Which cable and connector to connect a PI coil?

[joop]

I have build a 350uH pulse induction coil, which will have a shield added. The cable length to connect to the electronics box will be about 1 meter. The cable should have a low capacitance and resistance, so I am looking at the inner core diameter and the capacitance per meter. I am considering using:

• RG58 coaxial cable, 50 Ohm impedance, 95 pF per meter, 1mm inner core
• RG59 coaxial cable, 75 Ohm impedance, 69 pF per meter, 0.6mm inner core

I guess RG59 would be the better choice, even if the inner core is smaller then the wire used in the coil. Any suggestions?

The connector will be a low quality audio connector, see picture. Are they good enough? Thanks...

[MaverickITA]

I have build a 350uH pulse induction coil, which will have a shield added. The cable length to connect to the electronics box will be about 1 meter. The cable should have a low capacitance and resistance, so I am looking at the inner core diameter and the capacitance per meter. I am considering using:

• RG58 coaxial cable, 50 Ohm impedance, 95 pF per meter, 1mm inner core
• RG59 coaxial cable, 75 Ohm impedance, 69 pF per meter, 0.6mm inner core

I guess RG59 would be the better choice, even if the inner core is smaller then the wire used in the coil. Any suggestions?

The connector will be a low quality audio connector, see picture. Are they good enough? Thanks...

[ATTACH]30748[/ATTACH]

It is better to use RG59 connectors, they have the same impedance.
You can use a male for cable and a female for panel Mount.
For example, go in RS-online.com or similars and search "CRIMP BNC MALE PLUG RG59" and "FEMALE PANEL MOUNT RG59".
You need also a Crimp Tool for RG59 cables.

MaverickITA

[Bill512]

Hi Joop,
I don't think that a RCA type is suitable for a PI detector. Beside other considerations ,these connectors are for signal transmission, not power.
Usually, the hobbyists use this type

Also, the core of the coaxial cable must be a multi strand type and not solid.

[baum7154]

Joop,

If you can get it RG62-B/U is only 13.5 pf per foot and is far less capacitance than either RG58 or RG59 coax. No matter what targets you search for the lowest capacitance feed line is always the better choice in my opinion. I have been using RG59 BNC connectors for my PI mono coils and I know other connectors such as type 'N' are rated for higher power but I have seen no evidence of a problem with the BNC connectors in this application. I now use only twisted pair continuation of my PTFE (Teflon) insulated coil wire as a feed line and it is about 12 pf per foot (dependent on wire gauge)and I see no problems with type of feed either. Doing it this way eliminates all solder in the coil and the possibility that a solder joint might be detected at short sample times.

Best of luck!

Dan

[MaverickITA]

Joop,
if you prefer to use RG62 cable, the connectors to use are similar.
You can found them in the same way.

I suggest to use rs-online because has all items but after you have seen, you can buy them in everyplace.

MaverickITA

[joop]

Thanks guys, I have ordered some RG62 with some BNC connectors!

[6666]

Some of those rg62 cables can have very flimsy shields and take some work to get good connections to bnc connectors.

[joop]

Yes, I will borrow a shrink tool from my work...

[6666]

That will help.
RG62 tends to have a solid core wire, dont flex it too much.

[joop]

I have done some cable measurements with an LCR meter at a frequency of 10 kHz with cable lengths of 2 meters. I know, you can find this info on the internet but I though it would be nice to do these measurements myself.

RG58, 50 Ohm: 101 pF/m
RG59, 75 Ohm: 69 pF/m
RG62, 93 Ohm: 45 pF/m
H37, 150 Ohm: 29 pF/m

The last cable I found lying around when some old equipment was removed at my work. It is a cable with a 0.5mm inner conductor and either foam or PE/air as a dielectric. I can't find any reference to H37 on the internet but that is how it was marked.

[baum7154]

That H37 sounds like a very good feedline candidate. Is it a coaxial type of cable or is it a twisted pair or just twinlead?

regards,

Dan

[Davor]

Microphone cables are often 150ohm, but it is good to know their voltage rating to avoid arcing.

[joop]

It's a coax, the outer diameter a little bit more than RG58. One type has a foam dielectric, the other one partly PE, partly air. The inner conductor is solid but thin, which should explain the high impedance. Looks like it's a good cable which can stand a few kiloVolts. I doubt if it is still for sale.

[baum7154]

Thanks Joop! I have some microphone cable here that I'll have to measure this weekend.

Dan

[joop]

Okay Dan, i will make some pics of the cable tomorrow and post them here...