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Flex 6700 with DEMI 2MLDPA for EME

Mike PresnellMike Presnell Member
edited February 9 in SmartSDR for Windows
Looking for some tech assistance from folks who have been operating their Flex for EME.
I will preface everything by saying i have NOT yet attempted to operate. I do not want to **** the preamp before I ever get started.

I have a Flex 6700, DEMI 2M LDPA, BEKO 1.5K Amp,  BEKO Mast Mounted PreAmp

I have the BEKO PreAmp wired to receive 15VDC from the BEKO AMP, it has a built in sequencer to turn off the power to the preamp before it keys the amp.

So, I was thinking that my Flex will key the PTT to the BEKO Amp.  The BEKO Amp will turn off the power to the preamp, and then it's PTT Out will key the DEMI 2M LDPA.

Will this work?  Is the low level drive of the 6700 enough to **** the mast mounted preamp since it will be keyed before the BEKO?




  • WA2SQQWA2SQQ Member ✭✭
    edited December 2019
    I’ll defer the final response to someone else, but I will offer one piece of advice. Use a solid state buffer device between your Flex and anything you connect to the TX1-3 outputs. If you damage the TX outputs, you’re looking at a trip to FRS to replace a $2 part. I have one such buffer with 3 relays that isolates all 3 outputs. I think it cost be about $12.. The relays can safely switch 10A.
  • EA4GLIEA4GLI Salvador Member ✭✭
    edited December 2019
    Add 100ms delay to the tx just for safety, you can easily do that on the menus of the 6700.
  • Mike PresnellMike Presnell Member
    edited December 2019
    Thanks for the advice.  Is there any particular device that you recommend?  Which are you using?
  • paulpaul Member ✭✭
    edited December 2019
    I use a Ameritron ARB 704 in key line to amp. Check and see if Beko preamp relays can handle high power during transmit. Eme is a 100% duty cycle. I have 6500 connected to sequencer for it to key. Whole trick is to have transmitter keyed last in sequence.I have been using SSB MHP144 preamp for quite a few years. Let me know when you get it  up and running on eme for a contact from Delaware. 73 es gl, paul,wa3qpx , DXCC on 2m #141 now up to 151 entities confirmed via cards
  • Larry Loen  WO7RLarry Loen WO7R Member ✭✭
    edited December 2019
    I would figure out what the delay actually is. Our setup (I work with a team) ended up needing 350 ms delay after PTT was off before it was safe. With JT65, a substantial delay hurts nothing anyway.
  • Erika - KØDDErika - KØDD Member ✭✭
    edited December 2019
    Mike I have considerable experience with high gain type terrestrial and some EME QSO's all with tower mounted preamps.  You will not desire to send any RF up the backside of a preamp.  It will not be there when you lift the PTT.

    It would take writing a book about HOW to do it properly.  Don't know if this is exactly the place to start writing.  We could get on the phone and discuss it in depth and I'd need to put together some documents I have here.  and email them...  I'll need to look at the items you already have and you can sort of plan what you still need to get.

    I ran Heliax lines for transmit and LMR-400 receive lines all with N-Connectors.  The receive lines did NOT have power amplifiers inline...  only a very good relay in the preamp boxes.

    Whenever anything less was tried Somebody would come in the station and **** up a preamp. 

    Best to Keep things completely foolproof.  I've put this together at our farm, with multiple towers, and at our last location with a single tower.  I've found the dual coax setup with a sequencer is the best way to go.

    Sincerely Erika DD
  • Mike PresnellMike Presnell Member
    edited December 2019
    Thanks Paul, I will take a look at the ARB704!   The BEKO preamp specs states that it handles 2.0K … although the label on the case shows 2.5K  It's supposed to work well with my BEKO 1.5K amp which is supplying the 15VDC.   I should be able to get everything in sequence without a separate "sequencer" since that function is built in to the BEKO Amp.    My only concern is,  IF I ever messed up the delay setting in the Flex settings,  is the low-level drive of the 6700 enough to **** a mast mounted preamp?   I guess I need to check the 6700's specs, to see how much that drive is, and ask BEKO,   but I thought I would ask on the User Board here as well, since there are a lot of experienced users like yourself here.

  • Ha GeiHa Gei Member
    edited December 2019
    The drive from the Flex never reaches the preamp. The preamp is in the 144 mhz chain and you drive the transverter. Thus there is no difference to any other HF-XVTR combination. Also as stated befora, you can set up txdelay  and/or use 2 Relays in sequence.

  • WA2SQQWA2SQQ Member ✭✭
    edited December 2019
    https://www.ebay.com/itm/1-16-Channel-5V-12V-Relay-Module-Board-For-Arduino-Raspberry-Pi-ARM-AVR-DSP-PIC-/163629279846 Just select how many channels and whether you want 5 or 12v to run the board.
  • KF4HRKF4HR Member ✭✭
    edited December 2019
    I'm in the process of assembling an 2M EME setup.  For sequencing I decided to leave that chore to hardware, not software.  I'm using this programmable sequencer:  https://www.dxengineering.com/parts/dxe-tvsu-1b

    And I 2nd the comment about the Ameritron ARB-704 Keying Buffer.  I've used these to key amplifiers connected to my Flex-6700 for years.  It's simple to connect and provides the necessary protection.

    Check back in and let us know how your EME experience goes! 

  • KF4HRKF4HR Member ✭✭
    edited December 2019
    Mike - a follow on comment.  I recently took delivery of an ICOM IC-9700 and have been comparing its receive sensitivity to my Flex-6700 with the 2MLDPA.  I've only run tests with distant FM repeaters.  My tests indicate the ICOM IC-9700 has a much more sensitive receiver compared to the Flex6700 & 2MLDPA.  For example a distance full quieting repeater on the IC-9700 is barely breaking the squelch on the Flex-6700/2MLDPA.

    Conditions: SSDR set to NFM, and receive preamps turned on in the 2MLDPA and IC-9700, squelch level closely set to squelch threshold on both, same antenna switched between these two receivers.  

    There's a chance my particular 2MLDPA may not be as sensitive as it should or could be, so I'd be interested in hear from anyone that has made a comparison between the 6700/2MLDPA and some other 2M receiver. 

    In any case, since your goal is EME I highly suggest running your own tests and compare the receive sensitivity of your 6700/2MLDPA to other 2M receivers.


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