0

Which cable is better for ham radio antenna? RG 58, RG 59, or RG 6?

Based on [1], RG6 has lower signal loss. So, is RG 6 a better cable? Or there are no differences?

[1] https://sewelldirect.com/blogs/learning-center/what-is-the-difference-between-rg59-and-rg6

Rizky Luthfianto
  • 103
  • 1
  • 3
  • 2
    Hi! Welcome here! This is a question that is underresearched: For example, wikipedia does have an article on Coax Cable and comparison of different types, and you'll notice that these things differ in more than loss. What's a bit problematic here is that "ham radio" is not a single use case, and especially not a single frequency. or power. In engineering, there's no global "it's better", it's always relative to some aspect for some specific use case! You can easily fix the question by telling us what you want to do specifically, what you researched and what you've got that you want to connect. – Marcus Müller Aug 02 '20 at 10:05
  • I found a number of related answers in this search. But since this has an answer, I hesitate to close it as duplicate (is it a duplicate?). Do any of those Q&As answer your question? – Mike Waters Aug 03 '20 at 00:17
  • 1
    I don't think it's a duplicate. This question is more or less "what are the significant differences between RG-58, RG-59, and RG-6?" It's a step before asking about the differences of 50 and 75 ohm cable. – Phil Frost - W8II Aug 04 '20 at 13:24
  • @PhilFrost-W8II "What are the significant differences..." would be a better title for this question. – Mike Waters Aug 04 '20 at 14:27

2 Answers2

2

Loss is pretty important, but it's not the only thing to consider.

Firstly keep in mind while all RG-6 (or any other RG-*) is of similar physical dimensions and should be compatible with the same connectors, the quality of a particular cable can vary a lot. The loss you'll see quoted in tables typically assume a high-quality cable from a major manufacturer like Times Microwave, Belden, or CommScope. There are however a great many no-name manufacturers making much lower quality cable that will have much higher loss.

So to get an accurate number on loss, you want to find the manufacturer's datasheet. If you find some cheap cable on Ebay or Amazon and there's no datasheet, the cable will probably have higher loss, as its cheaply made. This is especially true for RG-59 and RG-6, which are aimed at nontechnical consumers wanting to put CATV cabling in their home.

Besides loss, coax has a characteristic impedance. Most coax is either 50 ohms or 75 ohms. RG-58 is 50 ohms, RG-59 and RG-6 are 75 ohms.

CATV and video applications conventionally use 75 ohm. Ham and other radio applications usually use 50 ohms.

You can use 75 ohm cable with radio equipment. In fact it can be quite a good match for a dipole, which has a feedpoint impedance around 75 ohms. Ideally you want to match the feedline to the antenna's feedpoint impedance, thus minimizing SWR loss. But you must also ensure the impedance seen by your radio, which is a function of the antenna impedance, feedline characteristic impedance, and feedline length, is within your radio's specification, or use a tuner or matching network.

On the other hand, 50 ohm coax, with a 50 ohm antenna, will work without a tuner with any modern radio.

You might also want to consider connector availability. Because RG-59 and RG-6 are used predominately for CATV, you will probably have a very hard time finding anything but an F connector for them. This means you will also need adapters to make any use of the cable.

Phil Frost - W8II
  • 51,701
  • 6
  • 88
  • 212
  • Note also that 75 ohm connectors and 50 ohm connectors have different diameter center pins, so while you may find adapters that look like they will work, putting them together may mutually damage both connectors. – user10489 Aug 02 '20 at 15:54
  • @user10489 true for some connector types, like N. But with BNC for example this is not the case: the impedance is varied by adding additional dielectric material rather than changing the center pin. And some connectors (like F) only come in one variety. – Phil Frost - W8II Aug 02 '20 at 17:45
  • The BNC 75 ohm plugs I've seen have a thicker center pin. It's barely visibly thicker, but it is enough to damage a 50 ohm BNC socket. N has tighter tolerances, so it's worse. – user10489 Aug 03 '20 at 02:29
  • 1
    @user10489 interesting, because a google search for "are 50 and 75 ohm bnc connectors compatible" turns up pages and pages of results that say "yes". – Phil Frost - W8II Aug 03 '20 at 03:05
  • Just because you find hundreds of people that have done it and say it works doesn't mean you don't have hundreds of people with damaged connectors and don't know it. Don't believe google, check the data sheets for your connectors, look at the diameters and tolerances. Oh wait, I bet you buy connectors that are so cheap they don't have datasheets. – user10489 Aug 03 '20 at 03:31
  • What are the consequences of a connector damaged this way? In the case of N where the tolerances are tight, it might actually break. If it doesn't break, it'll stretch, so it doesn't fit the right size pin anymore, maybe loose connections. And the impedance might be off a bit too. – user10489 Aug 03 '20 at 03:58
  • 2
    @user10489 it's the other way around (thinner inner is a higher impedance for the same diameter outer). A 75 Ohm BNC doesn't mate reliably with a 50, and a 50 damages a 75. – tomnexus Aug 03 '20 at 04:53
  • 1
    @user10489 If you want to make corrections, great. But "everyone on the internet is wrong, I'm right" is not a constructive way to engage. If you want to show that everyone is wrong, then you are the one that must be prepared to offer references. – Phil Frost - W8II Aug 03 '20 at 13:31
  • @tomnexus you have a reference for that? everything I find says for BNC, 50 and 75 ohm are mechanically compatible, with a nominal 1.35 mm diameter center pin in either case – Phil Frost - W8II Aug 03 '20 at 13:41
  • @PhilFrost-W8II I've seen them myself. I threw away A BNC lying on my bench a few months ago when I saw it was 75 Ohm. I may even have one I could photograph. But that's not as good as a reference, fair enough. Let me see what I can find. – tomnexus Aug 03 '20 at 15:38
  • I'm not saying everyone on internet is wrong...just the 100 you found are probably ignorant. And I'm not claiming I wasn't ignorant... even though I could feel the connector breaking and stretching as I pushed them together, it didn't occur to me that I was breaking it. – user10489 Aug 04 '20 at 04:52
  • @user10489 well by all means, publish an article yourself, and illuminate the internet with your knowledge. You should have no trouble rising to the top of the google results, since the other top 100 results are written by ignoramuses. – Phil Frost - W8II Aug 04 '20 at 13:19
  • 1
    @phil I did some research and it seems the big manufacturers 50 and 75 are compatible, and change the dielectric as you say. However I do have some, and can readily identify an old-style 75 Ohm BNC by the inner size. So I guess it has changed over time. – tomnexus Aug 04 '20 at 16:08
2

Phil is correct the major issue is the impedance needs to match to prevent SWR losses. Normally the impedance of our radios output is 50 ohms. Using a 50 ohm cable connecting it to a 50 ohm input on our antenna gives us the lowest SWR.

Signal loss is also important and it varies with the length of the cable and with the frequency. At the 3- 30 MHz HF frequencies the signal loss for most coax is minimal. The loss increases when you get to UHF and VHF. A 50 ft length of RG 58 at HF is acceptable for most people, but the loss is higher at UHF frequencies. You either want a shorter length or go to a cable like LMR 400 which does not have as much loss.

While it costs a little more, I buy LMR 400 for all of my coax cables. I can use it with HF, VHF, and UHF with fairly good results.

Spending a little more for coax and putting some effort in to improving antennas gives a good return on my investment.

Jim
  • 1,688
  • 8
  • 16