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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2 votes
1 answer
43 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 ...
1 vote
1 answer
52 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 ...
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1 vote
0 answers
86 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 ...
3 votes
2 answers
611 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 ...
1 vote
2 answers
142 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 ...
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8 votes
4 answers
273 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 ...
  • 424
5 votes
2 answers
353 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 ...
5 votes
3 answers
297 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 ...
5 votes
5 answers
406 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", &...
0 votes
3 answers
151 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, ...
0 votes
1 answer
101 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 ...
1 vote
1 answer
102 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 $\angle I_n$ ...
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0 votes
0 answers
46 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, ...
0 votes
3 answers
163 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.
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 ...
0 votes
2 answers
811 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 ...
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2 votes
1 answer
542 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 ...
  • 740
0 votes
2 answers
189 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 ...
  • 12.6k
3 votes
1 answer
110 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 ...
0 votes
1 answer
54 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.
2 votes
1 answer
175 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 ...
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3 votes
1 answer
163 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...
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3 votes
2 answers
191 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 ...
11 votes
4 answers
2k 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 ...
  • 1,169
2 votes
4 answers
210 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 ...
  • 1,013
4 votes
2 answers
228 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 ...
  • 12.6k
1 vote
3 answers
238 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. ...
3 votes
3 answers
203 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 ...
  • 12.6k
1 vote
1 answer
113 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 ...
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1 vote
0 answers
76 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. ...
  • 173
5 votes
2 answers
251 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, ...
  • 1,032
9 votes
4 answers
2k 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 ...
  • 18.2k
2 votes
3 answers
1k 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 ...
  • 21
1 vote
1 answer
375 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 ...
  • 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?
  • 11
5 votes
2 answers
552 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 ...
  • 12.6k
2 votes
2 answers
650 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 ...
  • 377
5 votes
2 answers
980 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 ...
1 vote
2 answers
211 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 ...
2 votes
1 answer
2k views

Feedline and balun for 80m horizontal delta loop

I am new to HF. I'd like to put up an 80m delta loop. Due to aesthetic considerations I need to use coax to the shack. If tuned for 3.55MHz, I anticipate having a good SWR on 80m, 40m, and 20m. The ...
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1 vote
3 answers
614 views

Total cancellation in corporate feed network for patch antenna

I'm trying to build an array of patch antennas in order to receive a GPS signal. The idea is to build 4 patches and connect them with a corporate feed network. An example of corporate feed is this one....
8 votes
6 answers
2k views

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 ...
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10 votes
2 answers
2k 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 ...
  • 23.2k
2 votes
5 answers
4k 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 ...
  • 255
2 votes
1 answer
183 views

What dictates ladder line max frequency? [duplicate]

When using ladder line to feed an antenna, I've seen it written that The spacing should not be over 1 percent of the highest-frequency wavelength, and that’s the only real consideration with ...
  • 255
4 votes
3 answers
803 views

Which is better in my situation: Balanced dipole, or as much wire as possible in the air?

I'm finally getting to the point of hopefully putting up a HF antenna. The idea is to start with a simple, straight wire dipole using trees as support points. (No traps or coils.) However, with the ...
  • 4,810
9 votes
2 answers
3k 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 ...
3 votes
3 answers
161 views

Switching 450 Ω window line

I have a very old Harvey Wells Z-Match antenna tuner (transmatch) with two outputs on the back for 450 Ω window line. One output is for “medium frequency” and works for 75 and 40 meters. The other ...
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0 votes
1 answer
47 views

Is there a lower limit to the usable frequency for PCB 'stripline' feedline?

I'm designing some low loss antenna switches for 160-10 meters, and my current plan is to construct the entire system as continuous 50 ohm microstrip feedlines on 2 sided FR4 PCB. All examples that ...
  • 1,814
5 votes
3 answers
2k views

Running ladder line through window from inside shack to outside dipole antenna - what to watch out for?

For HF operating, I am considering running a ladder line from the ATU just inside a window, through the window (squeezing it between the window and the window frame; not actually through the glass), ...
  • 4,810