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KX3 "Full" SDR

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Craig Schroeder

KX3 "Full" SDR

Happy New Year,

I want to move into the hobby aspects of SDR and have narrowed my list to the KX3 with 100 watt Amp or a Flex 3000. I have been told that though the KX3 will connect to a PC it is not a "full" SDR radio (my understanding of "full" is in regard to signal processing but there may be other factors implied that I am not aware of being new to the SDR world).

If this perspective is on target, what are the important SDR limitations with the KX3 that I should consider? If there are no important limitations, I do like the form factor and knobs on the KX3 over the Flex software-only interface.

Thank you,

Craig Schroeder
KD0TXL
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Fred Smith-2

Re: KX3 "Full" SDR

The KX3 is a real radio in every way not a computer and one that can be
taken with you for portable operations, batteries unlike a computer/monitor.
For another better receiver performance than the Flex and very small
footprint as far as limitations none only more advantages with the KX3.

73,
Fred/N0AZZ
K3 Ser # 6730--KX3 # 5210--K2/100 # 6470-KAT100
P3/SVGA--KAT500--W2
Amps Elecraft KPA500 HF/6m--Alpha's 9500 HF--87A HF--Mirage B-5030-G
300+w--(2) B-5016-G's 165w 2m

.

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Craig Schroeder
Sent: Tuesday, December 31, 2013 8:36 AM
To: [hidden email]
Subject: [Elecraft] KX3 "Full" SDR

Happy New Year,

I want to move into the hobby aspects of SDR and have narrowed my list to
the KX3 with 100 watt Amp or a Flex 3000. I have been told that though the
KX3 will connect to a PC it is not a "full" SDR radio (my understanding of
"full" is in regard to signal processing but there may be other factors
implied that I am not aware of being new to the SDR world).

If this perspective is on target, what are the important SDR limitations
with the KX3 that I should consider? If there are no important limitations,
I do like the form factor and knobs on the KX3 over the Flex software-only
interface.

Thank you,

Craig Schroeder
KD0TXL
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Don Wilhelm-4

Re: KX3 "Full" SDR

In reply to this post by Craig Schroeder

Craig,

The KX3 is a "full SDR" radio (the K3 is as well). By virtue of the
modulation and demodulation all being done the firmware rather than in
hardware. Yes, the KX3 does have knobs which are used to pass
parameters to the firmware - the "computer" is inside the KX3 and no
external computer is required.

There are some (maybe many) who believe an external computer is required
for the radio to be a "full SDR" but I am not in that group.

There are others who believe that one must have a panadapter display to
be a "full SDR", and again, I am not a member of that 'camp'. The KX3
with an external computer can have a panadapter display. It has RX I
and Q outputs which can be fed to a soundcard and applications such as
HDSDR, NaP3, or several other applications can provide that type
display, and even provide some level of rig control through the mouse
and keyboard.

If you choose the Flex, an external computer is required - with the KX3,
it is optional.
If you are one who would like to experiment with the SDR software rather
than using the 'stock' version, then you might be more interested in the
Flex or one of the other SDR radios that do use the external computer
for modulation and demodulation.

73,
Don W3FPR

On 12/31/2013 9:35 AM, Craig Schroeder wrote:
> Happy New Year,
>
> I want to move into the hobby aspects of SDR and have narrowed my list to the KX3 with 100 watt Amp or a Flex 3000. I have been told that though the KX3 will connect to a PC it is not a "full" SDR radio (my understanding of "full" is in regard to signal processing but there may be other factors implied that I am not aware of being new to the SDR world).
>
> If this perspective is on target, what are the important SDR limitations with the KX3 that I should consider? If there are no important limitations, I do like the form factor and knobs on the KX3 over the Flex software-only interface.
>
>

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Matt Zilmer-3

Re: KX3 "Full" SDR

In reply to this post by Craig Schroeder

Actually, a full SDR would have modulation and demod running in the
host software. A KX3 is self-contained in this regard, but can be
used with a PC or Mac for CW, RTTY, data modes, etc.

Signal processing capabilties are excellent on the KX3, and the array
of DSP features is both wide and deep.

Originally, the KX3 was intended to be a portable trail radio, which
is mostly the way I've used it. However since its introduction, the
KX3 has found a large following of ops that use it as their main base
station rig (either in addition to or in place of portable ops).

