RF mod – more controller channels

[ph2t]

Starting off in another thread is the discussion about the limitations of only four channels for Bit-g’s. As Pandabear states in this thread, no matter how many Bit-g’s you have, there is only 4 freqs to deal with.

So I thought maybee if we could pool our collective resources together somehow a solution might make itself known.

I’d be interested in collecting data first and from there then get into the design and problem solving.

The channels appear to be working together are.

27/35/45/57
OR
27/40/49/57

Thanks Panda for that info. Also we have the bandwidth of 8mHz between channels that Shypo has confirmed.

Thanking uA for his investigation (luck b***ard has a CRO!) it is also known that while the TX unit has a fundamental(the main signal) frequency set by the crystal, the RX unit has a wide specrum in which it can pickup the signal. This causes the restriction of 8mHz on the frequency separation between controllers.

I hope this thread will promote some valued discussion among us.
I would also like this thread to become a “register” for electronic/technical info in regards to Bits/clones.

Thanks,

ph2t.

ph2t.

[ph2t]

Bit-G Schematics

Transmitter – 49MHz

Receiver – 49MHz

ph2t.

[micro_Amps]

Excellent work ph2t. I have been looking for Rx diags for a while.
The Tx diag is accurate. I’ve been working with that one. The only real difference between the frequencies is the crystal (obviously) and the inductors (L1 L2 L3).
I would say the Rx ‘bandwidth’ is set by a capacitor value. Fine tuning this value would restrict the width of the signal that the Rx responds to, and hopefully exclude other frequencies a little better. A different value would be used for each frequency.
uA
🙂

[GT-ahh]

yeah i only had a quick look..it looks like its just a capacitor governing the reciever freq and L2 (the coil) ill see if i can trace the cap on a clone or bit…and compare them in different freqs

http://www21.brinkster.com/gtahh/
custom shells, mods and tips

[ph2t]

Pinouts of TX/RX chipsets (dunno if they are version dependent).

[PandaBear]

Electronics are totally meaningless to me, fellas… but just wondering…

If we invent a 15MHz or a 70Mhz car… would the higher freq car have better signal penetration?

[micro_Amps]

No, the higher or lower the frequency makes no difference to the range for close freqs, eg from 10 – 100 MHz in the AM band. It is difficult to make R/C gear in any other freq than those commercially available because they dont sell the crystals for the frequencies. Transmitting on these frequencies is not permitted in Oz, so naturally, neither is selling the crystals.
Although crystals for a few freqs under 12MHz are freely available. (now theres a mod idea !!)
Once you get up to the GHz ranges you get better signal range with low transmission power. Thats why bluetooth and cordless phones are using these frequencies

Hey ph2t, by any chance do you have a pinout of a TX6C chip. This is the chip in the booster Tx (and the 4B). That would shed a little light on things for me.
Also I know there is a TX7C & RX7C chipset that is digi propor R/C. I’d love to get a set of thos into a bit.
🙂 uA

[jamiekulhanek]

I noticed that the chip on the RX has a pin labled TURBO…….are u guys thinking what i’m thinking?

The world is mine

[PandaBear]

Quote:

Transmitting on these frequencies is not permitted in Oz, so naturally, neither is selling the crystals.

Actually no, that’s not true.
There’s no Law against selling the xtals, just illegal to be transmitting at certain frequencies. And besides, transmitters don’t have to be transmitting at the xtal frequency, I’m sure its easily ‘divisible’ using solid state logics to lower freqs.

I know a source which can supply custom xtals. Just tell them what freq you want, they’ll cleave the quartz and pack it into the standard can – all legit stuff. Not cheap but heck, its available.

[PandaBear]

Quote:

…Once you get up to the GHz ranges you get better signal range with low transmission power. Thats why bluetooth and cordless phones are using these frequencies.

Hmmm!

Now *THAT’S* an idea!!!

A Bluetooth retrofit into a BCG… haha, you can control the car from your PC or your mobilephone!!! 😀

[GT-ahh]

IPAQ controlled BCG..that would rock!

http://www21.brinkster.com/gtahh/
custom shells, mods and tips

[micro_Amps]

Quote:

There’s no Law against selling the xtals, just illegal to be transmitting at certain frequencies

I didnt actually mean that they were illegal to sell, just that generally they are not available. Good to hear that you have a supplier for custom frequencies tho…..

For those of you who are not sure how the frequency/range thing works, let me offer this explanation and maybe the likes of pandabear or ph2t can elaborate further if I am not clear.

Imagine that you were able to hear the transmitted signal of your transmitter as an audible sound.
The frequency would be the ‘pitch’ or the ‘tone’ of the sound.
The the higher the frequency,the higher the tone you hear. So then 40MHz would be higher pitch than 27MHz (eg, 40MHz beeeeeep…. 27 MHz baaaaarp)

The strength of the signal (or the range) would be the volume of the sound that you hear. If you increase the volume of the sound it will travel further. If we were to increase the signal strength of our little transmitters, the signal would obviously travel further.

The ‘pitch’ and the ‘volume’ of the sound (or signal) are two different things

Thats why there is no detectable range difference between our frequencies.
They are transmitting a different ‘tone’ to each other, but they are transmitting at the same volume, and will have very similar range to one another.
(Technically its not exactly the same but its close. Different frequencies of the same strength do travel different distances, but its not really relevant in our range of 20 feet or so)

Also….
The higher frequencies do not ‘travel’ faster than the lower frequencies because all freqs travel at the same speed in the same medium (ie air) So my 57MHz booster doesnt receive its signal any quicker than my 27MHz Toyota Bb. The transmitting frequency has no bearing on the cars responsiveness or performance.

