The AM Forum

Now that I'm retired, I'm doing a lot of CNC work PCBs. They're single sided so I find myself using jumpers to make a few cross-overs. Most of the boards are RF type. I use Eagle Cad for my layout and I  opt to use wire. I thought I could use 0 ohm resistors until I checked them across my LCR meter.  It seems they read out at 88 nh. Now this probably doesn't mean much on HF, but I think this might be a problem in the VHF/UHF region.


73 de Gary, KF9CM

  Gary,

    A piece of straight wire has inductance.

Look at this here:

http://www.ee.scu.edu/eefac/healy/indwire.html

  So I tried 3" of 24 awg into that formula, and it computes to 97 nh.

Take your setup and minimize the lead length. The inductance should drop down quite a bit. To measure that resistors inductance, you must have zero lead length, or a meter that can factor out the wires.

Jim
Wd5JKO

You have that much inductance in the curve on the wire.  Try putting the resistor directly across the binding posts, cut any extra lead length.  See what the reads, should see some change.

Fred

There's a straight wire (9nh) and the 0 ohm resistor (47nh) with short wire leads. I thought this might be of interest for guys working with RF PCBs.

Gary

Gary,

Seems that reducing the lead length reduced the inductance by about half.  88nH to 47nH.

Thanks for posting this info, good to know.

Fred

Thanks Fred,

28pf across that 0 ohm resistor will put you about in middle of 2 meters.

Gary

Gary,

What's the reason for using 0 ohm resistors??  Why not just a jumper wire??  I suspect that it's got something to do with production machines being able to better handle resistor bodies rather than pieces of wire.  Just a guess.

Fred

I think you're right on the pick and place machine. I picked them up for 25 cents for 100. I'll put them in a parts drawer and label them 0 ohm / 47nf choke ;D.


73 de Gary, KF9CM