I guess if you consider that all major functions are software-based
(either MCU or DSP) and executing on a robust and bulletproof
RF-hardware platform, the KX3 is an SDR. Depends on how you define an
SDR.

73,
matt W6NIA

On Tue, 31 Dec 2013 08:35:36 -0600, you wrote:

>Happy New Year,
>
>I want to move into the hobby aspects of SDR and have narrowed my list to the KX3 with 100 watt Amp or a Flex 3000. I have been told that though the KX3 will connect to a PC it is not a "full" SDR radio (my understanding of "full" is in regard to signal processing but there may be other factors implied that I am not aware of being new to the SDR world).
>
>If this perspective is on target, what are the important SDR limitations with the KX3 that I should consider? If there are no important limitations, I do like the form factor and knobs on the KX3 over the Flex software-only interface.
>
>Thank you,
>
>Craig Schroeder
>KD0TXL
>______________________________________________________________
>Elecraft mailing list
>Home: http://mailman.qth.net/mailman/listinfo/elecraft
>Help: http://mailman.qth.net/mmfaq.htm
>Post: mailto:[hidden email]
>
>This list hosted by: http://www.qsl.net
>Please help support this email list: http://www.qsl.net/donate.html

Tony Estep

Re: KX3 "Full" SDR

In reply to this post by Craig Schroeder

Craig, get the KX3 and use NaP3 on your PC. You will have a complete
superset of what the 3000 will do, except that your radio will also be
great on CW and will be portable. You can use the on-screen tuning etc when
you want, but you may find circumstances when you are glad to have the
knobs.

Tony KT0NY

On Tue, Dec 31, 2013 at 8:35 AM, Craig Schroeder <[hidden email]> wrote:

> Happy New Year,
>
> I want to move into the hobby aspects of SDR and have narrowed my list to
> the KX3 with 100 watt Amp or a Flex 3000. I have been told that though the
> KX3 will connect to a PC it is not a "full" SDR radio (my understanding of
> "full" is in regard to signal processing but there may be other factors
> implied that I am not aware of being new to the SDR world).
>
> If this perspective is on target, what are the important SDR limitations
> with the KX3 that I should consider? If there are no important
> limitations, I do like the form factor and knobs on the KX3 over the Flex
> software-only interface.
>
> Thank you,
>
> Craig Schroeder
> KD0TXL
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Craig Schroeder

Re: KX3 "Full" SDR

In reply to this post by Matt Zilmer-3

Thank you everyone for responding so promptly to my SDR question and with such great information!

A particular point made in regard to SDR on the KX3 was hardware filter options vs software filters.

Are there differences here that are important to consider from a user's perspective? Pros/Cons of either approach?

Perhaps I should add that I'm primarily interested in DX'ing. The portability of the KX3 is a real bonus, but a secondary consideration. I plan to use the radio I purchase as my primary rig.

Thank you,

Craig
KD0TXL

On Dec 31, 2013, at 9:23 AM, Matt Zilmer <[hidden email]> wrote:

Actually, a full SDR would have modulation and demod running in the
host software. A KX3 is self-contained in this regard, but can be
used with a PC or Mac for CW, RTTY, data modes, etc.

Signal processing capabilties are excellent on the KX3, and the array
of DSP features is both wide and deep.

Originally, the KX3 was intended to be a portable trail radio, which
is mostly the way I've used it. However since its introduction, the
KX3 has found a large following of ops that use it as their main base
station rig (either in addition to or in place of portable ops).

I guess if you consider that all major functions are software-based
(either MCU or DSP) and executing on a robust and bulletproof
RF-hardware platform, the KX3 is an SDR. Depends on how you define an
SDR.

