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DEMI 70CM Setup with Flex 6700

Mike PresnellMike Presnell Member
edited August 2018 in SmartSDR for Windows
I am having difficulty getting my DEMI L432-28HP configured with my Flex 6700.  There has been "some" discussion in the past, but nothing complete posted in the forum.

Specifically,  what Transverter settings in the Flex Radio Setup?

Here is what I have (and don't have):
RF Freq (MHz):  432.000
IF Freq (MHz):  28.000
LO Freq (MHz):  404.000
LO Error (Hz):  ????
RX Only:  Disabled
Max Power (dbm):  ???
Rx Gain (dB): ???

Also curious about IF cable connections.  My unit has Common RF and Split IF.

For cabling:
DEMI PTT:  to  6700's RCA TX3  (PTT is working)
DEMI REF:  to 6700's 10MHz out (The DEMI Lock Blue Light is on....working).
DEMI IF:  to 6700's transverter port.
DEMI TX IF:   Not connected

Any help is greatly appreciated.  Thanks!


  • Mike PresnellMike Presnell Member
    edited April 2019
    At the same time I posted this question here, I also sent the same question to Q5 Signal who makes these transverters now.

    Here is the information from Corey at Q5 in case anyone might need these details sometime later:

    " Hi Mike,    Here are the settings that you are missing:   

    LO Error is 0Hz

    Max Power is 0dBm

    RX Gain is 23dB

    The Transverter's TXIF connects to the Flex XVTR port.  And the Transverter's IF connects to the Flex RX-A or RX-B.

    Thanks!  Corey Abercrombie   Q5 Signal, LLC

  • Sergey R5AUSergey R5AU Sergey Member ✭✭
    edited August 2018
    Hi Mike ! I have DEMI L432-28HP as well and unit works successfully 

    I have separate one for full duplex purpose in combination with other bands and 0dbm TX input level.  In my case  
    DEMI IF TX - 6700 transverter port
    DEMI IF - to RX A

    In Radio setup you should enter RF Freq and IF Freq , RX Gain - just for compensation level of on PAN (Manual:  RX Gain (dB): this field is optional, but will correct the receive signal level reading in the Panadapter and Slice Receivers.) - you can adjust further to correct you zero noise level 

    and in my case I use universal tools like screwdriver and soldering iron where
    first one for tuning signals levels properly on DEMI side(TX (for TX power at 0 dbm output and max power on SSDR, and RX - to reach +10db increase of noise level on SSDR PAN after DEMI switch ON)   - access to variable resistors on the bottom side of the transverter)  however I was not satisfied with tuning and used "second tool" for changing attenuators resistors on DEMI PCB.
    BTW I need to mentioned what my DEMI unit some time start like oscillator after switch to TX and I found very usual problem in schematic - in RX and in TX parts of transverter in use integrated voltage stabilizers like 7805 (see schematic diagram), I have modified with add before stabilizer any resistors (20-50 ohm) and all input and outputs of stabilizers was blocked with capacitors (0.01 )
    all elements are SMD type.
    For now works perfectly  and many contacts via SAT in full duplex mode


  • WA2SQQWA2SQQ Member ✭✭
    edited August 2018
    Your LO Error is how you calibrate your actual frequency. I doubt it's 0. So set your transmit frequency to, say 435.0000. Measure the actual frequency. The "error" will be a positive or negative number, the actual number of cycles that you are off by. Wasn't aware that DEMI wasn't making them any more - they made some fine transverters.
  • Sergey R5AUSergey R5AU Sergey Member ✭✭
    edited August 2018
    Wayne you are right but in our case LO sync with GPSDO
  • WA2SQQWA2SQQ Member ✭✭
    edited August 2018
    Surgey if the local oscillator in the transverter is slightly off fequency which they usually are, isn't the L O error actually correcting that? GPSDO is actually controlling the Flex radio not to transverter, right?
  • Sergey R5AUSergey R5AU Sergey Member ✭✭
    edited August 2018
    No, Flex with GPSDO has output of 10mhz what synch LO (Apollo by N5AC) of transverter
  • WA2SQQWA2SQQ Member ✭✭
    edited August 2018
    Ok, but not all transverter s, right?
  • Sergey R5AUSergey R5AU Sergey Member ✭✭
    edited August 2018
    In DEMI case this is an option (LO PLL with ext 10mhz), but in my setup any RX/TX unit are synch with GPSDO with that I am sure completely with “True” of indicated freq )

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