Tag Archives: SDRplay RSP

FM Notch Filter for SDRPlay RSP1

RF filters are used (as the name implies) to filter/remove the frequencies you are not interested in and/or let frequencies you want pass . They come in lots of types. For example a band-pass filter lets the signals in a frequency range to pass through it and rejects/attenuates other frequencies. The opposite of band-pass filter is a band-reject or band-stop filter (also called a notch filter) which rejects/attenuates signals in a specific range and lets other frequencies get through the filter. Lots of different filters are used in SDRs and traditional radios. For example AM low-pass filters (only let frequencies lower than 1.7MHZ or so pass) or band-pass filters for various ham radio bands.

One of the popular use cases for a notch filter is in the FM broadcast range (88-108 MHZ in most parts of the world)

When you live near a powerful transmitter, it can affect the operation of your receiver in other near frequencies (or overload your receiver’s front-end), but I didn’t want the notch filter for this reason. I’ve got a SDRPlay RSP1 (among many other SDRs) which due to its architecture, has some images of FM band in the UHF range (for example in 330-350 MHZ). In fact they’re the images of the product of LO harmonics and FM frequencies.

You can temporarily move/shift the frequency by changing the LO frequency which does not remove them, but moves them around.

Another method to remove these images is using a band-stop filter.

This is the filter I’m using (Thanks to my friend Amirhosein Hasanpur who designed and built it):

Here you can see the effect of using a FM notch filter on my SDRPlay RSP1:

FM, without filter:

FM, with filter:

UHF (images) without filter:

UHF (images) with filter:

Here’s a link to a Zip file containing the PCB (in Protel), schematics (pdf) and S Parameters (pdf):

https://www.dropbox.com/s/l98kylrofohgqxf/SWLing.zip?dl=0

Note: Like any other SDR test/review, the results depend on lots of different parameters (various gain values, LNA, antenna, software, etc). These pictures are captured with the same conditions just to show the effectiveness of this filter and your milage will definitely vary, but expect a similar outcome. If you live close to a powerful transmitter or use LNAs, you will receive some signals, even when using the filter.

Final note: this issue is solved in the newer version of SDRPlay (RSP2) : it has software-selectable notch filters for FM and MW broadcast frequencies.

Mehdi Asgari, the author of this post, is a regular contributor to the SWLing Post. Mehdi lives in Tehran and is an active member of the EP2C amateur radio club.

SDRuno tutorial videos

SDRuno running the RSP2.

SDRuno running the RSP2.

Jon Hudson with SDRplay recently noted the following tutorial videos in an SDRplay discussion forum. Since I’m also trying to learn the ropes of SDRuno, I thought I’d share this here on the SWLing Post.

Jon notes:

These video guides are very helpful for newcomers to SDRuno and the RSP1 or RSP2:
RSP1: https://youtu.be/xBGHB0oMXHU

RSP2: https://youtu.be/92Ijh_NAEfc

Especially when used in conjunction with the SDRuno Cookbook from Paul and Mike: https://www.nn4f.com/SDRuno-cookbook.pdf

Aeronautical SDR: Ivan’s in-flight FM spectrum captures

Aircraft-Jet-Boeing-VOLMET

Many thanks to SWLing Post contributor, Ivan Cholakov (NO2CW), who writes:

Thomas, not sure if this is something relevant but airlines now state it is OK to use an am/fm radio on board aircraft.

Not much possibilities for AM unfortunately but on a recent flight from Ft Lauderdale to Dallas and Albuquerque I hooked up an SDRPlay receiver to a 3 inch stick antenna and recorded a few stations I was able to pick up along the way.

The first video is posted here:

I did take a few more videos flying between JFK and MIA as well.

I used the following equipment:

fm_dx

1. 13 inch laptop that I also use for work
2. SDRPlay receiver
3. Old scanner antenna that I happened to have
4. SDRUno software to drive the radio
5. Screen recorder that comes with the Win 10 Xbox app
6. Windows movie maker to stitch the individual clips together and annotate

If needed, the size of the setup above can shrink further if a smaller laptop/tablet is used and an RTL dongle instead of SDRPlay.

You will also need to equip yourself with a window seat. Otherwise, signals are significantly weaker.

I did not place the antenna in a special position, just next to me on the seat where it could not be noticed by other passengers. I uploaded a few more videos from my weekly shuttle flights between MIA an JFK.

Ivan NO2CW

Wow!  Thanks so much, for sharing this, Ivan.

I’ve always packed a simple FM-capable radio in my one, compact carry on bag and typically try a little FM DX travel while in flight. I was never aware there was a restriction on using an FM receiver in flight, but I’ve always kept my radio listening very discrete so it’s never been a problem.

I love the idea of doing in-flight FM spectrum captures! It would be fun to watch signals on the spectrum shift and change as the flight progresses. Very cool, Ivan!

Post readers: Have you ever made in-flight FM spectrum captures like Ivan?  Please comment!

Dave reviews the SDRplay RSP

SDPlay-RSP

Many thanks to my buddy, Dave Zantow (N9EWO), who writes:

My long awaited “SDRplay RSP” review is now available. My apologies for the delay. It took more time then I had planned and other issues got in the way. We also tested it with the popular DSD+ software and worked well after some troubleshooting.

http://webpages.charter.net/n9ewo2/perseus.html

I always enjoy your reviews, Dave! As you say, reviewing SDRs certainly takes more time than reviewing stand-alone receivers–especially when there are so many options for SDR applications! Like you, I feel like the SDRplay RSP offers a good value for the listener–especially at the $129 price point.

SDRplay releases new API driver for the RSP

SDRplay-Logo

Many thanks to SWLing Post contributor, Mike (K8RAT) who writes:

SDRplay has released a new API/hardware driver for the RSP (1.97).

Here is what they say about it along with a download:

http://sdrplay.com/platforms.html

So that’s a new SDRuno version and RSP hardware driver in less than one week. SDRplay has been busy!  Thanks for the tip, Mike!