73,
matt W6NIA

> On Tue, 31 Dec 2013 08:35:36 -0600, you wrote:
>
> Happy New Year,
>
> I want to move into the hobby aspects of SDR and have narrowed my list to the KX3 with 100 watt Amp or a Flex 3000. I have been told that though the KX3 will connect to a PC it is not a "full" SDR radio (my understanding of "full" is in regard to signal processing but there may be other factors implied that I am not aware of being new to the SDR world).
>
> If this perspective is on target, what are the important SDR limitations with the KX3 that I should consider? If there are no important limitations, I do like the form factor and knobs on the KX3 over the Flex software-only interface.
>
> Thank you,
>
> Craig Schroeder
> KD0TXL
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

Fred Smith-2

Re: KX3 "Full" SDR

Craig I'm a DX'er only and use my KX3 for QRP DX'ing. The band pass filter
works very well in the radio and IMHO a must have option

73,
Fred/N0AZZ
K3 Ser # 6730--KX3 # 5210--K2/100 # 6470-KAT100
P3/SVGA--KAT500--W2
Amps Elecraft KPA500 HF/6m--Alpha's 9500 HF--87A HF--Mirage B-5030-G
300+w--(2) B-5016-G's 165w 2m

for a DX'er.

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Craig Schroeder
Sent: Tuesday, December 31, 2013 10:10 AM
To: [hidden email]
Subject: Re: [Elecraft] KX3 "Full" SDR

Thank you everyone for responding so promptly to my SDR question and with
such great information!

A particular point made in regard to SDR on the KX3 was hardware filter
options vs software filters.

Are there differences here that are important to consider from a user's
perspective? Pros/Cons of either approach?

Perhaps I should add that I'm primarily interested in DX'ing. The
portability of the KX3 is a real bonus, but a secondary consideration. I
plan to use the radio I purchase as my primary rig.

Thank you,

Craig
KD0TXL

On Dec 31, 2013, at 9:23 AM, Matt Zilmer <[hidden email]> wrote:

Actually, a full SDR would have modulation and demod running in the host
software. A KX3 is self-contained in this regard, but can be used with a PC
or Mac for CW, RTTY, data modes, etc.

Signal processing capabilties are excellent on the KX3, and the array of DSP
features is both wide and deep.

Originally, the KX3 was intended to be a portable trail radio, which is
mostly the way I've used it. However since its introduction, the
KX3 has found a large following of ops that use it as their main base
station rig (either in addition to or in place of portable ops).

I guess if you consider that all major functions are software-based (either
MCU or DSP) and executing on a robust and bulletproof RF-hardware platform,
the KX3 is an SDR. Depends on how you define an SDR.

73,
matt W6NIA

> On Tue, 31 Dec 2013 08:35:36 -0600, you wrote:
>
> Happy New Year,
>
> I want to move into the hobby aspects of SDR and have narrowed my list to
the KX3 with 100 watt Amp or a Flex 3000. I have been told that though the
KX3 will connect to a PC it is not a "full" SDR radio (my understanding of
"full" is in regard to signal processing but there may be other factors
implied that I am not aware of being new to the SDR world).
>
> If this perspective is on target, what are the important SDR limitations
with the KX3 that I should consider? If there are no important limitations,
I do like the form factor and knobs on the KX3 over the Flex software-only
interface.

>
> Thank you,
>
> Craig Schroeder
> KD0TXL
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net Please help support this email
> list: http://www.qsl.net/donate.html

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Don Wilhelm-4

Re: KX3 "Full" SDR

In reply to this post by Craig Schroeder

Craig,

Most of the filtering is done in DSP. The 'roofing filters' add some
protection by restricting the bandpass seen by the ADC, but do not
provide the final filtering.

73,
Don W3FPR

On 12/31/2013 11:09 AM, Craig Schroeder wrote:
> A particular point made in regard to SDR on the KX3 was hardware filter options vs software filters.
>
>

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Greg Troxel-2

Re: KX3 "Full" SDR

In reply to this post by Don Wilhelm-4

Don Wilhelm <[hidden email]> writes:

> The KX3 is a "full SDR" radio (the K3 is as well). By virtue of the
> modulation and demodulation all being done the firmware rather than in
> hardware. Yes, the KX3 does have knobs which are used to pass
> parameters to the firmware - the "computer" is inside the KX3 and no
> external computer is required.
>
> There are some (maybe many) who believe an external computer is
> required for the radio to be a "full SDR" but I am not in that group.

There are several important questions that could be lurking behing "full
SDR", especially since Craig talked about hobby aspects of SDR -- people
often mistakenly equate SDR with "open-source SDR", blurring "functions
are controlled by software" with "user can control functions by
software".

