ebay LP harmonic filters - Page 1
Forum section: electronics / rf-microwave

author: rhb
author_rank: Super Contributor
timestamp: January 17, 2020, 02:00:53 am
content: I bought 1 & 2 GHz low pass filters marketed on ebay for use with the ADF4351. They arrived today. The ebay listing showed them labeled in English, but in fact it is all Chinese.Here is a picture of the two units I got, one opened and one with the label intact. This is the listing for the one which is open:https://www.ebay.com/itm/1-2000Mhz-ADF4351-Phase-Locked-Loop-RFID-Suppression-Low-Pass-Harmonic-Filter/264453222017I have no connection with the seller other than as a customer as I think most readers will recognize.The enclosure finish on these is poor, but not important. I've gotten some which were clearly done on a CNC mill with fresh carbide tooling by someone who *really* knew how to tune a CNC mill operation. So good I spent some good bit of time admiring the workmanship. The finish was equal to a hard drive part even though it is just a box. These look as if they were finished with a grinding disk by hand.I doubt that I can photograph it, but there is flux residue, so if you buy these, open them, scrub and rinse them with a toothbrush and isopropyl alcohol until all traces of flux are gone.I can't see any marking on the filter, but it looks a lot like a MiniCircuits part I've been looking at for this function. I'd really like to have a bunch of the enclosures and PCBs on hand so I could make up custom filters using MiniCircuits parts.Over time I'll subject these to the tender mercies of an 8560A and an 8753B/45046A and post plots. I'm also going to test them both as received and filled with microwave absorbing foam.I have now bought quite a few RF modules with the goal of having connectorized modules I can simply connect with SMA-M jumpers to build a radio, SA, VNA or whatever. So I'm buying mixers, doublers, filters, LNAs, eval boards, etc. As time permits I'll be testing and documenting the performance. Eventually I hope to assemble various configurations and document how the setup performs. The <$5 AD8302 eval boards using non-RoHS parts that are $25/1 from Digikey for the RoHS version are the silver lining of the EU silliness.Have Fun!Reg

author: radiolistener
author_rank: Super Contributor
timestamp: January 17, 2020, 09:17:27 am
content: Check SMA connectors. One time I got similar module with notches on the connector. Probably someone dropped it on the floor and crushed it with something heavy, may be heavy hammerWhen you use damaged connector it will damage your other connectors...

author: BigBoss
author_rank: Regular Contributor
timestamp: January 19, 2020, 04:10:55 am
content: Looks really terrible..Screws,soldering..

author: rhb
author_rank: Super Contributor
timestamp: January 19, 2020, 05:09:00 pm
content: Quote from: BigBoss on January 19, 2020, 04:10:55 amWTF?I'll certainly agree that it is overbuilt, but it's the standard fabrication method used for connectorized modules from MiniCircuits, JFW, Narda, HP, etc.I organized a largish number of such modules, made by MiniCircuits, JFW and Chinese the other day which is why I've not done SA sweeps and posted them yet. I want to compare performance with the cover off, cover on and cover on with RF absorbing foam filling the box. I did sweeps of one as received, but didn't take pictures.Once I get my new lab built I'll be doing detailed testing on all sorts of cheap RF modules. My goal is an assortment of connectorized modules such that I can in an afternoon assemble a 4 receiver VNA just by connecting modules.Reg

author: rhb
author_rank: Super Contributor
timestamp: January 19, 2020, 10:54:53 pm
content: OK, here's one of the filters.First, the thru normalized trace:Next the log magnitude transfer function with the cover off the box:With the cover on:With the cover on and the box filled with RF absorbing foam. Note the loss of stop band attenuation:Finally, once more with the sides and top lined with ~ 2 mm of RF absorbing foam.I don't see any benefit to the foam. I tried it to see if there was significant radiation from the input side reflecting off the interior to the output.The filter was sold as a 1 GHz low pass filter. However, the - 3dB point is around 1.2 GHz. The stop band attenuation is ~45dB. That's not apparent here because I stopped the sweep at 2 GHz to make it easier to tell the -2 dB point. I'll post a picture of the response out to 2.9 GHz once my camera battery is recharged.Have Fun!Reg

author: rhb
author_rank: Super Contributor
timestamp: January 20, 2020, 12:38:10 am
content: Here is the transfer function up to the 2.9 GHz limit of the 8560A. I've also put a marker on the -3dB point at 1.2 GHz.The 2 GHz filter can't be evaluated on the 8560A as it can't reach the stop band. I'll test it when I get my 8510C set up which will is months away as I have to build a shielded lab area and the 8510C is sitting 1250 miles away. However the - 3dB corner is at 2.0 GHz.Have Fun!Edit: Here's a photo of one of my module boxes. I've got another box of modules, but most don't have enclosures yet, so that box just looks like a bunch of anti-static bags.I've got a Creality CR-10 mini arriving tomorrow so I may make 3D printed boxes for some stuff and line with copper foil tape. Maybe.Reg