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6400 two antennas

I have owned my new 6400 for 4 weeks and cant resolve this puzzle

I have two antennas one is an 80m dipole and the other is a vertical for 20/15/10m

I want to operate SO2R with one slice/receiver on 80m using my dipole for TX/RX and below that slice/receiver the other slice/receiver using the vertical for 20/15/10m.

I find that although I can set up the two slices to TX on different antennas I cannot see a way to get them to RX on different antennas.

Searching the user guide and this forum has only provided confusing answers and I am sure it can be done because the radio is advertised and was sold to me on the basis of it having two independent receivers as in the snip of the Flexradio brochure below.

Any advice will be appreciated.

73 G4POP


  • Alan
    Alan Member ✭✭✭✭

    The 6400 has only one Spectral Capture Unit (SCU). Hence you can only use one receive antenna....because the receive antenna connects to the SCU.

    The SCU can support up to four slices, with each slice displaying different frequencies, modes, etc, within a 7 MHZ bandwidth.

    The M can display two independent slices. Hence the statement you quote about "Two Independent Receivers"

    Smart SDR, the Windows Flex application can display up to four independent slices.

    If you want to use multiple antennas, for greater then 7 MHZ bandwidth, you need a 6600 with two SCUs.



  • KD0RC
    KD0RC Member, Super Elmer Moderator

    Slight correction... The 6400 can display up to two slices (independent receivers), not four.

    The "independent receivers" refers to being able to listen to two frequencies at the same time (even on different bands), but not on separate antennas simultaneously.

    SO2R operation really requires a 6600 or 6700. These radios have two SCUs, and can receive on two antennas simultaneously. You can even transmit on one band while receiving on another at the same time. There are antenna proximity and transmit power considerations to be careful with when operating SO2R.

  • John KB4DU
    John KB4DU Member ✭✭✭✭

    The concept of receivers is different with a Flex. It’s sort of a cross between 2 vfo’s and two separate receivers. It’s like two separate receivers in that it’s possible to listen to two separate frequencies simultaneously. It’s like two vfo’s in that there is really only one facility, a signal capture unit (scu) attached to one antenna at a time. It is possible to listen on a separate antenna from the transmit antenna using the RX in for the receive only antenna. For example, on 40m I receive with a loop-on-ground and transmit on the 40m dipole. I haven’t tried receiving on one band, like 40m, and transmitting on another band. With guest staying in the shack/guest room,I can’t try it until later in the week.

  • Terry G4POP
    Terry G4POP Member ✭✭
    edited July 2021

    Just the sort of answers I expected and whatever you say the 6400 (Not the M) is specified to have 2 INDEPENDENT receivers and it does not.

    The SO2R facility is of no use because It is not possible to watch or work multipliers on a band not covered by the COMMON RX aerial.

    Basically the radio is misrepresented and I shall ask for a full refund and move on to something that provides the facilities falsely claimed by Flexradio.

    This is a pity because otherwise the radio is very nice so thank you for your clarification shame I had to waste your time and my pension!


  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    This is how I explain it.

    The 6300, 6400(M), and 6500 have 1 Spectral capture unit that sample the entire HF spectrum from 30Khz to 54Mhz all the time.

    You can use 2 slices or receivers on a single SCU radio on any part of the HF spectrum you wish. The only limitation is that you have to use the same antenna to do that.

    If you have a 160M to 6M multiband antenna, you can receive 160M and 6M at that same time.

    If you go to a 2 SCU radio then you can use 2 different antennas at the same time. They are independent of each other. You can do whatever mode you wish.

    That is the simple way to explain it.

    For full-fledged SO2R, you will need a 2 SCU radio. However, I have run a lot of contests with N1MM in SO2R mode on a 6300. I was just not able to receive while I was transmitting since you do not get the isolation you require on a single SCU radio.

    I hope that explains how it was designed.


  • Terry G4POP
    Terry G4POP Member ✭✭

    Yes Mike I understand the concept NOW but unfortunately the sales literature does not reflect that, it clearly states 'Two independent receivers' and that is what influenced my purchase.

    The buyer should not have to learn after the purchase that it does not do what it says on the box.

    No further comments are required as I have contact Flexradio direct and await their reply after they return to work, presumably tomorrow!

    73 Terry

  • Terry G4POP
    Terry G4POP Member ✭✭

  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    Hi Terry

    I am not sure what to say. We do a lot of online presentations and media on YouTube and Facebook where we discuss the differences between and 1 SCU radio and a 2 SCU radio and the limitations of both.

    BTW, I work for FlexRadio and if you wish to take this offline, please email me at [email protected] and I will discuss it with my VP.


  • Terry G4POP
    Terry G4POP Member ✭✭


    I am corresponding with Dan Quigly so will keep with one contact path but really the conversation is over.

    Bottom line is the brochure states INDEPENDENT and the receivers are not because not only is there the aerial restraint but also the RF gain is fixed, e.g. change the gain on one slice and the gain level on the other slice changes to match so if you need -8db attenuation on 80m but +16db preamp on 15m you can't have it which makes a nonsense of SO2R


  • Terry G4POP
    Terry G4POP Member ✭✭

  • Neil D Friedman N3DF
    Neil D Friedman N3DF Member ✭✭✭

    The product comparison chart on the Flex radio website (the link to it on the website homepage is “Which Radio?”) shows that the 6600 series is capable of SO2R while the 6400 series is not.

    GERRYV Member ✭✭

    If I use an antenna connected to antenna port 1 and 2, on my 6400, is there a danger of damaging the radio with RF on the port not in use? Let’s assume the two antennas are two inverted vee dipoles, one north/south and the other east/west on the same vertical support. May seem like a dumb question but, I recently suffer damage to port 2, and cannot figure out how it happened?

    Gerry, W0GV

  • KD0RC
    KD0RC Member, Super Elmer Moderator

    Hi Gerry, The 6400 only has one Spectral Capture Unit (SCU), so in non-Full Duplex (FDX), the TR switching covers ANT1, ANT2, XVTR and RX. While you are transmitting, all other inputs are made safe by the TR switch.

    If you are using Full Duplex, then you would use the Full Duplex Power Calculation Worksheet to be sure that you are not exceeding any limits.

    If you are not using FDX, you should be just fine. If you are using Full Duplex, fill out the worksheet to be sure that you will be OK.

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