Redefining The Radio (or, Nine Months With The Flex 1500)

Cooler than penguin poop.

I've not written much about the Flex 1500 since I brought it home about nine months ago, just a few mentions here and there. It doesn't get nearly as much use as my K3 but I reckon I've had enough cockpit time to become familiar with all the controls and tweak the software that an update might be in order.

Why the Flex 1500?

I first became interested in the 1500 shortly after it was announced by Flex Radio Systems. I was QRT at that time but I still kept my ear to the ground with respect to new equipment, especially QRP rigs, and this one really grabbed my attention. Around the same time Elecraft announced their KX3. I'm encouraged to see these two companies catering to the "little pistol" QRP op even as they shake up the "big gun" high-end/high-performance transceiver market with their K3 and Flex 5000/6500/6700 models. Especially fascinating is the different approach each of them take with respect to SDR design: the Flex 1500 is a black box device that sites between a antenna and a PC; the KX3 is a self-contained SDR radio that can be used independent of a computer (or an AC outlet, for that matter). Two completely different design philosophies.

Of course I wanted both radios; fiscal restraints, however, forced me to choose one or the other. I opted for the Flex partly because I really wanted to explore their universe a little bit after years of being fully in the Elecraft camp, and partly because of price -- the 1500 costs $699, the KX3 starts at $899, and the extra few hundred bucks really wasn't in my budget at the time. So the 1500 it was.

I envisioned this radio fitting into my current station primarily as a low-power digital-mode radio, and also as a second receiver. Now that I've become more interested in getting involved in QRP activities I can see it getting more use as a CW rig as soon as I work out a way of switching my key and paddles easily between the Flex and the K3.

First Light

My first impressions were mixed -- the initial PowerSDR setup was fairly straightforward but I had some issues getting it configured with the Virtual Audio Cable (VAC) and Virtual Serial Port (VSP) software and was finding some latency issues in CW mode  -- a very short but noticeable delay between key-down and hearing the sidetone that really is disconcerting while trying to send code at anything above Novice speed. It took some experimenting with the audio and DSP buffer settings before everything worked, if not perfectly then well enough. Nothing especially problematic, just a case of needing time to get acquainted with the intricacies of the different applications needed to get the rig working in a usable fashion.  

I eventually got everything working perfectly with both VAC and VSP. This allows a single USB cable between the 1500 and the Dell laptop to be used for the PowerSDR software (which is, for the most part, all of the radio after the RF stage), Ham Radio Deluxe (for additional rig control and logging), and DM780 or JT65-HF (for digital modes). No audio cables required!

The buffer and latency settings took a bit more work. Flex's Knowledge Center and the Flex-Radio email reflector are both great sources of information for dealing with these issues and any others. In particular, I found this post by VE3WMB to be especially helpful as a starting point for getting the 1500 dialed in. I also got some key advice on VAC setup from the Flex Radio SDR community on Google+. While there is still some latency when operating CW, it is useable in that mode, although I am limited to slower sending speeds than I'm comfortable with. The only way I can get around it is to reduce the CW buffer, which in turn limits the minimum bandwidth settings. Since others have reported success in eliminating this CW latency I'm still hoping to find the magic settings someday. 

Operating the Flex 1500

I noted above that the 1500 was purchased mainly for digital modes, and it's worked out extremely well for that purpose. I've been able to dabble with JT65 for the first time and have made some DX contacts running 1.5 watts. PSK operation is quite good, too. Channeling the audio I/O as data via USB seems to deliver a cleaner signal to and from DM780 than I'm getting from the desktop PC/soundcard setup I use with the K3. This is just the impression I get, I have not done any tests to support this hunch. At the very least, the possibility of RFI getting in through audio cables should be a non-issue now.

First, the positive:

• The cornerstone feature of this rig is it's spectrum display. It makes it easy to spot weak signals that are barely audible -- the kind you would tune right past if you were turning a VFO dial on a conventional rig. See a line on the waterfall, click on it and you're tuned! More on this below.
   
• I expected a great receiver from the reviews and receiver tests I'd read before purchasing it but it still took me by surprise. On CW the 1500 is simply amazing. The bandwidth filtering and it's ability to dig out weak signals is a match for the K3 in all but the most extreme cases, at least to my ears. It sounds great on SSB, too, though I haven't done much listening in that mode.
   
• MultiRX is super-useful in a pileup situation, when I want to listen to my RX frequency (the DX station) in my left ear and monitor my TX frequency (the pileup) in my right. Unfortunately it's not possible to use different bandwidth settings for each channel. 

On the downside:

• I find the Noise Blanker (NB) to be a bit disappointing. Perhaps I've been spoiled by the K3's NB, by far the best I've ever experienced. If it's just a simple matter of not having the the parameters set correctly, then I'd say that's one of the problems -- it shouldn't take that much tweaking and effort to work properly. I've spent a lot of time adjusting the 1500's NB settings and I'm unable to find the sweet spot where the background electrical noise that often plagues my QTH is eliminated without causing distortion to the desired signal. No such issues with the K3, where I can just increase the NB level until it distorts, then back it up a little.
   
• The DSP Noise Reduction (NR) is OK, but again not nearly as effective or easily adjustable as the K3's NR. I rarely use it.
   
• Portability is another issue. "QRP" is often synonymous with "portability," and this rig simply ain't. If field operation is high on your priority list, either look elsewhere or prepare to lug around a bunch of batteries to power both the 1500 and a laptop.

