[Elecraft] K2 and 756PRo owners - question

[Dale M. Boresz]

tlogan7@cox.net wrote:

>- do you get a
>sense of heightened noise or "roaring" when you tighten down the 756 filters
>below 500 - as compared to your K2's. ...
>73/Tim NZ7C
>
>_______________________________________________
>

I have an ICOM 746PRO which I liked a lot, until I finished building and 
began usinging my K2 (S/N 3039). I operate about 80 to 90 percent CW, 
mostly on 20m, and I've been using the K2 now for about a month, and it 
is now the only rig I use on CW for a couple of reasons. The complete K2 
setup here includes: KAF2 Audio Filter, KNB2 Noise Blanker, KSB2 SSB 
Adapter, and KPA100 100-watt amplifier. A few observations/comments:

- The 746PRO has some 'brittle' sounding artifacts which manifest 
themselves on cw whenever there is a lot of band noise (like on 40M), or 
when the cw signal itself has key clicks. For lack of a better 
description, it sounds like I'm listening to it through a pair of 
headphones in which the diaphragm rattles due to resonances, or through 
a loudspeaker with a voice coil which is rubbing against the magnet. I 
thought at first that it was just mine, so I stopped by AES in Ohio 
which is only about 2 miles from the QTH, and confirmed that their 
746PRO, and 756PR0-II sounded exactly the same. I remedied it months ago 
by building a passive rolloff filter which I insert between the rig and 
my headphones. It takes care of 90% of the brittleness. I should say - I 
use high-end audiophile headphones (because they happen to be 
comfortable as well) so they are particularly sensitive to this sort of 
thing, which is not as noticeable with 'normal' communications-quality 
headphones.

- Regarding the 'roaring' you describe, yes, I've noticed that when the 
filter bandwidths of the 746PRO are reduced to much less that 500 - 600 
Hz in the presence of a fair amount of band noise, they have 
considerable ringing. It helps quite bit if I change the filter 
characteristic from 'Sharp' to 'Soft', when I'm at a wider bandwidth 
such as about 800 Hz, but offers very little improvement with the 
narrower bandwidth settings.

- The K2 on the other hand, exhibits none of these problems, and I find 
it to be an extremely quiet receiver, and a real pleasure to listen to. 
With the KAF2 Audio Filter installed - which I think is a terrific 
addition,  between it and the crystal filters of the K2, I can narrow 
the filters all the way down to 100Hz, without ringing under any 
conditions, and with careful tuning can usually pull any signal out of 
the background for Q5 copy. I've actually switched receivers while 
listening to a weak signal under noisy conditions, and have found that 
the same signal ends up being just another 'ping' in the noise on the 
746 when the filters are really narrowed down, and is not copyable.

For these reasons, the K2 has become my exculsive cw rig. I still use 
the 746PRO on those occasions when I can't hear a single station on 20m 
cw, but find lots of activity on the phone section of the band. In my 
opinion, the 746PRO is hard to beat when it comes to SSB operation, 
where the IF-DSP really shines, and the receive audio quality is 
exceptional. But for cw operation, the K2 is a much more effective and 
better sounding rig - a real pleasure to use.

To the fine folks at Elecraft - Congratulations on the design and 
implementation of such a superior product, and enjoy your well-deserved 
holiday vacation time!

73, Dale WA8SRA