with some trees for other antennas. I have metal roof on my house. The first kit will be the oatmeal box crystal radio. Thanks for your concern and input as I have a lot of relearning to do.

Welcome back to radio. Once the bug bites it never leaves.

A crystal set needs the biggest antenna you can manage, and a good ground system. All of the power you'll ever hear is what comes down the antenna, and a good ground system makes a big difference on a crystal set, whereas you can get away with a poorer one when the radio has stages to amplify the signal. "High and in the clear" is the rule of thumb. I've never been a big fan of ground rods for ground systems, antenna-wise. I prefer radials that spread the ground system out and add to it. A ground rod is okay for lightning safety.

Start looking for antenna wire. You can use house wire, like single-conductor 12- or 14-gauge, but it's heavy and noticeable. Look around eBay, as you usually can find wire for a lot less than retail.

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/

1) so rg59 to run from ant to radio in house, but what about running a length underground in pvc pipes? ant trees are too far from the house for just a downwire.
2) also, how much difference does it make if ant is not run ew or ns?
3) i don't watch tv, so what if i connect my ant to the box in the attic and have ant distributed in every room like cable tv?

jw

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onct, when i was younger, i knew everything. now, i'm old and jeswondering.

Lot of 'ifs' here. Coax in underground pipes is okay. As far as orientation, for the broadcast band there may not be much difference. A short antenna, close to the ground, receives poorly in all directions. You have to try and see.

In discussing coax, I think it was mentioned that the shield should be grounded near the receiver end. The purpose of doing that is to shunt noise picked up by the shield from within the house. At cable-TV frequencies it doesn't matter, so the shields may only be grounded through a bus wire going to the box in the attic (if that). So the wiring inside the house could act as part of the antenna system with results that are impossible to predict. Random-length antennas in the real world, surrounded by trees, buildings and adjacent utility wires force compromises somewhere. You try one for a while, then compare it with another, and so on.

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/

I think overall that this would be a Bad Idea. All that extra coax cable is unnecessary added capacitance, but more importantly the extra unloaded cable would likely pick up extra noise (dimmers appliances etc).

I haven't tried one though, so I could be proved wrong on this.

It would probably be fine to pick one coax that goes to your radio room and use it directly as your lead-in from the attic.

To give you an example of odd ideas that Just Might Work, my current listening antenna is about 30 ft of second-storey aluminum eavestrough coupled to 10' of downspout, then about 20 ft of old RG-59 as a lead-in.

It's working nicely for shortwave listening, as long as I remember to turn one noisy kitchen dimmer off.

I agree. No real benefit from using coax on a crystal radio and probably not with a tube regen. RG-58 specs say about 25 pF per foot capacitance. I vote for a single wire feedline, as far away as possible from noise sources.

Rich

PS: I do have RG-8X buried in garden hose to feed my transmitting antenna.

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Homebrew Radio ex-Silicon Valley

In this case, notwithstanding the added capacitance, shielding the lead-in once it goes underground or enters the house might not be a bad idea.

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/