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.
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Roy Laufer

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"All's well that ends well."

I am glad that the powers to be have come up with an elegant solution to the problem.

In the end, I am fine with my setup, which only requires a single Rx and XVTR port and spares the other RCVR port - perhaps for that pre-distortion correction implementation, when using a linear amplifier, one of these fine days.

Have fun talking to things circling this crazy, crazy world <grin>!

Vy 73,
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K6OZY, Elmer

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The problem with this is that we ordered our 70CM DEMI XVTER with combined IF.  This design requires split IF.   Uggggggh....
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EA4GLI - 8P9EH - Salvador

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I got lucky. Along the way I figured I was better off with separate IF on the 70cm transverter.
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Just removing a relay in the 70CM DEMI XVTR with combined IF and ad a BNC would solve the problem.
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EA4GLI - 8P9EH - Salvador

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Good point. I was going to suggest to Chris to send it back to DEMI to make it separate IF and then have them return it together with the new purchase of the DIPS.
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EA4GLI - 8P9EH - Salvador

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I started this thread a while ago to try to understand the best way to work SATELLITES with a Flex 6700 and DEMI gear.

After a long process and a lot of help from the community I have reached a point where I am OK with the final result. I created a hand written diagram which I will try to put into VISIO but I thought that it might help others in their station integration.

I also included HF to get a whole idea of the station.

From Downeast Microwave I bought:

2M LDPA - 144MHz Amplifier (75w)
L432-28HP Transverter (60w)
DIPS (Diplexer/Switch)
10-4 10MHz HUB

As far as options go I went for the FTDI USB controller for the 144 Amp and common TX-RX Antenna port.
I selected wide RX filter on the 432 Transverter to cover from 430 to 450
Common Antenna (RX/TX), Split IF (RX - TX), AplLO board so I can use either the internal TCXO or inject a 10MHz reference from the GPSDO option of the 6700.

The 10-4 10 MHz HUB allows me to send the 10 MHz reference from the 6700 into (L432-28HP, 1.2GHz tranverter and Flex 1500) with a port to spare.


I use a small Coaxial Relay (AMRA MTI ZR30-5523-00) so that I can use the LOOP feature of the Flex 6700. It is pictured as coaxial relay above. These small relays cannot take much power IN but for RX they are perfect, DC to 26.5GHz, they work with 12v and they are very small. I use the KMTronic Web 8 Port Relay to turn it on and off. In combination with PSTRotator I can have the software read the frequency of the Flex 6700 and automatically decide if that tiny relay needs to be on or off. This is very useful because I can then daisy chain FILTERS for HF. I have a homemade AM Broadcast Filter (MW band), RX Only, that stops all the local AM broadcast signals and considerably reduces noise in HF. By having them in the RX LOOP I do not need to worry about power handling. It will also apply the Filter to any of the 4 HF antennas I use, all I need to do is to enable LOOP A in SmartSDR to ANT1 or ANT2.


@Mark, As you can see in the diagram the XVTR from Flex goes as follows:

6700 XVTR > DIPS XVTR > DIPS LDPA OUT > 2M LDPA > BYPASS to > 1.2 GHz transverter IF IN

6700 XVTR > DIPS XVTR > DIPS 28MHz OUT > L432-28HP TX IF 

6700 XVTR > DIPS XVTR > DIPS RX OUT > RX A (144 MHz)

What the DIPS does is when I am TXing 144MHz from 6700 XVTR Port it will send that signal to the 2M LDPA. But when I am RXing 144 it will send that signal to the RX A in the Flex 6700 instead of going back to the XVTR port that way I can TX in 432 (28MHz) and listen in 144 for FULL DUPLEX.
When I TX in 144 the USB port will send a signal to the 2M LDPA through the USB cable and engage the PTT on that amp and it will then send a PTT signal with the RCA cable into the DIPS PTT RCA IN port.

When I am in a frequency that IS NOT 2M 144MHz it will turn OFF the 2MLDPA and the XVTR signal will BYPASS the 2MLDPA and go on to another device. In my case an SG Labs 1.2GHz transverter that takes 144 IF. This is a temporary transverter as I only get 3w out of it. It will eventually get replaced by a DEMI 23cm Transverter.

