869.4MHz Bandpass - Page 1
Forum section: electronics / rf-microwave

author: nighthunter
author_rank: Newbie
timestamp: December 12, 2016, 09:46:31 am
content: Hi everybody. I am viewing EEVBlog for a longer time and learned a big from here, but now i have some problem. I am working on a TRX based on RFM12BP, but on the output i am getting a lot garbage on the whole range from 100MHz to 1Gig. I am using 869.400MHz (869.4MHz, while it is a long range device and i need to go to the limit of output power (500mW). The question is coult someone help me to design a bandpass filter for the antenna? In and out impedance is 50Ohms. The spectral graph that was measured is attached.

author: Lord of nothing
author_rank: Super Contributor
timestamp: December 12, 2016, 11:30:36 pm
content: Gratings from Austria.Do you look on Ebay? Some Ebay seller sold "cheap" Filter for common Freq Bands.Maybe you also would ask here: forums.radioreference.com/

author: nighthunter
author_rank: Newbie
timestamp: December 13, 2016, 06:08:48 am
content: Hi, yes ive searched on ebay, but did not found anything that is suitable for me. I will ask on the radioreference forum.

author: LaserSteve
author_rank: Super Contributor
timestamp: December 15, 2016, 12:54:37 am
content: How much space do you have?Most SMD filters cannot handle the power level you suggest.How many units do you need?This is where I would start....http://www.hparchive.com/Bench_Briefs/HP-Bench-Briefs-1989-01-03.pdfIf I only needed one or two:http://www.changpuak.ch/electronics/interdigital_bandpass_filter_designer.phpor get some US 850 Mhz cellular band filters on EbayLets narrow down some production parameters, shall we? One , Two, or Many?Steve

author: nighthunter
author_rank: Newbie
timestamp: December 15, 2016, 06:20:42 am
content: Hi LaserSteve. The problem is that now there are only 4 units (total there will be about 25 of this units), but i need to certify it. I have about 8-9 square centimeters in a place about 2cmx4cm in size. Would you be able to help me with this?

author: daqq
author_rank: Super Contributor
timestamp: December 15, 2016, 11:14:33 am
content: Take a look at what minicircuits is offering - they have a nice range of bandpass filters. Such as:http://194.75.38.69/pdfs/CBP-840C+.pdfAlso, wow, that's a whole lot of extra signal. How and where are you measuring this? On the antenna output, or just by air?Also, nice to see another Slovakian fellow here

author: LaserSteve
author_rank: Super Contributor
timestamp: December 15, 2016, 05:50:26 pm
content: Do you have access to CNC machining? If Not, CBP-840C+ is not a bad option for 25 units.Ideally filtering is done before and after final amplifier, may we have more details about your RF chain please?A two Dollar ceramic SMD filter from Digikey some place before your final amplifier may reduce your problem significantly.Steve

author: nighthunter
author_rank: Newbie
timestamp: December 16, 2016, 09:02:50 am
content: The spectrum was measured right on antenna connector - so direct coupled with spectrum analyzer. I ordered som of the ceramic filter, but will it handle the output power of +24dBm? CNC machining is right by me now a problem, but i have a workshop nearby.

author: daqq
author_rank: Super Contributor
timestamp: December 16, 2016, 11:28:41 am
content: Try contacting the manufacturer - minicircuits has a very good support line.

author: LaserSteve
author_rank: Super Contributor
timestamp: December 16, 2016, 09:29:48 pm
content: Do you have a schematic or block diagram? It helps to know where to put the filters.Steve