FlexRadio Review

I have both the Flex-6400 and Flex-6600; both arrived in 2020 during a pandemic, so they have seen substantial use. They’ve both been used during contests, some of which were serious efforts. I also have the Power Genius XL amplifier, which has been similarly used.

The features of each piece of hardware is different to some degree, but they all interoperate beneath FlexRadio’s proprietary SmartSDR. As they are all linked and function together, I figured the best way to review this equipment would be a “sixty-thousand foot” -view — things I like and don’t like about the entire Flex experience, instead of getting into the nitty gritty.

SmartSDR – The Software

I am impressed with SmartSDR. As a stalwart of knobs and switches, I thought the learning curve would be difficult. I even purchased the FlexControl knob, fearing that I would be uncomfortable using the mouse. That turned out to be untrue! The software is incredibly user friendly.

The ability to see the whole spectrum and to zoom in/out is indescribable. I cannot remember contesting without it! It makes finding multipliers effortless, but where it really excels is in finding a clear run frequency. I can QSY and find a clear frequency within seconds — that is perhaps the most unexpected utility I’ve yet found.

The only drawback, of course, is that the program is only as good as your computer. I purchased a new dedicated desktop for this, and it functions well. If I were using a laptop that shared radio, work, and personal functions, maybe I would have experienced more trouble. If you’re spending this type of money on Flex gear, however, you should consider buying a dedicated machine.

Flex-6400, Flex-6600, PGXL – The Hardware

The first thing you’ll notice is that the physical radio weighs practically nothing. All connections are located on the rear panel. Overall, the rig looks sharp, but unassuming. Non-ham visitors here often mistake it for a computer, especially given the low-level whir of the cooling fan.

The biggest unexpected advantage of the radio is what it eliminates. Prior to Flex gear, I was using dated Yaesu FT-1000MP radios that required soundcard interfaces and associated cables, breakout boxes to bring band data to different devices, and RS-232 connections to the computer. All of that is now unnecessary; the radio is connected directly to my home network and can be found by any device, even over WiFi. A single USB connection sends band data to the Hamation network. Soundcard interfacing is done completely internally via Flex’s DAX utility.

The main difference between the 6400 and 6600, at least in my usage, is that the 6600 has more slices available and can do SO2R all by itself. The receiver is slightly better than the 6400 as well, but after listening side-by-side, I’m sure this would only matter in very specific circumstances. If you are a casual operator, DX chaser, or single-rig contester, the 6400 is a great deal and you’ll be pleased with it.

The single-box SO2R capability of the 6600 sync up with the Power Genius XL perfectly. When someone complains about the price of Flex gear, I remind them that the 6600 and PGXL are essentially two radios and two amplifiers; if you do the math, you’re saving money already. Add in the cost savings of not having to buy an SO2R audio interface and the complexities of dealing with OTRSP, interconnections, and building cables, and you’ve stumbled upon the real value.

The 60,000-foot view

What I LikeWhat I Don’t Like
SmartSDR. Very intuitive yet powerfulSoftware upgrades. Common and a pain.
SO2R with one boxOccasional glitches — this is a computer after all
Integration between gearPGXL fan noise is very, very loud
Elimination of interface equipmentRemote exclusively via Flex’s system & servers
Flex support is very responsive and very fastLead time on new products

This is a living post; I’ll be adding to it as time goes on.

Two-mode laser transmitter and receiver

At the 2005 National BSA Jamboree, I saw a demonstration of a QSO via laser. I recently found the document I had been given at that time and am uploading it here as I can find very little mention of it online. I have not built this, and obviously the component prices no longer apply as RadioShack has long been out of business.

I had written KA8MID across it at the time; I am unsure if that was the person doing the demonstration, or the designer. If anyone has additional information, please contact me so I can credit the appropriate source.

Proper feeding of non-resonant antennas

Coax becomes very lossy at high SWR. If you are feeding your non-resonant antenna (vertical, dipole, or any other design) with coax and utilizing a tuner at the shack end of the feedline, you’d be surprised by the amount of power you’re losing. Remember that your in-shack tuner does not tune the feedline to the antenna, and thus it remains at high SWR on most bands!

Balanced feedline, on the other hand, is very tolerant of high SWR and is practically lossless. It can be built inexpensively, and a variety of instructions exist online or in print. The cons of this cable type are well documented, but essentially boil down to users failing to maintain balance; if the feedline comes near conductive material, or is wildly blown about, it can become unbalanced and radiate. Despite the drawbacks, it is a demonstrably superior feedline for non-resonant antennas. Let’s compare common 600-Ohm balanced feedline against a few common types of coax:

600-Ohm Balanced Time Micro. LMR-400 Belden 8237 RG-8 Belden 8240 RG-58
Length (ft.)100100100100
Frequency (MHz)14141414
Power In (W)100100100100
Total Loss (dB).12.721.031.95
Power Out (W)97.384.757963.8

The above chart assumes the SWR on your feedline is 3:1 — but it is likely to be significantly higher as with most non-resonant multiband antennas. Nonetheless, the 600-Ohm balanced feedline is clearly the winner. Let’s reexamine the results with a more realistic feedline SWR of 5:1:

600-Ohm BalancedTimes Micro. LMR-400Belden 8237 RG-8Belden 8240 RG-58
Length (ft.)100100100100
Frequency (MHz)14141414
Power In (W)100100100100
Total Loss (dB).
Power Out (W)95.8378.2770.9553.84

In this second example, the ham using RG-58 has lost almost half of his power in the feedline! With the high cost of radios and amplifiers, it seems silly to use lossy cable and sacrifice those expensive dB’s.

