BNC cables for test equipment

[jgalak]

I want to buy some premade short (2-6') BNC-BNC cables for connecting things on the bench - scope, specan (when I have one), signal sources, radios, etc.  Primary interest range of frequencies from DC to about 500 MHz.  Need to be 50 Ohm.

Most of the ones I'm seeing for sale use RG58.  That's a coax I generally avoid when running lines from radio to antenna, preferring things like RG8U or even LMR400/600, but that's for much longer runs.  Am I ok using the RG58 on the bench?  Or should I look for higher-quality premade cables (or even just make my own)?

[Benta]

RG58 comes in a lot of flavors, from cheap total cr*p to professional cable. It's a question of your wallet. Personally I'd not hesitate to use good quality RG58.

[gardner]

I think you're also going to find that LMR400 or RG8 is not practical for short runs on the bench because it is not flexible enough to be convenient.  For short runs I have found cheap RG58 to be too stiff to sit where I want it on the bench.  I use RG174 when I need the cable to sit where I put it and not jump onto the floor with the circuit board in tow.  For runs in the 50cm to 1.5m range, attenuation is not going to be an issue.  Loss in the connectors is going to be the dominant factor, most likely.

[CJay]

I've got a few 50R patch cables made with RG-174, they're good for non critical stuff, for the more 'delicate' stuff I have RG223 and just recently I've laid my hands on some really nice cables which I think are at least partially Teflon but I'd have to check the cable type and specs

[dmills]

It also depends a bit on what you are doing.

For example, if you are trying to tune a filter at 450MHz, and are looking at the thru path then cable losses can make things look worse then they are when you are looking on a 0.2dB/div scale.
You can of course calibrate that out, but especially if doing VNA type stuff cable losses can matter if you do not have the kit to calibrate at reference plane that calibrates out the cable losses.

I suffer from this because I can only cal at the APC-7 connectors and lack port extension cables for APC-7, so I cannot put the calibration kit where I would really like the reference plane.

That said, for run of the mill stuff RG58 from a reputable vendor, or '223 are just fine, I also have short cables in 316 (Lossy, but sometimes having something that will not try to pull the board around is nice).

Regards, Dan.

[Neomys Sapiens]

When buying RG58, make sure it is at least RG58C/U. But I have relegated most of mine to the reserve component of my TOE. As stated by the other posters, RG223 and the thin lines (174/316) are much used, while I tend to use more and more of RG400 (teflon, stranded inner conductor, size as RG223).

Now I have finally found out how to order the special locking BNC connector from H&S (it is locked by a nut behind the bayonet, so that it cannot be decoupled so easy). And I think about having a set of cables using them. Of course, the frequency range of the Sucoflex cables would be wasted with a BNC connector, but they make a special variant, which is decidedly the most flexible quality coax I ever saw. It feels almost like a 10mm² very fine stranded test lead! I'm much tempted here...

[CJay]

When buying RG58, make sure it is at least RG58C/U.

It's important to buy it from a reputable brand/supplier because I can have *any* marking I want printed on any grade of cable, that's been going on for decades.

[dmills]

but they make a special variant, which is decidedly the most flexible quality coax I ever saw. It feels almost like a 10mm² very fine stranded test lead! I'm much tempted here...

Be sitting down when you get the price quote!
Probably not quite as bad as gore port extension cables (**Stupid money**) but it is not going to be cheap.

Regards, Dan (Who is tempted to see what 3 feet fitted for APC7 on both ends would cost me).

[jgalak]

It's important to buy it from a reputable brand/supplier because I can have *any* marking I want printed on any grade of cable, that's been going on for decades.

So what's a reputable supplier in the US?  I've ordered a few off ebay, which claim to be Amphenol, but as you say, who knows what it actually is.  None of the (small number) of sources I know have pre-made RG174 or RG223 BNC-BNC cables in useful lengths (3 feet or so).  It's all either 25', or 6"....

[Dino KL0S]

If you're in this for the long term have you considered making your own jumpers? A crimp tool with a variety of die sets will allow you to crimp all sorts of connectors and coax types. There is a bit of a learning curve at first but once you get the knack of it (and make some notes to remember what/how you did it!) you'll be able to make whatever jumper/run you need. That way you can better control the quality of the coax and connectors for all your jumpers.

[jgalak]

If you're in this for the long term have you considered making your own jumpers? A crimp tool with a variety of die sets will allow you to crimp all sorts of connectors and coax types. There is a bit of a learning curve at first but once you get the knack of it (and make some notes to remember what/how you did it!) you'll be able to make whatever jumper/run you need. That way you can better control the quality of the coax and connectors for all your jumpers.

It's not a bad plan - I have crimpers, though I don't think I have the right dies for the thin cable (most of mine are for RG8X and RG8X, I might have one for lmr400, too).  I know how to install PL-259 connectors, but have never tried BNC.  Probably worth learning.

I was looking at pre-made mostly so that if I'm measuring something and get a weird result, I can be sure that it's the circuit, not my poorly made cable.  I'd have to figure out a way to test cable with just a scope - I don't have a vna or a SpecAn.  I think there was a video about it from w2aew.

[Neomys Sapiens]

but they make a special variant, which is decidedly the most flexible quality coax I ever saw. It feels almost like a 10mm² very fine stranded test lead! I'm much tempted here...

Be sitting down when you get the price quote!
Probably not quite as bad as gore port extension cables (**Stupid money**) but it is not going to be cheap.

Regards, Dan (Who is tempted to see what 3 feet fitted for APC7 on both ends would cost me).

Nay, not really. I specified a larger type of armoured, 'rubberized' Sucoflex 5m N-m/N-m for a project and made them get my a 'qualification test sample', which I put on the VNA, coiled/uncoiled 10times (which did already prove that it's more suitable than Ecoflex for recurring movement) and had it 'phased out' afterwards! So I know their pricing.

[Bassman59]

So what's a reputable supplier in the US? 

Pasternack. Pricey, but you get what you pay for, etc etc.

[jgalak]

Pasternack. Pricey, but you get what you pay for, etc etc.

Yikes!  $30-40 for a 3 foot cable.  Now I'm sure the stuff from ebay/amazon is crap....

[rx8pilot]

So what's a reputable supplier in the US? 

Pasternack. Pricey, but you get what you pay for, etc etc.

Is Pasternack as good as the pricing?

I am certainly hoping to build a better kit of cables and adapters to replace all of my unknowns.