When you connect the 2M LDPA USB cable into the Flex 6700 is shows up as LDPA Type USB device.
 If you double click that it will provide you with the option to rename it and the most important, to turn ON or OFF the internal Preamp. I have the amp next to the 6700 and not the antenna so the preamp this far from the antenna is counterproductive. It is better OFF than ON most of the time.

It would be great if I could automate the Preamp ON OFF or if I could have a button available in the main SmartSDR screen to turn it ON or OFF without having to go through a bunch of Menus. Maybe in a future version of SmartSDR *wink wink

This is what SMARTSDR looks like for a typical Full Duplex SAT

That signal you see there is CAS-4A Telemetry. it just happened to be going over my QTH when I was putting this text together.

You can see here PSTROTATOR in action as well:

I have a long list of SAT profiles I call upon when a SAT is visible from my QTH.
PSTROTATOR moves the antennas, I have a Yaesu G/5500 and EA4TX ARS-USB controller for that.

PROFILES are very important because they answer your TX (PTT Relay) question.

144 MHz doesn't need to use any of the 3 TX relays from the Flex 6700. In my case (as presented in the diagram) TX1 engages the HF Amp, TX2 the 432 Transverter and TX3 the 1.2GHz Transverter. The DEMI gear has a sequencer, so if i where to add an amp for EME, I will use the DEMI sequencer for PTT Relay of the amp.

BUT there is no easy way to assign TX1, TX2 and TX3. You are left creating Profiles for each case. For each SATELLITE I create a Profile. The profiles have the TX settings. If the SAT uses 145 MHz for TX then the RCA TX 1,2 and 3 and DISABLED. If the SAT uses 435 MHz for UPLOAD then RCA TX2 is enabled.


For HF I have an SPE Expert 1.3k. There are some neat features, very useful in combination with the Flex radio. I am utilizing all RX ports with VHF and UHF so the SO2R port on the SPE Expert amp is very useful here.

When I select INPUT 1  / ANT1 in the Expert AMP it will automatically connect SO2R ANT to INPUT 2.
By connecting INPUT 2 to ANT2 in the Flex 6700 I am making ANT2 of the Flex my 3rd RX antenna. This enables Diversity. I can listen to a 80m signal with both the T2FD and the Magnetic Loop. The SPE Expert is connected to the Flex radio by USB cable which automatically will select the correct TX antenna and power levels. 
The SO2R port in the Expert amp is an RX port, so I don't have to worry about mistakenly applying Watts to the Magnetic loop and blowing the PreAmp.
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OK your diagram was beyond helpful.  I'm going to use a very slightly less complicated setup but basically what you drew.  I just ordered all same stuff you did from DEMI and now Q5 signal.  I have a feeling its going to be a minute or two before I see any of it.  But, they make good stuff and have been around for many many years.  In fact I did business with them way back in the 1980's I think.  

I'll be back with operational questions I am sure when I get closer but wanted to pass along a thanks for the great diagram.

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EA4GLI - 8P9EH - Salvador

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I am sure you will enjoy it. It is quite spectacular to SEE in VHF and beyond. Too bad we cannot open receiver beyond 24,000 on WFM as it is a bit narrow for NOAA reception. I really would love if future versions of SmartSDR look at Sat work and VHF-UHF as there are some usability improvements that will make using the Flex for satellites a better experience.

I am kind of surprise Steve N5AC has not "pushed" for some Sat flavor update of SmartSDR as he designed the AplLO board for the DEMI and worked with them on the DIPS, so I believe he is a Sat operator as well.

Maybe soon....
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Maybe I goofed, I ordered the 1296 with a 28 mhz IF.  Can the LDPA pass 28 mhz through its bypass port?  If so that should solve the problem.
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EA4GLI - 8P9EH - Salvador

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Well, it will not if you are using the DIPS which routes 28MHz and 144MHz through different ports.....
If you are going XVTR out into LDPA and then from BYPASS of LDPA to 1.2GHZ XVRT you should be OK.