Which coax? - Page 1
Forum section: electronics / rf-microwave

author: apelly
author_rank: Unknown
timestamp: August 15, 2016, 03:18:51 am
content: I have a bunch of RG174 and connectors that I've been using for short lengths of low freq. stuff, but now I find myself interested in RF.I was just going to buy a roll of RG58 and make do with cables as short as possible. Then I thought, perhaps you guys have a better idea. Since I have nothing right now, I can start out with whatever is the most suitable. In the short term I'll just be dicking around with HF, but if it's not too much more now, maybe I can save money by not duplicating all my cables for UHF/microwave if I get interested in that later.I wish I was in a position to provide people more help on the forum. I have a lot more questions for you guys than answers, sorry. But thanks for your patience.

author: GEuser
author_rank: Frequent Contributor
timestamp: August 15, 2016, 04:34:10 am
content: Your not real good on supplying real informative information to calculate a informative answer , how long is a piece of string? = answer is , as long as it is from one end to the other .What power , what attenuation factor are you interested in , why use coax ? and the likes .imo

author: jopie
author_rank: Contributor
timestamp: August 15, 2016, 06:10:10 am
content: Inside your shack use RG58 with BNC connectors, as long as your frequency is below 50 MHz, power is below 100W and length is around 1-2 meters. At higher powers use RG213 with suitable connectors e.g. SO 239. That's okay up to 144 MHz if connectors are good quality and lengths are not to long. At higher frequencies use some form of foam- or air-coaxial low loss cable and good quality N-connectors.

author: apelly
author_rank: Unknown
timestamp: August 15, 2016, 07:43:01 am
content: Quote from: GEuser on August 15, 2016, 04:34:10 amDude. I thank you for trying to help me, but you're not too good at cooperating with how little I know. I was hoping for some short discussion that would surface deficiencies in my research.Quote from: GEuser on August 15, 2016, 04:34:10 amWe're allowed 1KW. As little as practical. It doesn't need to be coax.

author: apelly
author_rank: Unknown
timestamp: August 15, 2016, 07:46:37 am
content: Quote from: jopie on August 15, 2016, 06:10:10 amThis.The connectors are the same price, so if the coax is a buck more a metre I might as well get better coax in the beginning.Does anyone have an opinion about coax for higher frequencies?

author: GEuser
author_rank: Frequent Contributor
timestamp: August 15, 2016, 08:03:19 am
content: Quote from: apelly on August 15, 2016, 07:43:01 amIn bold above , that's exactly what i was thinking too .Still no mention of length or fitting styles , mention of 1KW so your still going to use PL259's aye Ha Ha Ha , I'll get out of here , bye .

author: Gyro
author_rank: Super Contributor
timestamp: August 15, 2016, 08:50:41 am
content: The Wikipedia article is quite a useful quick comparison of the characteristics of different coax types:https://en.wikipedia.org/wiki/Coaxial_cable

author: tggzzz
author_rank: Super Contributor
timestamp: August 15, 2016, 09:01:45 am
content: Quote from: apelly on August 15, 2016, 07:43:01 amAt the very least you need to state what problem you are trying to solve. 1kW and coax (or not) implies it isn't suitable for amateurs to play around.What research have you done? There's no point in asking us to duplicate your existing research, and if you haven't sone any research then it is impolite to ask us! FFI, seehttps://entertaininghacks.wordpress.com/library-2/good-questions-pique-our-interest-and-dont-waste-our-time-2/

