What is Pos/Neg shift?
 

What exactly is positive are negative shift. I have a JR XP7202 and I am looking for a receiver for a parkflyer foamie. I tried the Berg4L with my radio on channel 20 on the receiver and channel 20 on the radio and the receiver is not working. I don't know if I have a bad receiver are if the receiver does not work with my model radio. Has anyone used the berg with a JR XP7202 radio? JR radios are positive shift right? Positive/negative shift has nothing to do with the servos right? I have hitec servos on my Extra 260 foamie. I also messed up by getting the berg4l because I forgot about the throttle, so I need to get a 6 channel receiver, because I got 4 servos and esc. I was looking at the JR 610 sport, unless you'll have other suggestions.

Thanks, Mike

RE: What is Pos/Neg shift?
 

What is Pos/Neg shift? Well I don't have the technical expertise to know exactly but it has to do with how the signals are encoded by the Tx and decoded by the Rx. yes JR uses Pos shift and must have a Pos shift receiver to function. Futaba and Hitech use Neg shift with a few exceptions where I've seen Hitech being shift selectable by use of a curcuit jumper.
Your servos do not care what shift you are using. I have never used a Berg Rx so take a look at it and see if it says Pos or Neg Shift on it. I have also seen on GWS receivers where it will have Fut or JR printed on them to designate shift modulation.

RE: What is Pos/Neg shift?
 

The Berg Microstamp 4-channel receiver is supposed to autodetect the shift of your transmitter and select it automatically. It is compatible with Airtronics/JR or Futaba/Tower/Hitec transmitters.

If the receiver isn't working as expected, you might want to make sure that your transmitter is set for PPM/FM instead of PCM. The Berg receiver will only work in PPM/FM mode. You'll also need a flight pack battery or your ESC and LiPo cell connected to the receiver to power it during testing.

When used with a four servo airframe, most pilots will simply use a Y-connector for the two aileron servos so a 4-channel receiver will be fine.

RE: What is Pos/Neg shift?
 

;)The shift you ask about is a result of the receiver mixer stage. This is where the signal info is converted to "IF", intermediate frequency, for decode or processing. This can be gotten by adding or subtracting the crystal freq. in the receiver, hence + or - . The Jr 72702 can also go POS or NEG in the modulator. This goes hand in hand with the receiver.

RE: What is Pos/Neg shift?
 

Sorry, but no, the "shift" is in the way the transmitter sends the signal, specifically which way the frequency is "shifted" from center to encode the data.

On our FM and FM/PCM radios, the transmitter actually broadcasts on 2 frequencies, the "center" frequency, and another one 5khz away. Positive shift transmitters use the center frequency and another one 5khz above the center, while negative shift uses a frequency 5khz below center.

For example, channel 12 is 72.030Mhz. That's the center. A positive shift TX on channel 12 will be putting out signal on 72.030Mhz and 72.035Mhz, while a negative shift TX will be using 72.030Mhz and 72.025Mhz.

As noted, some receivers will check both above and below the center frequency to see which one the transmitter is using.

Exactly how the transmitters are using both frequencies is detailed here, which is a great article about how our TXs and RXs work (not including the new 2.4Ghz systems):

http://www.torreypinesgulls.org/radios.htm

RE: What is Pos/Neg shift?
 

Thanks for all the info. It all makes sense now.

I got the berg to work by changing my radio to PPM.

Thaks, Mike

RE: What is Pos/Neg shift?
 

I also have an XP7202, and that's one of the first issues I ran into. The radio will always default to SPCM, so I had to change it to PPM for all of my receivers. Just something to remember for the future. ;)