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Reviews For: FlexRadio FLEX-6400

Category: Transceivers: HF Amateur HF+6M+VHF+UHF models - non QRP <5W

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Review Summary For : FlexRadio FLEX-6400
Reviews: 25MSRP: 1999
Software Defined Radio Transceiver with 2 Independent
Band/Mode full performance receivers from 100khz to 55MHz
Product is in production
More Info:
# last 180 days Avg. Rating last 180 days Total reviews Avg. overall rating
W3DDF Rating: 2022-01-10
Excellent for remote operations Time Owned: 6 to 12 months.
I purchased a 6400 to be my remote operations rig. It has worked flawlessly in that capacity. I am able to use either Smart Link or VPN into my remote computer. Set up was easy and virtually no latency. If you need a remote ham radio option the Flex is the way to go.
K1BJS Rating: 2022-01-09
my experience with the 6400 Time Owned: 6 to 12 months.
I have been hesitant to send this review. I have been a Flex owner since the beginning of Flex SDR radios. I now have the 6400 and must say that when it is working , it is probably the best Flex product that I have owned.. I have owned SDR radios from Flex since the beginning.
From the onset, I have had issues with the software, particularly when operating remote. My comment is that this software has been out for several years now and it still has problems. It is not a mature product that works out of the box. I would advise future purchasers to know that this is not a plug and play for all issues. You need to have knowledge about software, Internet, etc.
Being a remote user for 4 months out of the year, I find that there are times when I must go to a total factory reset. You cannot do this! You must be able to push the button on the front of the radio to do this. Am I going to keep this radio? Yes because it is the best SDR out there.
KK9H Rating: 2022-01-05
Remote operation is really fun Time Owned: more than 12 months.
Every year I like to try something new in our hobby. Toward the end of last year one of my friends bought a second Flex radio due to a deal he couldn't pass up and then immediately loaned it to me to try. I have been very interested in trying out remote HF operation, but I am not much of a computer guy. The first thing that impressed the heck out of me is how easy it was to get this 6400 operating remotely. I have the SmartSDR app on my iPhone which works great, but I prefer using the SmartSDR on my laptop where, with a little help, I have been able to integrate WSJT-X, DX Keeper and JTAlert-X to be able to operate FT8 from anywhere. The Flex 6400 itself is a wonderful radio. It has superb receiver characteristics, transmitter performance and the built-in antenna tuner works very reliably. I have the Flex 6400 connected directly to my Xfinity router via an ethernet cable and that has provided very reliable access from wherever I am. One thing I have been quite successful with is adding to my 160M DXCC total using the Flex on FT8 which I can do from anywhere I happen to be and that has proven to be very handy. I have been a ham for over 50 years and this rig is not my primary rig, but it has provided a tremendous amount of additional fun. One thing I love to do is show my non-ham friends what I refer to as "the ultimate in nerdom" by pulling out my iPhone and demonstrating the operation of the Flex by working someone on SSB for them. I hope my friend will let me keep it for a good while longer. Maybe I should make him an offer he can't refuse!

I have had no transmit audio problems on SSB using either my laptop with a headset or my iPhone. I am careful about setting my audio level to not overdrive it and I left the transmit audio frequencies at their flat (default) settings.
KE9ND Rating: 2022-01-05
I Sold It After A Few Months Time Owned: 6 to 12 months.
I owned a Flex 6400 for about 9 months. I wasn't very happy with it for various reasons. I still have a Flex 3000 that I enjoy very much. The SmartSDR software needs much improvement, it is very basic with a lot of importance leaning toward remote operation. I get much better audio reports with my Flex 3000 than the Flex 6400, the audio section needs improvement. I got the blinking red led on powering it on a few times and had to do a factory reset to clear it, then of course had to reconfigure the settings. I hope Flex works on their software (and hardware) before their next radio is introduced. I thought the 6400 would be better than my 3000, but that was not the case for me.
UA3LM Rating: 2022-01-04
Great radio Time Owned: more than 12 months.
I have been operating the 6400 for several years and during this time there are no glitches ! FlexRadio has a great transmitter ! I don't know why people complain about the transmitter, probably losers. A lot of people buy sdr radios after conventional transceivers and cannot cope with the new technology .That's why they write about problems, but it's not about the radio))). Thanks.
DL6EAT Rating: 2021-12-06
Not good at all! Time Owned: more than 12 months.
I owned a Flex 6400 (non M version) for more than one year - it was simply disappointing. Modulation is never distortion free.....the best result was achieved by using Marcus's iPhone/iPad-S/W. But again - all the time people told me that the sound was not "crystal clear".
Also 3 friends of mine purchased the very same radio - same results!
I really wonder why so many people are just fine with that bad modulation! Have you never used an ICOM 7700, 7800 or an ANAN 7000? I also tried several different microphones (USB, Sennheiser, Rode, dynamics and electret and finally the iPad and iPhone 12 with Air Pods....)
To me it appears that the Flex 6400 / 6600-series has general build-in rf inrush problems what so ever.
After many, many tests I have never heard a crystal clean signal from any Flex 6400 or Flex 6600...

