RTL SDR Front End Filter Demonstration

[@357Shakey]

Very good presentation on the practical description of front end filtering. I find that some engineers and technically inclined folks get so far involved in the "paper work" side of something like this that they over kill it. Your video is a great example of practical engineering in action.

[@mudspringermusic5934]

I'm just getting into this stuff. Awesome video. I'm trying to figure out why AM comes in on every frequency as we speak and you have duplicated and solved my very problem!! Thanks for the demo.

[@colinsmith4185]

Thanks for the demonstration,your production reminded me that my SDR would indeed be useful when designing and constructing bandpass filters for the 20-40 meter ham bands,many thanks Colin

[@kugellagers]

@Dan M RE: Capacitors. When I ordered from Allied Electronics I got a lot of odd valued ones such as 68pf, 180 pf, 330pf, 680pf, 47pf (off the top of my head) as well as some like 2200 pf, 3300 pf, 1000 pf based on the first filter I made and tried to get ones they had on sale as I could get a bunch and use them for other projects...more filters as it seems. I didn't intend to put them in pairs...just came out that way. I built a 7th order Cauer elliptical MW bandpass filter (my first filter by the way - crazy) and put it in the same little aluminum case as all of the others I have made. I used 3-4 capacitos sometimes. Imagine seven toroids and seven capacitor groups squeezed into that case. I can't imagine how some people build SMD circuits. I'd go mad.

[@bobkozlarekwa2sqq59]

Use silver mica caps and you will see sharper skirts. Good demo - thanks

[@gmcjetpilot]

Thanks just what I needed.... I just bought a RTL.SDR up converter (the cheap one $40) Works great but I am near powerful AM and FM stations and in general live in a concrete apartment building down town. Not ideal. Have Wellbrook loop in patio.

[@estefan2020]

what type of Toroid did you use for the 1800khz band pass, size wire, and number of turns for the 3 chokes please. And thank you for your time showing your build.

[@kugellagers]

Dan M Hi Dan, Are you referring to the 1.8 MHz (1800 kHz) high pass filter? I didn't demo a 1700 Mhz band pass filter. However, the toroids I used for the 1.8 MHz high pass filter are all FT50 type 61 material. I am using 24 gauge magnet wire and they have 10, 16 and 13 turns on them to get a computed (not measured) inductance of 6.9 uH, 17.7 uH and 11.7 uH respectively. The 16 turn inductor is the middle one. I hope that answers your question.

[@estefan2020]

kugellagers thanks much, I like the dual serial fm traps, love the am bcb brick.that will be so much welcome.

[@kugellagers]

sent18inel Sorry for the slow reply - I was on vacation/holiday. The main reason I wind my own is that I can get more exact inductance values in a ferrite type that is best suited for the frequencies of interest and easily adapt my filter design to measured component values. Toroid inductors also suposedly have less interaction with one another due to their shape/design. I also like making my own components.

[@jollyjumper496]

Hi Matt, can you tell me where you got the Antenna switch please, or a brand & Model No Please ??

[@roarydinosaur7825]

That antenna switch is of the type that can be found at most hardware and electronics stores as well as all over the place online. It's just a basic cheapie switch. Would definitely not use it for any sort of transmitting and not great for really good signal isolation. It was fine for my demo though.

[@estefan2020]

Sorry for another question tr the hi-q ceramic capacitors on the am bcb brick, it looks like you are using 2 per capacitor section, I am having a hard time combining caps to get the required values, how did you get yours in pars? I got 3200pf 682+682++682+682+471=3199 1220pf 682+223+223+82+10 900pf 682+201+15=898 853pf 682+151+20 800pf 682+101+15=798 503pf 33+471=504 104pf 82pf+22pf Thanks So Much Dan

[@Frizizo]

Just so no one gets confused, a cap marked 682 is not 682pf, its 0.0068uF, or 6800pf. The "2" denotes the number of zeros for the value in picofarads. Same for the other values-the third digit is the number of zeros. So, to make 3200pf would be: 102+222. Please watch this and check your calculations. More here: www.elecraft.com/Apps/caps.htm

[@kugellagers]

Nice catch. I think you must be right with his cap values...which means for most of them he is using the incorrect values. Another reason to have an LCR meter to measure actual values. Of course you need to have it on the correct settings as well.

[@Frizizo]

Looks like the cheapo LCR meter will only measure down to 0.01mH (1000uH). Bummer.

[@Frizizo]

Here is what I came up with for the caps: 3200pf 102+222 = 1000+2200 = 3200 1220pf 102+221 = 1000+220 = 1220 1040pf 102+30P+10P = 1000+30+10 = 1040 800pf 471+331 = 470+330 = 800 853pf 681+151+22P = 680+150+22 = 852 700pf 681+22P = 680+22 = 702 503pf 471+33P = 470+33 = 503 Let me know if I made any errors.

