> I have bought a couple of different lengths, mainly from Chinese online sellers at AliExpress.
You can stop reading right there...
This is not a new problem however. 20 years ago you might go to the local ham store and pretty much any cable in a plastic bag was going to be total crap.
I got a NanoVNA for about $60 and it works way better then I had any right to expect. If you have any need to figure out some kind of RF issue it is well worth the money for the amount of time you will save.
I used it to diagnose a VHF issue on a boat. The AIS was reporting high VSWR but only sometimes... It turned out that the antenna was seriously affected by it's angle relative to the metal poles that support the Bimini top.
Also, a lossy cable is not always a bad thing. A lossy cable can stabilize a PA if you are forced to have bad match at the load end.
recently picked up a nanovna as well. I am having a lot of fun characterizing antennas and cables. suddenly it’s clear to me why this cheap 144mhz whip on my desk is only useful on a very narrow set of frequencies.
Bending coax that tightly is usually bad. I once put a time-domain reflectometer on some RG-58 and, and it would show a 3" radius bend. The center conductor to braid distance has to remain constant. The price of high-flexibility coax is some loss.
This is very true. Good terminations and good materials matter. By far the best coax is silver semi-rigid -- brilliant for the bottom of my lHe cryostats, not exactly a cable in any other terms.
One thing this article didn't mention is hope the length really matters if that meter isn't perfectly impedance matching. Stub and strip lines and all that.
You've touched on what is probably the real issue, but without further measurements, we cannot know for sure. The author said (in the comments) that they used an antenna as the load. With a minimum SWR of 2:1, it's obviously not a very good match. If the match is bad, the length of the cable could have a big effect on the measured power. Other comments suggested using a resistive dummy load instead of an antenna. THAT is the way to go if you are measuring cable insertion loss.
The two cables with the poor insertion loss were 3 and 10 meters in length. None of the good cables were of these lengths.
I don't if I would call it a "horror story". A horror story would be that someone bought cheap coax cables off Aliexpress, and when they hooked them up all of the smoke came out of the radio.
In this case, the radio operator hooked up the cables and weren't transmitting as well as they thought they should be. Some measurements indicated that the cables were signal-attenuating crap. Cables that were purchased from AliExpress. It's almost as if one gets to the end your campfire story, and one of the campers pipes up and says, "don't tell me, the call was coming from inside the house?", only I piped up at the beginning and said to myself, "coax cables from AliExpress? Don't tell me, you found out that about half the transmission power went to creating heat and not radio signals."
I don't know, about the requirement of smoke to be a horror story. I have been in my own cabling hell, and no smoke was ever present. Cabling issues can be tricky, especially when they are intermittent. Everything works except when you sit in a chair. That chair with weight puts pressure on something that then squeezes something else. Specific example of something that happened.
I've managed post production facilities where there were thousands of cables running in multiples to/from various pieces of gear. You can pre-terminate, test, label all at a work bench with whatever test equipment you like, but once you start running the cables in, through, under, over other cables, plumbing, etc, things can just get weird.
We are remodeling our house so we fished coax and ethernet through the office, to TVs, and to strategic mesh hotspot areas.
When I hooked up my modem to the new coax in my office, the modem appeared to connect. However, my TPLink Deco (mesh network) wouldn't connect to the modem. I could hardwire my laptop into the modem and it worked. Confused, I spent a few hours, unplugging, resetting the Deco (never want to do that again), and finally giving up.
I told my electrician about it when he passed by a few days later and he cut off the coax tip and put a new one on. Lo and behold it worked. The Deco connected.
I'm still confused. His insight was that maybe the Deco was tracking the signal and the tip didn't have a clean connection.
Is coax still popular in the US (and presumably in other countries)? Over here in the UK I don’t think I’ve seen it used for 10 or so years now as terrestrial TV antennas have fallen out of use. Genuine question as I never even considered it as used for anything other than A/V so TIL.
It's used for cable television and cable internet (which is most high-speed internet in the US). Generally you don't have to think about it too much: you'll have a coax jack in the wall and then you connect it to your TV and/or cable modem and then leave it alone, but yes.
Outside of cable internet / TV service, it's frequently used by amateur radio operators, though in a 50 ohm resistance. Most (all?) cable/TV coax is 75 ohm.