At the end I sold the Flex 6400 and purchased a pre-loved Flex 6300 again with S/W version 3.2.39. No problems at all with this radio! Perfect modulation with any of my microphones - no rf inrush! All fine.....
WD1V Rating: 2021-10-12
SmartSDR Mac Version 1.9.14 (124) Time Owned: 0 to 3 months.
I was an early adopter of Flex SDRs back with the 1000 and 5000 series. Since I've owned Kenwood 990s and TS-2000, a few Elecraft K3s, and Icom 7300 and 7610. All had strong points that make them great radios. But I returned to the Flex 6400 wanting to try the Mac version of SmartSDR.

As I enter my second week I have 3 takeaways.

1) Flex radios sound the best and not by a little, by a lot. The filtering, DSP, AGC, and richness of sound quality perform where I can't imagine better for a ham radio experience.

2) The Mac SmartSDR is superb. On my 27" iMac I can easily see (panadapter) and click select, filter (choose and fine tune filter), and operate with great signals in and out. DSP noise reduction is incredible - no garbled result - just less to no noise. Memories and profiles let you return to same freq/same settings. I suggest external PC stereo driven by the Flex direct.

3) Flex has a community web site for newest software downloads, FAQs, and find specific answers to your questions and gain insight as to how others are Flexing.

Hope to meet you on the bands. 73
MM0TWX Rating: 2021-09-27
Great radio, if you are not a CW operator Time Owned: 6 to 12 months.
The 6400 with Powersdr software make a formidable combination. Everything has been said already.

My experience however is that:

a) when switching to TX, the receiver doesn't mute entirely. Say that, on CW mode, I activate MOX: the radio stops receiving, but in the headhones I still hear some receiver noise. It's mildly annoying, but no more than that.

b) on CW, either full- or semi-break in, when the radio switches on TX the receiver stays on at full audio level for about 100-120 milliseconds, and then goes down to the mildly annoying level described above. This means that the first dash, or couple of dots of my transmission are heard in the headphones together with a burst of receiver noise.

This makes the radio very unpleasant to use on CW, my almost exclusive mode of transmission.

I made a video documenting the problem and posted it to the community - no answer. I opened a ticket with Flex and sent them the video. At the end of a long and useless process, I was told that "the issue has been passed on to the software development department" to be addressed in future releases.

Summary: great radio, useless for CW. What a crying shame.
G4POP Rating: 2021-07-06
Nice radio but beware! Time Owned: 0 to 3 months.
I would have given this radio a glowing 5 stars but the issue about being presented as a radio with TWO INDEPENDANT RECEIVERS?

These are my comments after the first two months of using a 6400 having previously used SDR receivers extensively with various software interfaces.

It must be understood that Flexradio decided not to use the normal amateur radio terminology, so a receiver is called an SCU and a VFO is apparently a ‘Slice’ “confused you will be”!

Hardware - Pros
Performance of the radio is particularly good being as good or better than my Elecraft for sensitivity, selectivity and rejection. Signal blocking is exceptional when adjacent station interference is present and no sign of any intermod at any time.

Connectivity with external hardware is easy and there are plenty of connection sockets of different types.
Construction is exceptionally good and durable with a nice case finish and illuminated logo.

When interfaces like microphone, key and speakers are connected directly to the hardware PTT the CW break-in behaviour is like any standard radio, there is however some latency when interfacing via the PC both on phone and CW.

Dedicated transverter socket is usefull as are the two aerial sockets and RX only connection.

The provided microphone is particularly good and produces nice punchy audio, also provided is a LAN cable, power lead and high-quality leatherette cover with embroidered logo.

Hardware - Cons.
My major issue is that 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. Although I can set up the two slices to TX on different antennas, there is no way to get them to RX on different antennas. Although the radio is advertised and was sold to me based on it having two independent receivers as in the Flexradio brochure.

The hardware is physically much larger than other SDR transceivers, taking up as much space as some of the older boat anchors. It could be stored under a bench or on a shelf but if regular access to connections is required this would be unsatisfactory.

The start-up time is about a minute which is probably caused by using an SD card to boot from. I am not comfortable with an SD card as the fundamental operating system storage although backup and restore to the PC and any of its connected drives is available.
Access to the SD card requires the radio to be dismantled instead of being available via an external socket.

There are no in line fuses, you need to remove the case to replace the fuse if it blows!

Software -Pros
Filtering and AGCT work exceptionally well especially on CW and when dealing with QRM and if used in conjunction with the tracking and automatic notch filters seems to work some kind of magic!

The included Winkeyer emulation works very well with any software that properly supports Winkeyer so not hardware is required.

