Saturday, May 13, 2017

Initial thoughts on Elad's FDM-Duo

See also: Farewell to the FDM-Duo

Some initial thoughts on the FDM-Duo compared to other stand-alone or SDR rigs (only the
FDM-Duo is both):

Flex 6xxx and Anan 10E - full SDR but no stand-alone operation
Flex 6xxx and Anan 10E - no callsign population of pan display
KX2 - portable but no pan display, digital audio connectivity for WSPR, JT65, etc
KX2 - CW, AM, SSB but no DRM, ESSB, WFM, and more
KX2 - 10 to 80m; DUO - 6 to 160m
KX2 - limited configuration for many parameters; DUO - perhaps overly configurable

For a QRPer who wants to operate casual CW and SSB, either portable or at home, the KX2 is the go-to rig, hands down. Advantages of the Duo over the KX2 come into play when the operator has other interests in mind and wants to use the Duo with a computer to unlock the many capabilities over what is possible with a stand-alone radio. In the short time I've had my Duo, I've operated it both stand-alone and via the SW-2 software.

Operating CW stand-alone, compared to the KX2, was an exercise in frustration. Setting the speed of the internal keyer requires a series of button presses to get to the proper menu. Or you can change it via the E1 knob provided you are willing to send a string of dits over the air as you make the adjustment. That's right - you have to be transmitting in CW in order to make the adjustment on the fly! At home I'll use an external keyer with a speed pot, but afield - there's no convenient way to change keying speed without subjecting your QSO partner to a string of dits as you tweak the setting.

Soon after setting up the rig, I configured the F5 button to enable split VFO operation and was then able to work SV9DJO on 20m and E51DWC on 12m. OH0Z was operating simplex on 20m with a lot of callers but he too went into the log with this new rig. If I don't use the rig for a while will I remember that it's the F5 button and not the F4 that enables split operation? And what's the F3 button for again? The inability to label the buttons with something descriptive is due to the variety of options those buttons can provide based on what is programmed into them - a disadvantage created by the advantage of having so much capability.

So while the FDM-Duo is capable of CW operation, it is not a CW op's rig - in the stand-alone method of operation.

Then I loaded Elad's SW-2 software and that's where this radio begins to shine. Installing SW-2 went without a hitch and every step is detailed in the online manual (there are two manuals for the FDM-Duo: one for the radio itself and one for the software). Watching the 3-part YouTube series of videos from W8KFJ was infinitely helpful.

Elad's 25 year history of making test equipment and their recent foray into shortwave SDR receivers is evident in the software and it soon becomes clear what is meant by phrase "Multi-use" on the front panel of the Duo. Although there are no band select buttons on the radio itself, there are in the software and they include buttons for the popular SWL bands as well. Modes available include DRM, AM, synchronous AM and many others of interest to SWLers. A recording function allows the user to either record audio-only or full spectrum IQ data. A right-click on the record button brings up a window where a future recording can be scheduled. Selectable within this window are start and end times, freq, modulation, bandwidth and more. There are also a pair of markers that can be placed on the pan display with the delta between them displayed.

Operating the Duo as a transceiver via the computer is a bit less user-friendly than the Flex. Others may disagree with that statement. I like to operate my Flex "my way" and that includes, among other things, being able to control both the symmetry and degree of bandwidth filters. With the Flex, I can create a bandwidth of whatever value I want - and I can center it where I want. In other words, a 400 Hz filter doesn't have to be centered 200 Hz below and 200 Hz above a center frequency as it is in the Duo. Instead, I can make it for 50 Hz below and 350 Hz above, which is exactly what I do if I'm listening to CW on the upper sideband. With the Duo, the filters are not infinitely variable (they are stepped) and they are symmetrical.

Three USB cables are required for full capability of the Duo (TX, RX, CAT control) whereas all of this (and more) is taken care of in the Flex by a single ethernet connection to the computer. But the Flex stays at home, costs over twice as much and can't operate without having a PC attached. The Duo can and that's a major advantage IMO.

Perhaps the best analogy for the Duo is to think of it as the Swiss Army knife of radios. You can filet a fish with a Swiss Army knife but you'd rather use a dedicated filet knife. Same with the scissors attachment, the corkscrew or the screwdriver. If you want to explore the large amount of diversity that our hobby entails, you can buy several rigs to do them expertly or one FDM-Duo to do them quite well.

More to come.....


  1. Then again Flex is about to release v 2 software which will allow remote operation of your home station on a laptop Maestro or iPAD

    Thanks for the dope on the Duo. I bought one but haven't had the time to fire it up yet


    1. I'm looking forward to the v2 release of SSDR and have been reading the speculation about it on the Flex forum.

      I also read the thread last week from a semi-anonymous poster who simply goes by "john" criticizing Flex software compared to Elad's SW2. If I'd known then what I know now, I would have asked him some very specific questions on how he arrived at his opinion regarding the two platforms.