Hardware overview between the FLEX-6400 and FLEX-6600
All Videos

Hardware overview between the FLEX-6400 and FLEX-6600

Mike VA3MW goes over the hardware differences between the FLEX-6400 and the FLEX-6600.

For more details and to answer any questions, you can reach out to our ham operators at hams@flexradio.com.

View the complete video transcript.

Video transcript

This video’s full transcript has been provided below for your convenience.

Mike Walker VA3MW — One of the questions we often get from our customers is “what is the difference between the FLEX-6400 or the FLEX-6600 radios? And which one should I get? What has the features that I need?” I’m going to take a few minutes and we’ll go through the connections in the back of the radio because that sort of drives the entire story. I think you’ll find a station that works for you, incredibly cost-effective depending on your type of station. And let’s have a look. So, this happens to be a FLEX-6600, but from the front panel it’s really hard to tell the difference. We can only tell by looking at the nameplate here. If this was a 6600M or a 6400M model, we would have the front panel display that looks like the Maestro. But for the purposes of this discussion, that doesn’t matter at this time. So, let’s have a look at the back.

This is the back of a FLEX-6600. I’ve put some colored dots on here to help differentiate a few things. So, let’s talk first about the green dot. We have two antenna connectors. On the 6400, this is an antenna switch. You can only use antenna one or antenna two at the same time. You have the option to split your antennas for receiving and transmitting, so that you could be receiving or transmitting on antenna one, say it’s a low band 160 meter, but you might have a receiving antenna, and you could have it hooked up to here. Or you might be doing weak signal work and making use of transverters. That’s where we use this port. The transverter port has up to 10 dBm RF out, works incredibly well with Q5 Signal transverters. As we move our way across, we’re going to ignore anything with an orange dot. I’ll talk about that in a minute.

And we’re going to… The yellow dot is for an external display that is only available if you have the M model to allow you to hook up an external display. Over here on the left, we’ve got your power pole connection, 25 amps. That’s not 20 amps, that’s 25 amps. So, Astron 20 Amp power supply is likely a little too small. We recommend the Power Works amplifier. We sell them. They’re a great price and they’re great value. Work really well.


I power my host station with that. And as we work our way across, we see that we have, let’s look at these bottom three, transmit one, TX1, TX2, TX3. These are used to hook up any amplifier or amplifiers. You have three of these and they can be assigned by band. This one here is, if you have a 10 megahertz reference oscillator, you can hook up that and just send it a 10 megahertz signal. We don’t care if it’s square wave or a sine wave.

Or you can add an option with the GPS internal option that gives you your own high stability oscillator, and then you have a 10 megahertz reference that comes out here that you can use to feed other devices like test equipment. Across the top, we have a push to talk lead. That’s where yowu hook up your foot switch if you had one. TX request is generally used for contesting multi-op stations, so we’ll just bypass that. ALC out is used for some amplifiers if you happen to use ALC. Most people don’t today, although some people prefer to have it. And REM on is a remote on. That’s where you’d hook up with some sort of remote web switch to turn your radio on and off remotely if you were going to use this radio remotely. You can put a toggle switch here type of thing and flip it on and off and it will quietly turn off and on. It is safe to leave it off with 12 volts on all the time, much like a television.

Over here we have a LAN connector because that’s how the radio communicates with clients. That’s the clients that we use to operate today. How we control the radio, how we see things. These two USB ports are for CAT data to send data to external devices using very inexpensive RS-232 devices. You can actually buy them on Amazon. We sell them. They need to be made by FTDI. FTDI chip set or include the FTDI chipset. They also have what’s called bit or parallel cables. In case you wanted to say every time I went to a band, I want this particular level to go high. And that’s really helpful for controlling external devices. Case in point with the bit relay we have, you can buy these online. They’re 8 channel USB relays. This is one I use for testing. It plugs into here and you could hook up a transmit light “on the air” type of thing, which is pretty handy.


The 6400 has two slices or receivers, full-fledged main receivers. And that’s pretty much the summary on the 6400. There are band pass filters in here that are about 35 dB. Excellent enough for field day operation and band isolation. They work really well actually. We’ve got many clubs that contest with these. So, these four black squares here are really key as well. Powered speakers hookup here. There is no speaker on this radio, so you do need to provide your own speakers, or you can play the speaker audio through your personal computer through turning on what’s called PC audio in SmartSDR when you get to that point. Headphones plug into here, regular old headphones. These are all one eighth inch stereo, one eighth inch stereo because the radio does output a stereo signal.

A CW key, a one eighth inch, again stereo. You can actually use a straight key, you just have to configure it in the settings. We tell you how to do that. And lastly, a mic goes here. Pretty much any microphone will work here. That is a fairly typical gaming headset connection. Can be ordered with or without a tuner if you need to save some money or you don’t use a tuner. The tuner is an antenna matching unit designed to extend the operating range of an already resonant antenna. This means the antenna at the coax if you were to measure it with an analyzer, needs to be about three to one or better. If you’re using something that has higher impedances and you need to take some steps to get it to three to one, just about every tuner and every HF radio today is designed to extend the operating range of an already resonant antenna.

