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Re: Making a SHV connector

Posted: Sat Mar 30, 2019 4:19 pm
by Harald_Consul
Of course the 3rd photo is an SHV connector (not MHV). I have corrected this now.

Well John, afaik connectors in contrast to cables do not have a significant resistance at all.

As the 50 Ohm ending (as working resistor) has been a standard in the lab for a long time, I thought "50 Ohm" had become some brand name for lab quality, which would reference to in regards to voltage more universal equipment.

In contrast to 75 Ohm, which is designed (for well standardized) video signals.

Isn't that true?

Re: Making a SHV connector

Posted: Sat Mar 30, 2019 6:23 pm
by John Futter
what do you mean by this
"Well John, afaik connectors in contrast to cables do not have a significant resistance at all."

The cables do not have resistance they have a characteristic impedance (ratio of inner conductor to outer conductor diameter)
When you want to send pulses of arbitary shape then you have to match source impedance the cable characteristic impedance and the sink impedance so that you do not get reflections that will modify the shape and height of of the pulse.
In Nuclear physics coaxial cables are made in 50 75 93 and 120 ohms characteristic impedance.
In the RF world every thing is referenced to 50 ohms which has become a defacto standard for most equipment with BNC connectors on them. But check the catalogs from suppliers like Keysight Rhodes & Swartz you will find in the options the instrument is available in impedances other than 50 ohms

Re: Making a SHV connector

Posted: Sun Mar 31, 2019 4:18 am
by Rich Feldman
Yes, what John said.

Just found a report by a couple of ham radio operators who needed a some quarter-wavelength pieces of, ideally, 121-ohm coax for a narrowband antenna matching solution. Instead of using bits of RG-63 (like Belden 9857), which is hard to get (in France?) unless you buy 1000 feet, they rolled their own. Removed braid from some RG-62 (95 ohm), added extra dielectric from a larger-diameter kind of coax, and put the braid back on. :-)
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Very much in the same spirit at making a Safe High Voltage plug.

Characteristic impedance is the voltage/current ratio in propagating waves. Connectors optimized for 50 or 75 ohms have different conductor and dielectric dimensions, to minimize the reflection when conducting a high-frequency change of voltage and current. Regular (50 ohm) BNC in a 75 ohm path would behave as if you'd added a little capacitor between signal and ground at that place.

Harald, I will also refer you to the second post in a fusor thread I started last year. The active section of a BF3 neutron detector tube was characterized as a coaxial transmission line. Its characteristic impedance was found to be about 320 ohms! viewtopic.php?f=13&t=12394.

One very gentle introductory tutorial on the subject is the "all about circuits" link that I cited and borrowed pictures from in that post.

Re: Making a SHV connector

Posted: Sun Mar 31, 2019 6:06 pm
by Harald_Consul

Before, I thought a connector would be much too short to significantly influence the impedance (AC resistance) of a cable.

One learns a new thing every day.

Re: Making a SHV connector

Posted: Tue Apr 23, 2019 2:23 am
by Luke Weston
The "official" standard describing the Safe High Voltage connector is IEC 60498 : High-Voltage Coaxial Connectors Used in Nuclear Instrumentation.

But this is one of those annoying things where the standards-making agencies want $$$$.

And just to make things more confusing - when we say SHV connector we are usually referring to the 5 kV SHV connector which is the most common.

However the 5kV SHV is only one of several versions - you can also encounter 10kV and 20kV variants in the SHV connector family, recognisable easily as they are physically longer.

Here are some example pictures. ... insul.html ... %2D01%2DCF

MIL-STD-348 has some nice mechanical drawings of SHV (and other coaxial) connectors and can be considered practically equivalent to the IEC standard.

And unlike other standards agencies - you can have this one for free which is an advantage. ... 48REVB.pdf