I'm sure some (plenty) of Brits do still plug-in their TVs to those antennas, but anecdotally I can't think of a single friend or family member in the UK who I've noticed still doing that.... most either use a TV package from their ISP, or no TV at all. And yet we all still have those antennas on the roofs because why bother removing them?
On the other hand, doesn't Virgin Media (pretty much the only cable provider in the UK) use coax into routers/TV boxes?
A common issue with outdoor coax cable is when the connectors are not sealed well, water seeps in and causes gain reduction from water being in the cable. Especially with diy sealed cables, I've run into this. The giveaway is weirdly high SWR ratios.
Another problem, one that I experienced as I was new and unschooled: It was a long run to the antenna and I left too much slack before the transmission equipment. I just bunched the slack into a jumble and then hooked it up. Of course the engineer that lectured me about conductivity, magnetic fields and SWR remains a memory. He neatly coiled the coax and my problems disappeared. Even something as simple as coax benefits from experience and a small bit of knowledge.
Any standard cable, wallwart, etc from Alibaba cannot be trusted. They take liberties with the specifications in order to cut costs. Worst case scenario you're outright scammed.
"I can not say, if it is a loose connection, a faulty plug or if my handling was too rough. It could be that all cables arrived fine, and I damaged the cables during my usage. But to be honest, I don’t care."
That doesn't seem a good test, aside the fact that the RG316 is a quite a lossy cable, Chinese or not.
Hi, I apologize for being the RF pedantic, but did you mean "2.5 dB"? dB is a ratio; "dBm" is just one way to declare a given power, in this case because it is referenced to 1 millwatt (the 'm' in dBm). Ergo, 0 dBm = 1 milliwatt; 30 dBm = 1 Watt, etc.
I hope you were very careful with your fixturing going up to 20 GHz; poor fixturing can be masking the cable's true performance.
And, no, I wasn't very careful at all. This was done with an uncalibrated 30+ year old sweep generator with questionable attenuator, a 40 year old power meter that's only rated up to 10GHz, AliExpress connector adapters, and an assortment of coax cables that I took from my stack.
At 20GHz, it shows a trend at best. (I wrote as much at the bottom of the blog post, but I forgive you for not reading that far!)
Also beware of bad quality SMA connectors from cheap Chinese sources. They may have significant dimension error, and have the potential of destroying mating good ones.
I had no idea what QRP is so I looked it up. Wikipedia says it's for HAM radio lower power devices.
> The term "QRP" derives from the standard Q code used in radio communication, where QRP is used to request "Reduce power" and QRP? is used to ask "Should I reduce power?"
RG-213 vs something like RG-400 is a big weight difference. Admittedly, also a big price difference.
After 50 years of putting on traditional soldered connectors, I finally bought the DXEngineering crimpers and those are great. Mind you, every single solder connector that I ever make is 100% reliable jewelry and never fails — except for the one at the top of the tower. That one is sneakily intermittent.
The amount of loss up a cable is down to a few complex and interacting factors, but the three you care about are the construction of the cable, the length of the cable, and the frequency you're operating at.
On the HF bands (High Frequency, in the terms used in the 1920s, so up to around 30MHz) it doesn't (or shouldn't) really matter what you use. It's barely above audio frequency, really, and does not exhibit any truly weird behaviour.
At microwave bands, the exact type of cable becomes really important, and the expensive stuff starts to come into its own. For things like mobile phone masts and TV transmitters they use stuff called "Heliax", which is almost not flexible at all with an outer made of corrugated copper tape wound into a helix, a seriously high end polyurethane foam inner insulator, and a copper tube like microbore heating pipe because RF only travels on the outside of a conductor so the middle bit is a waste. You can pump water up the tube if you like, with special equipment, to cool the cable.
Yes, at high-power high-frequency RF, you want to get into water-cooling your *cables*. Yes, really.
Anyway RG213 is the "jack of all trades" stuff. It works just fine up to about 1GHz even over very long runs (say 100m) so you often see it used to connect microwave "Outdoor Unit" (ODU) heads to the "Indoor Unit" (IDU) inside. The microwave signals up around say 24GHz are downconverted in the ODU head to somewhere around 500Mhz-1GHz and amplified, and the transmitter signal goes up at around the same frequency and gets upconverted to 24GHz, and power goes over it, and it all just runs over one cable about as thick as a Sharpie which you can fit very boring and simple "N Connector" plugs onto in the field without special tools.
