Testing bandwidth of RF attenuator and DC block - Page 1
Forum section: electronics / rf-microwave

author: okw
author_rank: Frequent Contributor
timestamp: January 16, 2025, 04:58:50 pm
content: I have these cheap AliExpress attenuators and two DC blocks. Many people said they were good, so I bought a few. One DC block is 6GHz and the other 8GHz. All attenuators say 8GHz.How do I test that they actually handle the frequency? Does the level typically drop off or signal go haywire, above the specified bandwidth? And how much drop is acceptable? Is it the same procedure for "speccing" my cables too? I wanna label them, so I know which are capable of what.For the job, I have a VNA (LiteVNA-64 50KHz-6.3GHz), spectrum analyzer (tinySA Ultra, 100kHz-5.3GHz), signal generator (SME-06 5kHz-6GHz) and a 1GHz scope (Tektronix TDS784D).I also have newer scopes (Tektronix TDS5054B and DPO4054), if their functionality makes a difference (but they are both 500MHz).If the above is insufficient (probably OK for the cables, but perhaps not for the attenuators/DC block?), would a frequency multiplier help me, and would it be reliable? If I need it, does anyone have recommendations for a good layout/gerber/etc.?

author: joeqsmith
author_rank: Super Contributor
timestamp: January 16, 2025, 06:11:26 pm
content: Why are you concern how well they perform, if you do not have the equipment required to measure them? Just curious.You never state what attenuators you have or their value. Of what you have for TE, your LiteVNA-64 to directly measure S21 would be your best bet. The dynamic range is pretty limited in the 8GHz range.Yes, it is possible to extend the frequency range of your VNA with some sort of multiplier. You may be able to also improve the dynamic range this way. I am not aware of any OTS products that will support the LiteVNA. Link showing one I put together to allow me to use the LiteVNA in the X-band.https://www.eevblog.com/forum/rf-microwave/experimenting-with-waveguides-using-the-litevna/msg5086456/#msg5086456

author: tszaboo
author_rank: Super Contributor
timestamp: January 16, 2025, 06:16:00 pm
content: Measure S11 and S21 with the VNA. S21 should be the nominal gain +/- whatever you find acceptable. S11 should be small. I found these small metal SMA attenuators very good, especially for the 3-4 EUR pricing they go for.How good? It all depends what you want to do with them.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 16, 2025, 06:51:24 pm
content: Quote from: tszaboo on January 16, 2025, 06:16:00 pmCan you measure a 40dB attenuator with the LiteVNA at 8GHz? Seems like a fairly tail. Could you measure a 10dB attenuator .... Maybe.With a 40dB attenuator, would you measure anything for S11? Again, seems like a stretch.OP would need to provide more details.Dynamic range of various VNAs including the LiteVNA64. At 8GHz, maybe you could measure 20dB.https://www.eevblog.com/forum/rf-microwave/experimenting-with-waveguides-using-the-litevna/msg4597240/#msg4597240With the extender, showing measuring a 50dB attenuator at 11GHz. The key is I am running the Lite in its sweet spot (<4GHz).https://www.eevblog.com/forum/rf-microwave/experimenting-with-waveguides-using-the-litevna/msg4599727/#msg4599727

author: shabaz
author_rank: Frequent Contributor
timestamp: January 17, 2025, 12:56:19 pm
content: Depending on the use-case, the risk might be too high to consider AliExpress attenuators, because decent brand ones are sometimes not excessively priced (worth checking in your region anyway).Even if the AliExpress attenuator measures well, it could break internally when least expected (to me this seems plausible, because of the forces when tightening connectors, depends on a level of good internal construction). I'm not trying to bash Chinese products, I'm simply suggesting that for some things, a good known brand with a reputation is worth shopping around for, if the cost falls into an acceptable category.If it's a high-power attenuator, then those are indeed expensive for a good brand, but it's a stronger reason not to trust a high-power attenuator from AliExpress because the impact of damage to attached equipment is even higher. I feel the pain, too; I do need to purchase a high-power attenuator to enable some testing and I have been putting it off for ages because of the cost.

author: tszaboo
author_rank: Super Contributor
timestamp: January 17, 2025, 02:47:31 pm
content: OK, so I just realized I had 3 of these low cost attenuators to still test. IDK if OP has these or something else, this is how I test them.Some pictures of the attenuators and a Mini circuits to give an idea about their size.Set VNA to measure between 10MHz- 6GHz (max). Cables attached. Calibrate with the SMA calibration kit.Connect attenuator between the cables.For me, this three measured OK, the -20dB one was between 19.9 and 20.1 over the range. S11 is practically a dot. I also ordered an oddball -2dB one, that was the worst at -2.3dB on the high end. For my purposes, at home this is OK. They are labeled as 2W attenuators, I would never use the above 20dBm or 0.1W. Or I wouldn't use them to protect an expensive SA.