Does anybody still use a Comb Generator? - Page 1
Forum section: electronics / projects

author: Stray Electron
author_rank: Super Contributor
timestamp: September 15, 2023, 01:06:16 pm
content: I noticed in another thread on here that a member had some TE for sale on E-bay about a month ago. I went and looked at his listings this morning and I saw that he still has an HP 8406A Comb Generator for sale. I was rather surprised that it hadn't sold. His price was reasonable and they still sell well here in the US for twice the price. OTOH I haven't used my 8406 in many years and I was wondering how many people still have one and still use it and what uses people are using them for today.

author: nctnico
author_rank: Super Contributor
timestamp: September 15, 2023, 03:45:42 pm
content: Quote from: Stray Electron on September 15, 2023, 01:06:16 pmA comb generator without a calibrated antenna is of little use. Nowadays you can buy comb generators with an integrated antenna which is calibrated. Tekbox has a really cheap one although it starts at 100MHz.

author: pdenisowski
author_rank: Super Contributor
timestamp: September 15, 2023, 07:16:15 pm
content: Comb generators are still widely used to verify EMC testing sites / setups, for both radiated as well as for conducted testing.

author: pdenisowski
author_rank: Super Contributor
timestamp: September 15, 2023, 07:41:32 pm
content: Here are some pictures of my small USB-based comb generator - puts out carriers with roughly 8 MHz spacing. I use it on a semi-regular basis.

author: Smokey
author_rank: Super Contributor
timestamp: September 16, 2023, 03:40:56 am
content: https://bazar.preciousplastic.com/moulds/injection-moulds/plastic-comb-injection-mold/

author: pdenisowski
author_rank: Super Contributor
timestamp: September 16, 2023, 11:33:17 am
content: Quote from: Smokey on September 16, 2023, 03:40:56 amWhat's even funnier is that "comb generator" is considerably more expensive than my "comb generator"

author: kerouanton
author_rank: Regular Contributor
timestamp: September 16, 2023, 11:59:25 am
content: I'm still learning all of this, so be kind. Is an arbitrary waveform generator able to create harmonics can be used as a comb generator for the same tests? I was thinking about the Siglent SDG series for example?

author: pdenisowski
author_rank: Super Contributor
timestamp: September 16, 2023, 01:32:29 pm
content: Quote from: kerouanton on September 16, 2023, 11:59:25 amNot sure about the Siglent products, but Rohde & Schwarz vector signal generators have a multi-carrier CW (MCCW) option that allows them to create a series of narrowband (CW) carriers over a defined bandwidth and defined spacing. For example, the SMW200A can generate up to 8192 carriers at a time.https://www.rohde-schwarz.com/webhelp/SMW_HTML_UserManual_en/Content/subprojects/rs_smw_operating/d2e601a08f3b4679.htm?Highlight=mccwIt's usually used for things like testing filters, noise power ratio, group delay, etc. -- it would be very serious overkill for replacing a simple comb generator.

author: pdenisowski
author_rank: Super Contributor
timestamp: September 16, 2023, 01:39:57 pm
content: The issue with trying to use a function generator to replace a comb generator using harmonics is that the harmonic amplitudes would (hopefully) fall off very quickly with increasing harmonic order.Usually the point of a comb generator is to produce discrete signals over a range of frequency, with all of these signals having (more or less) the same amplitude. That way if there is something wrong with your (EMC) receiving system, this can be easily seen because some of the carriers will be missing or noticeably attenuated.This is, I believe, what nctnico meant by needing a calibrated antenna: it's no good having a box that produces uniform-amplitude harmonics over a wide frequency range if the antenna that radiates them then attenuates them in an uneven manner.It looks like the Tekbox comb generator (which I have not personally used) has an integrated antenna and is only about $100. Even if you could .... somehow ... get a function generator to create equal amplitude, evenly-spaced carriers --- perhaps by creating a suitable ARB file -- you would still need to get a good antenna and/or somehow compensate for the uneven gain. Frankly, it'd probably be cheaper and less work just to buy the $100 box

author: kerouanton
author_rank: Regular Contributor
timestamp: September 16, 2023, 03:27:35 pm
content: Thanks for your explanations. Yes it's certainly much cheaper and efficient to get a dedicated comb generator that will output the right amplitude through the spectrum, I was just asking because I do have a Siglent SDG and wanted to have a try (being curious, I don't have any projects involving such measures).