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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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450-ohm ladder line fact vs fiction

I am considering many possible doublet antenna scenarios for a multi-band antenna (80 meters to hopefully, 6 meters) customized to my specific home situation. Everything is a compromise. I will be ...
Michael's user avatar
  • 13
-1 votes
3 answers
102 views

longest practical feed line length

So for a HF vertical antenna (DX commander Rapide), what is the longest feed line that that I can practically use using high-quality coax? I realize shorter is better, but my HOA (my wife) is raising ...
KQ4QKF's user avatar
  • 1
0 votes
3 answers
255 views

QRP operation SOTA, what coax cable feed-line for HF?

I've done outdoor activities, POTA and WWFF, with a coax RG58 feed line with PL conectors, around 3 meters (9.8 feets), for wire EFHW antennas working HF bands (40m, 20m and 10m). Now I want to do ...
Trimax's user avatar
  • 103
3 votes
2 answers
174 views

Can I run my antenna coax near a gas line?

I just moved to a new place and would like to put an antenna up in the attic. My shack location is in the basement with the furnace and water heater. In my explorations, I've discovered that there is ...
byl's user avatar
  • 131
4 votes
2 answers
418 views

Ladder line vs twisted pair: where do the losses actually occur?

I don't understand why 14 AWG XHHW-2 wire would work fine when used in ladderline for high-power HF transmission, but the same wire would exhibit higher losses when used in a twisted pair ...
Mark K1LSB's user avatar
0 votes
0 answers
79 views

Is using 14 AWG XHHW-2 twisted pair wires for high-power (legal limit) HF TX feedline a bad idea? [duplicate]

My question is specifically regarding using a homemade twisted pair of 14 AWG XHHW-2 wires as twin lead feedline for high-power HF ham transmissions. A somewhat similar question has been posted in the ...
Mark K1LSB's user avatar
2 votes
4 answers
180 views

Wave bounce inside a resonant antenna

Let's assume we have a transmitter, a feed line, and a standing wave antenna (dipole, etc.). The transmitter is matched with the feed line, and the feed line is matched with the antenna, which is why ...
elgroovy's user avatar
4 votes
2 answers
508 views

Coax in the wall, or around the house?

I am mounting a hex-beam antenna to the peak of my house (assuming that I can find someone with a cherry-picker or a scissor-lift that can help me get it up there). Right at that end of the house is ...
Don Levey's user avatar
2 votes
1 answer
160 views

Is a 1/2-wave coax cable shorter or longer than the full-speed 1/2-wavelength?

If I want to cut a half wavelength segment of coax for the two-meter band and the velocity factor is 85%, is my cable going to be shorter or longer than a meter? I'm trying to figure out if the ...
KJ7LNW's user avatar
  • 759
2 votes
1 answer
113 views

Can I use 14/2 UF-B wire as transmission line?

I'm wanting to build an antenna system utilizing twin lead feedline running to an 80 meter doublet. I'd like to avoid the typical hassles that accompany 450 or 600 ohm ladder line so I'm considering ...
Mark K1LSB's user avatar
7 votes
1 answer
196 views

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 ...
KJ7LNW's user avatar
  • 759
2 votes
1 answer
124 views

Mix 300 ohm window line with LMR400 for long feedline run to 6m/2m/70cm?

I have about 150 feet of LMR400 going to a tri-band 6m/2m/70cm antenna, and unfortunately the loss is quite high at these high frequencies, at this length. About 70 feet of that run is non-negotiable ...
User5754448's user avatar
1 vote
1 answer
274 views

Feedpoints for stacked antennas?

I'm considering building some stacked 70cm quad antennas (home brew / DIY build) -- and... I'm having a devil of a time trying to figure out how/where to feed these antennas. For a single home-brew ...
Alan T's user avatar
  • 11
1 vote
0 answers
288 views

Is this amount of loss normal with LMR400?

I have a run of about 150 feet of LMR400 (specifically, it's this DX Engineering "400MAX" product). It connects to an Ed Fong antenna (2m, 1.25m, 70cm tri-band J-Pole) about 75 feet up a ...
User5754448's user avatar
3 votes
2 answers
1k views

SDR Transceiver over LAN

The feed line is a limiting factor when designing a home HAM system. The further the antenna is placed from the transceiver, the greater the cost and attenuation. Is there a way to solve this with ...
Christopher J. Grace's user avatar
1 vote
2 answers
580 views

How do you calculate the impedance of a parallel-wire balanced feedline (ladder line)?

