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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.

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10 votes
2 answers
3k views

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 ...
Kevin Reid AG6YO's user avatar
  • 24.6k
9 votes
1 answer
797 views

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 ...
Danny Paul's user avatar
13 votes
2 answers
5k views

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 ...
BenSwayne's user avatar
  • 691
8 votes
3 answers
1k views

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 ...
ITChap's user avatar
  • 209
15 votes
2 answers
7k views

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's user avatar
  • 2,336
5 votes
5 answers
681 views

(When) does a transceiver re-reflect 100% of reflected power?

There has been a long discussion of one question here. Phil, W8II and I agreed that it's better to post a separate question. There are several sources (some editions of "The ARRL Handbook", &...
Aleksander Alekseev - R2AUK's user avatar
3 votes
3 answers
5k views

Choke at antenna and feedpoint?

I'm planning on putting up a G5RV. From the ladder line I connect 5m coax to the shack; would it be worth doing a common mode current choke at both the antenna feedpoint and the coax feedpoint? (I ...
s3c's user avatar
  • 837
2 votes
5 answers
5k views

Balun and tuner configuration for multiband dipole

I'm putting up a multiband dipole in some tall trees. (Perhaps it's more correct to call it a "dipole-doublet"). The situation I'm imagining looks like this: The legs of the antenna are each 100 ...
bcattle's user avatar
  • 255
15 votes
4 answers
2k views

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 ...
VU2NHW's user avatar
  • 2,834
11 votes
2 answers
4k views

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 ...
natevw - AF7TB's user avatar
9 votes
4 answers
4k views

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 ...
Glenn W9IQ's user avatar
  • 18.6k
8 votes
4 answers
876 views

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 ...
pgibbons's user avatar
  • 444
6 votes
2 answers
900 views

Power dissipation in transmission lines?

I was wondering, does the impedance of a transmission line have any effect on the power it dissipates? I'm familiar with the fact that an impedance equal to the load will provide maximum power ...
s3c's user avatar
  • 837
5 votes
2 answers
1k views

What are the implications of pulling LMR400 through EMT conduit with several 90 degree conduit body fittings

In order to route my antenna feedlines out of my house, I have to pass through a wall, into the garage and through another wall. All of this involves four 90 degree turns. I am wondering what the ...
ghendricks's user avatar
5 votes
1 answer
2k views

Connect Printed Yagi-Uda Dipole Array with Balun to coaxial cable correctly

I am making the Printed Yagi-Uda Dipole Array with Balun (that is the full name). I used Antenna Magus to calculate dimensions. I am not sure how to properly connect it to coaxial cable. Here is what ...
Triak's user avatar
  • 153
4 votes
2 answers
1k views

What impedance matching do I need between my 300Ω feedline and Softrock receiver?

I will be assembling a Softrock Ensemble II HF receiver, and I know I'm going to want it on air as soon as I build it, so I'm challenging myself to build an antenna for it first. The plan is to do a ...
Adam Davis's user avatar
  • 12.1k
4 votes
2 answers
4k views

Does effective grounding of mobile (vehicle) antenna mounts address common-mode currents?

While researching how best to install my mobile amateur radio in my car, I didn't understand if there was optimum Antenna Feedline Length for mobile installations? Understanding that this is caused ...
BenSwayne's user avatar
  • 691
1 vote
1 answer
120 views

Is this antenna "system" really work? [closed]

I posted yesterday asking how can I have signal inside my house which my house is obstructed by a hill from direct signal from the cellular's operator' Base Transceiver System (BTS). The schema of the ...
Sitorus's user avatar
  • 77