Building and testing microwave duplex band pass filters

I thought I’d post some good news to keep our spirits up. After about 5 weeks of constant toil, I’ve now got working band pass filters for my Femtocell project. I used the LimeSDR and GQRX to check their functionality. If you want to see the latest project log, check it out here: CLICKY LINKY I actively encourage constructive criticism so please make suitable comments on the page.

PS. I cant help thinking that the LimeSDR should have the facility to create the four digital band pass filters required. They need to be up to 75 MHz wide - any thoughts?

I’m not a filter expert, but from what I think I know, the highest quality filters are going to be cavity filters, especially for microwave. They seem to come in different forms.
I’ve been wanting to get into filtering/dsp for audio using FPGA, which is doable at high quality, but I have a serious problem with too many hobbies.

1 Like

Yes the cavity filters are the best and they’re tunable but lowest price is £500 new. Mine were still expensive at £40 each but seem to be very high quality :relaxed:

So you got the ceramic monoblock filters?
I have not seen them before.

Time for a cup of coffee and some reading, they look good!

Interesting project. More pictures of the filters is what I found I was wanting.

This looks like the filter, also interesting.

Yes that’s pretty much it except I’m using USD020 types. I think the project is a bit too simplistic at the moment. I’m going to swap over to the LimeSDR and try and get it running as a cell phone repeater at the end of the week. Hopefully I wont destroy it! Then I want to control it via Arduino and SPI.

I am so conditioned to think that USD mean US dollars that my brain never thought that was a part number when I read the hackaday page.

Yes I also find myself concerned that I might destroy the LimeSDR somehow. My imagination mostly since I don’t know enough yet to detroy it properly.