Band pass filters

shadoe42 · #1 10-15-2002, 09:10 AM

I have seen some talk about band pass filters here. Does anyone have any information on them? A link or two perhaps?

latency · #2 10-15-2002, 09:29 AM

...but you've got mail.

shadoe42 · #3 10-15-2002, 11:19 AM

I replied to the one you sent me last night

so maybe YOU are the one with mail

I ask about the filters cause I want to find out if it is possible to use them with micro RCs. I want to be able to race several cars at once not just two. Without having to go try to get illegal imports

#4 10-15-2002, 01:46 PM

A band-pass filter probably wouldn't help you too much, as you'd still be limited to only the 2 frequencies. You could maybe figure out how the car is determining frequency (I couldn't find a crystal on the board, maybe the wire wound thing determines the tune of the car) and replace the crystal in the controller, you could be in business. You'd still be breaking the law doing it

The FCC has to monitor everything between DC Current and Light, the chances of them hunting down people using R/C Cars on unlicensed freqs is next to nothing.

Shacky · #5 10-15-2002, 02:33 PM

The idea behind the band pass filter is to narrow the band frequency the ZZ is listening to. With a well tuned band pass filter, you could narrow the range to 20 khz difference resulting in different frequencies for the same 27 Mhz band. As long as the transmitter was also tuned to only use this narrow band, then the transmitter and receiver could use the same waveform as another transmitter and receiver.

Here's a link to band pass filters

All this is just theory. I don't have the tools to retune the cars and add a band pass filter to narrow the band and test it with.

BUT... I have seen a post where someone was able to retune the ZZ for a 20 khz difference and narrow the band so they didn't interfere with each other, but I never got the info on what to change on the transmitter.

shadoe42 · #6 10-15-2002, 03:43 PM

Right shacky,

That is what I want to do. This is also what allows the larger RC cars to run more than 2 at once. Not talking about breaking the law here..simply talking about narrowinly the frequency the car looks for still in the 27 mhz range.

Nightwing · #7 10-15-2002, 11:07 PM

The catch is how steep you can get the skirt of the filter. A small multi PI filter { look like the output stage on a ZZ transmitter } using very small toroids or if posssible shielded coils could work.

Another way is to replace that rengentive receiver pile of junk section with a mixer and osc. If they still make NE602 or equ could bypass the receiver and use it as a receiver. The OSC size of that chip will work with an crystal. WOuld be a direct conversion but better than that regenative junk.

The input on a ZIP, Bit, can car whatever is a single capactor-coil combo that good as a trap but is so broad its almost usless for what they are using it for.

Grab a ARRL handbook. They have always had a nice section on filters. Its expensive but really packed with info.

Want to setup some simple tools info to construct to measure signal and also tune the receiver for max smoke so to speek. Something you can either use off the shelf tools or simple mods to maintain the electronic side. Try for a RS peg rack bld of matterials. Been so bussy on DB projects of late cant even breath. This is the only break I get!

ts185r · #8 10-15-2002, 11:29 PM

Now, if only someone could mod a way to get a standard set of r/c crystals to work on a ZZ. then more of us would figure out how to fit them in.
I can ask it because I don't know how it works.

Nightwing · #9 10-16-2002, 02:26 AM

That is the best part about the NE602. It has both a mixer and osc in a 8 pin package. Proabbly today you can get it as surface mount. Simply hang a xtal with a small adjustable cap off of it. Feed the antenna in and feed its output to the RX-2 if that is what is under the epox goo.

Would pick up a signal +- but better than the regenative receiver it has now. And with a bit of luck allow you to change freq.

keith20 · #10 10-18-2002, 10:57 PM

Hey guys, love the discussion. I too wish I could change frequencies on my ZZ. I'm familiar with 27Mhz R/C in larger scale, switch crystals and go, but I would love to see this in small scale. I know yoykmo has the Puchi Maru that works on all 6 "Standard" 27Mhz Freqs, but it looks like its board is larger, and I think they make 6 different receiver boards. I don't know how much it would cost, but I would REALLY be interested in a replacement receiver for the ZZ on different freqs, along with a crystal conversion for the trans. RS transmitters DO use crystals don't they? Also would you have to narrow the band on the trans? I'm no electronics genius, but I think I understand a little of what you're talking about. This small scale stuff just blows me away

Nightwing · #11 10-19-2002, 12:55 AM

Yes they do use a xtal. To physically change freq may take about 4 parts on the controller and 4 to 5 on the receiver. Including that micro variable coil formally know as a pot.

#12 10-19-2002, 01:09 AM

I bought a couple clone bit racers from the radio shack from canada and they come in the 27 -49 mhz but they also come in a 27 mhz 2 band and a 27 4 band. Same thing with the 49 mhz.. That might not be the right bands but they do come in different bands......

keith20 · #13 10-19-2002, 10:08 AM

Hey Timm, you might be on to something, maybe the board swap I've been looking for. Would probably boost speed too.

Nightwing, any idea what the total $ for the freq mod would be using the parts you're talking about?

Nightwing · #14 10-19-2002, 09:31 PM

Off hand, sorry dont know. As soon as I can get a circuit diagram of the reciever put together should be able to tell then. Rather have a passive one but the active one with chanagable xtals would be greate.

Mostly it the IC a few pasive parts and the xtal.

keith20 · #15 10-19-2002, 09:42 PM

Nightwing, If I get you, you're saying this is do able. Thats too cool. I'll bet if you could get it working, you could sell a few..Hint,Hint