Home made transmitter???

[eyedoc]

I would like to build my own transmitter using parts from an old futaba radio and some stock servos and receiver.

I have an elementary understanding about how transmitters work so I would like for someone to help me out or point me to a link that explains how they work and how to build one.

If there is already a thread here that explains it that would be great.

Thanks for any input:D

[MattLarson29]

It's not that cut and dried.

You can build your own gear for the amateur bands, but you must have an amateur license first.

You can't build your own gear on 27/72/75 MHz. In order to be legal, gear used on these bands has to be type accepted by the FCC.

So technical issues aside, this project is a non-starter.

Sorry.

Matt

[eyedoc]

Matt,

Sorry for the confusion. WHat I want to do is canabalize two of my radios and make a 3rd one.

Nothing home brewed.

[MattLarson29]

If I understand correctly, you want to use parts from a couple of old transmitters to make one working one?

If they are the same brand and model, this migth be OK. If, however, you are trying to use the RF deck from a Futaba with the gimbals and encoder circuitry from a JR, then you woule br creating a new radio design, which would have to be type certified to be legal.

Matt

[eyedoc]

I have 2 futabas (72) that I want to piece together. all parts will be from the sam brand, both FMs......

[jester1a]

( I shudder to make this response) Even though they are from the same manufacturer, if they are from different models you would void the type acceptance of the resulting unit thereby making the unit illegal. It may work but things like signal level mismatches may drive the output out of specifications in frequency and/or deviation.
Another thing that is a problem is that it would void your insurance were an unfortunate accident to happen.
I'm with the other responders here-- trying to disuade you from doing this. Sell them both on E-Bay and buy something in their place.

JESTER

[eyedoc]

hmmmmmmmm.... oh well no help here...

[BMatthews]

If you keep the RF and encoder deck from the same TX you should be fine for your type acceptance. So just plan on moving the gimbals over. Or better yet since the gimbals probably won't fit the other box move the RF deck and encoder to the box with the gimbals already in it.

But before you do this use a VOM to check the resistance values of the pots in the preferred gimbals. If they match the ones in the "bad" box then you're good to go. If they don't match then forget the whole idea as you won't get the right response....

Unless they use the constant voltage at the one end of the pots and ground at the other so that there's a set voltage change at the wiper contact that matches the other gimbals. To check this you would have to run tests on both sets before you take them apart. And you'd have to know enough to understand why this is important.

Otherwise forget the whole thing. It's probably time you upgraded anyway.... :D

[MattLarson29]

The other issue is how old the radios are. In 1991 the bandwidth requirements were changed.

So it would be possible to build a radio from pre-1991 components that worked exactly as designed and yet it would still be unlawful (and unsafe) to operate.

Matt

[Mr.RC-CAM]

I have an elementary understanding about how transmitters work so I would like for someone to help me out or point me to a link that explains how they work and how to build one.
http://www.omegaco.demon.co.uk/mechtml/fmectech.htm
http://www.rchelibase.com/radio/radio.pdf
http://home.nordnet.fr/~fthobois/anglais/engl-index.htm

Not that you asked, but: Keep in mind that the FCC Part 95 approval will probably not be valid on your Tx creation. The Registration is based on the EXACT data supplied to the FCC at the time of the filing. Everything matters -- even photos of the Tx's enclosure and internal component layout are part of the FCC submission. Changes to an RF product would normally begin with the original mfg having a conversation with the test facility that prepared the docs. I mention this because a AMA flying site could deny the field to you if you tried to use your home made Tx.

RC-CAM

[eyedoc]

thanks

[vaughan@world.s]

Mr.RC-CAM

I have just read the articles in your links. I was particularly interested in a reference to the 7 channel encoder part NE5044N from philips. This part is no longer made and looks quite difficult to obtain. Might anyone know of a substitute part with similar features.

My interest is in how to implement servo reversal, dual rate and channel mixing with simple circuits.

Thank you for the references.

Brian

[Mr.RC-CAM]

There is no sub for the NE5044. It is a purpose designed IC that went away years ago in response to the introduction of cheap microcontrollers.

However, you can harvest one out of an old junker R/C Tx (just desolder the chip). Or, you can contact the various R/C repair firms and buy a replacement chip from them. I heard awhile ago that Futaba Service Center had them.

Servo reversing is done with a cross-connected DPDT switch connected to the stick's pot. One of the links I provided has info on implementing Dual Rates (or so I recall). Beyond that, channel mixing becomes very complicated -- I do not have any schematics to post.

RC-CAM