Differences in Balanced Feedline

Most amateurs opt to build their own 600-Ohm balanced feedline from wire and inexpensive spreader insulators. However, commercial 450-Ohm “window line” is available and very sturdy. Is it critical which one we select? Not particularly, as seen in the chart below:

600-Ohm Balanced450-Ohm Balanced
Length (ft.)100100
Frequency (MHz)2121
Power In (W)100100
Total Loss (dB).19.27
Power Out (W)95.894

The 600-Ohm balanced feedline exhibits somewhat less loss, but the difference (even at 21 MHz) is negligible. If you must purchase a commercial 450-Ohm balanced feedline, you will be pleased with its performance.

Also see: W3LPL’s Coax loss charts

Coax loss charts (from W3LPL)

Frank, W3LPL posted helpful coax loss charts to the CQ-Contest email list some time ago. I’ve used them extensively, particularly in deciding if it was necessary to use LDF4-50a hardline over RG-8. I’m reprinting this here, with credit to Frank, so it is not buried in the email list archives.

Note: charts may not format properly on a mobile device.

From: Frank Donovan W3LPL
Subject: CONTESTER's coax cable attenuation charts
I developed and have been using the following charts for some years.  
The CONTESTERs I've given copies to have found them most useful as 
well.  The first table is the common attenuation per 100 ft chart, but 
with specific values for each ham band.
The second table is in cable feet per dB, which can be very handy for 
tradeoff analysis (e.g. do I really need to use Andrew LDF5 for my 1000 
foot run to my Beverages or is RG-8X good enuf?).
The third table shows the results of just such a tradeoff analysis, each 
entry in the table represents the cable length in feet before Andrew 
LDF5 offers a 1 dB advantage vs the various cables listed
The last table is identical to the third table, except these trades are 
for Andrew LDF4.
                            CABLE ATTENUATION  (dB per 100 ft)
             1.8   3.5   7.0  14.0  21.0  28.0  50.0   144   440  1296 
LDF7-50A     .03   .04   .06   .08   .10   .12   .16   .27   0.5   0.9
FHJ-7        .03   .05   .07   .10   .12   .15   .20   .37   0.8   1.7
LDF5-50A     .04   .06   .09   .14   .17   .19   .26   .45   0.8   1.5
FXA78-50J    .06   .08   .13   .17   .23   .27   .39   .77   1.4   2.8
3/4" CATV    .06   .08   .13   .17   .23   .26   .38   .62   1.7   3.0
LDF4-50A     .09   .13   .17   .25   .31   .36   .48   .84   1.4   2.5
RG-17        .10   .13   .18   .27   .34   .40   .50   1.3   2.5   5.0
SLA12-50J    .11   .15   .20   .28   .35   .42   .56   1.0   1.9   3.0
FXA12-50J    .12   .16   .22   .33   .40   .47   .65   1.2   2.1   4.0
FXA38-50J    .16   .23   .31   .45   .53   .64   .85   1.5   2.7   4.9
9913         .16   .23   .31   .45   .53   .64   .92   1.6   2.7   5.0
RG-213       .25   .37   .55   .75   1.0   1.2   1.6   2.8   5.1  10.0
RG-8X        .49   .68   1.0   1.4   1.7   1.9   2.5   4.5   8.4
                            CABLE ATTENUATION (Ft per dB)
             1.8   3.5   7.0  14.0  21.0  28.0  50.0   144   440  1296
LDF7-50A    3333  2500  1666  1250  1000   833   625   370   200   110
FHJ-7       2775  2080  1390  1040   833   667   520   310   165    92
LDF5-50A    2500  1666  1111   714   588   526   385   222   125    67
FXA78-50J   1666  1250   769   588   435   370   256   130    71    36
3/4" CATV   1666  1250   769   588   435   385   275   161    59    33
LDF4-50A    1111   769   588   400   323   266   208   119    71    40
RG-17       1000   769   556   370   294   250   200    77    40    20
SLA12-50J    909   667   500   355   285   235   175   100    53    34
FXA12-50J    834   625   455   300   250   210   150    83    48    25
FXA38-50J    625   435   320   220   190   155   115    67    37    20
9913         625   435   320   220   190   155   110    62    37    20
RG-213       400   270   180   130   100    83    62    36    20    10
RG-8X        204   147   100    71    59    53    40    22    12
             1.8   3.5   7.0  14.0  21.0  28.0  50.0   144   440  1296
LDF4-50A    2000  1430  1250  910    715   625   435   250   165   100
RG-17       1666  1430  1110  770    560   475   420   120    60    30
FXA12-50J   1250  1000   770  525    435   355   255   120    75    40
9913         835   590   455  320    280   220   150   85     53    29
             1.8   3.5   7.0  14.0  21.0  28.0  50.0   144    440  1296
RG-17         -     -     -    -     -     -     -     220     90    40
FXA12-50J     -     -   2000  1250  1100  835    625   250    145    65
9913        1430  1000   715   500   455  345    235   135     75    40
RG-213       910   600   285   200   150  120    85     45     20    12

