[Elecraft] IC-746 PRO A/B Test Results (LONG)

[Dale Boresz]

As an owner of both an ICOM 746PRO (for about a year now), and also K2 
S/N 3039 w/ KPA100, KAT100, KIO2, KNB2, KAF2, KSB2, and KDSP2 options, 
I'd like to share with the group some of my observations (admittedly 
subjective, empirical, and not scientific) of the two radios.

Approximately 95% of my operating is cw on the 20, 30 and 40 meter bands 
(in that order), and I occasionally will operate SSB on 20M as well. My 
antenna on 20m is a mono-band Hex Beam (great antenna!!!) and I use a 
linear-loaded vertical doublet fed with 450 ohm ladder line on the other 
bands. I have a coaxial switch which allows me to instantaneously switch 
either antenna between either radio, and each radio is connected to 
identical external speakers (Radio Shack/RCA 4.5" bookshelf speakers  in 
a wood cabinet). I make use of this instantaneous switching capability a 
LOT while comparing the two radios.

First the cw-related observations:
- The K2 'sounds' much better, and is far easier on the ears, than is 
the 746 which very frequently imparts a brittle character to the sound 
of cw - depending upon a number of factors, some of which seem to be 
related to the type of noise on the band, and the rise-time of the 
signal. If the band is quiet (noise-wise), and the cw signal being 
received does not have a very fast rise-time, the 746 sounds fine. The 
K2 on the other hand, exhibits no brittleness under any circumstances.

- The DSP bandwidth filters of the 746 work very well, although they 
'seem' to tend toward ringing at the narrower bandwidths. According to 
the spec's they should not, and indeed what I am hearing may not be 
ringing of the filters at all, and it may simply sound like that to my 
ears because of the very steep rolloff and narrow bandwidth of the 
filters. But even if the filters aren't ringing, they 'sound' like they 
are. The 746 allows the selection of "Sharp" or "Soft" filtering, and 
switching to "Soft" usually reduces this effect, but it's still there to 
some extent. As noted by other users, the DSP NR has very little effect 
at narrow filter settings. The K2's filters do not exhibit this same 
kind of ringing. There is a slight amount of ringing at a very narrow 
filter setting of say 100 Hz, but I rarely find the need to narrow it 
down that much so it's not an issue. What I do instead is to use the 
50Hz bandwidth setting of the KDSP2 in combination with about a 200 Hz. 
IF bandwidth. This combination yields great selectivity with minimal 
perceived ringing.

- The DSP Noise-reduction of the 746PRO is pretty effective as long as 
the bandwidth is not reduced to much below about 600 Hz. The ability to 
quickly adjust the amount of NR simply by turning a front panel knob is 
really nice. However, that single adjustment is the only one available 
for noise-reduction. The KDSP2 on the other hand permits far greater 
tailoring of the noise-reduction characteristics, including the ability 
to adjust gain levels at several stages, as well as attack and decay 
times, and aggressiveness. I've also noted that while the effects of the 
KDSP2's noise reduction are most pronounced at wider bandwidths (as are 
all NR systems), they are still perceptible at bandwidths as narrow as 
100Hz and even sometimes at 50Hz.

- Regarding weak-signal capabilities, while I cannot attest to 
performance on 160 meters because I don't operate on that band, much of 
my time on 20 meters is spent trying to pull the weak ones out of the 
noise so I have some experience in that regard. In the absence of QRM, 
I'd consider the two radios close without engaging the K2's DSP, but by 
using the KDSP2 I've been able to copy a few signals which were not 
copyable by either the 746, or the K2 w/o the DSP. I've found that using 
the most aggressive setting on the KDSP2 when trying to copy a very weak 
station, actually sharpens the edge of the signal, allowing it to be 
copied. The 746's DSP will do the same, but it is not as effective as 
the KDSP2.

- Under crowded band conditions, the differences between the two radios 
become much more pronounced. The 20m cw portion of the band during Field 
Day was the perfect test medium, and I spent a lot of time deliberately 
seeking out weak signals flanked by much stronger signals. With the K2, 
using both the standard crystal filters and the KDSP2, I was always able 
to copy the weak station, most of the time  without any indication at 
all that there were any strong stations nearby. When I'd switch over to 
the 746 and attempt to isolate the same signal, I usually could isolate 
it well enough - BUT - the 'clicks' from the nearby stations caused so 
much pinging in the filter passband, that copy was very difficult. Upon 
switching back to the K2, I heard only the desired station. These 
differences were very dramatic, and easily repeatable.

SSB observations:
- In heavy QRM situations, the twin passband tuning of the 746PRO 
definitely gives it an edge over the K2. I've found that I can quickly 
optimize the passband - both center frequency and bandwidth - for the 
particular voice characteristics of the operator of the station I'm 
trying to receive. The K2's fixed filters don't allow that, although 
passband tuning can sort of be simulated by setting each of the K2's 
filter responses to favor a different part of the spectrum. I've also 
found that John Grebenkemper's (KI6WX) 2.5KHz bandwidth modification 
significantly improves the sound quality of both transmitted and 
received audio, and I've received excellent audio reports since making 
that modification. Prior to making this change, I always used the 746PRO 
whenever I operated SSB, however, now the reverse is true. Although the 
sound quality of the 746 is excellent on a high-quality signal, I find 
the K2's audio quality to be less fatiguing to listen to on the vast 
majority of signals. On the transmit side, I still think the 746 has 
more 'punch', but part of the reason for that may that the microphone 
I'm using (Heil HC-10 w/ both HC5 and HC4 elements) doesn't interface 
nearly as well with the K2 as it does with the 746.

Bottom line:
I'll keep the 746PRO around as a backup rig, (I already took a big 'hit' 
when I bought it new, so why sell it off now?) but the K2 remains my 
primary rig, and without a doubt, my favorite.

-Dale / WA8SRA