1) Is the modulation/demodulation done in some sort of processor under
software control, from a wide IF (perhaps at 0, perhaps higher)? This
is the normal definition, and indeed the KX3 meets it.

2) Is the user of the radio able to change the firmwmare, in order to
experiment or for other purposes? One might call this "user-changeable
SDR". Here, the KX3 does not meet that definition -- while Elecraft has
released updates and improvements and can be expected to keep doing so,
users cannot improve or even read the software.

2a) Can someone who changes the firmware share their improvements with
the world? This is a further nuance, leading to "open-source SDR".
Flex used to be like this, but I understand (from speaking to a Flex rep
at Boxboro 2012) that the software used with their radios is now
proprietary rather than open source. And, it is limited to Windows
only, which leads to an unreliable system (as described by a Flex user
who gave a talk at a local club). Note that there is hardly any
discussion of KX3s locking up and being flaky and needing to be
rebooted.

Then there's a related question separate from SDR definitions, having to
do with packaging and interconnects:

3) Does the radio function without having to carry along an external
computer? There is great merit in a small low-power box being
functional by itself.

Craig:

So it really depends why you think you want an SDR. If you want to
understand the software and contribute towards a community of people
improving it, the KX3 won't let you do that, and I would suggest that
you look at GNU Radio and other open-source projects and their
associated hardware (some of which has open designs). If you want a
radio which has features typically achievable in SDR, and that you can
expect to be improved by the manufacturer, and you don't mind not being
able to change it (and that others can't either), then the KX3 fits the
bill.

If what you want is to experiment with code to demodulate, the KX3 is
also a good choice because it provides I/Q output. But I know of no way
to transmit custom signals (other than soundcard modes, which generally
are viewed as below the SDR definition).

My advice is to think about what you really want in terms of an
experimentation/learning platform vs. a really well designed useful
radio. And if you are going to experiment with code, stay within the
open-source world, so that you can share your changes with everyone.

73 de n1dam
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David Gilbert

Re: KX3 "Full" SDR

In reply to this post by Craig Schroeder

An equally important consideration for any rig, SDR or not, is what kind
of signal you are transmitting. All of the FLEX rigs have a very bad
reputation for transmitting lots of wideband phase noise, while the KX3
is near the top of the heap for cleanliness of signal. The difference
between the two is not slight ... it is spectacular.

Coincidentally enough, there was a very recent thread here discussing
this very topic. Based upon the published test results I've seen, if
everyone used FLEX SDR rigs nobody would enjoy SDR rigs ... or any
other rigs for that matter. Check out
http://www.sm5bsz.com/dynrange/dubus313.pdf for the details.

73,
Dave AB7E

On 12/31/2013 7:35 AM, Craig Schroeder wrote:

> Happy New Year,
>
> I want to move into the hobby aspects of SDR and have narrowed my list to the KX3 with 100 watt Amp or a Flex 3000. I have been told that though the KX3 will connect to a PC it is not a "full" SDR radio (my understanding of "full" is in regard to signal processing but there may be other factors implied that I am not aware of being new to the SDR world).
>
> If this perspective is on target, what are the important SDR limitations with the KX3 that I should consider? If there are no important limitations, I do like the form factor and knobs on the KX3 over the Flex software-only interface.
>
> Thank you,
>
> Craig Schroeder
> KD0TXL
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Tony Estep

Re: KX3 "Full" SDR

In reply to this post by Craig Schroeder

On Tue, Dec 31, 2013 at 10:09 AM, Craig Schroeder <[hidden email]> wrote:

> ...I'm primarily interested in DX'ing....

=========
Craig, if you're a DXer and you want an SDR, get a K3 and LP-Pan and set up
NaP3 on your computer. Forget the Flex radios.

I actually worked DXCC with a Flex 1500 just to prove it could be done, but
it wasn't a good experience. Neither was my time with the 3000. You'll want
to be working split a lot of the time (most of the time if you're a CW op),
and on-screen tuning with a mouse is just not up to the job. And for the
times when you do want to do that, NaP3 has all the capabilities of the
Flex. In fact, you can listen to the NaP3 SDR, use its filters, NB and NR
if you wish -- but they're not up to those in the K3. And the CW on Flex
radios is poor. The K3 is the weapon of choice for DXers all over the
world, for good reason.

