Filters 101 : Improving reception with your SDR or radio - a look at RF filters

[@rider275]

I found this video while watching the 2020-2121 SDR Guide series. The series and this video are very informative. I am new SDR's. Your videos are helping me to decide next steps beyond listening to broadcast FM and a local repeater using the RTL-SDR v3. Thanks again and Merry Christmas!

[@FrugalRadio]

Thanks for your comment. Wishing you a happy new year!

[@jplacido9999]

Congratulations!!! You are the perfect speaker. Very well explained. I'm a 50 + years on the job tech and also radioamateur but it is quite clear that even a newbie WILL understand everything very, very, well !!!! CONGRATULATIONS !!!!! (simple, but technical 👍👍👍👍)

[@FrugalRadio]

Thanks Joao. Appreciate your kind words.

[@jplacido9999]

@@FrugalRadio 🙏🙏🙏🙏

[@davidsdude]

I'm so happy I found your page. So much reading condensed into a 12min video. Thank you!

[@FrugalRadio]

Ha ha, you're welcome!

[@Bumpyuphere]

Very informative - I had no idea my HF+ Discovery and RSP1A had built in filters until I watched this - I'm on a steep learning curve - thank you.

[@FrugalRadio]

You're welcome. There's always so much to discover it seems!!!

[@eonrucm]

Because of your excellent videos I now have a Noolec FM Flamingo filter on every SDR, and Scanner I own. On my SDR’s I have a Noolec AM filter followed by Noolec V2 FM filter and then a DC block filter. Unfortunately, with the SDRplay devices because of the band filtering I must turn the DAB filter on or 120MHz to around 250MHz is swamped. You may want to try the Noolec DC filter on you setup and see how it works for you. Also, as a side note I am big on grounding, I find it makes a dramatic difference to interference and particularly the noise floor as well as improving the all-important Signal to Noise Ratio.

[@FrugalRadio]

Sounds like you've nailed it when it comes to the filters. Good job! Nothing beats a nice clean signal.

[@conductormtm]

Thanks! I am back in the hobby since I was a teen in the 80s and I am having to re-learn many things. This video was very helpful in understanding something that I had limited knowledge of 40 years ago

[@FrugalRadio]

Welcome back to the radio hobby Marty. Certainly a lot has changed in 40 years! Glad the video was helpful 🙂

[@Swede_4_DJT]

Greetings from Sweden! You, Sir, just got yourself a new subscriber 🎉

[@FrugalRadio]

Welcome, from Canada!

[@slosolo2]

Thanks for the very timely video. I recently got my first RTL-SDR blog sdr and hooked it up. I'm happily monitoring a few local P25 systems but quickly found out I'd be needing filters for just about anything else due to a very powerful local am broadcast station.

[@FrugalRadio]

Yes, the broadcast transmitters throw out a lot of power. My local FM transmitters are pumping out over 100kW. Haven't looked up the 3 local AM transmitters yet.

[@acestudioscouk-Ace-G0ACE]

Thanks for another really useful video. I knew a little about filters but you explained them so clearly, I feel I'm up to speed. I like the way you explained filters generally and specifically for SDR. I know some filters you have to physically disconnect but would have liked to have heard the difference by switching them in then out but maybe you will do that in another video.

[@FrugalRadio]

I think there is an example showing the SDR being unusable in 1 or 2 of the videos. You don't hear the difference so much as see it on the waterfall display & FFT.

[@davechurchman]

As a newbie, that was so much easier to understand than other videos, thanks so much for explaining it all so clearly. Don't know how the algorithm got me to your video, but Subscribing for more!

[@FrugalRadio]

Great. Welcome to the channel Dave!

[@bart.grantham]

Another incredibly informative video! I really appreciate how you give a good before/after example of the effect of filtering. Also, it's great how you compare popular products and explain feature details that experts might take for granted but newbies don't even know is something important to consider.

[@FrugalRadio]

I'm glad to be of help, and appreciate your thoughtful comments.

[@Tommy_Boy.]

Real nice video Frugal! 👍👍 It gave me some good clarity on the function and use of filters. 📻

[@FrugalRadio]

Thanks @Tommy Boy. Glad it was helpful!

[@anthonywebber1155]

Can the RTL-SDRv4 derived signals be filtered out in software using GNU Radio ( a program I haven't yet played with yet)? I'm particularly interested in getting the best possible typical ISM Lora bands.

