Audio Spectrum Software for Receiver Crystal Filter Alignment? - Page 1
Forum section: electronics / rf-microwave

author: AJ3G
author_rank: Regular Contributor
timestamp: February 02, 2022, 02:43:02 pm
content: All:I thought I would pose this question to this group. I am working with a very old Military Receiver made in the UK (Murphy B40D). It is a pretty well documented receiver, but I had to reinvent a lot of the test procedures to accommodate test equipment that is commonly available today. Test Equipment that is 20 years old requires one to really think about the procedures called out in the B40D's service manual, and then apply more modern equipment to test at hand.Inside the B40D there is a 500KHz IF Filter which 8, 3, and 1KHz is selectable. There are two tuning capacitors inside of the IF Filter. I was trying to come up with a way to tune this filter, and the few attempts I have tried allowed me to view the filter passband at 1KHz, but adjusting is just not practical due to the relatively low sweep speed, and slow update rate.With the above in mind, I was thinking I could simply inject noise into the front end of the receiver, and then tune the shape using the audio output. I wonder is this a practical approach, and if so, does anyone have a recommendation for audio spectrum analysis software? I was thinking I could impedance match the 600Ohm output down to something a audio soundcard would be happy with, inject noise into the front end of the receiver, and then tune for the best shape @ 1KHz B/W.73Rich, AJ3G

author: radiolistener
author_rank: Super Contributor
timestamp: February 02, 2022, 05:39:08 pm
content: Quote from: AJ3G on February 02, 2022, 02:43:02 pmHDSDR:https://www.hdsdr.de/You're needs to select sound card as RX source. If your sound card is ASIO compatible you can choose Options=>Select Input=>ASIO 24 bit driver to get 24 bit dynamic range. Classic drivers provide only 16 bit audio recording, but it still enough.By default it uses both channels as IQ quadrature stream, so you're needs to select single channel mode, use option Options=>Input Channel mode for RX=> Left channel onlyYou can choose input sample rate with Bandwidth button.You can resize spectrum and waterfall area with right mouse button on the ruler.You can zoom spectrum area with slide bars under waterfall area.Near power meter you can found modulation type button. By clicking with right mouse button on modulation button you can enter listening bandwidth.

author: AJ3G
author_rank: Regular Contributor
timestamp: February 02, 2022, 07:17:30 pm
content: Hi Radiolistener:Thanks for the response, I had not thought about using HDSDR for this application. I am reviewing some of the information, and this seems very promising.Now to determine if tuning a XTAL Filter via the method I describe is even plausible. I am sure there is some catastrophic pitfall of conducting the test as I outline in my original post.73

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: February 05, 2022, 12:50:33 am
content: Yes your approach is sound.I've used the Frequensee app. Mentioned here.Here is where I use it to test receiver bandwidths.I have also used it when experimenting with homebrew crystal filters for both receive and transmit.

author: AJ3G
author_rank: Regular Contributor
timestamp: February 05, 2022, 06:42:44 pm
content: Thanks for the useful feedback -FYI - Prior to you posting a response to my inquiry here on the eve blog, I had seen many of your video’s on YouTube. I did not correlate the call to your YouTube channel until I heard the voice when reviewing the two links you provided!73Rich, AJ3G