Also see my article: Proper feeding of non-resonant antennas

Inverted-L myths

The venerable Inverted-L is the most popular antenna for the low bands, due in large part to its simplicity. It has enabled many hams to get on 80, 160, or even lower from their city lots. Unfortunately, its ease-of-use has allowed substantial misunderstandings as to design theory.

This article will address several of the most oft-repeated myths regarding single band Inverted-L’s. In a future follow-up article, I will detail the construction of a 160m Inverted-L at my new QTH using the “Ten Commandments” provided below.

Myths and Realities:

  • “I feed my Inverted-L directly and my SWR is great.”
    If you feed your inverted-L without any type of matching network but you have low SWR, your antenna is probably very poor. The low SWR is due to tremendous ground losses near the feedpoint. As you improve your radial system, SWR will actually rise and will likely require additional capacitance at the feedpoint. SWR is a poor design metric.
  • “Radials reflect your signal.”
    Your radial field provides a return path for RF (similar to the shield side of a dipole), but does not “reflect” your signal. The actual reflection happens several wavelengths away from the antenna and is due to something called the pseudo-Brewster Angle.
  • “This is a great limited-space antenna. Four radials should be fine!”
    How many radials do I need? Bad news: you need a bunch. For our poor soil conductivity, you’re going to need at least thirty and they should be ¼-wave long. I’ve found the length to be less important than the density near the feedpoint; for this reason, try to keep them evenly spaced, even if they are shorter in some directions. If you are extremely space limited, you can add a galvanized ground screen around the feedpoint (in addition to as many radials as possible, as long as possible). Good news: 30 radials appears to be the point of diminishing returns per tests by N6LF and others, so you will have achieved reasonable maximum performance with this setup.
  • “My vertical hears just fine.”
    Verticals are noisy receive antennas. Often, my very short beverages-on-ground have been 6 or 7 S-units quieter than the Inverted-L on 160 and allowed me to make QSOs that simply wouldn’t have been possible otherwise.
  • “The vertical should be a quarter-wave long.”
    Your Inverted-L should actually be longer than a ¼-wavelength. Making the antenna slightly longer will raise the current maximum in the vertical section well above the feedpoint (this is good). The trick, of course, is keeping the maximum beneath the horizontal portion; if the antenna becomes too long, the horizontal portion will act as a radiator instead of a capacitance hat (this is bad). If you’ve done this properly, of course, you will still need to provide some capacitance at the feedpoint. Based on modeling at my specific QTH over the years, I’ve found 135’ to 150’ lengths to be the sweet spot for 160. Again, SWR is a poor design metric — a small L-network at the base will easily solve the problem.
  • “I don’t need a feedline choke.”
    Unless your ground is outstanding (think radials over saltwater), the shield of your feedline is being used as a radial. This can cause all sorts of ugly RFI in your home and, worse, your neighbors’ homes. Consider using a commercially available choke (occasionally called an “isolator”) or construct your own.  K9YC’s popular design calls for seven turns of RG-8 through five 2.4″ o.d. #31 toroidal cores.
  • “The wire is just thrown over a branch. It works fine.”
    Verticals are easily coupled with anything nearby, including trees. While trees aren’t as bad as metallic structures, it is still best to have your vertical out in the open away from the greenery. A catenary support rope can help. Additionally, there will be substantial voltage at the end of the antenna when running high power, so be sure there is sufficient space and insulation between the endpoint and any vegetation.
  • “Feedline losses are so low on 160 that the coax doesn’t matter.”
    It’s true that loss decreases with frequency, however most coax is inherently leaky. This means that while feedline loss isn’t the primary concern on 160, intermod and mechanical considerations might be. Consider using a high quality coax like LMR-400 or hardline. This rule holds true for any antenna on any band, and especially so if you intend to operate radios on other bands at the same time. True hardline has the added benefit of direct burial and is widely available on eBay and government surplus websites.

Ten Commandments for your Inverted-L

By way of summary, here are my basic design requirements for a good Inverted-L. Many of us, myself included, can’t have all of them, but we should attempt most of them. After all, who among us is without sin?

  1. Don’t use SWR as a design metric
  2. Make the vertical section as tall as possible
  3. Use as many evenly-spaced radials as possible
  4. Use a decent choke at the feedpoint
  5. Avoid lossy bottom-loading
  6. Place the vertical element in the open, away from trees and buildings if possible
  7. Use high quality coax or hardline to feed the antenna
  8. Match at the feedpoint, only use a tuner in the shack as a last resort