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.
71
questions
17
votes
4
answers
8k
views
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 ...
- 7,530
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 ...
- 2,814
15
votes
1
answer
8k
views
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.
- 428
15
votes
2
answers
6k
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?
- 2,306
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 ...
- 681
11
votes
4
answers
3k
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 ...
- 1,189
10
votes
4
answers
9k
views
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 ...
- 203
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 ...
- 23.9k
9
votes
4
answers
3k
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 ...
- 18.4k
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 ...
- 7,104
9
votes
1
answer
720
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 ...
- 193
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 ...
- 83
8
votes
4
answers
407
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 ...
- 444
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 ...
- 199
7
votes
1
answer
93
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 ...
- 619
6
votes
2
answers
848
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 ...
- 817
5
votes
5
answers
6k
views
What type of solder is best suited for radio and electronic use?
Many types of solder are available today, such as acid-core, silver, rosin-core and aluminum solder. What kind should I use for building antennas and radio equipment? Why?
From test question: T7D08
- 901
5
votes
2
answers
289
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, ...
- 1,042
5
votes
4
answers
222
views
When should an adapter be used to marry a coax to a connector?
A quick follow-up to What should I consider when choosing a coaxial cable?
Most commercial rigs come with a PL259/SO239 connector for use with something like the RG8/RG11. In the event the diameter ...
- 2,814
5
votes
3
answers
516
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 ...
- 51
5
votes
2
answers
378
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 ...
- 644
5
votes
2
answers
641
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 ...
- 13.1k
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 ...
- 637
5
votes
1
answer
1k
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 ...
- 153
5
votes
1
answer
486
views
Why is coax the most common feedline?
Why is coaxial cable the most common feedline in use? What are the advantages/ disadvantages of coax compared to other feedline types?
From test pool question: T9B03
- 901
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), ...
- 4,798
5
votes
1
answer
938
views
Why exactly would cable lengths to a duplexer matter?
So a very experienced friend of mine is making a portable suitcase kit with Yaesu FTL-2001 (VHF), Yaesu FTL-7002 (UHF) and DX-720D duplexer* plus power supply and other miscellaneous gear. FTL-2001 ...
- 2,783
5
votes
5
answers
450
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", &...
4
votes
2
answers
256
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 ...
- 13.1k
4
votes
3
answers
865
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 ...
- 4,798
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 ...
- 681
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 ...
- 12.1k
3
votes
2
answers
931
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 ...
3
votes
3
answers
188
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 ...
- 329
3
votes
3
answers
4k
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 ...
- 817
3
votes
2
answers
208
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 ...
- 51
3
votes
1
answer
133
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 ...
- 867
3
votes
1
answer
176
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...
- 2,912
3
votes
3
answers
249
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 ...
- 13.1k
2
votes
4
answers
252
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
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
192
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
2
votes
1
answer
109
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 ...
- 619
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
2
votes
1
answer
62
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 ...
- 23
2
votes
2
answers
732
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
2
votes
1
answer
69
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 ...
- 373
2
votes
1
answer
220
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 ...
- 377
2
votes
1
answer
3k
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 ...
- 23
2
votes
1
answer
695
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 ...
- 781