BNC / RG-59 for low frequency applications

[girishv]

Hi,

Can I use BNC connector with RG-59 cable for low frequency / dc applications? For example, connecting 50MHz or less op-amp connections between boards?

I have lots of good quality RG-59 BNC connectors and would like to put them for good use.

[Vovk_Z]

Yes.
But it may be not very convenient, because a cable may be rigid (stiff), and may break somewhere at the soldering point.

[jmelson]

Hi,

Can I use BNC connector with RG-59 cable for low frequency / dc applications? For example, connecting 50MHz or less op-amp connections between boards?

I have lots of good quality RG-59 BNC connectors and would like to put them for good use.

There is a version of RG-59 that has a solid center conductor.  You probably do NOT want that type for lab interconnect cables.  Otherwise, you can certainly use RG-59 or RG-58 for lots of lab hook-up applications, connecting signal generators, scopes and such together.

Jon

[janoc]

Well, careful - RG-59 is 75 cable. If you use this to connect DC it doesn't matter, it doesn't matter if you use 75 BNCs and only use 75   impedances everywhere. Just be aware that common lab equipment (generators, oscilloscopes, spectrum analyzers ...) all uses 50 standard and if you mix the two, you are going to get reflections.

RG-59 is meant for video applications.

[ejeffrey]

I wouldn't use RG-59 cables or the associated BNC connectors for general lab use because they are 75 ohm.  At low frequency the impedance doesn't matter but the connectors won't mechanically mate properly to test equipment that almost universally uses 50 ohm BNC jacks.  50 MHz is also not really low frequency unless you are only using short cables.  The wavelength in the cable is about 4 meter, so a 1 meter cable is lambda/4.

[TimFox]

True-75-ohm BNC connectors are mechanically compatible with 50 ohm BNC connectors.  This is not true for type-N connectors, where the 50 and 75 ohm versions are not compatible.
Most BNC connectors for RG-59/U 75 ohm coaxial cable are actually 50 ohm BNCs, but with cable-interface dimensions to work with RG-59/U.  The short length of mismatched line through the connector is only important at relatively high frequencies.  The cable length in a mismatched system may be important, since it is much longer.
For applications at frequencies where the cable length is short compared with the wavelength, the foam-dielectric "low-loss" RG-59 variants have less capacitance per unit length than the solid-dielectric cables, which can be useful.  High-voltage coaxial connectors of similar size to BNC (e.g., MHV and SHV) usually use RG-59/U for a few kilovolts of DC.  The foam-dielectric cables are not appropriate (I learned the hard way) for that application.  In grad school, we replaced the MHV panel connectors on photomultiplier power supplies with SHV, since a determined student could mate a BNC plug with the MHV panel connector, with possible damage and insufficient voltage rating.

[TimNJ]

Regarding Vovk_z's comment, if flexibility is a concern, maybe RG-58C is what you want. "C" means stranded conductor. I've tried a variety of RG-58C cables, from different manufacturers. Some are more stiff than others.

I've found this one from Cal Test (CT2942-100) to be soft and flexible, almost doesn't feel like PVC, but it is: https://www.digikey.com/en/products/detail/cal-test-electronics/CT2942-100/6005475

That said, a more flexible cable means it can be bent more severely with a tighter bend radius, so probably not as durable long-term. So far, so good, though.

[girishv]

I wouldn't use RG-59 cables or the associated BNC connectors for general lab use because they are 75 ohm.  At low frequency the impedance doesn't matter but the connectors won't mechanically mate properly to test equipment that almost universally uses 50 ohm BNC jacks.  50 MHz is also not really low frequency unless you are only using short cables.  The wavelength in the cable is about 4 meter, so a 1 meter cable is lambda/4.

I have 50\$\Omega\$ BNC crimp connectors compatible with RG-59 cables.  So, mechanical connections should not be a problem. I do know a bit about losses in RG-59 cables, but not enough.

[girishv]

Regarding Vovk_z's comment, if flexibility is a concern, maybe RG-58C is what you want. "C" means stranded conductor. I've tried a variety of RG-58C cables, from different manufacturers. Some are more stiff than others.

I've found this one from Cal Test (CT2942-100) to be soft and flexible, almost doesn't feel like PVC, but it is: https://www.digikey.com/en/products/detail/cal-test-electronics/CT2942-100/6005475

That said, a more flexible cable means it can be bent more severely with a tighter bend radius, so probably not as durable long-term. So far, so good, though.

Thanks for the information. Can I use RC-58C cable with a connector designed for RG-59 cables?

[girishv]

Most BNC connectors for RG-59/U 75 ohm coaxial cable are actually 50 ohm BNCs, but with cable-interface dimensions to work with RG-59/U.  The short length of mismatched line through the connector is only important at relatively high frequencies.  The cable length in a mismatched system may be important, since it is much longer.

I will use this calculator for calculating losses https://www.qsl.net/co8tw/Coax_Calculator.htm

[TimFox]

Regarding Vovk_z's comment, if flexibility is a concern, maybe RG-58C is what you want. "C" means stranded conductor. I've tried a variety of RG-58C cables, from different manufacturers. Some are more stiff than others.

I've found this one from Cal Test (CT2942-100) to be soft and flexible, almost doesn't feel like PVC, but it is: https://www.digikey.com/en/products/detail/cal-test-electronics/CT2942-100/6005475

That said, a more flexible cable means it can be bent more severely with a tighter bend radius, so probably not as durable long-term. So far, so good, though.

Thanks for the information. Can I use RC-58C cable with a connector designed for RG-59 cables?

RG-58 cables have a considerably smaller dielectric diameter than RG-59 cables.  You can put an RG-59 BNC on RG-58C/U cable, but the fit will be loose.