[@johnsobel4409]

What would I need for a filter to stop the LED lights in my basement from interfering with my TV? My TV is attached to a antenna

[@brazoon1]

This was both concise and useful. Thank you.

[@FrugalRadio]

You're welcome, and thanks for taking the time to comment.

[@JULIOAIS]

I'm excited to start with this hobby in a low budget. What is your advice?

[@FrugalRadio]

My advice is really contained in the first few episodes of the 2020 / 2021 SDR Guide: kzbin.info/aero/PLe5ZKeM2hRBJ2G_Gvt1JnBxqtjHMMej3q

[@SDR-DXobserver]

Very informative video for the newcomers. Seems radio related items has enjoyed increased interest with the coming of the better RTL based sdr's. Do you know of a 137 MHz bandpass filter with amplification? I have only found one from Garex UK many years ago. Looking forward to the next video ;-)

[@FrugalRadio]

Hi Ron, good to hear from you again. Thanks for the comments. Yes, these SDRs are certainly widening the hobby which is great. The Nooelec Sawbird NOAA filter linked in the video description actually includes a bias t powered LNA, so I expect you would receive quite favorable results with it!

[@Scotscan]

A caveat of using the mw/FM sdrplay incorporated reject filter is it knocks off around 3 dB from the airband spectrum. Be nice if it was sharper. Same can be said for the dab on the milair band.

[@FrugalRadio]

Glad you've identified the issues. I didn't get into the issue of filters not being perfect, rolloff, and insertion loss. I wonder if their filtering in the RSPdx is tighter?

[@Scotscan]

@@FrugalRadio Sadly it is the sdrRSPdx I'm referring to. I'm lucky in the respect that if I use my dedicated airband antenna the FM breakthrough is non existent. If I use my J pole however I get a little breakthrough like you at around 118 - 120MHz and that's when I noticed the distinct attenuation to the frequencies within the airband spectrum. I guess it's a tradeoff and that said the function of the software defined reject filter does do what it says on the tin.

[@FrugalRadio]

Oh, interesting. That's one thing I like about the Airspy HF+ Discovery. The bandpass filter starts at 118 MHz and seems to be rock solid. It's the highest SNR I've seen on 119.5 & my local tower freq of 118.3. But having these filters built in certainly does help. Even if there is some loss, you do get signal coming through.

[@panoshountis1516]

Thank you for this. I am new to the hobby and I have found in your channel wealth of knowledge shared in layman's terms that REALLY make a difference in my absorbtion of all that knowledge. May I ask what kind of antenna you are using for your air frequency monitoring, please?

[@FrugalRadio]

Thanks for your kind comments, and for taking the time to get in touch. Right now I'm using a simple home-made dipole for civil air monitoring. In Ireland I was using a bow tie antenna, which I hope to make a video on someday...

[@eljam8138]

Great video ! Have you tried the HackRF?

[@FrugalRadio]

No, haven't played with a HackRF. Looks like it could be a fun device.

[@joe10117]

Requesting a tv antenna hook up for same idea

[@n1kkri]

Does anyone make an adjustable filter or a switchable filter for different ranges?

[@TheStevester2]

I bought the flamingo am notch filter. I live a few blocks from an AM broadcast (1,000kHz). The filter does good on the entire AM band, except for the pesky 1,000 khz. Its too powerful. Any insight on what I can do? I'm trying to listen to SW

[@FrugalRadio]

When you're a few blocks away from an AM site, that's going to be tough. You can try a double filter (i.e. 2 filters in series), or you could make / order a specific notch filter for the offending frequency. You could try someone like PAR Electronics who will custom make one for you.

[@madmax2069]

I have both the RTL-SDR AM And FM filters, at my mother's when I'm visiting has an AM broadcast station across the street and overloads the heck out of my SDR, the filter stops it. At my home I have a few FM broadcasts stations pretty powerful close by overloading my SDR and the filter stops them pretty good. BUT my issue in both places is AC interference due to the power lines are right next to the room I'm at in both places, at my mother's the pole transformers (3 on the pole) is like 15 feet away from the window and it's pretty much overloading the SDR across the entire frequency coverage of the device. I need a filter or something to get rid of the AC interference.

[@FrugalRadio]

Good to hear the RTL-SDR fillets are working as intended, even with such strong sources nearby. As for the AC, I'm not sure what the best way to take that is. Which part of the band does the interference show on?

