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Ron Morgan, AD9I, of East Peoria, Illinois, has been appointed ARRL Illinois Section Manager, effective February 16. He succeeds Tom Ciciora, KA9QPN, of Sandwich, who stepped down for personal reasons. ARRL expressed its thanks to Ciciora, who has served at the helm of the Illinois Field Organization for more than 10 years, since July 2006.
ARRL Field Services Manager Dave Patton, NN1N, appointe...
ARRL Headquarters will be closed on Monday, February 20, for the Presidents’ Day holiday. Headquarters will reopen at 8 AM EST on Tuesday, February 21. We wish everyone a safe and enjoyable holiday!
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):
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.
Choon E20HHK informs DxCoffee Readers:
“I’m will be have weekend IOTA DX, Lipe Island AS-126, on March 11-12 use E20HHK/p”
QSL via bureau or direct.
