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6400 vs 6600

Good Evening Flexradio community,

I have been toying around with the idea of purchasing a Flex 6000 series radio. I know the basic differences between the 6400 and 6600. Such as 2 slice receivers versus 4 slice receivers. I also know that the 6400 has one SCU vs two for the 6600. Plus diversity receive if I have 2 receive antennas. And I have also read that the filtering is different between the two radios. Though I don't understand what that means because I would think the filtering would be controlled via SmartSDR and would be the same for all of the radios.

I do like to operate contests. I do have 2 receive antennas. One is the HY-Z 3 element and a 250' beverage. I have a Ram 34 XL RX Preamp System. And with this I have both Receive Antennas connected and can automatically switch between one or the other. Plus with N1MM as far as I know you can only have 2 VFO's operating at the same time anyway. I hate to admit it, but am just unsure which would serve me better. Both now and the future also. I am not interested in operating SO2R, so that is of no concern to me.

I would like to hear users opinions on this. Thanks! Mark Griffin, KB3Z


  • KD0RC
    KD0RC Broomfield, COMember ✭✭✭✭
    edited March 31

    Hi Mark, You hit the highlights correctly. The thing that the 6600 gives you for contesting (especially SO2R) is 7th order vs 3rd order filters on the contest bands (80, 40, 20, 15, 10). These filters keep strong local signals from other bands out of your receiver. So, for example, if you have one station on 40 and one on 20, the 20 meter receiver can get clobbered by the second harmonic of the 40 meter transmitter. The 7th order filters can make the difference between a successful SO2R operation and having to go SO1R.

    The second SCU of the 6600 lets you use a separate antenna on each band of an SO2R operation. With the 6400, the single SCU limits you (even when using Full Duplex). Someone with actual SO2R experience would have to chime in to let you know if it is practical at all with a 6400 (I kind of doubt it).

    If you are interested in satellite work, the 6600 is the better choice as it has a pair of XVTR ports (one on each SCU). That way you can listen to your downlink frequency while you transmit.

    As a casual operator (can't even begin to imagine the panic of SO2R operation...), I opted for a 6400 and am very happy with it. If I had a 6600, it would be the diversity reception from the second SCU that I would be after.

    Last year a buddy of mine and I operated Field Day with our 6400s within 150 yards of each other and had very few problems, even when operating simultaneously on the same bands. If we were on the same band, same segment (CW, SSB), then my 500 W bothered him some. His 100 W didn't bother me until he was right on top of me. In this scenario, the 6600 would not have been better than the 6400. The higher order filters are only to keep out of band signals at bay, not strong in-band signals.

    The high dynamic range of these rigs makes them really great in multi-station environments.

    EDIT: Well, I guess I can't read... I just realized that you said not interested in SO2R.

  • Trucker
    Trucker Member ✭✭
    edited March 31
    The Contest grade filters in the 6600(M) are actual filters. They help with out of band interference. I could tell the difference between my 6600M and the 6500 I had previously. I have a couple of hams who live not too far from me. And I could hear them sometimes when we were on the same band. I no longer hear them with the 6600M unless I tune to their transmit frequency. Also, I had an AM broadcast station about 5 miles from me that I could hear faintly, and see on 80 meters with the 6500. I have never heard them on the 6600M.
    Having never used the 6400, I cannot say how much better, other than what you have listed, it would be as opposed to the 6600. I have had a 6300, it was a good radio. But, when I moved into the city, it couldn't handle the issues i mentioned above. (it's filtering was not as good as the 6400)
    The only other significant difference would be the cost. If that's an issue, then the 6400 wins. But, if you want what " I " consider the best current radio Flex Radio offers, then the 6600(M) is it.
    Good luck. Either one will be fun to use.
  • John KB4DU
    John KB4DU Member ✭✭✭

    Well Mark, there is no shortage of opinions on here, mostly valid for each ops situation. I have a 6400, because for me it is the practical compromise. Two panadapters are about all I can manage. For me, the M models occupy a lot of desk space with a box that is mostly empty, so I put my 6400 on a shelf under the desk. A Maestro combo is about the same price as an M model, and is more flexible arrangement. Plus the Maestro can go on trips for remote operating.