[@kugellagers]

Yeah I think those numbers are correct. I would still check the actual capacitance values with the LCR meter once you combine them in parallel but before you solder each group to anything else.

[@coriscotupi]

Whats the square shoulders to either side of the two FM stations shown? The left-most station does not show it. I assume it is RDS data is being sent by the stations?

[@kugellagers]

The square shoulders in the FM signal are the digital signal. I am not 100% sure what they consist of but they are definitely the digital components. From what I understand, in addition to them carrying the HD audio signal they can also carry sub channels as does digital TV. You can see them as IBOC in the AM band as well and why they are the bane of AM BCB DX'ers due to their overlap with adjacent frequencies.

[@coriscotupi]

Kugellagers Noodle Thanks. Makes sense. cheers!

[@gabrielmartinmiguel2173]

Habria alguna forma de hacer filtros variables para un transceptor multibanda sdr ?

[@kugellagers]

Puede agregar condensadores e inductores variables con múltiples derivaciones.

[@tubeDude48]

If I have this correct, you just series 2 of the 33-341 for the FM Trap.? BTW- MCM no longer sells the 33-341! For the 1.8MHz Filter, it looks like you Paralleled Capacitors to get the correct value. Will you please advise as to what values you used? I live in a small town and the AM/FM stations are barely 1 mile away! So I need these Traps/Filters desperately!! One more item, where did you get the aluminum cases? Thanks!

[@kugellagers]

You are correct on both accounts. I have two of the FM traps in series and the capacitors are in parallel to get the values I need for the construction of the filter. I just noticed that the traps are no longer available about a week ago. :( They had been on clearance for some time. The aluminum case is from MPJA and I will put the link above in the video description.

[@tubeDude48]

Found out there are plenty of traps on Ebay. Thanks for the feedback! --- Will the 15-577 Traps works just as well? I happen to have a couple.

[@kugellagers]

I do realize that there are many others out there. The reason I had used these particular ones were that a TV DX group had swept various different FM traps and found the MCM model to be one of the best at eliminating FM for the money and one of the better ones at that. You can see their thread on FM traps here: www.avsforum.com/forum/25-hdtv-technical/1431548-fm-filter.html Try to find the best for the money and maybe get two as I did. Seems like you are a lot closer to the offending stations than I am. Cheers.

[@FrankBartson]

I really like your vids you do great builds, where can I get the rf type metal enclosures to put the electronics into? Frankie :-)

[@kugellagers]

I get the ones I used in my videos from MPJA. They seem to have decent prices on enclosures and components. They don't have everything though. www.mpja.com/

[@EdEditz]

This is what I need. I have an FM transmitter sitting 100 meters from my house. Makes normal RTL-SDR use almost impossible.

[@mvssarma3387]

EdEditz, you need need to use two such filters and also shield the RTLSDR in same steel enclosure., for effective working at your QTH, regards sarma vu3zmv

[@EdEditz]

Thanks! I'll try that.

[@LA9RKA]

Good presentation of how effectful a good frontend filter are. Good work. 73 de LA9RKA

[@axandio]

Schematic for the that 7th order high pass?

[@kugellagers]

Jay Tee Yes. The schematic in the last ten seconds of video is for the 1.8 Mhz high pass filter.

[@axandio]

kugellagers Perfect!

[@radiorob007]

274/5000 good video! BUT how on earth have you combined those capacitors into those values? how do you get: 700pF - 800pF - 1040pF - 1220pF - 503pF - 853pF ??? very coincidentally a value 3200pF will be 2X 1600pF ? ;-) LOL I can not get out? friendly greetings from The Netherlands! Rob.

[@kugellagers]

They were some weird value high Q caps that were on sale that I guess they had a difficult time selling.

[@raccoonnyc]

Excellent demo. Tom, ak2b

[@j69chevelle]

Does this filter only attenuate FM broadcast band or does this also attenuate all other bands? How do you receive any other signals through the attenuation in any other band if they are affected? I think you are trying to attenuate just FM broadcast to reduce / eliminate IM on other bands, right?

[@kugellagers]

The ganged FM Trap filter I made in the video only blocks out the FM BCB with only a little lap over out of the band. This thread over on the AVSForm: www.avsforum.com/forum/25-hdtv-technical/1431548-fm-filter.html#post29973297 can give you and idea of how these FM traps perform. There are several plots of several different FM traps on that thread. The FM signals in my area are just so strong that it overloads the SDR and causes spurs and images all over the place. The IM you see in the video is created in the SDR itself due to these strong signals coming in on the antenna wire. Once the overloading FM signals are removed the IM goes away too.