[@madmax2069]

@@FrugalRadio I hear it pretty much everywhere, but it is a lot stronger in the lower frequency ranges from medium wave up into the 20mhz range but I can still hear it in the higher frequencies bit not as bad, I can at least get some air traffic and some VHF and UHF activity, but the noise floor is still high enough to where it's harder to hear anyone talk.

[@FrugalRadio]

Sounds terrible! A post that might help you get started solving the AC noise is swling.com/blog/2021/03/guest-post-indoor-noise-and-ferrites-part1/ That chap's experiments seem to have paid off.

[@madmax2069]

@@FrugalRadio the interference even effects my Eton Elite Executive, but it seems to be able to reject the interference lot better than the SDR. Medium wave on the EEE isn't effected by it. The interference starts on the EEE at around 1700kHz up to 30mhz, the air bands aren't effected either, the FM broadcast bands aren't effected by it either (being that they're right next to the air band and the air band isn't effected).

[@dc9999ify]

Hi, another great and helpful video. I have a question though, i just got a SDRplay1A - in your video you are listening to 119.5 air traffic, and you are talking about notch filters and the effect they have of blocking nearby FM Broadcast stations. You derogatory the RF gain and then talk about Athy 88-100mHz notch filter? I don’t see you clicking anything though? Is the filter automatically engaged when you drop the RF gain? or did you do something i can’t see to engage the FM notch filter? I do see that in a panel to the right there are specific Notch (filters?) Notch1, Notch2 etc. Are these separate?

[@FrugalRadio]

Hello. There is a switch for the Broadcast & DAB filters. There is a graphic on the following link that shows it. www.sdrplay.com/explaining-filters-for-newcomers-to-sdr/ The notch filters also work, but in a different way. They are better for dealing with noise on the audio side, and are used for processing the audio signal. The preselect (automatic) and MW/FM & DAB filters deal with the RF side of things.

[@LaneLarson]

Great videos! Very informative!

[@FrugalRadio]

Thanks Lane.

[@humaxf1]

It's easy to understand now why the rsp sdr receivers are that bit more expensive given the builtin filtering.

[@FrugalRadio]

Yes, and each model builds upon the others in terms of features and components.

[@frequencywatchers]

Can You make A Band Reject Filter With Low Pass Filter And High Pass Filter Together?

[@FrugalRadio]

That would depend on what you're trying to accomplish, and on which frequencies. A lot of single filters are band reject. Eg a typical high pass filter would only allow frequencies over 30 MHz. This is effectively an HF band reject filter.

[@frequencywatchers]

@@FrugalRadio Yes, My RTL.SDR Is Going Up To 30MHz With Q Branch Settings, When I Switch To Disabled Then It Goes To Whatever Frequency, But With Q Branch I Can Listen To HF Bands, I Made Antenna, But The Thing is That AM Is Cutting In To My 80 Meter Receptions, Makes Me So Sad. ;D

[@mxcollin95]

Great video! 👍

[@FrugalRadio]

Thanks.

[@thebluegrassfarmer]

Question: I live about 18 miles from our International Airport. I can hear Approach Control, Departure and Radar Contact just fine on my SDR. However, when an aircraft flies near my home location and transmits.. the SDR overloads. I've adjusted the "gain" and that does help.. but it's still distorted in the transmission. Is there a "filter" I can use to help reduce this overload situation as mentioned above ? Thanks in advance for the help. TBGF

[@FrugalRadio]

Hi. No, a filter generally wouldn't help in that situation, because the signal causing the overload is on the same frequency you want to monitor. I'm not sure what SDR hardware / software you are using, but you could possibly try enabling the auto gain control (AGC). An SDR with a higher dynamic range would probably help in this situation as well.

[@thebluegrassfarmer]

@@FrugalRadio Appreciate the sound advice. Thanks for getting back with me.

[@FrugalRadio]

You're welcome. We are all here to help each other in this hobby 😃

[@TheBILOXY]

Hello from France. I ´m the LFPG liveATC feeder. I encounter some serious issues with FM band while monitoring airband. So My setup is a jpole antenna+AOR ABF128 filter+Moonraker 100 preamp+an airband radio. Do you think the adding of a flamingo+ will help me receiving better ? And where should I install it, before or after the preamp or somewhere else ? Thanks a lot for your helping videos.

