How-To 2m and 70cm DEMI Transverters on a 6700 & Questions

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I have researched the forum for Transverter installation options/ideas and there are several threads floating around with information. It is a bit scattered so I thought that I would put my findings and decisions on a new thread that might be helpful to others.

The goal for me is to add the 2m and 70cm capability that I get out of my TS2000 to the Flex 6700. I want to have an all mode HF, VHF, UHF rig capable of working repeaters, SSB DX and SAT (even EME).  

After talking to FRS (Thanks Dudley) and DEMI (Thanks Sandra for your help) I have a better idea on how to proceed. But I would like suggestions or comments if you guys find holes in my current configuration idea.

The 2m part will be covered with the Amp-Preamp DEM 2MLDPA. In my case I went for the 60w version.

I added the following options:
  • LDREM-OPT for remote ON/OFF
  • LD-HP Common RF for a single connection to antenna
  • XVRT IN and XVRT OUT ports (Default)
For the 70cm part I selected the L432-28HP which is the fully assembled 28Mhz IF 60w output 440 Transverter.

The image above doesn't have the TX IF and 10 Mhz ref input BNCs.

I wanted to be able to use it with the 6700 and the Flex 1500.
I added the following options:
  • Split IF configuration (this is important for Full Duplex)
  • IF Drive 0 - 100mW
  • HP Common RF Configuration (Single antenna)
  • DUAL LO OPTION: Allows the use of either the internal clock or external 10Mhz source.
  • Optional filters to be able to work at both ends of the band for SAT work and Repeater work.
  • I also went with the larger heatsink. 
I also added a 10Mhz reference HUB. The DEMI 10-4:

This is a very interesting device if you happen to have the GPSDO option in your 6700/6500. It allows you to use the 10Mhz reference from the Flex radio and input that into 4 devices. In my case I will use it to send a 10MHz ref to the 70cm transverter, the Flex 1500 and the Kenwood TS2000 with this TXCO replacement (

Remember to add BNC 50 Ohm 1w  to the unused ports.

Now on to the schematic for the connection with the Flex 6700.

Which finally brings me to my questions and concerns:

  1. I have to share the XVTR port for both 2m and 70cm so, how do I tell from the 6700 to engage TX2 or TX3 based on the panadapter that is TX in SmartSDR? Those are the blue lines on the schematic.
  2. I see how if I TX in 2m I can RX in 70cm because I will TX out of XVTR and RX on RXB on the Flex (green line). But what about TXing in 70cm and receiving in 2m? Do I need another port in the DEMI 2m Amp to send the receive preamped signal into RXA? And if I do that? Where do I put a Magnetic Loop for RX?
  3. Am I missing anything in my configuration? Is this doable? 
  4. I have tested with dummy loads and I can move both the TX and RX frequency in 2m and 70cm while I transmit which should allow me to move to compensate for doppler effect when working SATs, but I can't move both panadapters at the same time... I can't find a way to sync them to move them simultaneously. I guess orbitron/sat32/hrd sat will have to take care of that. 
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EA4GLI - 8P9EH - Salvador

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Posted 4 years ago

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Steve - N5AC, VP Engineering / CTO

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Official Response
With SmartSDR v1.10, we will be introducing the capability of adding cables to the FLEX-6000 that will provide CAT and/or BCD/binary outputs.  The system is quite flexible and we'll do a post on this soon, but I wanted to point out a couple of products that Downeast Microwave has that will allow simultaneous, full-duplex 144/432 operation on the FLEX-6700.  The first is the DEMI LDPA (low drive power amplifier) which can be found here:  This amplifier will put out high power on 2m from the low output on the FLEX-6700.  If you order the LDREM-OPT with this, the unit will ship with a USB cable that plugs directly into the FLEX-6700 which will allow complete automatic and/or remote control of the LDPA from SmartSDR.  

The second one is a new switch/diplexer that allows operation of a 432/28 transverter in conjunction with the LDPA, model name DIPS:  With both of these and a 432/28 transverter you can have a full-duplex 144/432 station for satellite or terrestrial operation.  The DIPS PDF above shows how to connect the system.  We expect to have a more complete description on how to do this including the software setup in the next few weeks.