EduardoLM

Good day to everyone! This is my first post in this forum, and I would like to apologize if this question is too basic or naive.

I have acquired 2 used Futaba radios (2DR model) and also some Futaba receivers (R122JE model). They are AM and supposedly calibrated for the 75MHz band.

However, they work erratically, and the behavior changes as I swap crystal, transmitters and receivers. I think they need to be calibrated.

Since I have some electronics knowledge, I would like to ask about the general procedures on how to calibrate both transmitters and receivers. I suppose I have to tune LC filters for a narrow output for the nominal frequency, to maximize power on that frequency and reject nearby frequencies.

I also suppose I need and RF generator, oscilloscope and/or a spectrum analyser to do the job.

Am I on the right track? Is there any info, manual or online tutorial on how to do that?

Many thanks!

Eduardo

Roelof

You are sure that both transmitter and receivers are 75mhz? Looking at the Futaba site I only see a 27mhz version of that transmitter.

But OK, if they all are 75mhz be sure you have AM crystals. Be also sure you have a TX and a RX crystal (they have a 455khz difference).

And sometimes the 1st thing to do is get a fresh set of crystals. On the other hand, for almost the same price you have a simple GT2 transmitter or if you want sticks Futaba has a 2.4GHz stick transmitter for just 40 dollar.

Andy Koback

iTrader: (280)

When changing crystals make sure they are matched pairs. Each frequency has a receive and transmit.

EduardoLM

Thanks for the replies.

Yes, the transmitters are (or were) 75MHZ when made, the box has a label mentioning the frequency of the crystals that originally came with the transmitter.

The receivers (R122JE model, bought used at eBay) I have no idea, but I have found some pages on the internet mentioning 75MHz and 27MHz versions of them. So I may or may not have the correct ones, and I would like to use my electronics gear to find out.

I'm also sure I'm using AM crystals, matched to TX and RX. The RX ones have a sticker that I use to easily pull them from the mounting on the receiver. The TX ones are bare crystals, no sticker.

Thanks for any help you can give me!

Eduardo

Roelof

Normally the receivers are also maked for which frequency band, if you have the wrong ones then yes, there is your problem.
I believe it can be seen at the length of the antenna... yep:
https://traxxas.com/forums/showthrea...antenna-length

tamiya wrc

Hello!

I don't know if my question is regarding to this topic but still I am searching the answer to this problem:
- I have 2.4 GHz 2 channel radio transmitter and during the use I always open the antenna to full length (even during calibration the transmitter and ESC is recomended to do the setup at full antenna length)
- I always turn on first the transmitter switch and then turn on the ESC switch on my car
- I have set up the transmitter trimming function always in neutral position
- I have a filling that the steering servo is always slightly off the position, the position of servo is sometime different if I turn on and off the ESC and transmitter...why the position of servo motor is not always the same...what cause this difference in position of servo motor...any advice?

Thanks.

540bilotilo

for tamiya dude above
if im understanding right when you turn off the radio the steering does not stay centered?
if thats the case its cause you radio has a built in fail-safe. it positions everything where it was when binded.

hope that helps

firemanfires

iTrader: (2)

I think it also depends on the brand of radio you have.

tamiya wrc

Hello!

I added some pictures for better understanding my problem: picture 1: proper steering setup the servo motor is straight, picture 2: when I turn again the transmitter and ESC the position of the steering servo is slightly OFF the centre it is not the same as it was set up at the first time like picture 1.

Thanks for help!

Roelof

Do you have something like a 995mg servo? That model is very well known with its center issue.