    The flex ecosystem requires a mental shift from traditional knob radios. The radio box is a server for the data to be displayed on the pc, iPad, Mac or whatever along with other software products. So the filters you mentioned are in the radio to be switched in or out as appropriate. This is partially automated by the radio. If the panadapters are on different bands, the filters are bypassed, and the SmartSDR software displays “Wide” to indicate such. If only one band is in use, the appropriate filter is switched in.

    Flex has a 30 day return policy, so it is ok to just get one and try it. With COVID havocing the parts supply chain, I’m not sure what is available.

    More opinions to follow.

  • Mark Griffin
    Mark Griffin Member ✭✭

    Thanks so far for all the comments and opinions. Yes, I realize that each radio fits to what their operating habits are. As for the additional Antenna ports, I only have one coax coming into my station from my tower coax switch. Very convenient if I say so my self. Have I really done a comparison between my Hi-Z and my Beverage. There are times I take a look and listen. But I basically use the Hi-Z 98 % of the time. Is that to say that if I had the additional features that the 6600 has, I really can't answer that question at least at this point in time.

    I guess I am just too old fashioned in the way I operate. I agree with the point about having 2 slice receivers being enough. I agree with that point. Yes, I agree having 4 would be nice, but would I really take advantage of that, I'm not sure. Operating SO2R is not something I am looking to do, so that function I would not take advantage of. Having better rejection filters on Man Made Interference would be nice. Maybe, what I'll need to do is flip a coin and pick heads for one model and tails for the other. HA HA on that thought. Looking forward to hearing more today.

    Mark Griffin, KB3Z

  • Don_N5SKT
    Don_N5SKT Member ✭✭

    One thing I like about having the 6600 is that I have 2 transverter ports and full duplex. That makes it possible to use the radio for Satellite work. I find it odd that the 6700 does not have 2 transverter ports.

  • KØKQ
    KØKQ Member ✭✭


    You've narrowed your search to two great radios. You won't go wrong either way.

    The Flex 6400 is the best **** for the buck ever in a radio. If you decide you want more SCU's, buy a second 6400 someday. Two 6400's are about the same money as the 6600. (keeping in mind the 6600 comes with an ATU, extra in the 6400 + 7th order order filters which may not be a factor)

    I paid $500 more for my 6300 six years ago than than the 6400 is now.

    6300 has been powered up 6 years (except lightning storms) at the remote site, sitting on a laptop cooling pad. Super reliable radio and software, always works.

    Went through the same thought process as you- bought the 6600, here's why:

    1. I don't 'churn' radios. I plan to have my 6600 a long time. Hardware platform that will endure.
    2. Dual SCU's give me more antenna selection flexibility. 
    3. Based on experience with Flex radio, I will continue to have an up to date relevant radio.
    4. All the things everybody said above!
    5. Just read the book "Die With Zero" I'm not leaving a bunch of money, I'm enjoying it!  😃



  • Mark Griffin
    Mark Griffin Member ✭✭

    Thanks Dave for the great comments. I understand your point of view totally

    Mark Griffin, KB3Z

  • Neil D Friedman N3DF
    Neil D Friedman N3DF Dayton, OHMember ✭✭✭
    edited April 6

    With regard to the 6700 having only one transverter port for satellite work, bear in mind that the 6700 has 144MHz built in, making 144/440 cross band satellite work relatively straightforward (with an external 144MHz amp).

  • Mark Griffin
    Mark Griffin Member ✭✭


    The 6700 would not be of any interest to me. If I do operate VHF/UHF it is usually DMR or Dstar.

    Mark KB3Z

  • Dave KC9EI
    Dave KC9EI Member ✭✭

    I do like to operate remotely when I'm on the road. I have a 6600M with a 2M transverter hooked up to keep me connected with the the locals while gone. I'm not sure if the 6400 has those capabilities or not.

  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin
    edited April 19
  • Mark Griffin
    Mark Griffin Member ✭✭

    Thanks Mike for the video uplink.

    Mark KB3Z

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