Making a discharge load box for capacitor

Thread Starter

RichW

Joined Nov 8, 2019
13
I am very new to electronics, but have the equivalent of a capacitor and I want to make a discharge box consisting of a single resistor:



I have been recommended a 470kΩ 2W Carbon Film Resistor ±5% because it is non inductive.

I have found the following t piece....

https://www.msdist.co.uk/unbranded/coax/n-type-t-piece

Although, I have no idea what Leaky feeder cable means, my cable is RG400.

But I am struggling to find a metal box to house the resistor, does anyone here have any ideas?
 

Thread Starter

RichW

Joined Nov 8, 2019
13

Thank you jpanhalt, I didn't know the words to search for; I searched for resistor housing but it already had a resistor inside. I will take a look, thanks again.
 

Thread Starter

RichW

Joined Nov 8, 2019
13
Do any of these already have a thread for an n type connector? I've never made anything like this before so really don't know where to start, do I drill a thread for the connector into the enclosure?
 

jpanhalt

Joined Jan 18, 2008
8,717
That's probably the way most people do it routinely. My concern from this, " the equivalent of a capacitor and I want to make a discharge box," was that it was not really a capacitor and/or you were worried about the discharge resistor exploding.

I started to add to my post, but decided not to, that putting something that explodes inside a box can be worse than not doing that. The box can act as a "tamper" (read about the need for a tamper in bombs). Instead, I would use a thick (1/2") acrylic ("Plexiglas') or polycarbonate plastic shield.

Be very careful if it is high voltage. That is the biggest risk you face.
 

Thread Starter

RichW

Joined Nov 8, 2019
13
It is actually an ultrasonic transducer, the stored charge is not so dangerous; I get mild shocks from them often when handling, but I have had some trouble in the past when they discharge into the generator. I've used a resistor in a box before, but someone made it for me. The resistor did occationally get very hot and almost set on fire, but i think this was due to the signal from the generator, rather than any discharge. Thanks for your help and the warning on the voltage.
 

Thread Starter

RichW

Joined Nov 8, 2019
13
N type connector is simply a coax connector for extremely high frequencies
https://www.amazon.com/s?k=n+type+connector&ref=nb_sb_noss_1
Yes, our frequency range is 20 kHz to 3 MHz. We have RG400 and RG213 coax.

Since you seem familiar with n type connections, can I ask: for making a n type connection with RG213 cable why do we need the following:

Cinch connector 50 Ohm straight cable mount N connector, plug, solder termination, rg213

Radiall 50 Ohm straight cable mount n type connector, plug, crimp termination, rg213

I don't understand what the crimp termination and the Cinch connector do. Do both attach to the cable or have I got confused? Do I just need one of these to attach to the rg213 cable?
 

SamR

Joined Mar 19, 2019
1,796
N type connectors at that frequency are vast overkill as PL-259/SO-239 connectors up to ~30MHz or BNC connectors for VHF/UHF are typically used. Type N designed for frequencies above VHF/UHF although they are starting to be used at lower frequencies. As a Ham Radio operator, I AVOID crimp style connectors as they are very leak-prone and inadequate compared to a properly made and soldered connections. Crimps are common practice for TV coax where they are used for the antenna to TV or wall Cable receptacle to TV usage and not used for transmission signal levels and much less expensive/easier to install.
 

Thread Starter

RichW

Joined Nov 8, 2019
13
I understand about the n type connectors, they were supplied with the generator. So either of the connectors above can be used, but you would recommend the solder termination, is that correct?
 

SamR

Joined Mar 19, 2019
1,796
Note that there are N type to other type connectors/converters available. I keep a few PL-259 to BNC handy as needed. None of my radios have N type connectors as they are not the industry standard below 450MHz frequencies. Most coax is 98%+ shielded from loss so the transmission loss from the connectors is minimal to start with if properly made. If you need a short coax jumper for what you are doing it doesn't matter whether it is crimped or not. BNC components at the box (easier to connect) with a BNC to N type converter to attach to would work well for the box. The outside shell of the connector is a standard. Screwed into the cable end of the shell is a bushing sized for the OD of the coax used. Where it gets "interesting" is the coax may have more than one layer of shielding that can be either woven wire or foil that have to be terminated to GND which is the outside of the shell. The center transmission cable of the coax is connected to the insulated center terminal of the male or female shell. Read up on cable termination instructions for the type of cable used. Single shield coax cable is not difficult to terminate but multiple shielded coax cable is.
 
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