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Author Topic: Comparing KX3 to Flex-6300 for weak signal CW?  (Read 641 times)

N1BBR

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Comparing KX3 to Flex-6300 for weak signal CW?
« on: June 25, 2021, 09:52:49 AM »

Hi all,
For a few years now, I've had the RF-Space SDR-IQ receiver
I use it primarily for CW-Skimmer and sometimes with Ham Radio Deluxe
The primary rig is the Elecraft K3s
And in some instances I've found the SDR is quieter than the K3.
And that makes me curious about playing with a full-blown SDR rig.

I've never found contesting of much interest.
But I get a kick out of pulling weak CW signals out of the noise floor.

I've been pondering either a used Elecraft KX3 or a used Flex-6300 because they both incorporate a full-blown SDR receiver.

I'm wondering if anyone has both of those rigs and could provide a comparison between them for weak signal CW listening?

Thanks in advance
N1BBR
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G4AON

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Re: Comparing KX3 to Flex-6300 for weak signal CW?
« Reply #1 on: June 25, 2021, 10:18:56 AM »

Recently I have been comparing the following on weak CW signals:
K3 (with 400 and 250 Hz roofing filter and “K3S” synth)
KX3 (with the KX3 audio “roofing” filter)
Icom IC7300
My home brew single superhet with 600 Hz roofing filter and audio peak filter

The best is my home brew RX, followed by the KX3. The IC7300 is in 4th place. I also have a QS1R but it wasn’t tested, it is used exclusively for CW Skimmer service.

The problem with the IC7300 is that it is too “lively”. It presents low levels of band noise at irritating audio levels, you can turn on the attenuator or narrow the bandwidth to the point where you can miss callers who are slightly off frequency. By comparison my home brew just works, weak signals are easy to copy without needing to do anything. There is some noise but nothing too annoying and off frequency signals are still audible.

I haven’t tried a Flex, but for me less digital equals nicer sounding receive.

Many have become fixated on the 2 tone lab tests by Rob Sherwood, perhaps it is time to return to overall audio quality? Older analogue radios with narrow CW filters might make a comeback. A friend with a TS830 says they sound particularly good.

73 Dave
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NO9E

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Re: Comparing KX3 to Flex-6300 for weak signal CW?
« Reply #2 on: June 25, 2021, 10:29:05 AM »

I remember when RSP1 had a clearer copy on a quiet 10m than my old K3. SDRs may have a cleaner audio path and less distortion due to filtering. Perhaps SDR had lower noise figure on 10m than early K3. K3S had a very low noise preamp.  Of course, under busy conditions RSP1 would collapse while K3 would keep on going.   

With Elecrafts, the smoothest signal was by K2. KX3 is smoother than K3 but its audio sounds harsh unless a certain AGC setting is turned off. Strong AM stations sometime bleed into KX3.

I have Flex 6600. Very clear audio from the back of the radio and less so remotely. With Flex I operate only 50% of time and use the remaining 50% to fix issues.  If you like fixing things, Flex is for you. 6300 has less effective bandpass filters than 6600.

Everyone tells the importance of antennas. FT450 with higher antenna may beat IC7851 with lower antenna. 
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KX2T

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Re: Comparing KX3 to Flex-6300 for weak signal CW?
« Reply #3 on: June 25, 2021, 11:05:49 AM »

Dave try and use NO PRE AMP on the 7300, its really more sensitive than most of the other radio's without the pre amp on in the 7300 and the sensitivity of the other radio's with there pre amp engaged. Use of the RF gain will be almost like an adjustable attenuator on the 7300 and to reduce what you are calling band/radio noise just press on the NR button and adjust to around level 2 to 3, you should see a real difference. The 7300 next to the Flex rigs will seem deaf cause they have almost zero front end gain so most none technical hams thing they are quite rigs but in reality they are slightly deaf, If Icom would bring out a 7300MKII version maybe they should add an adjustable step ATT circuit, you could use the 20db pad on the 7300 and that would be the same sensitivity as the Flex rigs without pre amp.
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KX2T

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Re: Comparing KX3 to Flex-6300 for weak signal CW?
« Reply #4 on: June 25, 2021, 11:37:10 AM »

