A.T.

The shift is the way the FM signal is modulated. Because the modulated signal is different, you cannot use a negative shift transmitter with a positive shift receiver or visa versa. Hitec and Sanwa transmitters are shift selectable and can be changed to match another brand of receiver in use whilst JR 72 Mhz & 75 Mhz TX are fixed positive shift and Futaba are negative shift. Hitec used to produce two types of receivers marked for Hitec/Futaba use with negaitive shift and the other marked positive shift for use with JR & Airtronics 72 & 75 Mhz TX. New Hitec 72 & 75 MHz RX now have auto shift and automatically change shift to match the Transmitter (caution = Golden rule applies now more than ever with auto shift, PLL and IPD receivers = TX On First - TX Off Last or the receiver may not lock on to your TX - picking up some other close to frequency signal instead). JR also now produce some receivers with either positive shift as used with 72 MHz for JR and Sanwa (aka Airtronics) and Negative shift for use by Futaba and Hitec on 72 Mhz. and 75 Mhz.
Regardless of frequency, all shift select TX are to be set on "SFT.N" i.e. 35 Mhz, 36 Mhz, 40 Mhz & 41 Mhz except when used with JR or Sanwa(Airtronics) RX operating on 72Mhz and 75 Mhz. Reference in need, "Transmit Shift SFT.N SFT.P" Eclipse manual page 11 download manual .pdf .
Much more information under "Radio Systems, Accessories, Alterations and FAQ" sub section "Receiver - FAQ, guides and aids to best reception" and "Transmitter - FAQ - Additions, Adjustments, Clonepacs & Repairs" amongst others on my web page.
Regards
Alan T.
Alan's Hobby, Model & RC FAQ Web Links