[@FrugalRadio]

Hi Elie. Thank you for your contributions to the radio community via Live ATC. It is great to have people like yourself providing these feeds 😄 Interesting to hear you say you are still suffering from FM Broadcast issues even though you are using the AOR Bandpass filter. The first thing I would try would be removing the pre amp. Preamps often make things worse in urban environments. It will probably be amplifying whatever Broadcast signals are coming though. I would also check the coax to make sure extra signals aren't getting in. The FM notch filters are quite inexpensive, so I guess it could be worth trying as well. I would place it before your bandpass filter.

[@TheBILOXY]

@@FrugalRadio Hello, I've just received and add to my setup the Flamingo v2. Now I don't have any problem with the FM band while receiving planes on the ground. Thank you for your help. Today I'm receiving the signal over a Uniden 9000XLT. Do you think it will help if I change it for a Malachite, knowing I'm searching for the cleanest signal possible ?

[@FrugalRadio]

I haven't yet used a Malachite, so I'm unsure. If you decide to try one, report back and let us know if it cleaned up the signal some more!

[@robbehr8806]

Nice presentation! I'm a ham located near Phoenix, AZ where the lowest TV channel is actual 8, which is in the 174 MHz high-VHF band. I'm looking for a high-pass filter that will allow local TV through, but block below 174 MHz. Any recommendations?

[@FrugalRadio]

www.parelectronics.com/index.php will make any filter you need, if they haven't got a standard model that will work for you.

[@robbehr8806]

@@FrugalRadio Thanks!

[@Lordabememes]

Does the wideband LNA from RTL SDR BLOG improve the signal strength ?

[@FrugalRadio]

It depends. The correct method of installing an LNA is to position it as close to the antenna as possible. Generally when you do this you will experience an improvement in signal strength, as the signal is boosted before being sent through the coax. You may received mixed results if the LNA is located closer to your SDRs.

[@TheMikeSirois]

I got a flamingo the other day but didn't have a good chance to play with it. I did notice though that it didn't fully block FM broadcast stations when tuned to the assigned frequencies. Is that normal?

[@FrugalRadio]

If you tune to signals in the regular FM Broadcast band you can expect to still find the stations. Their signal strength should be lower than without the filter. Although it creates a notch, many are still strong enough to cover through. However where you see the real improvement is in the areas the signals were breaking through before - e.g. other VHF / UHF frequencies. But if you are finding that you are still being breakthrough from FM Broadcast on other frequencies, then there is a problem. You can test by lowering the gain on your SDR. At the lowest setting, tune to an FM station, and note the SNR. Next insert the filter and take the SNR reading again. If it is not significantly lower, then there is a problem.

[@paulnortham]

Another great video, thank you. Learning all the time! I have the "Ham It Up" for the NooElec - does this do any filtering, or is it just a different beast altogether?

[@FrugalRadio]

Hi Paul. Yes, the Ham It Up actually starts with a low pass filter, although it is quite wide. It attentuates 65 MHz and up when activated. You can see the charts on the datasheet for more detail. www.nooelec.com/store/downloads/dl/file/id/98/product/16/ham_it_up_v1_3_barebones_datasheet_revision_2.pdf

[@paulnortham]

@@FrugalRadio You are a mine of information, sir.

[@FrugalRadio]

If you ask the wife, it's useless information 😮 But we know better, don't we!

[@SirThunderPants]

Could I please ask your advice? I listen to public safety: (153.785Mhz - 159.1050Mhz.) (477.800Mhz - 478.625Mhz.) & (744.0312Mhz - 774.6312Mhz.) using an AOR BCD396XT with a Discone antenna. I have VERY strong 88-108Mhz. & somewhat strong TV broadcast in my area. Could you help me chose the correct filter or filters? Thank you very much.

[@FrugalRadio]

Hi @JustSomeGuy. It would be important to note which signals are breaking through on which frequencies. For example, are you hearing Broadcast FM in all these bands? Or does Broadcast FM just impact the VHF Public Safety band? Do you have a cell tower nearby? They can also cause interference in the 700MHz band, but like you say it can also be TV transmitters. I would start with a Broadcast FM filter. The Flamingo+ filter (amzn.to/39ZJtHP) has greater attenuation than the Flamingo model I tested, and is only $1 more. I would also try to move away from a Discone. An antenna tuned closer to the bands you are interested in will also attenuate out of band signals to some degree. The antenna I use for Public Safety monitoring is designed specifically for the bands you wish to monitor. It covers the VHF, UFH & 700/800 frequencies. See amzn.to/2MDMNza - I have this antenna paired with a Ground Plane Kit (amzn.to/3aDJVuc) mounted 40ft up. I also have 2 for vehicular use that work really well. If the TV channel interference is quite strong, you would need to work out which channels are causing issues. You can then pick a filter that will help reduce those from somewhere like www.markertek.com/category/rf-channel-filters. Hope that helps!