[@j69chevelle]

So are you seeing a combination of intermod and harmonics? Isn't intermod a combination of more than one frequency the sum of which is the actual intermod signal or maybe a harmonic of it?

[@j69chevelle]

By the way, I'm asking because I'm new at all of this. Trying to figure out the magical world of SDR and the RF spectrum. lol

[@kugellagers]

First off I am not an expert in RF or EE etc. But I think intermod is as you state but I think also can be caused by strong signals being re-radiated within your equipment. Regardless, the cheap RTL-SDRs, such as the one I am using, have WIDE open front ends and usually benefit from some sort of front end filtering. I intend over time to build a selectable front end with various filters for different bands...but I have not done much in this regard lately.

[@heidirodmarsh658]

ive got the 820T and im waiting for the hf up converter to arrive.i want to listen vlf around 30 Khz or lower if it'll tune. do i need build any pass filter for that low please ? Im NEW n love the hobby of radio already. Cheers Robby N

[@kugellagers]

Heidirod Marsh You will definitely want to build some sort of low pass filter for your front end. If you do not, you will have lots of noise and intermod from the MW BCB and depending on where you live, noise from NDBs or LW broadcasts as well as DGPS signals around 300 kHz.. In addition, the noise levels in general increase as you get into the LF and VLF frequency range. In general, the upconverted cheapie dongle SDRs are not very sensitive when listening to MW and lower.

[@heidirodmarsh658]

i took a screen copy from your hi pass filter with the values on it. what do i need change to go lower to vlf OR is your filter ok to go VLF ??

[@kugellagers]

Heidirod Marsh Sorry for the slow reply - I was on holiday/vacation. If I understand your question correctly you are asking if the 1.8 MHz high pass filter will also cut out noise/signal in the VLF range? The answer to that is yes. It will also filter out and eliminate noise in the VLF range. If you want to use the highpass at a lower frequency you will have to redesign the filter pretty much from the beginning. I use the free student version of the Elsie filter design program for my filter construction. See my 520 kHz High Pass Filter build video for more info. kzbin.info/www/bejne/ipqWZJZ5n818ppY The student version of Elsie filter design software that was used to design all of my filters. This can be found at www.TonneSoftware.com

[@circattle]

Heidirod Marsh If you are interested in VLF, you don't even need an SDR dongle. Connecting a long wire antenna to the "MIC" input on any reasonable sound card will do the job in conjunction with SDR Sharp. The frequency range of the radio will be f/2 so a sound card that does 192kHz sample rate will hear DC - 96kHz. This is more than adequate to receive VLF beacons and time signals.

[@heidirodmarsh658]

ty thats truly incredible.only,im not sure about direct connection...would a isolation transformer be ok or too lossy ? cheers robby n

[@gavargas22]

What antenna do you use to receive AM and HF?

[@kugellagers]

Hi Guillermo. I am using three low-noise verticals for AM and HF as described in this other video of mine here: kzbin.info/www/bejne/noTanIBvlsZ6hLc

[@Etherionix]

do you have any idea what the insertion loss is at HF?

[@kugellagers]

Because of the nature of the signal bouncing around on the screen, I could not get a precise value but it appeared to be less than 3dB. But that would only be a very rough estimate.

[@lyrez62]

Great, thanks !

[@dl8cy]

awesome work - thank you for explaining and demonstrating - 73 de dl8cy

[@avijitdas6872]

What antenna are you using?

[@kugellagers]

It depends on which band I am DX'ing at the time. All of them I make myself.

[@viajero31]

can i use this device close to power lines ?????

[@kugellagers]

The front end filters will help with specific frequencies. If you know what specific frequencies the noise from close by power lines is you could design one to help filter it out. A phaser that phases a signal antenna with a noise antenna would probably do a better job if rf noise from the power lines is the issue. I use a Quantum Phaser to phase out noise when I DX MW: kzbin.info/www/bejne/qF6tqH2vad-YjsU

[@viajero31]

Thanks

[@HalfLife2Beta]

which wire do you use for inductor? can u give me an ebay link? thx in advance

[@kugellagers]

I use 22, 24 or 26 gauge magnet wire. There are many vendors on ebay - just search for magnet wire.

[@yxhankun]

what software is running on the notebook?

[@kugellagers]

If you are referring to the SDR software it is SDR# or SDR Sharp. If you are referring to my ancient and slow laptop it is...are you ready for this...Windows Vista - Yech!

[@yxhankun]

thanks! airspy.com/download/

[@DAVIDGREGORYKERR]

what about using a PI5V331 operating as a QSD driven of a Johnson counter driven via a 4x LO would that give a better signal without having to use a first IF?

[@saifhudinwahyu5350]

Harga

[@bigpimp347]

dee bee, for fucks sake stop saying Decibels, just say db..!!!!