Amateur Radio Stack Exchange
Amateur Radio Stack Exchange

Questions tagged [feed-line]

Questions about RF feed lines. Also tag with coaxial-cable if the feed line in question is a coaxial cable; also tag with connectors if the question is about connectors for an RF feed line.

Questions on topic in this tag include anything to do with the use of any type of RF feed line, coaxial or otherwise. The selection of cables and connectors; how to route, solder, and splice cables; the use of cables in outdoor and other environments; the use of leaky coaxial cable as an incidental radiator; or the building of a balun or antenna using feed line are all on topic in this tag.

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Understanding coax impedance

I keep doing research, and trying to grasp it, but when it comes to RF impedances, and coax, I still have trouble trying to grasp it. So first, I think you have to have a 50 ohm coax for a 50 ohm transmitter to keep the impedances matched. I think I…
Skyler 440
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What should I consider when choosing a coaxial cable?

Given a middling-power rig (up to 100 W) requiring a 50 Ω antenna, a few options for the coaxial cable with a 50 Ω impedance are RG-174 RG-58A/U RG-8 RG-213 Apart from cost, what factors are relevant in deciding which coaxial cable to use?
VU2NHW
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What is the purpose of a balun and a unun in a feed line?

I have never understood how a balun or a unun works and under which situation I need to use either of them in an antenna feed line.
Dinesh Cyanam
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50 Ohm coaxial cable vs 450 Ohm or 600 Ohm ladder or window line?

What are the relative advantages and disadvantages of using 50 Ohm coaxial cable as opposed to 450 Ohm or 600 Ohm ladder or window line?
Timtech
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Is there an optimum Antenna Feedline Length for mobile installations?

I bought a ham radio antenna mounting kit for my car that includes ~16' of coax. One end has a trunk lip NMO antenna mount, the other end has a re-solderable PL-259. I asked the sales person if it is best to shorten the coax after installation to…
BenSwayne
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Is "low loss" cable required for HF?

I use RG-58 for all my HF antennas, since it's light, flexible, convenient, and cheap. And super easy to choke. Whenever I have a problem I just loop a few turns of it on a ferrite core and the problem goes away. Since I operate 100W max and all my…
hjf
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What is the actual loss in a feed line with high SWR?

It is well-known that it is unwise to have standing waves on the feed line between one's antenna and one's transmitter, unless it is a very low-loss type (e.g. ladder line), because the transmitted signal is reflected multiple times through the feed…
Kevin Reid AG6YO
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Phasing harness for antenna array

I understand that certain antenna designs (particularly phased arrays) require feeding each radiating element with a certain number of degrees of phase separation in order to achieve a desired radiation pattern or beamwidth. I found this 2-meter…
Craig
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Why isn't twisted pair used for feedlines?

My son was asking about some Ethernet cable (Cat 5 unshielded twisted pair), and since he recently passed his Technician exam and we both have "radio stuff" on our minds, I tried to make the analogy between coax transmission lines and the balanced…
natevw - AF7TB
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Why must twin-lead conductor spacing be small to avoid radiation?

A transmission line does not radiate when the spacing between the two wires is very small when compared to the wavelength, but the transmission line begins to radiate when the spacing between the lines becomes comparable to the wavelength of the…
Danny Paul
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Why does ladder line generally have a lower loss than coaxial cable?

It is well understood in the amateur radio community that ladder line, window line, etc. have lower losses per foot than say RG-213 or LMR400, particularly on HF frequencies. It is also understood that this loss is a function of the RF resistance of…
Glenn W9IQ
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Use a TV coax and balun for a poor-man's OCFD?

Can I use TV coax and a cheap TV balun to build a poor-man's OCFD? Marginal performance is acceptable if it saves money. If I could listen to 10% of transmitters within a 100 mile radius that would be acceptable. And as for the coax length, probably…
SlowBro
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What happens in a low loss feed-line with a high SWR

I was recently reading an interesting article from the ARRL to get a better understanding of the SWR. The following case is still unclear: A low loss feed-line with an impedance that doesn't match the antenna's impedance and the receiver's…
ITChap
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Tuner at antenna side versus transmitter?

I figure the transmitter has a 50-ohm pure resistive output and that the transmission line is 50-ohm as well. I think it's usually the antenna itself that actually needs to be tuned, yet it sounds like everyone places the tuner at the transmitter…
pgibbons
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How do you solder/crimp a 90-degree BNC connector?

I ordered this 90-degree BNC connector, but I'm not sure how to connect the center pin. The back of it looks like this: The small screw plate threads into the back when you're done connecting the wire. But how does the wire connect? The hole is…
KJ7LNW
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