MarkP wrote on 2022-07-21, 21:56:
50 ohm coax, joiners, Ts and terminators are still available at our local electronic store. XP down still support NetBeui and a simple Work Group between the XP system and older kit using network shares will be easy to set up. This can been mdone with coax or RJ45 cabling.
Yes, but how good/bad is the electrical quality?
I've bought a lot of 50 Ohms cable for my radio hobby. Online, as well as in a local store.. Even used pre-made 50 Ohm network cable.
The results were horrible. Extremely. Horrible. Shielding was very thin, a single (1!) wire at the center. Thin like a hair.
No match for real, 40 year old RG58CU that my father had stored in the attic.
The results of these 50 Ohms cables were shameful.
A measurement with a friend's Rigexpert AA170 (a VNA) showed an endless roller coster ride. Like a sine. Horrible.
Such cables shouldn't be allowed for sale.
They aren't even adequate for vintage networking.
They will make people think their equipment was defective.
Because, who expects a brand new cable to be totally defective?
A continuity tester will see no damage, after all. It works as a power lead.
A bad one, at least, considering how poor the center wire is. 😓
The only solution, for me, is to make my own cables from scratch, testing them with NanoVNA.
And use quality 50 Ohms cables like Beiden H155 or Aircell, Airflex etc.
Or buy ready made cables from a honorable amateur radio shop.
Edit: Appendix. In case it wasn't obvious, CB and amateur gear normally use unsymmetric coaxial cables with 50Ω impedance as a feedline. In the distant past, ~60Ω, too.
Popular connectors are SO239/PL259 (aka UHF or PL connectors), N or BNC. Miniature devices use SMA these days.
That's how it came that I tested 50 Ohm ethernet cables, too. I needed affordable 50 Ohms cables for a temporarily setup.
And these cables seemed promising thus. 50Ω, RG58 family (RGxx merely is a specification)..
And the BNC connectors were no problem, since there are high or medium quality adapters available.
But even without using one, soldering my own plugs on them, the results turned out to be the same (unexpected bad).
That's why I mentioned it. Sure, RGxx is just a loose specification (diameter, metal type, etc) ,but I haven't expected things to be that horrible.
Anyway, it's true that 75Ω impedance is commonly used by receivers. FM radios, FM scanners and TV equipment (satellite dish cables, old school terrestrial cabling).
Conmonly used is RG59 (75Ω) rather than RG58 (50Ω)..
Especially the satellite dish cables are low loss and cheap, but can't handle much power.
That did not stop CBers from using it, though. 😉
Thing is, that impedance mismatch causes a bad VSWR, sheet waves etc.
It can be corrected by 50/75Ω and 75/50Ω transformation on each end, respectively.
But the conversion is lossy. So some CBers rather live with a not so good VSWR.
Edit #2: Pictures added. Because a picture says more than a thousand words.
The exact cable types shouldn't cause this extreme differences, also not the length.
I had tested 10m of RG58 before that was flat (fine) like in the picture with the short one.
Sure, longer cables may have some reflection vs short ones, but that's just crazy.
Edit #3: Please notice the yellow line on the device.
A good cable stays near the bottom all the time (best SWR ratio).
Edit #4: Picture added. Let's see what's inside the modern ethernet cable (left).
Notice the quality of the braid (shielding) and how well (bad) its woven.
On the right is an ordinary, medium quality coaxial cable from the 1980s, as it was common.
Edit #5: Close-up picture added.
I know there are different flavors (hence the suffix C, U etc), but come on!
The center wire in the left should either be at least twice the size
or there should be 4-5 of them, at least.
Edit #6: Tried to fix the attachment witg the two cables.
Unfortunately, something broke. Can't attach a new picture.
Anyway, it's okay the way it is.
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