recomended values for 455 KHz filter - Page 1
Forum section: electronics / general

author: Simon
author_rank: Unknown
timestamp: November 18, 2011, 10:19:41 am
content: I'm looking to match an L and C to make a 455 KHz filter, what is the best range of values to use ?

author: ejeffrey
author_rank: Super Contributor
timestamp: November 18, 2011, 10:29:07 am
content: Why not use a standard ceramic filter?

author: Simon
author_rank: Unknown
timestamp: November 18, 2011, 10:52:10 am
content: well basically my idea is to make a small oscillator, I was going to square wave pulse the filter and let it generate (filter) the 455 KHz wave from that, will a ceramic filter do this.

author: sub
author_rank: Regular Contributor
timestamp: November 18, 2011, 11:50:03 am
content: That should be fine, though the distortion will probably be rather higher than if you were to use a Colpitts oscillator or such. What's the application, if I might be so bold?

author: Simon
author_rank: Unknown
timestamp: November 18, 2011, 12:02:09 pm
content: ah um well, I wanted to just make a small generator of 455 KHz of low power. Plan is to mute (jam) a nearby (within metres) radio but with limited range of course (I don't really want to go to jail)

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 18, 2011, 03:12:48 pm
content: Maxim makes some one chip oscillators that can be programmed over a very wide frequency range.

author: Armin_Balija
author_rank: Regular Contributor
timestamp: November 18, 2011, 05:46:45 pm
content: Maybe I'm a bit dense but I'd like to know what kind of a filter you're exactly thinking of?

author: Simon
author_rank: Unknown
timestamp: November 18, 2011, 09:08:02 pm
content: well you see as far as i know the simplest way of generating a sinusoidal wave of given frequency is to pulse an LC filter (resonant circuit) that will resonate at it's frequency, because a square waveform contains many sinusoidal frequencies the one the filter is set at will be filtered out, I also assume that it is best to pulse the filter at the filtering frequency or a sub multiple and that by using PWM I can change the power of the oscillations.

author: gregariz
author_rank: Frequent Contributor
timestamp: November 18, 2011, 11:21:14 pm
content: Quote from: Simon on November 18, 2011, 09:08:02 pmA one transistor colpits is pretty simple and should be all over the net at 455KHz. Just search for a 'radio BFO circuit' or similiar.For the L and C just use a transistor radio IF can.

author: vk6zgo
author_rank: Super Contributor
timestamp: November 19, 2011, 02:48:53 am
content: Apart from the fact that if you are successful,you are breaking the law,I'm very dubious about how effective it will be.For one thing,the IF circuitry is fairly well shielded,& is also at quite high signal levels,as compared to the RF stage.Also,not all IFs are on 455KHz,if it is an FM radio,the IF is probably 10.7MHz.With your squarewave source, after the filter you may still have substantial output at 910 KHz,which is right in the middle of the MF AM Broadcast band,so you may interfere with other listeners,who won't be very impressed.Why not just yell at the person with the radio to "Turn that @#$%^&&&%$#!!! thing down!"VK6ZGO

author: Armin_Balija
author_rank: Regular Contributor
timestamp: November 19, 2011, 03:55:51 am
content: Would any of these be what you're looking for? To be quite honest I don't know what 'exactly' I'm looking for!http://www.qsl.net/kb9mwr/projects/voip/apco25/Simple%20455%20kHz%20to%20sound%20card%20IF%20design.pdfhttp://www.lulu.com/items/volume_65/7219000/7219361/1/print/7219361.pdf

author: Simon
author_rank: Unknown
timestamp: November 19, 2011, 09:30:46 am
content: Quote from: vk6zgo on November 19, 2011, 02:48:53 amWell that means yelling at the whole factory(does not make you popular), you see the problem is they all like a different radio station so they all play their favorite at high volume to cover the others and get over the noise in the factory. So every time i go up there i can't here a damn thing. I had some fun a while ago with one of those little FM transmitters sold often for playing CD's into a car radio that does not have a CD player. By setting the same frequency on it as the radio station but not putting anything into it i was able to mute any one radio but of course this does not work on more than one radio at a time, some of us had a hilarious time. As they transmit BBC stations on more than one frequency one poor welder kept getting up to change the frequency at which point I'd hunt again and blank it. I had to take the transmitter away when one clever person offered to man it and started playing porn over someone else's radio who could really not figure out what was going on and was very bewildered hahahahaNaturally I do only want very limited range of a few metres which is why I thought of using square wave PWM so that I can limit the power. If I'm going to send out other frequencies to though maybe it is best not do it. Of course if the IF in the radio is well shielded and a big signal then yes all a waste of time. I'd be better off doing multiple oscillators at the main radio station frequency.

author: ejeffrey
author_rank: Super Contributor
timestamp: November 19, 2011, 09:54:37 am
content: I am also skeptical this will work. Aside from the legality, the easiest way to jam a radio is to overload the input RF amplifier. A strong signal in the middle of the FM band will drive the input amplifier into saturation and it won't pick up the tuned signal. If you make it halfway between two stations you even reduce the likelihood it will cause interference at greater distances.You may not need to be within the FM band. I used to have a set of UHF two-way radios that would jam cheap FM radios within a few meters. I assume their input filters were not up to the task, and enough bled through to overload the RF amplifier.

author: Simon
author_rank: Unknown
timestamp: November 19, 2011, 11:56:23 am
content: yea basically use a cheap FM transmitter sold even in supermarkets, I might get creative and put some darth vader over the ether

author: Bored@Work
author_rank: Super Contributor
timestamp: November 19, 2011, 12:23:50 pm
content: Unless you are the floor manager or H&S responsible it is non of your business what kind of bullshit they do on the factory floor.Get one ofthoseto protect you and let them continue ruining their hearing.