Dave try and use NO PRE AMP on the 7300, its really more sensitive than most of the other radio's without the pre amp on in the 7300 and the sensitivity of the other radio's with there pre amp engaged. Use of the RF gain will be almost like an adjustable attenuator on the 7300 and to reduce what you are calling band/radio noise just press on the NR button and adjust to around level 2 to 3, you should see a real difference. The 7300 next to the Flex rigs will seem deaf cause they have almost zero front end gain so most none technical hams thing they are quite rigs but in reality they are slightly deaf, If Icom would bring out a 7300MKII version maybe they should add an adjustable step ATT circuit, you could use the 20db pad on the 7300 and that would be the same sensitivity as the Flex rigs without pre amp.
In the 7300 manual Icom recommends you use the RF gain control at times instead of the attenuator button, most never RTFM and are used to radio's that they need to use the pre amp on, Icom's have always been way to sensitive compared to the rest except for Kenwoods. This is easily seen on most lab test reviews if one knows what those Db numbers mean compared to others plus the MDS numbers as well.
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G4AON

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Re: Comparing KX3 to Flex-6300 for weak signal CW?
« Reply #5 on: June 25, 2021, 12:30:37 PM »

I have the IP+ turned on and no pre-amp with the 7300. On a really quiet band (at a portable location) it is OK, but at home with even an S1 to S3 background noise, it is noticeably poor by comparison with the KX3 and my home brew.

73 Dave
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K6SDW

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Re: Comparing KX3 to Flex-6300 for weak signal CW?
« Reply #6 on: June 25, 2021, 01:02:18 PM »

I own the KX3 and IC-7300...hands down the Elecraft is much quieter than the ICOM - but I use the 7300 because 100watts output and I love the waterfall and a lot more convenient .. I've never owned a Flex but I've heard good things about the rig.

If you like numbers, then I highly recommend Sherwood Engineering site.

GL/73
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N2DTS

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Re: Comparing KX3 to Flex-6300 for weak signal CW?
« Reply #7 on: June 25, 2021, 05:11:17 PM »

The sdr-iq was very good for its day, a good dynamic range and no spurs, but its not a quiet receiver.

All the newer rigs seem great at weak signal if you operate them in weak signal mode.
The 7300 does seem to have a lot of gain in default mode.

I have had the Anan 100b and 10e, the Flex 6300 6400m, the 3000 and 5000 (lots of spurs),
a few icom 7300's the ftdx 3000, the airspy hf plus discovery, the sdr-iq, the mchf clones, the Hermes lite 2 and the Icom 7600, along with the Elecraft k1, k2, kx2 and KX3 radios.
The newer Anan and Flex radios seem to have the edge these days, I have not had a K3.

I think the antenna might be more critical for weak signal work if the rig is in the ballpark....
A loop antenna you can turn and point to the signal and null noise is a big help.

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KX2T

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Re: Comparing KX3 to Flex-6300 for weak signal CW?
« Reply #8 on: June 26, 2021, 05:43:04 AM »

The problem with the 7300 it had a pre amp in front of the SDR section just like all Icom's superhets so if you read the manual and even if you don't just look at some of the excellent YouTube vids that show users adjusting the RF gain control so the band noise as you call it is low. If you look at the MDS figures of the 7300 without the pre amp in the cw mode its around -131Db compared to a Flex at -112Db and the Yaesu FTDX101D at -127Db and the KX3 at -120Db so if you are comparing the KX3 and the 7300 there is over a 10Db difference between the two so to compare apples tp apples you have to at least use a little more than 10Db of attenuation on the 7300 compared to the KX3. If you compare the Flex 6400 to the 7300 you should use the 20Db attenuator in the 7300 and then the comparo would be a fair one. Basically it seems that nobody really either understands what these numbers mean when they start to compare rigs side by side. BTW the onlt other SDR that is up around the Icom's sensitivity in cw is the Anan at around 132Db and all the above numbers are in the CW mode 500Hz bandwidth on 14 Mhz.
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N2DTS

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Re: Comparing KX3 to Flex-6300 for weak signal CW?
« Reply #9 on: June 26, 2021, 08:25:17 AM »

My comments were based on side by side listening to various radios at my QTH on the same antenna's and various bands.
I suspect my background noise level on many bands is well above what the new radios can provide.

Very few people are going to be able to use a -130 dB noise floor RX, although almost all noise seems cumulative (additive).

Then you also have the filter to consider on CW, a really sharp good filter removes a lot of noise from the signal you want to hear.

The 7300 is also subject to overload more then many others which may disrupt a weak signal.