User Interface

Despite it's (relatively few) shortcomings, I love the Flex 1500. Still, the K3 is my go-to rig and the Flex has been getting only occasional use. Why? It's not merely because of the additional output power of the K3 -- that may be part of it, but I'm fairly certain I'd do the same if the Flex were a 100W rig driving an amp. And not because of any performance issue, either -- as I noted above, the Flex is pretty much equal to the K3, and possibly better in terms of audio quality (my K3 is one of the early ones and has none of the revisions that address some audio distortion issues).

More than anything, it's just that I still prefer a conventional button-and-knob rig to a point-and-click rig. When I want to turn the volume down, it's unintuitive for me to fumble with the mouse and drag a slider on a computer monitor. When I want to change bands, it seems so much more natural to push a physical button than click on a virtual one. Is this just a generational thing? Would a younger user, someone who has been exposed to computers from the cradle, be more comfortable with PowerSDR and find a conventional radio to be a quaint relic of the past? I don't know.

Whether I'm "old school" or just stubborn, the K3 suits my operating style. This often includes tuning slowly across the band listening for weak signals with my eyes closed, something that is not easily done with PowerSDR. I ride the RF Gain control, too, and again find it cumbersome to work a slider control with the mouse to do that. I suppose the awkwardness of PowerSDR can be lessened with time as I use it more, but I don't think the point-and-click interface will ever match the tactile feedback I get from an honest-to-God front panel. 

But then there's the panafall display! That is what for me sets this radio apart from anything I've ever experienced before. PSK users know all about waterfall displays which show signals in the audio passband; panadapter spectrum displays have been a mainstay on rigs from Icom since the IC-780 and R-9000 in the 1990s and now feature prominently on rigs from nearly every manufacturer. The panafall display is a combination of the two, showing real-time band activity in both the frequency/amplitude and frequency/time domains.

PowerSDR's Panafall Display

A CW or digital signal too weak to really stand out on the panadapter display will often still leave a faint line on the waterfall. These are the signals that one risks tuning past on a conventional rig. But on the Flex... see a line, point and click, bang. It almost feels like cheating.

Here's an example of a station (HC5AI) I found while doing some A/B tests between the 1500 and the K3. It was so weak that it didn't register at all on the panadapter display (top) but was clearly visible on the waterfall (bottom):

Odds are that I wouldn't have found this signal if I were just tuning the band on my K3 or if I were using just the panadapter display on the 1500. (This was one of those extreme cases in which the K3 beat the 1500 in terms of copying a signal so far down in the background noise that it was barely audible. Not a huge difference in readability, but noticeable.)

So why not use just the waterfall? Why have a panadapter display at all? Maybe the panadapter is just gravy, but I find it to be very useful when there are a lot of signals on the band, especially during a contest or while hunting DX. Observing a pileup of big signals spread out over a 2-3 kHz range just disappear when a weaker signal starts transmitting on a lower frequency -- the telltale sign of a DX operation -- is something that just doesn't come across as well on the waterfall. On the other hand, the waterfall is my tool of choice when monitoring a quiet band, especially the higher bands which open and close intermittently at night. That's when I will just leave the waterfall on and wait for the broken lines to appear.

This panafall method of finding and tuning weak signals is a paradigm shift for me, another one of those things that I could never have imagined when I was a kid listening to hams on a DX-160 receiver with a simple bandspread dial. Back then, a simple digital frequency readout seemed miraculous to me! I'm happy to say it's not unique to Flex radios these days, either. The Elecraft P3 panadapter option for the K3 includes this feature; NaP3, an SDR software program based on the open-source PowerSDR code, brings many of PowerSDR's user interface to the KX3 and, with devices like the LP-Pan, other rigs with suitable IF outputs; most if not all other SDR radios support software with similar functionality; the Kenwood TS-990S has it on its built-in display, and I expect Yaesu and Icom will follow soon enough. Maybe someday a panafall display will be as ubiquitous as digital readouts and computer interfaces are on radios today.

Elecraft P3

NaP3

Kenwood TS-990S

Just for the hell of it I recently hooked the K3's IF output up to the Flex 1500 and tuned the 1500 to the K3's IF 8 MHz frequency. The results were not great -- the signal level of the IF signal was pretty low so only the strongest signals on the band were showing up in the PowerSDR panafall; tuning the K3 up in frequency moved the waterfall in the opposite direction (i.e., higher frequencies are to the left of the center marker, lower to the right), something that makes perfect sense if you think about it but still less than intuitive when operating; and of course the point-and-click facility was missing. In all, and interesting exercise but a rather useless way to add a spectrum display to the K3.

My Wish List
Two things would make me even happier than I already am with this radio: A Macintosh version of PowerSDR, and an internal ATU option.

The $900 Question

Anyway, these are my random thoughts about the Flex 1500. If I had to do it all over again, would I have gone for the KX3 instead of the Flex 1500? I've been asking myself that question a lot lately and the answer is a definite and resounding "maybe." The appeal of having a stand-alone, fully functional QRP rig that I can use outside the shack wasn't a huge factor for me last June. Today I really wish I had one. I have no complaints with the Flex when it's used as I originally intended -- as a digital-mode rig -- and actually use it more than the K3 these days for PSK. At the same time I wish I had a KX3-type rig that I could use both in the field and in the living room.

That said, I have no regrets. I chose the 1500 knowing what it was and how it worked, and it honestly has met all my expectations. So I don't know if I'd go the other way and get the KX3 instead of the 1500. Hopefully I will own both someday because they each fulfill a particular need for me.

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Resources and Links

Monitoring Times review by NT0Z - Part 1 and Part 2 (PDF format)
DL4YHF's Overview of Spectrum Displays
W9XC: Flex 1500 CW Latency Issues