It's got a boring old PVC jacket, a copper braid for shielding and the earth return, a polythene insulator, and a stranded copper inner about as thick as a headphone plug. It's great stuff, super versatile, really tight minimum bend radius, doesn't really kink, mechanically strong, inexpensive, and easy to work with.
You get thinner stuff called RG58 which you might know from CB aerials if you've ever played with those, and you get RG59 and RG214 which are the same basic cable but designed for 75 ohm circuits instead of 50 ohm - if you've played with video or digital audio, or for that matter E1/T1 lines, you might have run across RG59. RG58 is about as thick as a pencil, and you can go even thinner to RG174 which is 3mm thick, about as thick as the copper core up RG213!
The only real downside to RG213 is all that copper makes it heavy, and it doesn't coil up particularly tight. If you roll it up about the smallest coil you can make is about 30cm across, which is neat because one turn is about one metre of cable.
The stuff mentioned in the article uses really fancy high-tech PTFE outer (it's weirdly slippery to handle and leaves your hands feeling a bit odd - ever got that "can't wash the soap off" feeling from hand-washing clothes in laundry powder? It's like that), a double layer of a silver (or silver-plated) braid because silver is awesome at high frequencies (way more conductive, and because of the skin effect plating is fine), then some crazy PTFEish stuff foam insulation in between, and then a silver-plated inner core.
The good stuff is supposed to be super low loss at very high frequencies and also very low leakage - very little signal escapes from it which contributes to loss but also can cause problems in RF equipment. I used to use similar stuff (can't remember the code, but it was the same size as RG58 but looked like that stuff in the article, same earwax-coloured PTFE). It was about a tenner a metre, but since I was making up 30-50cm patch cords to connect duplexers to repeaters it wasn't a huge investment. I found I could get 3dB better receive performance from the repeaters from a combination of lower loss cables and also less interference from the transmitter part deafening the receiver!
Anyway, TL;DR yes, RG213 is a thicker cable about as thick as your pinky and quite heavy with low losses, but it doesn't coil up as neat as the stuff in the article.
Do it! Get your amateur radio licence, and get into the hobby!
You don't even need particularly expensive kit, either. My "laptop bag" 2m rig for a long time was a very old Icom IC2E that I paid two quid for in a junk sale, a 9V adaptor from a broken ADSL modem, and a homebrew "twinlead J-pole" antenna that I clipped to the window frame with a clothes peg.
It worked. Wasn't great, but for a total outlay of £2.50 on a radio and a couple metres of "twinlead" FM radio aerial ribbon, and a couple of junkbox parts (PSU and BNC cable) it was quite effective.
The guy you're talking to might have the latest SDR-based DSP wunderkind and a massive SteppIR antenna on a 50 metre tower, but if he can hear you and you can hear him then whatever radio you've got is working pretty okay.
213 seems a bit overkill for the frequency and length requirements of most SOTA / POTA folks, right? RG8 or even 58 should be plenty at 14mhz and ~20'.
I use rg-213, rg-316, and several other coaxial cable types. They all have their place. Rg-213's place is not in the field.
One of my 3ft rg-213 jumpers takes more space and weighs more than one of my 25ft rg-316 cables. 25ft of rg-213 would weigh more than the rest of my field setup combined and be too large to fit in my pack!
Given their longest cable from the article is 33ft, that's several pounds saved! This is pretty meaningful considered many SOTA operators are the type who measure their entire field radio setup in ounces. The author doesn't seem that extreme, but they still pack pretty light. Here's a couple pictures of them out in the field. rg-213 would not fit in that pack.
My mum was a sport climber back in the 1960s when it was developing as a sport that non-millionaires did, rather than eccentric Victorian gentlemen scaling the Eiger with a team of borrowed Gurkhas.
Anyway, she was always baffled by the folk who did stuff like sawing the handles off their toothbrushes to save a gram or two in their backpack. "The weight of a couple of raindrops..."
You can stop reading right there...
This is not a new problem however. 20 years ago you might go to the local ham store and pretty much any cable in a plastic bag was going to be total crap.