The K3s wins big at -145!!
« Last Edit: June 26, 2021, 08:30:56 AM by N2DTS »
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W9IQ

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Re: Comparing KX3 to Flex-6300 for weak signal CW?
« Reply #10 on: June 26, 2021, 08:29:06 AM »

My usual friendly reminder that the unit abbreviation for the decibel is dB, not Db.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

N2DTS

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Re: Comparing KX3 to Flex-6300 for weak signal CW?
« Reply #11 on: June 26, 2021, 02:17:49 PM »


Audio quality is different from filter quality and background noise.
And you cant base digital sound on crappy ham radio dsp digital, something like the Anan or Flex radios is more hifi then hifi audio was 20 years ago.

That TS830 may sound ok audio wise, but otherwise its a very poor performer.
113 dB LO noise levels and 70 dB of close in dynamic range will make for rough copy.

I am very fond of simple single conversion analog receivers for low noise and fidelity, but a good sdr (Flex/Anan) will top it.

I am unsure about the audio quality of the FTdx 101 and 10 radios....
LO noise and dynamic range are tops though....
 




I haven’t tried a Flex, but for me less digital equals nicer sounding receive.

Many have become fixated on the 2 tone lab tests by Rob Sherwood, perhaps it is time to return to overall audio quality? Older analogue radios with narrow CW filters might make a comeback. A friend with a TS830 says they sound particularly good.

73 Dave
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NO9E

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Re: Comparing KX3 to Flex-6300 for weak signal CW?
« Reply #12 on: June 28, 2021, 07:15:49 AM »

Quote
That TS830 may sound ok audio wise, but otherwise its a very poor performer.
113 dB LO noise levels and 70 dB of close in dynamic range will make for rough copy.

People are obsessed with LO noise and dynamic range even though for not too busy band both numbers are irrelevant.

TS-830 has excellent speech processor via RF clipper with 2 crystal filters. Makes the transmit audio punchy well above many "superior" radios with lousy speech processing. I  contrast, KX3 has a very inefficient speech processor,  and while the the implementation of speech processing by Flex 6000 series is claimed to be best of any, the implementation falls far short IMHO. So in a summary, you will be be making more comfortable contacts with TS830 than with many newer radios. 
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KX2T

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Re: Comparing KX3 to Flex-6300 for weak signal CW?
« Reply #13 on: June 28, 2021, 10:04:56 AM »

This is my point with the 7300 comments about overload and the RX section having too much noise which directs anyone that does read the manual to READ IT! Most off the time on bands above 20m there is really no need for the pre amp in and if someone is that strong then use the RF gain control, this advice is from there manual plus many YouTube video's that show cause and effect but again it must be lack of reading things today. On the low bands you could get away with the 20db pad in which would make it right around were the Flex is at, perfect for the lower bands. The newer Yaesu has 2 pre amps and 6/12/18db steps for there attenuators but for some strange reason today many ops use the pre amp stages, why I have no idea but they think they will hear that weak station better but they must think like when they use that 30 to 40 year old tube rigs of yesteryear. Another area is the S meter, my guess is hams just like to see it wiggle allot!
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N2DTS

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Re: Comparing KX3 to Flex-6300 for weak signal CW?
« Reply #14 on: June 28, 2021, 04:56:37 PM »

Not obsessed, but poor LO noise makes for a dirty transmitter and noise on RX.
There are so many ways to get super punchy audio you do not need to use just the radio, although the Anan radios have serious broadcast audio processing in the software which can make you punch through OR sound like a broadcast personality.

So the 830 getting torn up by strong close in signals is no problem because you only use that super punchy audio on quiet empty bands.....what happens when you want to operate on 80 meters at night, or on field day???



Quote
That TS830 may sound ok audio wise, but otherwise its a very poor performer.
113 dB LO noise levels and 70 dB of close in dynamic range will make for rough copy.

People are obsessed with LO noise and dynamic range even though for not too busy band both numbers are irrelevant.

TS-830 has excellent speech processor via RF clipper with 2 crystal filters. Makes the transmit audio punchy well above many "superior" radios with lousy speech processing. I  contrast, KX3 has a very inefficient speech processor,  and while the the implementation of speech processing by Flex 6000 series is claimed to be best of any, the implementation falls far short IMHO. So in a summary, you will be be making more comfortable contacts with TS830 than with many newer radios.
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