author: Simon
author_rank: Unknown
timestamp: November 19, 2011, 12:27:25 pm
content: Quote from: BoredAtWork on November 19, 2011, 12:23:50 pmuh anything against having some fun ?

author: Bored@Work
author_rank: Super Contributor
timestamp: November 19, 2011, 12:54:46 pm
content: Quote from: Simon on November 19, 2011, 12:27:25 pmIt sounds all very funny, until you consider the risks. I can think of at least three:1) Getting caught by the authorities. Depending on local laws and regulations this might have an impact on your EE career. E.g. being on record for illegally operating a transmitter might later prohibit you from getting a license to operate or service some professional RF equipment. Is it worth that little bit of fun?2) Getting caught by the manager. Managers don't like if someone distracts or annoys their workers. They don't like to have to deal with trouble and they don't like if productivity goes down. You could risk your job. Is it worth that little bit of fun?3) Getting caught by the workers. In the companies I have worked, and where there had blue-collar worker, they always had simple conflict resolution procedures. These procedures typically consisted of dragging the troublemaker behind the factory building or into some lonely spot to teach that person a lesson by beating him up. Is it worth that little bit of fun?

author: Simon
author_rank: Unknown
timestamp: November 19, 2011, 12:59:05 pm
content: Quote from: BoredAtWork on November 19, 2011, 12:54:46 pmuh as for illegal equipment I am now referring to a transmitter available off your local supermarket's shelf. As to the explosive atmosphere you refer to we don't have that sort of an atmosphere where i work. As for productivity nobody gives a shit, I'm about the only one that does ! and if as a quality inspector i have to speak to someone who insists on a loud radio well that can be curbed for the time needed to talk !As for dealing with trouble where i work - they don't bother, everyone is a free soul where i work, infact my honest opinion is that we won't last

author: slateraptor
author_rank: Frequent Contributor
timestamp: November 19, 2011, 11:00:16 pm
content: Quote from: Simon on November 18, 2011, 10:19:41 amSee attached image for Excel-calculated values for a 455kHz resonant tank circuit. Given 2 decades of E6 series cap values (100nF to 6.8uF), corresponding L's were calculated.For low-power filtering applications, you won't actually need any L, regardless of how many henries; 2 op amps, a few resistors and caps is all you'll need. Look into synthetic inductors. There are at least two well-known topologies published. They are not a replacement for power inductors but work well for signal conditioning.

author: vk6zgo
author_rank: Super Contributor
timestamp: November 19, 2011, 11:32:57 pm
content: Quote from: Simon on November 19, 2011, 12:59:05 pmIt's not the transmitter which is illegal,it is what you are going to use it for!It is analogous to the situation where a crowbar is a legal tool,available in any hardware store,but if you use it to do a burglary,---that is illegal.I am quite certain that interfering with a broadcast radio service is illegal in the UK,& just about anywhere else,for that matter.It is also not a good idea to post your intention of breaking the law in a public forum.VK6ZGO

author: Unknown
author_rank: Unknown
timestamp: November 19, 2011, 11:46:51 pm
content: Not arguing with the people that consider this a bad idea and illegal, but is jamming the IF really considered interfering with the broadcast radio service? I'm sure it's illegal use of the spectrum, and possibly willful interference with other people's equipment, but it's not actually interfering with the spectrum of the broadcast stations.

author: baljemmett
author_rank: Unknown
timestamp: November 20, 2011, 12:06:48 am
content: Quote from: alm on November 19, 2011, 11:46:51 pmI doubt it -- but note that the discussion had grown to encompass the possibility of using an FM transmitter to perform the jamming, which definitely is.

author: vk6zgo
author_rank: Super Contributor
timestamp: November 20, 2011, 02:33:32 am
content: Quote from: baljemmett on November 20, 2011, 12:06:48 amThe OP didn't initially allow for the different IF frequencies; 455kHz for AM b/cast.10.7MHz forFM broadcasting.VK6ZGO

author: Simon
author_rank: Unknown
timestamp: November 20, 2011, 08:12:54 am
content: well I had considered that different radios would have different IF frequencies but obviously the idea is not feasable anyhow, although I know that many early mobile phone chargers did a good job of completely wrecking radio reception and my laptop charger also does.The actual transmitter i am considering using is very low power and will only affect anything in a few metres as it is probably designed to do in order to be legally sold, it is designed to transmit on the same frequencies as FM radio so I can't help it over powering any more distant reception. There are versions of these transmiters that only have 4 fixed frequencies (mine is fully tunable) I wonder who is at fault if radio reception is disrupted, the user who has no choice but to use one of 4 frequencies or the manufacturer who is supposed to know every frequency used by every radio station in the world (in fact likely at least one station will be affected)Naturally I don't condone radio jamming, this is (and has been) some light hearted fun in the knowledge that only radios within a few metres are affected.

author: Simon
author_rank: Unknown
timestamp: November 20, 2011, 08:25:19 am
content: h and as a side note, can i prosecute the manufacturer of my laptop charger ? it's a flipping nuisance ruining radio reception every time I charge it up !

author: jahonen
author_rank: Super Contributor
timestamp: November 20, 2011, 08:51:32 pm
content: Quote from: Simon on November 20, 2011, 08:25:19 amYou can always claim that the laptop charger does not meet relevant EMC requirements.Regards,Janne