Thread Tools
Aug 23, 2019, 02:31 AM
Registered User
Thread OP

XPS module on a 2ch radio?

I am trying to use an XPS module (graupner IFS) to convert an old retro 2ch 27mhz transmitter. I managed to find a PPM signal inside the TX but itís not being accepted as a valid PPM signal by the module. Can the XPS module be used on a 2-channel radio or am I on a dead track?

If it is possible I need to figure out what is wrong with the PPM signal (it is not particularly clean) and perhaps add some electronics to tweak it. I am stubborn to get this retro TX running again.

Attached a picture of the module for reference

Sign up now
to remove ads between posts
Aug 26, 2019, 04:10 PM
The Graupner module is set for a specific signal (logic) level on the PPM input. If your 27MHz radio happens to use a very low current or really low voltage, the Graupner module will not work. Our Universal Module can be used with any PPM level.
Aug 27, 2019, 04:56 PM
Registered User
Thread OP
Thank you. So if I can tweak the levels of the PPM signal there is a chance it could work? I mean the 2 channel only is not the problem?

The PPM signal that goes into the RF part of the electronics looks like this
Name: IMG_20190827_103107 - Copy.jpg
Views: 11
Size: 1.60 MB

Compared to a standard PPM signal the pulse width is shorter (about 0.2ms). Total frame length is 18 ms and the voltage level goes from about 4v to 9.8v (2.7v at the lowest). Now this is all analog components and when I connect the module the signal changes into this:
Name: IMG_20190827_103359 - Copy.jpg
Views: 8
Size: 1.36 MB

The amplitude drops and signal is between 2v to 4v. Not ideal.

These are PPM high signals. I believe Graupner uses PPM low (inverted) signals. On the RF section in the transmitter I managed to find an inverted PPM-ish signal that looks like this once the module is connected:
Name: IMG_20190827_100204 - Copy.jpg
Views: 12
Size: 1.19 MB
Name: IMG_20190827_100246 - Copy.jpg
Views: 12
Size: 1.19 MB

9.8V high and 0.2V low. I thought this would work but it did not.

Any thoughts? Is the problem voltage levels, frame rate, pulse width or "curvy" shape? I figure I can tweak the signal to some extent by replacing some components on the board but what should the signal be like to work? Or is using a pullup resistor on the module something that could help in accepting any of the above signals?

Aug 28, 2019, 02:40 PM
It could be current. The input to our RF module has to have sufficient drive current (the input is a transistor). The "low" value needs to be as close to 0v as possible. 0.2v is about the absolute maximum low pulse you can get away with.
Oct 11, 2019, 07:57 AM
Thermals, Tom
RyanNX211's Avatar
you probably want to do it yourself, but Tony Stillman has converted a lot of these old metal box transmitters to XPS. The Krafts he's done for me have performed well. And old gold Futaba with the plug in module hasn't worked as well (rudder and elevator will only move from center to full deflection in one direction)
Latest blog entry: Steak and Old Timers

Quick Reply

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Is it possible to easily turn a XPS Futaba module to universal style module Ghia Xtreme Power Systems 13 May 30, 2017 10:25 PM
Discussion Maiden of my new xps module on the profi 4k danielphantom Xtreme Power Systems 3 Dec 12, 2016 11:56 PM
Discussion Putting a XPS module in a FrSky radio? Uff-Da RC Xtreme Power Systems 17 Apr 06, 2014 03:53 PM
Discussion Hobbyking 2CH 2.4GHZ Radio on Boats? Taiping Dock Talk 6 Jul 13, 2010 09:24 AM
Discussion Meter on Airtronics does not operate with XPS module installed RICHARD3851 Xtreme Power Systems 3 Nov 26, 2007 12:22 AM