73,
Tony KT0NY
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Bruce Beford-2

Re: KX3 "Full" SDR

In reply to this post by Craig Schroeder

Many people seem to be either forgetting, or missing the point of Leif's
article (referenced below). The entire thrust was in the context of using an
HF transceiver as an IF rig with VHF/UHF/SHF transverters. Band noise on
those higher freqs is low enough that transmitted phase noise can be an
issue. This is especially true when running high power.

His summation was that the Flex-1500 is marketed as being perfect for
driving microwave transverters. His article outlines why this may not be
true. The FLEX SDR radios are not as objectionable on the HF bands, where
atmospheric and other noise dominates.

Bruce, N1RX

> Based upon the published test results I've seen, if
> everyone used FLEX SDR rigs nobody would enjoy SDR rigs ... or any
> other rigs for that matter. Check out
> http://www.sm5bsz.com/dynrange/dubus313.pdf for the details.

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Dave-7

Re: KX3 "Full" SDR

While it is true that, for a station receiving via skywave on the HF
bands, the path loss will usually drive the noise from a Flex TX below
the distant stations noise floor, let us not forget those within range
of the ground wave.

For those, the noise from a Flex at 100w, at -77 dBc (which is -27
dBm), can be quite substantial. Recall that S9 is approx -72 dBm. A
Flex is transmitting wideband S9+45 noise.

I would think that a Flex would be absolutely intolerable for any
event involving nearby stations, such as Field Day.

And I would think anyone running a Flex who happens to have neighbors
within a few miles would not be a popular fellow.

73 de dave
ab9ca/4

On 12/31/13 12:57 PM, Bruce Beford wrote:

> Many people seem to be either forgetting, or missing the point of Leif's
> article (referenced below). The entire thrust was in the context of using an
> HF transceiver as an IF rig with VHF/UHF/SHF transverters. Band noise on
> those higher freqs is low enough that transmitted phase noise can be an
> issue. This is especially true when running high power.
>
> His summation was that the Flex-1500 is marketed as being perfect for
> driving microwave transverters. His article outlines why this may not be
> true. The FLEX SDR radios are not as objectionable on the HF bands, where
> atmospheric and other noise dominates.
>
> Bruce, N1RX
>
>
>> Based upon the published test results I've seen, if
>> everyone used FLEX SDR rigs nobody would enjoy SDR rigs ... or any
>> other rigs for that matter. Check out
>> http://www.sm5bsz.com/dynrange/dubus313.pdf for the details.
>
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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Bruce Beford-2

Re: KX3 "Full" SDR

In reply to this post by Craig Schroeder

> For those, the noise from a Flex at 100w, at -77 dBc (which is -27
> dBm), can be quite substantial. Recall that S9 is approx -72 dBm. A
> Flex is transmitting wideband S9+45 noise.

OK, I'm not a Flex user. But, I don't agree with your math. I am not trying
to defend the transmitted phase noise performance of the Flex products,
but... Your math is flawed.

Assume 100w transmitter is delivering +50 dBm to an antenna. (100W is 50 dB
greater than 1 milliwatt) Also assume you are at a receiving station, and
hearing this station at S9+30 dB, on a receiver calibrated to 6dB/S unit,
S9=50uV at 50 Ohms, or -73dBm for S9. Your receiving the fundamental signal
at -43dBm (S9+30dB). With the transmitted phase noise 77dBbelow the carrier,
it would be received at -120dBm, or about S2.

Granted, it would be 10 dB stronger (abt S3.5), if you were receiving the
fundamental transmission at S9+40dB, etc. But... the Flex is not "
transmitting wideband S9+45 noise."

Let's not blow this out of proportion.

Bruce N1RX

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NJ3K

Re: KX3 "Full" SDR

So I have been setting here with the ARRL handbook and trying to understand
this stuff. This is what I have come up with using the formula in the
handbook;
Aqrm = NL + 10 x log (BW)

Aqrm = interfering signal in db
NL = noise level on the receive frequency in dBc
BW = receiver IF band width in hZ (I am using a 500 hZ filter)

Aqrm = -77 + 10 x Log (500)
= -77 + 10 x 2.69897
= -77 + 26.9897
= -50.01 dB
If the tx signal is S9 +20 dB then you add +20dB to the -50.01dB
and you get -30.01dB which is a S4 signal. So a S4 signal is a lot of QRM.
If the band width is 1000 hZ the signal would be S5 plus 3 dB. And all
of this is at 350kHz away from the Tx signal.