author: apelly
author_rank: Unknown
timestamp: August 15, 2016, 10:33:23 pm
content: Quote from: jopie on August 15, 2016, 06:10:10 amThis is a great response. Thank you jopie.Looking at element14, digikey & RS it's not that straight forward to identify what's going on with what coax. Doesn't seem to be for me anyway.What I'm seeing is that, weighing up cost, availability, and pliability, RG58 is a good compromise for short or temporary installations. It appears that I'm better to get set up with a bunch of that and worry about how to deal with higher frequencies and longer runs on a case by case basis as they come up.In doing further research I see LMR-400, LMR-600 and Heliax. These don't appear to be available from the usual suspects. Should I be looking at specialist suppliers for these things?Quote from: GEuser on August 15, 2016, 08:03:19 amWhy? PL259s are shit at UHF.Quote from: Gyro on August 15, 2016, 08:50:41 amThere's a bunch of information on the internet. There are also a thousand kinds of coax; different standards, sort-of-standards, names, pseudonyms, and trademarks. This is a too much information for a noob.Quote from: tggzzz on August 15, 2016, 09:01:45 amOK:Quote from: apelly on August 15, 2016, 03:18:51 amQuote from: tggzzz on August 15, 2016, 09:01:45 amOKQuote from: tggzzz on August 15, 2016, 09:01:45 amI'm not asking anyone to do any research. I thought that was clear from the tone of my original post. If you've already done the research, and you're prepared to burn a minute or two dropping me a line of insight, that'd be great.Quote from: tggzzz on August 15, 2016, 09:01:45 amI don't know ifI'mhaving a bad day, or you are. My initial reaction to this is a big Fuck You. I re-read my original post, and the tone seems fine to me: Light, inviting casual comment. I'm no word-smith though.Anyway, mate. I've spent days looking at specs, suppliers, charts and graphs. I've decided what I'm doing, and I thought I'd raise it here in case someone else's experience would save me $500 replacing cables in the long term.

author: Electro Fan
author_rank: Super Contributor
timestamp: August 15, 2016, 10:58:34 pm
content: I might have missed it, but maybe it would help if you could say how long the cables are going to be and what they are going to connect on each end. (Sorry if I missed this info.)

author: G0HZU
author_rank: Super Contributor
timestamp: August 15, 2016, 11:13:31 pm
content: The people with the most experience at the 1kW level will be the US hams on the QRZ forum.Eg see the sub forum below that covers antennas and feedlines:https://forums.qrz.com/index.php?forums/antennas-feedlines-towers-rotors.33/I really should warn you in advance that some of these guys on QRZ are old guys that love to argue and there will be a few that are short tempered and highly opinionated. But they will have everyday experience of operating a station at 1kW+ through HF/VHF and probably UHF. So you can bet they will know their stuff when it comes to choosing coax cable for long runs to an antenna for example.As for choosing cables for general low power use around a test bench (sub 1W levels?) then I think it's best to choose lots of cable types to suit different requirements. I do a lot of RF research work here from LF through to many GHz and I have plenty of RG58 cables here with BNC connectors, plus I have some nice MiniCircuits microwave cables with SMA connectors and I have some very exotic Gore cables for use up at many GHz. I find that you can never have too many RF test cables like this and the real challenge is managing them all to keep them accessible. I think diversity is the key here because thre are times when you want cables that are flexible and you don't care about a bit of loss. But other times you need to make precise measurements requiring careful management of all sources of mismatch uncertainty. RF cables and RF adaptors can be the weakest link here and sometimes you 'need' to use the expensive (but inflexible and awkward) precision cable that you paid $$$ for.

author: apelly
author_rank: Unknown
timestamp: August 15, 2016, 11:15:09 pm
content: Quote from: Electro Fan on August 15, 2016, 10:58:34 pmI didn't say.Where I am at the moment they'd be up to 30' connecting HF radio to antenna. That will change, as I plan to move house soon and buy more radios. But I don't know where I'm going yet, so your guess is as good as mine.I'll also make up a bunch of short cables for use between T&M equipment, antennas and radios as required. Say a couple of feet or so.From another thread it looks like I'll be using N connectors where practical.In the short term, I'm quite sure it doesn't matterwhatI use. There's plenty of scope to experiment and have fun. All I'm thinking is, knowing how much all this costs, I don't want to make a noob judgement error requiring me to make all new cables for future dicking around if I might be able to spend 15% more now and be fine later.