I've looked around and maybe I'm just searching for the right terms to find the answer. I know that the impedance of ladder line has to do with the distance between wires: What is the generalized form ...
KJ7LNW's user avatar
  • 759
8 votes
4 answers
946 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
5 votes
2 answers
533 views

Can coax be run through the center of a radiating element without currents being induced on the coax shield?

I run a λ/2 vertical dipole for 20M that's fed to a 1.5:1 balun at its center with coax that is perpendicular to the dipole (parallel to the ground), for about 30 feet before it comes down to the ...
Louis Seaman's user avatar
  • 1,127
5 votes
3 answers
1k views

When a dipole antenna is fed via coax, what powers the ground-side of the dipole?

I've been trying to understand how dipole antennas work, and I believe I understand the basics when they're fed via a balanced feed line. In fact, every dipole physics YouTube video and web page I can ...
Asker2093022's user avatar
5 votes
5 answers
725 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
0 votes
3 answers
262 views

What happens to the signal level if the antenna has high SWR?

I'm currently reading "Reflections: Transmission Lines and Antennas" by M. Walter Maxwell, W2DU. This book explains well why the energy is not lost because of high SWR during transmitting, ...
Aleksander Alekseev - R2AUK's user avatar
0 votes
1 answer
128 views

What type of Cable Should I use between a Long Wire antenna and a Transmatch?

I installed a Yaesu System 600with a MFJ Versatuner 2 on my 31ft sailboat and Idont know what type of cable should I use between the MFJ and the long wire antenna I have on my back Stay. Any ...
Fernando Villanueva's user avatar
1 vote
1 answer
332 views

Excitation coefficient of a linear phased array

it's well known that in a linear and equispaced antenna array, the array factor is equal to: The array is then called uniform if $|I_n| = I$ is the same for all elements. The phase terms $\angle I_n$ ...
Kinka-Byo's user avatar
  • 279
0 votes
0 answers
48 views

How to decide between Dipole and Monopole antenna for Cubesat Uplink (433 MHz)? [duplicate]

We are currently deciding between a dipole and a monopole for uplink (435MHz) , while the monopole is easier to feed, we are unsure of how effectively we'll be able to implement the ground plane, ...
Rishabh Hulsurkar's user avatar
0 votes
3 answers
621 views

Is there an instance where you can directly feed a half wave dipole with coaxial cable without having to worry about balanced to unbalance?

Like the question says, can you feed a dipole with coax with no ill effects? Nothing else in the system, just the antenna and the cable.
Francis Archibald's user avatar
1 vote
0 answers
47 views

J Pole, what is the best way to deal with Common Mode Current? [duplicate]

I am planning on utilising a ferrite choke on a J Pole antenna for CMC. Placement directly on the feedpoint poses possible mechanical restraints. Is it okay to place it a quarter wave down the coaxial ...
Francis Archibald's user avatar
0 votes
2 answers
2k views

How to use 75ohm (RG6) coax?

I know that there have been many similar threads on this, but I still need clarification. At the moment, the only thing I have is a 500' roll of RG-6 and a (very) tight budget, and I should be ...
Galaxy's user avatar
  • 199
2 votes
1 answer
1k views

Should I bother with a doublet if I can't go straight to the tuner with open wire?

I have two trees about 135 feet apart and about 55 to 65 feet tall. I have been trying to determine which kind of wire antenna to put up there. Initially I was considering either a fan dipole or ...
Paul's user avatar
  • 791
0 votes
2 answers
247 views

Relative disadvantages of impedance mismatch vs. non-resonant length wire antenna

So given a choice between a non-resonant length of wire antenna center fed by 50 Ohm coax, or a resonant length of wire fed highly off-center by 50 Ohm coax, or a resonant length of wire fed by high ...
hotpaw2's user avatar
  • 13.5k
3 votes
1 answer
163 views

impedance matching with window twinlead

Question from new ham here, regarding ways of matching impedances between a feedline and an antenna. Is it possible to fashion a broadband HF impedance matcher from a length of windowed twinlead, in ...
niels nielsen's user avatar
0 votes
1 answer
115 views

On a horizontally setup 20m delta loop I am looking to determine the calculations for the proper length of a feed wire

Base of loop will be about 6 feet above ground. RG-8 or 213 will be used for the feed wire. Ugly balun as well.
Artemus's user avatar
2 votes
1 answer
312 views

Glass Block Pass Through

In my future shack I will have glass block windows consisting of 6 x 8 blocks and a 6 x 16 vent. I've been searching, but cannot find the best solution to pass coax through the windows. I've thought ...
K8KV's user avatar
  • 377
3 votes
1 answer
186 views

Do the Horizontal Conductors of a Ground Plane Antenna Adequately Decouple Its Feedline?