K3
Doing the same math but using the 120 dBc at 360kHz we get a interfering
signal of -73 dB, which is 75 dB below an S1.

Now no one has ever accused me of being the brightest bulb in the box, but
this is what I have come up with.

73 and HNY looking forward to SKN in a few hours!
Bruce NJ3K

-----Original Message-----
From: Bruce Beford
Sent: Tuesday, December 31, 2013 4:38 PM
To: [hidden email]
Subject: Re: [Elecraft] KX3 "Full" SDR

> For those, the noise from a Flex at 100w, at -77 dBc (which is -27
> dBm), can be quite substantial. Recall that S9 is approx -72 dBm. A
> Flex is transmitting wideband S9+45 noise.

OK, I'm not a Flex user. But, I don't agree with your math. I am not trying
to defend the transmitted phase noise performance of the Flex products,
but... Your math is flawed.

Assume 100w transmitter is delivering +50 dBm to an antenna. (100W is 50 dB
greater than 1 milliwatt) Also assume you are at a receiving station, and
hearing this station at S9+30 dB, on a receiver calibrated to 6dB/S unit,
S9=50uV at 50 Ohms, or -73dBm for S9. Your receiving the fundamental signal
at -43dBm (S9+30dB). With the transmitted phase noise 77dBbelow the carrier,
it would be received at -120dBm, or about S2.

Granted, it would be 10 dB stronger (abt S3.5), if you were receiving the
fundamental transmission at S9+40dB, etc. But... the Flex is not "
transmitting wideband S9+45 noise."

Let's not blow this out of proportion.

Bruce N1RX

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Richard Ferch

Re: KX3 "Full" SDR

In reply to this post by Craig Schroeder

AB9CA/4 wrote:

> I would think that a Flex would be absolutely intolerable for any
> event involving nearby stations, such as Field Day.

I can attest to that from personal experience.

A couple of friends and I did a two-transmitter FD operation. His rig
was a Flex-1500, mine was a K3. Both running 5W, on battery power
(separate batteries), on separate antennas.

We had hoped to be able to operate on the same band on different modes.
In fact, when I was operating CW low in the band and he was listening on
SSB higher up the band, he said he could not tell when I was
transmitting. However, the reverse was definitely *not* the case.
Whenever he pressed the PTT button on the mike on his Flex-1500, my
received band noise went up by several S units. I could only hear the
strongest signals through the noise; everything else was covered up. The
noise level was high as long as his rig was in transmit, even when he
was not talking into the mike.

73,
Rich VE3KI
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Dave-7

Re: KX3 "Full" SDR

In reply to this post by Bruce Beford-2

Well, I don't understand your math . . .

Yes, 100w is +50 dBm.

The TX noise is 77 dB below the carrier (for a SSB bandwidth).

We subtract 77 from 50 noise level = -27 dBm

This is the level of the wideband TX noise as it leave the TX.

S9 = ~ -72 dBm

-27 dBm is 45 dB above -72 dBm

Hence the TX noise level is S9+45 as it leaves the TX . . .

Now . . . the RX noise level is whatever the TX noise level is minus
the path losses.

Assume skywave path losses of 100 dB.

RX noise level is -100 - 27 = -127 dBm.

This would be approx the MDS of most RX and would usually be buried in
the band noise.

Now assume ground wave path losses of 60 dB.

RX noise level = -27 - 60 or -87 dBm.

If S9 is -72 dBm this is only 15 dB below that or about an S6 noise level.

The level of any RX signal is irrelevant (except for whatever AGC
action it may induce). It is what it is. This is wideband noise which
the RX will hear as wideband noise. The noise level will jump up each
time the Flex is keyed. Note that no modulation need be sent. All that
is necessary is to key the TX.

And, no, the station listening to the Flex TX does not hear the noise.
He hears the signal. The guy tuned to another signal, even one 300 kHz
away, is the one that gets blasted by the wideband TX noise.

