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Questions tagged [coaxial-cable]

Questions about coaxial cables, including different types of cable, connectors, adapters, and other topics.

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17
votes
1answer
4k views

How does an SWR meter really work?

For ham radio operators, the SWR meter is a ubiquitous piece of equipment. There are dozens of standalone models on the market and most modern transceivers and antenna tuners have this functionality ...
17
votes
3answers
7k 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 ...
15
votes
2answers
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?
14
votes
4answers
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 ...
12
votes
2answers
4k 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 ...
11
votes
4answers
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 ...
10
votes
4answers
208 views

Why are there so many coaxial cable impedances?

Why do we have 50, 75, 62 and 92 Ω coaxial cable, to name a few? Why not just one standardised cable? Is there some technical reason or did Mr. Coax and Mr. Cable have a disagreement, like Mr. Tesla ...
10
votes
1answer
2k views

How do I design a round or square coaxial transmission line to have a specific impedance?

Certain Hex Beam antennas use a coaxial center support post to send the RF to each antenna section, which is superior, in terms of maintenance, to a post with screw terminals connected by short ...
10
votes
1answer
257 views

Does Coax Limit the Maximum SWR a Transmitter 'Sees'?

A recent discussion about SWR led to the assertion that a length of coax cable will ultimately limit the SWR to which the transmitter will be exposed. By experimenting with an SWR calculation tool ...
10
votes
1answer
459 views

How terminate RG8 coaxial cable using PL259 (UHF) - screw - gasket - solder type?

Today I came across a problem in terminating RG8 cable using this PL259 plug. I have never had this type and it arrived in a pile of parts; I have tried to puzzle it together but without positive ...
9
votes
4answers
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 ...
9
votes
2answers
5k views

Does a balun need to be made with coax?

The short version My understanding is that one of the main reasons to use a balun with coax is to prevent the outside of the shield from becoming part of your antenna system. If that's the case, won'...
9
votes
1answer
113 views

overhead power-line safety

A set of utility lines, and above them some high voltage power lines, run almost directly over the backyard fence. Some radio antennas are situated so that they can't fall onto the utility or power ...
8
votes
6answers
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 ...
8
votes
4answers
15k views

How is a 1:1 current balun different from a choke?

I have a 10m dipole and am going to feed it with 50 ohm unbalanced feed line (coax). My understanding is the feed point of this style antenna is about 50-75 ohms, and since it is a balanced antenna I'...
8
votes
2answers
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 ...
8
votes
1answer
126 views

What is the logic behind RG cable codes

What is the logic behind the names of different RG cables? The Wikipedia's Coaxial cable page has a list of different coaxial cable standards but I cannot find the internal logic of the naming. I ...
8
votes
2answers
1k views

How to keep a disconnected coaxial connector weatherproof?

The advice I have seen on lightning safety is that if you don't have high-quality lightning protection (and associated grounding) installed on your feed line, it is advisable to, during a storm and ...
8
votes
3answers
5k views

How do I extend broken coaxial cable?

I have a piece of 75 ohm coaxial cable of unknown type (outer diameter is around 7 mm) which has developed a breakage in the center conductor (which is stranded). This cable is an adapter cable which ...
8
votes
2answers
890 views

What chewed my coax

Today I noticed that a piece of RG-58 that's feeding a Beverage antenna for HF was in two pieces. On further inspection it turned out to be cut. On further inspection I think it's actually chewed by ...
7
votes
4answers
7k views

I have 60 feet of coax but only need 20 feet; can I loop up the excess?

I was given about 60 feet of good cable with connections but only need about 20 feet. Can I loop up the end or do I need to cut and put a new connector on?
7
votes
2answers
173 views

Can ferrite beads lower coax cable velocity factor?

For VHF and UHF, it seems reasonable to slip ferrite beads over a coaxial cable to act as a transmission line common mode choke. It also seems reasonable to use beads with the smallest diameter ...
7
votes
2answers
344 views

What does an antenna analyzer tell me about these coaxial cables?

Note: more measurements added after graphs below I recently acquired a RigExpert antenna analyzer and I am trying to learn how to use it to test cables. I took two cables to start with to try and ...
7
votes
5answers
732 views

Coax fed dipole: shield goes to one side, yet is grounded via chassis line to Earth

Suppose I have a coax-fed half-wave dipole antenna. The coax shield goes to one side of the antenna, the center conductor to the other side. The transceiver's chassis is connected (via the coax ...
7
votes
1answer
185 views

What are the electrical differences between smaller and larger coaxial cables?

