Direct Sampling SDR vs. Superhet (KX-3 vs. IC-7300)

The KX-3 has the better keyer – by a margin

The IC-7300 has the quieter receiver – by a margin

On 40M – listening to T30L at 0900z – which is normally a fairly quiet time of day – but where this month it has been really noisy – I wanted to just listen to each radio to see its on air S/N response.

http://www.sherweng.com/table.html

Sherwood has the KX-3 ahead of the IC-7300, but there is something wrong with this picture. The IC-7300 has a noise level of S1 – 2. The KX-3 is S7 – 9, and the 7300 is  LOT more enjoyable to listen to in this environment.

I wanted to find out why – and it took just a minute to see that it is the pre-amp. In the IC-7300, I can hear the signal clearly with less noise, but on the KX-3, without the preamp (which is much better noise wise), the signal also drops too much. It just isn’t as clear as the 7300. With the preamp in on the 7300 – the noise level jumps up to S5 – 7 – closer to the KX-3, but still not quite as bad. The point is – I seem to need the preamp in on the KX-3 and on the 7300 – I don’t at all. Signal loss on the KX-3 seems to be a problem where it is not on the 7300. It sure seems to be a signal to noise ratio difference as far as direct sampling vs. superhet designs are concerned.

http://www.ab4oj.com/sdr/apdxc16_sdr.pdf

This presentation confirms my findings. All of this also answers the question “If I were to get the Elecraft K4, which flavor would I buy?”. Its easy – the Direct Sampling, basic stock version. Maybe with the Dual Diversity receive option – IF I were still into having a nice NCC-2 with 2 Wellbrook ALA-1530LNP receiving loops.

But I am not at all interested in 160 or 80M DXing any more – 40M and above is it for me. This means there is NO reason for me to drool over the Elecraft K4. However, like I have mentioned before – if the KX-4 were to be a direct sampling receiver, then Elecraft would beat the IC-7300 and whatever the IC-705 ends up being.

I have to say, ICOM really disrupted things with the IC-7300. For the money, nothing else comes close – it really is an amazing DX rig – and if you don’t need the bells and whistles of say the IC-7610, or the new K4, I just don’t see any other radio offering so much for such a price. In fact, if you don’t care about size or power consumption – the 7300 is the better radio (receiver wise) in my book. You can listen a lot longer without getting the “noise fatigue” that you get with the KX-3.

Sherwood lists the KX-3 higher, and in the slide presentation, the author intimates that the 7300 does as well as legacy superhet receivers (like the KX-3). Personally, I think the 7300 and direct sampling is better – in noisy conditions.

When I saw a demo with Wayne, N6KR, he did discuss how you can add a superhet option to the K4 so you can better block out close in signals. Since I don’t care anymore about DXCC or big DXpedition pileups – this is not of interest to me. Here is a line from the Elecraft K4 product website page:

The K4 and K4D, like other “pure” direct-sampling radios, do not require crystal roofing filters. Digital signal processing is used to provide advanced demodulation, filtering, and signal display. The K4HD can operate either in direct-sampling or superhet mode. Typically the latter is only needed in the presence of extreme signals.

I will continue testing – and will try the close in dynamic range test (by ear) between the two rigs some day. I will also see if in less noisy conditions, how the two rigs compare.

For now – in this simple “Part 1” test – the IC-7300 wins this round for ease of listening in noisy conditions – but the KX-3 keyer is a LOT better than the clunky 7300 keyer.

I do expect that the K4 will be a GREAT radio – since its stock version is a direct sampling receiver. But at $4000, that is too much for my FREQ 300 pursuit.

2 Comments on “Direct Sampling SDR vs. Superhet (KX-3 vs. IC-7300)

  1. Hello Rich, this confirms my experience in the CQWW SSB last year. We used a Elecraft K3S and a IC-7300. I found the IC-7300 was much more quiet in receive during the busy contest traffic. My fellow contesters told me it was just how you set the filters and pre-amps. But I was definitely sold by the receive of the IC-7300.

    https://pe4bas.blogspot.com/2018/10/cqww-ssb-2018-pa6aa-contest-review.html

    Happy to own a IC-7300 now and a pleasure to listen to. 73, Bas

    Liked by 1 person

    • I’ll play with more preamp and filter settings, but “wide open” the 7300 beats the KX-3 handily. I know the KX-3 is very close in performance to the K3 I had, which was upgraded to be close to a K3S.

      I am quite sure that this KX-3 will be the last superhet I will own. It will be direct sampling for me from now on

      Like

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