No idea how to switch between rf filters/mix them, help for a project please - Page 1
Forum section: electronics / beginners

author: azigta
author_rank: Regular Contributor
timestamp: August 04, 2017, 10:23:48 pm
content: Hi, I'm trying to make a project but I've come up with an idea and I don't even know if it's even possible to do because my knowledge on electronics and so on isn't so great...I have an sdr radio, a frequency upconverter (to be able to receive hf frequencies) , a commercial fm trap filter, a commercial am trap filter, and finally the sdr radio. I want to integrate it all in a box with some switches so I don't have to connect or disconnect the fm traps. The upconverter has its own switch to enable it or pass the frequency directly to the sdr so that part is already done. The diagram for connecting one rf trap it's like this, from antenna to the receiver.Antenna->am/fm trap->upconverter->sdrThe thing is thatI want to make something that is able to make the antenna signals go to the am filter or to the fm filter, or to take the am and fm filter connect them in series (output of one to the input of the other one) and then take that result and input it into the upconverter.I'm trying to at least figure out how I would do it even if I end up not doing it because the cost it's too high or the switches I can get acces to can't handle switching rf, because apparently switches for rf are special?(all the rf switches I've seen are intended for use in microwave rf technology and are expensive, so I don't know if I can use regular switches with this project) No idea really... I tried drawing it on paint (I know, so lame) And all I came up with is a way to select between the am/fm traps and then there's a part of the "schematic " that is missing because I don't know how to do it. Really pathetic, yes.I don't know much about this thing, but I read that the traps have to have a shield to discharge all that frequencies it's blocking. So I figured outthe following schematicto select just between am/fm filter and also switching the shield of the antenna to the shield of the traps (and finally to the shield of the sdr that will end up going to the usb cable shield to the pc)But that's not even what I want to do because it's missing the part where the two filters get mixed together (output of one get connected to input of the other one and then the result goes into the upconverter)Really, I don't know if what I want to do is hard, or easy, because I don't know how to do this, I've tried. Maybe is a simple thing and some user here can shed some light and come up with a great easy schematic that I can follow to get what I want, or maybe is too damn complicated and I will simply get the two filters permanently connected to the upconverter and never select beween them, that will be:antenna->am filter->fm filter->upconverter->sdr. Easy, but I want to find out if what I want to do is possible, because hey I also like to listen to some am radio and fm radio while I'm using the sdr.Can someone help me? Sorry for the very long post but I just need to find out if what I want to do is possible and if I can do it.Thanks

author: danadak
author_rank: Super Contributor
timestamp: August 05, 2017, 11:12:45 am
content: PIN diode frequently used to switch RF -http://www.radio-electronics.com/info/circuits/diode-rf-attenuator/pin-diode-switch.phphttp://www.qsl.net/va3iul/RF_Switches/RF_Switches.pdfLayout is crucial in handling RF, requires PCB design. There are ap notes on webthat discuss REF PCB layout. You might contact Radio Amateur community forhelp. If you have no experience here relay operated coax switches mightbe easiest. Search ebay for "coaxial relay".https://forums.qrz.com/index.phpRegards, Dana

author: azigta
author_rank: Regular Contributor
timestamp: August 05, 2017, 11:40:59 am
content: Quote from: danadak on August 05, 2017, 11:12:45 amHi, I will try to make what I need with coax switches, didn't know they exist. I will also think about contacting my local radio amateur comunity. Thanks!