A NEC4.2 analysis of this configuration may reveal an unexpected truth about this...
Richard Fry's user avatar
  • 2,932
3 votes
2 answers
263 views

How do I use a signal generator + oscilloscope to measure feeder length?

I could relatively easily take the feeder down and use a tape measure but it’s more of a challenge to learn how to measure the length using my oscilloscope -Red Pitaya - but I have to admit I have no ...
forestDM's user avatar
11 votes
4 answers
4k views

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 ...
hjf's user avatar
  • 1,219
2 votes
4 answers
380 views

Why do we talk about common mode current from an antenna, but not from a transmitter?

There's a lot of information available about how to block common mode current originating at the antenna end of a coax cable. But, I haven't seen any reference to common mode current originating at ...
mrog's user avatar
  • 1,023
4 votes
2 answers
328 views

Why isn't some form of twinax commonly used for antenna feed lines?

Twinax (shielded controlled impedance balanced line pairs) is said to be used in 10G ethernet signaling for greater noise immunity that other cabling types. Why isn't twinax (or similar) commonly ...
hotpaw2's user avatar
  • 13.5k
1 vote
3 answers
300 views

Do I always need a tuner at both ends of the transmission line or is that only for certain types of antennas/circumstances?

Last night was my first night on the air as a General licensee and at HF. I've got an IC-7300 with the built-in antenna tuner. I'm pretty sure I understand how to operate the radio, for the most part. ...
NonYaBidnezz's user avatar
3 votes
3 answers
317 views

Antenna testing, minimizing feed-line radiation?

Assume that one does not have access to a multi-million-dollar RF anechoic chamber. When testing an amateur radio HF or VHF antenna, how would one absolutely minimize the amount of any RF radiation ...
hotpaw2's user avatar
  • 13.5k
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
1 vote
0 answers
82 views

advice needed for balanced line terminals

I am designing a portable antenna with a radiating element and a balun that are not close to each other. The impedance has been designed to be close to 50 ohms. ...
rodv92's user avatar
  • 173
5 votes
2 answers
421 views

How to estimate ladder line loss?

There have been a number of questions regarding the issue of feed line loss and ladder line eventually gets discussed. So I am curious, how does one begin to estimate the loss in ladder line? So, ...
Chris K8NVH's user avatar
  • 1,042
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
2 votes
3 answers
2k views

Doublet with ladder line vs coax w.r.t. noise

I live in the city, with 50’x 100’ lots. I use an 80 meter doublet at 30 feet, fed with ladder line to a tuner. My noise floor ranges from S5 to S9 depending on the time. Would a coax feed reduce ...
Steve's user avatar
  • 21
1 vote
1 answer
721 views

Using LMR400 and RG8x in the same feedline

I am putting a run together from my shack to a new 2 meter antenna I've built. I'm blessed to have many trees on my property and I'll be placing the new antenna about 90 ft from the ground by hanging ...
Hogstrom's user avatar
  • 187
1 vote
2 answers
5k views

What is Electrical length in RF and how to electrically cut and measure the RF cable in degree?

What is electrical length in detail? Why is it so that 1/4 wave , 1/2 wave dipole antenna works properly and not a full wave antenna? What is the role of electrical lengths in degree?
Rumi's user avatar
  • 11
5 votes
2 answers
835 views

What are the effects of different feed-line incidence angles?

Consider a dipole antenna fed by a coax (say, longer than the antenna) with a signal reasonably close to the dipole's resonant frequency. Various sources say that the feed-line should approach the ...
hotpaw2's user avatar
  • 13.5k
2 votes
2 answers
910 views

G5RV Jr. fed with ladder line and coax

I am a new ham and I was just given a G5RV Jr. I have about 20 feet of coax plus about 60 feet of 450 ohm ladder line I can feed it with. Can I extend the G5RV Jr. feed line with the ladder line I ...
K8KV's user avatar
  • 377
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
1 vote
2 answers
267 views

Is a "shorted" coax feedline ok for a G5RV type antenna?

I have "inherited" what I believe to be a G5RV antenna with two 51 foot wire centerfed radiators. If I remember correctly from measuring 2 months ago, there is about 31 feet of 450 ohm ladderline ...
Bob Horton's user avatar