How do different sized coaxial cables, such as RG-58 and RG-8, compare in terms of electrical properties such as loss? Do different cable types have different losses at different frequencies? From ...
6
votes
4answers
683 views

Weather-proofing antenna connections

Here's a problem: you buy a fancy new vertical for a fair bit of coin, but there's no coax connector on the thing. There are just screw terminals. You need to attach coax to it, but in such a way ...
6
votes
4answers
1k views

Can a common-mode current exist on the inside of a coax shield?

People often say common-mode current flows on the outside of the shield, while the current on the inside of the shield is always opposed by an equal but opposite current on the center conductor. This ...
6
votes
3answers
3k views

Will coaxial cable degrade over time?

I have a 40' section of RG-8 that is about 35 years old. One end was terminated with a standard PL-259 and the other was soldered directly to an antenna. When I removed the connector from the one ...
6
votes
2answers
3k views

Understanding coax radiation and "current on the shield"

I'm having trouble understanding what seems to be the fundamental principle behind baluns (and probably other related topics). Perhaps some of my confusion comes from an audio background, where one ...
5
votes
4answers
341 views

50Ohm Coax presents 50 Ohms of impedance on which frequency?

Either there's a simple answer that I'm not finding in a spec sheet somewhere, or, I'm asking the wrong question!
5
votes
2answers
1k views

Why is my calculation for added length of coax for a double cross antenna different to everyone else's?

I'm an amateur amateur radio enthusiast finally building my own antenna, and have decided on a double cross antenna, with the goal of pulling data from NOAA satellites. Four coax cables, two of ...
5
votes
5answers
235 views

Grounding a vertical antenna from a balcony

I have a multiband vertical antenna mounted onto the railings of my balcony apartment high up on the 6th floor of an apartment building. The antenna is not grounded. This antenna comes without radials....
5
votes
4answers
195 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 ...
5
votes
4answers
847 views

Testing for 'Bad' Coax

I have a lot of 'donated' coax that has been given to me with unknown provenance. I'm wondering what things I can do that can determine whether I keep it or send to the tip? Some of the things I have ...
5
votes
2answers
404 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 ...
5
votes
1answer
51 views

For air coax calculation, what is correct diameter metric vis-à-vis tube stock thickness?

I am interested in creating a square outer-conductor with round inner-conductor air coax post for a hex beam antenna. I found the extremely useful information at: How do I design a round or square ...
5
votes
1answer
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 ...
5
votes
3answers
3k views

How to feed coax from inside car?

What is the best (or standard) way to get coax from the radio in the car to the outside of the car without smashing it and damaging the line? If I just put it through the door crack, it seems to ...
5
votes
1answer
424 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
5
votes
1answer
11k views

How to calculate single-stub match (general case)?

I'm trying to build a 1/2 wave "Coaxial J-Pole" antenna, similar to what is described here: Such an antenna would be great for stringing up in a tree when operating remotely, no tuner needed. The ...
5
votes
1answer
799 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 ...
4
votes
4answers
487 views

Soldering PL-259.. with a torch?

I came across this article about torch soldering PL-259 coax connectors. It seemed like a good idea since the body needs a lot of heat to get solder to flow into the holes. It's a little vague when ...
4
votes
3answers
2k views

It it really useful to terminate unused 75Ω outputs on a coax splitter?

When discussing improvements to my home HDTV Antenna/distribution system a colleague brought up the need to terminate all coax, even unused splitter ports. My understanding of the way terminator ...
4
votes
5answers
542 views

Coax cable as antenna for 5 watt handy

For a normal 5 watt handy working in VHF or UHF freq with 50 ohm antenna , is it possible to use a same length coax cable instead of a stub antenna, so as to work like a crude antenna. Will this only ...
4
votes
3answers
141 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 ...
4
votes
3answers
652 views

Height and feedline loss tradeoff for VHF

Currently my 2m antenna is about 3m above the ground inside, my HF antenna is connected to 30m (2db loss) coax and is about 12m up. Since the loss for 2m is a lot more when traveling down such a long ...
4
votes
1answer
186 views

Suspected Damage in Coax Cable

I suspect that the "white residue" between the coax cable jacket and connector is the result of environmental damage but I could not confirm it yet. Did anyone have a similar issue and if so what was ...
4
votes
2answers
329 views

How do I know if my coax connectors are good?

In installed a couple of compression style PL-259 connectors to the ends of RG8/U FOAM coax. It's about 16 feet in length. Here is an example of one of the connectors: How do I know if the coax is &...
4
votes
1answer
152 views

Why is the insertion loss of my coax cable higher than expected?

I am testing a long cable run (about 90m). This cable has been used outside and inside, for temporary setups. I've set up my VNA with the correct values (velocity factor,...) and the distance to ...
4
votes
1answer
347 views

How to choose a coaxial cable

How do you know which coaxial cable to choose for your application? For instance; I require a cable that has a 50ohm impedance, an operating frequency of 2.4GHz, length of 100mm, and needs to be ...