I made a 50 ohm load with BNC connector, Is this correct? - Page 1
Forum section: electronics / projects

author: daisizhou
author_rank: Super Contributor
timestamp: May 04, 2024, 04:12:40 am
content: I test the RF signal.I made a 50 ohm BNC interface resistor,I used 2 100 ohm chip package resistors in parallel.and mount them inside a BNC connector.Can this be used?Is it different from a standard 50 ohm load resistor?

author: Kim Christensen
author_rank: Super Contributor
timestamp: May 04, 2024, 04:22:58 am
content: I've made similar. Mine were good up to about 1Ghz when tested for SWR with a VNA. Test yours and see.

author: daisizhou
author_rank: Super Contributor
timestamp: May 04, 2024, 04:25:51 am
content: How can I test it?

author: Kim Christensen
author_rank: Super Contributor
timestamp: May 04, 2024, 04:38:41 am
content: You need a RF network analyzer: something that can check the VSWR of the load across your required frequency range.

author: daisizhou
author_rank: Super Contributor
timestamp: May 04, 2024, 04:48:16 am
content: Initially I purchased a ready made product,But its inner core is very short and slim,Looks like an inferior product.So I disassembled it,The resistance accuracy was found to be 5%，Looks like a resistor with inductance,Would a non-inductive resistor be more effective?So I made a new oneCurrently I only have a 100M digital oscilloscope and a 20M signal generator,There are also digital multimeters and digital bridges.Can I test them?

author: Kim Christensen
author_rank: Super Contributor
timestamp: May 04, 2024, 05:10:00 am
content: Quote from: daisizhou on May 04, 2024, 04:48:16 amIf you mean this one, it doesn't look inductive (wire wound) to me. Looks like a regular film resistor which would be OK.QuoteIf they pass a simple DC ohm check, they'll probably be fine up to 20Mhz anyway. What's the upper frequency you want to use these at?

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 04, 2024, 05:55:00 am
content: Quote from: daisizhou on May 04, 2024, 04:25:51 amWith a VNA. You may want to consiider required frequency range.

author: jonpaul
author_rank: Super Contributor
timestamp: May 04, 2024, 06:02:06 am
content: dont bother.Mini Circuits sells fine 50 or 75 Ohm BNC/SMA terms good to 3 GHz.SM-BM50+EU/$10j

author: TERRA Operative
author_rank: Super Contributor
timestamp: May 04, 2024, 06:07:25 am
content: Quote from: daisizhou on May 04, 2024, 04:12:40 amYou can make it perform better by placing one of the 100 ohm resistors on the other side, so the two resistors are 180 degrees apart, on symmetrically opposite sides of the BNC center contact.Quote from: Kim Christensen on May 04, 2024, 05:10:00 amAt higher frequencies, the spiral cut in the resistive film used in through-hole metal and carbon film resistors will cause parasitic capacitance (between the spirals) and parasitic inductance (from the spiral itself) to have an effect on performance.

author: daisizhou
author_rank: Super Contributor
timestamp: May 04, 2024, 07:27:31 am
content: Usually I use 300Khz-750Khz。

author: daisizhou
author_rank: Super Contributor
timestamp: May 04, 2024, 07:28:23 am
content: Good idea, I've updated it

author: MarkT
author_rank: Frequent Contributor
timestamp: May 04, 2024, 08:32:17 am
content: Looks good to go. Perfectionists would be reaching for the 200 ohm resistors and use 4, or 300 ohm and use 6, but that's diminishing returns unless you need the extra power-handling.

author: coppercone2
author_rank: Super Contributor
timestamp: May 04, 2024, 08:35:53 am
content: someone on the forum got worse performance with 4 then 2

author: MarkT
author_rank: Frequent Contributor
timestamp: May 04, 2024, 09:06:48 am
content: Too much choice for the electrons, they got confused (!!)

author: TERRA Operative
author_rank: Super Contributor
timestamp: May 04, 2024, 10:20:55 am
content: Quote from: daisizhou on May 04, 2024, 07:28:23 amYep, spot-on, looks great. Even cut the center contact down, that can help reduce parasitics a little at higher frequencies, nice job!