author: apelly
author_rank: Unknown
timestamp: August 15, 2016, 11:33:29 pm
content: Quote from: G0HZU on August 15, 2016, 11:13:31 pmGood advice. Thanks. I signed up over there some time ago, but haven't spent a lot of time there. I'll make the effort to go and lurk there some more.In the short term I do not have the money, requirement, or enthusiasm to be experimenting beyond 100W. I only mentioned 1kW because that's our legal limit. That doesn't mean it isn't interesting though.Quote from: G0HZU on August 15, 2016, 11:13:31 pmQuote from: G0HZU on August 15, 2016, 11:13:31 pmYes. Now you point it out, it seems pretty obvious.Quote from: G0HZU on August 15, 2016, 11:13:31 pmI'm coming to that conclusion myself, and you're helping me arrive.There's no perfect solution, just get what you need when you need it.

author: G0HZU
author_rank: Super Contributor
timestamp: August 15, 2016, 11:44:21 pm
content: RG58 BNC to BNC cables can be very handy for general low power stuff but I'd advise against buying cheapo 'new' BNC-RG58-BNC cables from places like ebay. I'd even include the cheapest cables of this type from places like Farnell. It's very tempting to buy their cheapest offerings but they really aren't suitable for serious/multiple use.The tolerances in the connectors and the plating will be poor and it can be argued that they may even subtly damage your precision cables when you mate these cables to them.My best RF cable bargains always came from salvaged cables from decommissioned military kit that was fitted in racks. Often there will be several high spec cables that will be 15 years old that came from within these racks but they may have only been mated once or twice in all this time. I always look for BNC cables with Radiall or Suhner stamped on the connectors or cables with the HP logo. Radio surplus fairs/rallies used to be the best places to find stuff like this. Otherwise, you can try and find sales of similar (salvaged) cables on ebay because some dealers will salvage cables like this at auction and sell them on.I really do think that it is false economy to buy the budget 'new' BNC cables from Farnell or ebay no matter how tempting the price is. I think it is reasonable to assume that the cable would not pass a wiggle test on a VNA. i.e. you would see a performance degradation as the cable connector is wiggled. The branded BNC cables are much more immune to this, even if they are old and have seen lots of use.

author: G0HZU
author_rank: Super Contributor
timestamp: August 15, 2016, 11:52:10 pm
content: If you find yourself wanting to buy cables and adaptors with SMA connections then I think the same advice applies. With some experience it's easy to spot the cheap/fake SMA connectors from china. These will have a very shiny gold finish but will use cheaper materials. Once you get to know what a genuine Suhner SMA connector/adaptor looks and feels like you will easily be able to spot the difference.I won't allow any cheapo SMA adaptors in my workroom. The risk of accelerated wear and damage to my other SMA connectors is far too great. However, if you were making stuff in mass production that demanded the use of cheap connectors for a low spec product you could use connectors like this as long as you kept them away from your good stuff. Or you could use SMA-SMA (M-F) inter series adaptors to act as sacrificial protectors.

author: hendorog
author_rank: Super Contributor
timestamp: August 16, 2016, 12:22:37 am
content: I'd suggest just getting started with RG58 and SO239 for your first antenna.It's cheap and simple and will get you up and running quickly. The loss below say 50MHz is small enough that it won't matter for a 30' run.The antenna can be difficult to get right, I'd focus on that instead. Also consider that as you learn you may well end up changing antennas and/or moving the feedpoint around, which might require a longer cable.

author: apelly
author_rank: Unknown
timestamp: August 16, 2016, 12:36:33 am
content: Quote from: G0HZU on August 15, 2016, 11:44:21 pmI've heard this before. And it's not good news. I make my own, but I do use connectors from ebay. At this stage of the game there's not a lot I can do about it apart from keep an eye on things.It pisses me off not having the correct tool for the job, but I remind myself that this is just a hobby, albeit an expensive one.

author: apelly
author_rank: Unknown
timestamp: August 16, 2016, 12:44:06 am
content: Quote from: hendorog on August 16, 2016, 12:22:37 amThat's my leaning too.By now I'm pretty weary of research and I agree with you.

