low cost fixed attenuator kits - Page 1
Forum section: electronics / rf-microwave

author: joeqsmith
author_rank: Super Contributor
timestamp: April 27, 2021, 11:58:29 am
content: I needed a couple of SMA attenuators for a project. Prices and performance vary from tens to hundreds. I nomally order the VATs from Mini-circuits.I decided to order a set similar to these. The set is about the cost of one VAT. They were spec'ed 0.1dB to 3GHz. The ones I received are all within 0.2dB to 3GHz. Looking at the them with the microscope, they seem to have decent enough quality.https://www.ebay.com/itm/384104025297?hash=item596e624cd1:g:aBYAAOSwea5gfUmXIf you have bought any of these, I would be interested in knowing your experience with them. I assume there is one company producing these as they look identical.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: April 27, 2021, 03:31:44 pm
content: I bought such ones too, but for less $$$; seems to me a bit too much on ebaythey are quite acceptable, though they'll not withstand 2W, barely 1W; my guess'd be to stay at about 0,5W. accuracy seems ok; I got a 10dB pad with 9,5dB and a 6dB with 5,7dB, others were within 0,2dB. S11 parameter was not worse than -27dB at 2GHz at all tested pads, so everything fine there

author: radiolistener
author_rank: Super Contributor
timestamp: April 27, 2021, 03:49:09 pm
content: I'm using it for a long time. I have 1, 2, 3, 5, 6, 10, 20, 30 and 40 dB values. I bought it on aliexpress, the price is about 3-7 USD depends on the value. The most expensive is 40 dB, it cost 7 USD.I don't have professional VNA, but it looks that they have pretty flat response up to 1-2 GHz.The only problem that I found is that factory error may vary from piece to piece.My 40 dB actually has 38 dB, this is the most worse deviation in my kit.10 and 20 dB error is about 0.2 dB, they are good.1 dB actually has 0.9 dB.They are very useful, but buying it is a lottery because you never know what factory error you will getAlso I hear from one people that he caught a broken contact inside after some period of usage. The center pin detached from the metal sputtering on the ceramic plate. Probably because of mechanical force. And it looks that they are not repairable.I have burned out 5W version which looks like the same construction, but with a heatsink instead of sleeve. Here is a photo what is inside. The ceramic plate is soldered to the center pin and metal chassis.Note, that they are designed to work in one direction. SMA-male with marking SU is max power input side. If you put too much power on the output it will be burned out. I didn't know that and burned out it by applying 4 W power into the output side. Unfortunately there is no documentation, no warning and even no marking where is input and output and many sellers also don't know that.One seller told me that SMA male is input for max power. I suspect that SU marking is an indication of the input side.

author: joeqsmith
author_rank: Super Contributor
timestamp: April 27, 2021, 10:59:43 pm
content: Thank you both for the added info and experiences. I would have never expected them to be unsymmetrical and wonder if that is true across the board.

author: radiolistener
author_rank: Super Contributor
timestamp: April 28, 2021, 03:44:06 am
content: Quote from: joeqsmith on April 27, 2021, 10:59:43 pmI burned several different Chinese attenuators just after unboxing, one SMA 30W 40dB and one SMA 5W 40dB (teardown picture above), because they don't tell that this is one direction and there is no marking where is input and output.The seller of 30W 40dB told me that it is designed to put max power to SMA male only. It was marked as SU, so I suspect that my 5W 40dB also was burned out because it also single direction and it's SMA male also marked as SU. I applied 4W to SMA female. Unfortunately there is no information which side is input and no any mention that this is a single direction attenuator.These 2W small attenuators are the same as my fried 5W 40dB, but they have sleeve instead of heatsink. All other parts is exactly the same. May be there is some difference on the ceramic plate, but I didn't desoldered it. I'm using burned out attenuator as a dummy load. It's input still 50 Ω. It also still works, but it's attenuation is about 37 dB now and output impedance is 114 Ω. Before burning out it was exactly 40 dB and 50 Ω on both sides.For a low power signals (10 dBm and below) I'm using these 2W attenuators in both direction and they are ok. But I suspect they will burn out if you put 20-30 dBm (0.1-1W) on SMA female