Tag Archives: SDRplay

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.

SDRplay RSP2 Pro now shipping from HRO

Many thanks to SWLing Post contributor, Ken Hansen (N2VIP), who notes:

Ham Radio Outlet has the SDRplay RSP2pro in-stock for $192.95.

As a reminder, the SDRplay RSP2pro is the version enclosed in a full-metal case for maximum RF shielding. Like the SDRplay RSP2 it has three software selectable antenna connections (long wire and two SMA), whereas the original SDRplay RSP1 has just the one SMA connector.

http://www.hamradio.com/detail.cfm?pid=H0-015447

Propagation-Triggered Spectrum Recording

Many thanks to Jon Hudon of SDRplay who shared the following on the SDRplay Facebook page:

One of the SDRplay user community, Jukka, has started an interesting discussion on what he has called ‘propagation-triggered recording’ – he outlines the concept, and what he is doing, on our forum – see http://www.sdrplay.com/community/viewtopic.php?f=9&t=1839

The idea is that you monitor signals to determine if conditions are particularly good and can thereby trigger an I/Q recording of a whole band during that particular propagation high point -Jukka welcomes more comments on this idea.

Many thanks, Jon. I would certainly be a fan of this as so many times I’ve missed fantastic band openings while travelling. It would be nothing short of brilliant to come home to automatic SDR spectrum recordings taken during prime propagation. At the moment, propagation is so dismal, rare openings are worth recording!

As Jon points out above, check out the SDRplay forum for more details.

SDR-Console V3 Preview now supports the SDRplay RSP2

Many thanks to Jon Hudson at SDRplay who has just informed me that SDR-Console V3 Preview supports the new SDRplay RSP2.

SDRplay posted the following on their blog:

Many thanks to Simon Brown for updating SDR-Console V3 Preview to fully support both the RSP1 and the RSP2- you can download the software from http://sdr-radio.com/v3_preview_downloads  (be sure to click on the software link  under where it says ‘Downloads’ unless you want to download the software from the advertisers who support Simon’s work!)

As new YouTube demo videos of SDR-Console V3 in action become available, we will add them to the playlists on our YouTube Channel:  www.youtube.com/c/SDRplayRSP

Click here to read on the SDRplay blog.

Very cool, Jon!  Happy to see app support for the new RSP2 is propagating. Thank you for sharing!

Holiday Deals: SDRplay RSP1 and RSP2 availability and Cyber Monday at HRO

sdrplay-rsp2-antennaports-2

The SDRplay RSP2

Many thanks to SWLing Post contributor, Ken Hansen (N2VIP) who writes:

HRO stores are taking delivery of the new SDRplay RSP2, and having a great deal on the original SDRplay RSP, now on sale for $119.95.

HRO link to SDRplay RSP2 selling for $169.95: http://www.hamradio.com/detail.cfm?pid=H0-015446

HRO link to original SDRplay RSP selling for $119.95: http://www.hamradio.com/detail.cfm?pid=H0-014408

Thank you, Ken! Click here to read more about the RSP2 and here for a great review at RTL-SDR.com.

 

hamradiooutlet-cybermonday

In addition, HRO has a wide array of products in their “Cyber Monday Savings” event.

Click here to view HRO’s sale.