[@MrDwadi84]

I have question for you about what sdr is better for HF RSP1A or HF+ Discovery? Also i found that AirAware Pro Plus (blue version) is much better than Plus versions - orange one, since it have all filters included.

[@FrugalRadio]

The HF+ Discovery beats the RSP1A in terms of VLF, LF & HF performance. It is a great SDR. The RSP1A offers much greater frequency range though. And yes, the FlightAware blue dongle has done filtering built right in 🙂

[@MrDwadi84]

@@FrugalRadio OK, so will buy HF+ next month :).

[@FrugalRadio]

Happy days. Guess we know what you're Christmas money is going on 🙂

[@MrDwadi84]

@@FrugalRadio rather, from the January payoff

[@FrugalRadio]

Fair enough @MrDwadi84

[@danduane1413]

I have a FlightAware RTLSDR dongle with a built in filter. Thanks for all the information. Your videos are well done and informative....!

[@FrugalRadio]

Thanks for your kind comments Dan. I use one of the FA dongles too.

[@danduane1413]

@@FrugalRadio Yeah, I've been in an out of ham radio for awhile. Started in 2001 or so and had lots of life "things on my plate", and starting to get back into it again. Lots has changed and for the better. JS8CALL, digital modes [D-STAR, DMR, etc] and of course, SDR. Came across your channel a few weeks ago and getting right back into it, so I will be monitoring your channel. My QTH is at CYWG. I used to live at CYEG in 04-06 when I was going to NAIT, so we could have been neighbours....

[@FrugalRadio]

Yes, there have been loads of developments in radio over the last few years. I love what is possible now, and would have bitten someone's arm off to have virtual radar and inexpensive SDRs when I was a teen! I enjoy some HAM activities as well, and use DMR through reoeaters and a hotspot. We might indeed have been neighbors in 05/06! Hope you're keeping safe out there in YWG.

[@canuckchris5733]

Are The filters in the sdrplay reliant on the software being used Example, Mac using cubic vs windows with uno Cheers.

[@FrugalRadio]

There are 12 preselect filters that are fully automatic. So if you tune to the fairly active 11175 kHz USAF GHFS frequency, everything above 12000 kHz is automatically filtered out. You can see a list of the automatic filters at www.rtl-sdr.com/a-review-of-the-sdrplay-rsp1a/ There are 3 extra notch filters that can be accessed via SDRUno. I don't know if these are available on Mac or Linux when using Cubic SDR.

[@canuckchris5733]

@@FrugalRadio thank you I appreciate you

[@wild-radio7373]

Thank you ♡

[@omon316]

how do I know which is the in/ and the output connector?

[@FrugalRadio]

I wondered the same thing Fritz. I had thought it would have been marked. In the end I tested mine in both directions, and both seemed to work. If yours is not marked, I guess trial & error is the way forward!

[@omon316]

Ya some of my filters are marked, especially the professional ones but the Noelec filters and amplifiers are not marked.

[@FrugalRadio]

I don't know why they aren't marked. With an amplifier, your think that it would be important to know the direction. Seems odd that Nooelec have opted not to make things clearer, especially since some of their photos show markings!

[@SarahC2]

Very useful! Thank you!

[@FrugalRadio]

Glad to be able to help!

[@SarahC2]

@@FrugalRadio I've subbed, lots to learn on here. It's great that you go to this effort to make some quality videos to teach others. Very appreciated. :D

[@FrugalRadio]

Welcome to the channel @Sarah Cartwright!

[@uncle870]

Great helpful video

[@FrugalRadio]

Thanks.

[@joe10117]

can this work for HD FM radio s ?? some are illegally bleeding on 104.7 103 101.9 nyc connecticut marjet NPR bleeds on my redosx TIC FM HD 2 ... can this clear my issue up ?...

[@FrugalRadio]

Yes, FM broadcast filters are designed to reduce the bleed from high power commercial stations.