There are two noise blanker’s, a normal one and a wide band one (WNB) the WNB is extremely efficient without effecting the actual signal.

The software offers most functions necessary and in every respect is easy to use.

Layout of the SmartSDR windows, waterfalls etc is flexible allowing the user to tailor the UI to his own requirements, for a first time SDR user the UI will be very useable.

Updates are often and usefull, being downloads from Flexradio and easily updated in the software.

Remote operating is exceptional, although there is some latency, and I could even operate using a cheap Windows tablet.

Software – Cons
No CW Spot facility in the software is a huge oversight which Flex do not acknowledge despite many requests from users ever since the launch of SmartSDR.

When changing the preamp setting on one SO2R slice it also changes on the other slice, not INDEPENDENT at all!

Grouping of controls in the UI is ill considered, with controls that are related not grouped in the same area. E.g., RF Gain control is in the aerial control whereas AGCF and AGC speed are grouped with the audio control!

No voice keyer necessitating the use of external programs for this function – This is a huge oversight when everyone of the major manufacturers includes a voice keyer.

Maintenance updates and minor development updates are free within a release but when a new major release is provided the cost is a hefty US$200.00.

The manufacturer/developer while providing good support for their products they are unresponsive when users request extra features, some of which are essential. e.g., Many users on the Community forum have been requesting for years the addition of a CW Spot (Net/Tune) facility, Flexradio support personnel dismiss this request saying that clicking on the signal is enough to net the CW tone, clearly, they are not CW operators.

More avid and experienced SDR operators will expect more control over the SDR signal processing although the existing processing is exceptionally good already it does not go far enough for the seasoned SDR operator.

It is a shame that there is no software for android OS as used on many tablets and smartphones, Apple IOS devices are of course supported well!

Overall impressions.
Although the forgoing may seem critical, I am incredibly pleased with the radio as it has exceeded my expectations regarding performance and fulfils my need for operational ease of use, I would find it difficult to revert to a conventional amateur radio transceiver other than for specific portable use with my Elecraft.

For many years I have used SDR receivers in conjunction with normal transceivers but although mostly satisfying it does not compare with the true all in one SDR transceiver.

I contemplated adding the expensive built in ATU but its range, like most main line built in units, is limited to matching 3:1 so doublets would not be possible to match on all bands. Having interfaced my LDG AT-200 ProII using auto mode I find this straightforward and easy to use and would advise against purchasing the internal unit.

Nothing can beat operating from a 27-inch monitor and being able to watch the full band activity with cluster spots superimposed on the Panadaptor, it is like living inside the radio! And as other SDR users already know having a proper Panadaptor takes the ham radio experience from a 2D experience into the world of 3D.

But beware if you need a true two receiver radio you need to purchase the 6600 or 6700 at at least double the cost.
WA1KPD Rating: 2021-03-14
Upgrade from 5000 Time Owned: 0 to 3 months.
Summary: a great radio with a lot of capabilities and extraordinary customer support. I'm very glad I bought it.

I bought a 5000 about 8 years ago and it served me very well. I decided to treat myself to a 6400 and it came with many improvements and some issues. I am also comparing it to the 7300 I run in the house and a FT-891 I run mobile.
I love the general concept of SDR; monitor layout, point and click, and the ability to view many different things on the screen. I was very excited about the remote control. The 6400 is a vast improvement over the 5000.

This is an odd spot to start but it is a compliment and shout-out to Flex. It took 12 weeks for the rig to arrive after a quote of about 4 weeks. Production happens. One week into having it, the rig experienced a fatal component failure. Flex worked with me that day to diagnose the issue and when it was apparent they needed to look at it they issued, at no cost to me, an overnight shipping label from my QTH in Maine to their office in Texas. The rig was back, repaired, and in use here in ONE WEEK. That is AMAZING CUSTOMER SUPPORT.
Now on to the radio experience:
The software and system is more stable than the KE9NS/5000 which would crash or shut down with no apparent reason or pattern.
Reception below the BC band is tremendous. On the 5000 it was impossible.
Received audio is an absolute pleasure to listen to, transmit audio is easy to set up and feedback (no pun intended) is good.
Sensitivity and selectivity are good. I'm no expert, but they work fine for me.
Steep learning curve, but I am getting there.

Issues: No rig is without user feelings on the downside.

My major issue is the rig is designed to connect to your PC via your router. I can not emphasize enough that this needs to be a hardwire connection. Although Flex sells, with some caveats, a device that will allow your rig to be a wireless connection it simply is not up to the task. As a result to take advantage of all the capabilities I will have to run about 100 ft of ethernet cable to the router. I have followed all online recommendations and have to agree with most posters the wifi set up just cannot handle the traffic load.

I wish the memory function was much more obvious and front and center to the main screen.

I miss the band stacking of the 5000.

Overall, I'm very happy with the radio and Flex as a vendor.