I hope I dont sound patronising by making it this simplistic, but I just thought that if it was explained in this way it would be easy to undersand

:)uA

[PandaBear]

Quote:

I hope I dont sound patronising by making it this simplistic, but I just thought that if it was explained in this way it would be easy to undersand

Pretty good job there, uA – Einstein couldn’t have done it better himself. 🙂

Quote:

I didnt actually mean that they were illegal to sell, just that generally they are not available. Good to hear that you have a supplier for custom frequencies tho…..

Its a local (Oz) guy too, so I doubt if he’s the only one who can do it. I haven’t tried his services yet so cannot vouch how well it works.

As for the actual xtals… some RC guys use “custom” freqs, they may have one thats slightly out of the normal range or a split. It does solve some freq clash problems but it might also cause interference to other guys on nearby freqs. Funny freqs are usually not allowed at major competitions anyway.

The *only* real reason I haven’t bothered ordering custom xtals is… I think they’re about $20-25 each, for AM stuff. So hmm…

[ph2t]

RX analysis

What we have is an AM Super-regen receiver on the car that is tuned to receive a serial encoded OOK AM transmission (whatever that is).
The centre frequency is tuned (27Mhz, 35Mhz, 40Mhz, 45Mhz, 49Mhz, and 57Mhz) so the receiver is most “selective” on one of these frequencies. More information can be found here and here.

From what i’ve read up about regen receiver designs is that they are super-sensitive, BUT not very selective. That’s why we have the requirement of such a wide seperation between controller frequencies (approx 8MHz).

I’ve isolated the receiver circuit to help understand the roles of the various components.

1) The Base Oscillator

This part of the circuit provides positive feed back to the transistor and gives the AM receiver a high gain, or in other terms high sensitivity to an incomming signal.

The Tuned LC Circuit

The capacitor and inductor run at the RF frequency you want to receive the signal on, eg: 27Mhz, 35Mhz, 40Mhz, etc…

The value of the inductor can be tweaked to acheive the strongest signal for your car. This also gives you better distance.

The tuned circuit is the throttle for the base oscillator. Through the transistor it amplifies the signal it receives from the controller.

The Q Capacitor

This part of the receiver is the one I think we want to look at.
This capacitor controls the Quality of the transistor amplifier. Quality (or Q) is a hard thing to describe. It’s like looking at a fountain of water side on and noticing the upsidedown U. Quality is the width of this upsidedown U. Higher quality, thinner U. Lower quality, fatter U. Confused?

With this we might be able to make the receivers on the cars more “selective” and then mod them with inbetween freq’s such as 31Mhz, 37Mhz, etc…

ph2t.

[micro_Amps]

Think I’d better get the CRO out again

[ph2t]

Thanks to some very resourceful germans, I’ve managed to get the datasheet for the TX2/RX2 chipsets. This will make for some damn fine reading for all us techies out there. (I bet uA would be salivating already…:smiley2:)

Get it here.

ph2t.

[DaveF]

Is there any way Ausicro can host those documents, so instead of this thread having links to external documents (small file size anyway) which may one day disappear off the web because we have no control over them, they live as long as the thread does on this site.

---

👿 DaveF!
My track – http://community.webshots.com/album/58669595eliwuK

[ph2t]

The site I link most of my doc/pics and stuff to in these threads is maintaned by me. If you want to move them and/or setup a permanent area for tech goodies just say or PM me.

cheers,

ph2t.

[ph2t]

When I should of been working I’ve been stuffing around trying to get more info about these amd little machines.

I’ve found some datasheets on the TX6/RX6 series chips that are known to be in the 4-chan controller. (possibly the new MS’s as well?)

This datasheet is in Chinese so I don’t know how much use it will be, but some info is better than none.

Get it here.

Also, another company makes a pin-for-pin replacement to the TX6/RX6 chipsets, it’s known as the PT8A9701 (TX) and PT8A973/973L (RX). The reason why I post this is that the datasheet is in English and since it’s a pin for pin replacment of the TX6/RX6 I would assume that the timings and other essential info are compatible for the TX6/RX6. This should do till I get the English version of the datasheet for the TX6/RX6.

Get it here.

Cheers,

ph2t.

[ph2t]

Shenzhen Electronics (http://www.hlec.com.cn), finally mailed my some more info on the TX/RX chipsets.

Here is the full, official datasheet for TX6C/RX6C

Also there is the little known about TX5/RX5 series chipset which seems to have NINE functions (Fwd, Rev, L, R, Turbo, + 4 trigger functions!!!)
Here’s the datasheet

This would be great to get one’s paws on this sucker…. The ideas of what you could do are endless.

I’m trying to get Shenzen to send me some free samples (my day job in an Engineering firm sorta helps… :smiley2: )

Oh yeah, you need to re-install acrobat with the Chinese TRADITIONAL font version. I found that if I downloaded this version from acrobat it installs itself on top of the english version. You then get prompted when loading the PDF for either Chinese or English. It’s funny you need this font to read what’s in English :approve:, go figure…..

ph2t.

Edited by – ph2t on 04 April 2003 11:56:19

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