It’s not designed to take an antenna that has a highest WR the connector like 10 to one and make it function. Sometimes it works, but again, that’s not the design, so keep that in mind, depending on your antenna system and what you are using. Both the 6400 and the 6600 have the ability to add the extended transmit module to it and the antenna tuner is actually included in the 6600. So, that’s the 6400. Again, really good for most of us.


If you don’t have a big station or you’re not doing six things at once and you’re just usually on sideband or digital mode or CW. Nice and simple, no complications. It does also support multiFLEX, which is a technology we have to share your station with two users at the same time. Okay. Now, this is a 6600. It’s like having, simply put, two 6400s on your bench, that you’re sharing a lot of the resources.

Instead of having an antenna switch here, you now have two spectral capture units. So, you could hook this antenna up to, say, your 8040 Dipole, and you could hook this antenna directly to your tribander. And use both at the same time or your six-meter antenna or something else, so that you could be on an 80-meter net and on six meters at the same time listening with the proper antenna for the proper band. And that’s like having two radios because to do that before you would’ve had to have two radios. Because we have the second spectral capture unit here, we now have two more, another transverter port and another receiving antenna port. This makes us a great radio for many things, but satellite operation, because you can run full duplex, the ability to receive while you’re transmitting at the same time. And no, you won’t damage the radio at all.

So, in my case, when I’m on my satellites, I have a VHF transverter on this port and a UHF transverter on that port works beautifully. And I have videos on our Flex website regarding that. Now this orange dot up here, we have the ability to add a balanced microphone input. So, that’s really cool. The band isolation goes from about 30, 35 dB to almost 55 to 60 dB. So, that’s another huge improvement in band isolation as well. Pretty much everything else is the same on a 66. We again have the GPSDO, or 10 megahertz input, the remote on, and et cetera, all this stuff I discussed earlier. And if this was a 66M, you would have a display port here. This would be an HDMI connector there. And that pretty much that sums it up. Think of the 6600 too as having two 6400s on your desk with better band-pass filters and a shared transmitter because you can only transmit in one spot at a time.


And as well as 6600 comes with four slices instead of two to just give you more flexibility. Believe it or not, I use three a lot during six meter season. I will have a one slice on 50.313 for FT8, another slice on 50.318 for FT4. The band’s really open. I might open a third slice on 50.323 for the DX stuff off North America. And then I might take the fourth and move it over to 50.125 to keep an eye on any side band QSO’s going on, or anything a little further down the band in terms of CW. And that’s how you utilize multiple slices if you’re grid counting or DX or just trying to find some new stuff. And that works incredibly well. Without this type of radio, the only way to do that would’ve been multiple radios hooked up to different antennas. Make it incredibly, well, just not practical.

And on a Flex world, you now can share all that information on the same antenna because these antennas on both the 66 and the 6400 are receiving a hundred percent of the time from 30 kilohertz to 54 megahertz. Allowing you to poke around and look and listen to a baseball game while you’re on six meters on AM radio versus the six-meter band because we grab all the data from the HF spectrum and we digitize it, and there you go. And we digitize it, and then it comes to the client and you get to use it. So, incredibly powerful. That’s just some of the hardware features of this radio, the 6400 and the 6600. So, thanks for listening. Key points to remember are whether the radio has one spectral capture unit or two spectral capture units. You may only have one antenna, as we said. That is a perfect candidate for the 6400 model.

And if you’re a contester and you’re building a big antenna farm, then certainly having two spectral capture units is an incredibly efficient way to build out your station, especially if you’re considering something like an SO2R operation, SO2R operation, or maybe even some multiFLEX work where you’re sharing your radio with others. Another thing to consider is how many slices will you use? Many people just use one receiver at a time, or maybe two. Digital operators or digital contest operators can use up to four at the same time and make full use of them. Again, depends on your personal preference. So, thanks for listening. Have a great day. Mike, VA3MW from FlexRadio. Take care.

By using this website you agree to our updated Conditions of Use and consent to the collection and use of your personal information as described in our updated Privacy Notice, which includes the categories of data we collect and information about your preferences and rights.


Pay Over Time

To use Bread, please add products to your cart and follow the prompts for checkout — then select the “Bread” option in your checkout’s Payment section. Follow the prompts to submit your application. Check out now →

Bread Pay™ is a simple way to buy the products you want now and pay over time at your favorite online stores.

Apply for financing in seconds without ever leaving our site! Make easy online payments using our member portal or sign up for auto-pay for worry-free payments. You also have the flexibility to pay off your loan at any time with no penalty.

Paying over time through Bread Pay™ is quick, easy, and transparent. Learn more about how it works →

If your items are already in your cart, feel free to check out now and start the process!

*Availability of terms may vary based on purchase price and/or product. Down payment may be required. Subject to approval of credit application. Rates range from 0% to 29.99% APR, resulting in, for example, 24 monthly payments of $46.14 at 9.99% APR, per $1,000 borrowed. APRs will vary depending on credit qualifications, loan amount, and term. Bread Pay™ loans are made by Comenity Capital Bank, a Bread Financial™ company.

**Availability of terms may vary based on purchase price and/or product. Down payment may be required. Example payment is based on the listed product prices assuming a 24 month term loan and a 9.99% APR. Subject to approval of credit application. Rates range from 0% to 29.99% APR. APRs will vary depending on credit qualifications, loan amount, and term. Bread Pay™ loans are made by Comenity Capital Bank, a Bread Financial™ company.