author: apelly
author_rank: Unknown
timestamp: August 16, 2016, 01:01:58 am
content: Quote from: blueskull on August 16, 2016, 12:58:49 amOK

author: hendorog
author_rank: Super Contributor
timestamp: August 16, 2016, 03:16:45 am
content: Quote from: apelly on August 16, 2016, 12:44:06 ambtw, if you haven't come across it already, this is a decent program to use for antenna design:http://www.qsl.net/4nec2/I'm using it to try and fit a better antenna onto the property for 40m - that won't annoy the neighbours or the significant other, decapitate the kids, get in the way of mowing the lawn, get me offside with the council, and which doesn't just heat up the clouds.

author: apelly
author_rank: Unknown
timestamp: August 21, 2016, 01:14:58 am
content: Quote from: hendorog on August 16, 2016, 03:16:45 amJust installed it. It looks amazing! There goes another weekend!Thanks for the tip mate.Quote from: hendorog on August 16, 2016, 03:16:45 amAmbitious much?

author: hendorog
author_rank: Super Contributor
timestamp: August 21, 2016, 10:15:45 am
content: Quote from: apelly on August 21, 2016, 01:14:58 amHeh, yeah definitely too ambitious - got everything sussed except for the antenna actually working like an decent antenna part

author: VK5RC
author_rank: Unknown
timestamp: August 21, 2016, 10:55:02 am
content: I use the lower loss RG58 for general coax with reasonable BNCs or Ns if at all possible. For a long run to the antenna do the calculations of cable loss for RG213 or LM400 or even Heliax ; see if you really need to spend the money. Also for the antenna run is it buried? Some have extra water rating.Some while ago I had a cross band (146- 440MHz ) satellite set up 6m away from the transceiver, for the 146MHz run I used RG213 but for the 440MHz run used LMR400. All N connectors, For the flexible connection at the AZ-EL rotator used 2x 1m of LMR250.1kW is a LOT of RF, you have to be pretty careful at that level in many respects.For real life antenna experiments at 0.1W , have you used WSPR? (wsprnet.org)

author: nctnico
author_rank: Super Contributor
timestamp: August 21, 2016, 02:34:08 pm
content: Quote from: apelly on August 15, 2016, 07:46:37 amBe reasonable. Sure you can spend lots of $$$ on cables with golden connectors with square formed oxygen free silver plated over gold on copper wires but you'd be entering into the world audiophools tend to populate.What you need to know is the frequency you want to use, the amount of power and the amount of loss you can tolerate. If you google for 'coax cable types' you can find lists like these:www.jyebao.com.tw/files%20download/RG%20TYPE.pdfI also recommend to just buy cables from Ebay with premade connectors (you can buy any quality grade you want). Usually they are better than DIY cables unless you have all the right tools.

author: apelly
author_rank: Unknown
timestamp: August 21, 2016, 10:05:53 pm
content: Thanks for the info guys. I've settled for RG58 and N connectors for general use. I'll follow the advice here and worry about more specialised coax if required by the math in future experiments.Quote from: VK5RC on August 21, 2016, 10:55:02 amI can't see 1kW happening any time soon. But thanks.Quote from: VK5RC on August 21, 2016, 10:55:02 amThanks for the heads up. I've just taken a look. Very cool. I see more cool stuff from them over athttp://physics.princeton.edu/pulsar/K1JT/Quote from: nctnico on August 21, 2016, 02:34:08 pmI've been buying stuff from ebay userconnekt; they were recommended by someone in another thread a long time ago. Stuff seems OK, and a fair price.I'm not much into pre-made cables, but I do buy a few. The question is, how do you find a supplier with quality cables if not by asking around. I'm presuming high price isn't necessarily an indicator of good quality. Are you talking about second hand name brand cables?

author: nctnico
author_rank: Super Contributor
timestamp: August 22, 2016, 07:02:47 pm
content: Quote from: apelly on August 21, 2016, 10:05:53 pmI'm talking about new cables. I usually buy one or two cables to check quality after checking the seller's feedback. If the cables are OK I order more. BTW the crappiest BNC cables I ever bought came from Germany (probably also made in China) and I threw all of them away. So far the cables which worked the best for me have heatshrink tubing over the crimped part and the cable.