And the paper linked-to was indeed about VHF/UHF contesting. But for
those ops the path loss is mountain-top to mountain-top and is much
less than skywave path losses. So any Flex model is really, really not
welcome by the VHF contesting crowd. That was the point of the paper.
And the same thing applies to most ground wave paths as well.

73 de dave
ab9ca/4

On 12/31/13 3:38 PM, Bruce Beford wrote:

>> For those, the noise from a Flex at 100w, at -77 dBc (which is -27
>> dBm), can be quite substantial. Recall that S9 is approx -72 dBm. A
>> Flex is transmitting wideband S9+45 noise.
>
> OK, I'm not a Flex user. But, I don't agree with your math. I am not trying
> to defend the transmitted phase noise performance of the Flex products,
> but... Your math is flawed.
>
> Assume 100w transmitter is delivering +50 dBm to an antenna. (100W is 50 dB
> greater than 1 milliwatt) Also assume you are at a receiving station, and
> hearing this station at S9+30 dB, on a receiver calibrated to 6dB/S unit,
> S9=50uV at 50 Ohms, or -73dBm for S9. Your receiving the fundamental signal
> at -43dBm (S9+30dB). With the transmitted phase noise 77dBbelow the carrier,
> it would be received at -120dBm, or about S2.
>
> Granted, it would be 10 dB stronger (abt S3.5), if you were receiving the
> fundamental transmission at S9+40dB, etc. But... the Flex is not "
> transmitting wideband S9+45 noise."
>
> Let's not blow this out of proportion.
>
> Bruce N1RX
>
>
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> .
>

Bruce Beford-2

Re: KX3 "Full" SDR

In reply to this post by Craig Schroeder

Dave, I agree with your math, except...

Having a noise level of -27dBm delivered by the transmitter to the antenna
system, does not mean the antenna has 100% radiation efficiency, yes?

So -27dBm is 2 microwatts in transmitted noise to the antenna system, at
this particular spacing, in a 500Hz bandwidth.

You must make some allowances for not only path loss, but antenna efficiency
on each end, yes?

As I said, I am not trying to defend these performance (or lack thereof)
claims. I just disagreed with the statement that the "Flex is transmitting
wideband S9+45 noise"

"S9+45dB" is a receive measurement, not a transmitter measurement. The Flex
is sending 2 microwatts to the antenna at the frequency in question.
Admittedly, that's too much, in many situations.

Peace,
Bruce N1RX

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David Gilbert

Re: KX3 "Full" SDR

In reply to this post by Bruce Beford-2

The article itself is far less relevant to this discussion than the data
included in it. There has been lots of complaining in various contest
forums regarding the insidious wideband trash caused by rigs with bad
phase noise, and if you think that 30 to 50 db difference is not
noticeable at HF you either don't live in a very quite area (I do) or
you don't do much contesting where several hundred other stations are
operating at the same time on the same band.

Besides, what do you think happens during events like Field Day, or when
the ham three miles away is putting out that kind of trash??

I stand by my statement ... if everyone used FLEX SDR rigs (you do know
that noise power is additive, right?) we'd all have a major problem.

Dave AB7E

On 12/31/2013 11:57 AM, Bruce Beford wrote:

> Many people seem to be either forgetting, or missing the point of Leif's
> article (referenced below). The entire thrust was in the context of using an
> HF transceiver as an IF rig with VHF/UHF/SHF transverters. Band noise on
> those higher freqs is low enough that transmitted phase noise can be an
> issue. This is especially true when running high power.
>
> His summation was that the Flex-1500 is marketed as being perfect for
> driving microwave transverters. His article outlines why this may not be
> true. The FLEX SDR radios are not as objectionable on the HF bands, where
> atmospheric and other noise dominates.
>
> Bruce, N1RX
>
>
>> Based upon the published test results I've seen, if
>> everyone used FLEX SDR rigs nobody would enjoy SDR rigs ... or any
>> other rigs for that matter. Check out
>> http://www.sm5bsz.com/dynrange/dubus313.pdf for the details.
>
>
>
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Bruce Beford-2

Re: KX3 "Full" SDR

In reply to this post by Craig Schroeder

> I stand by my statement ... if everyone used FLEX SDR rigs (you do know
> that noise power is additive, right?) we'd all have a major problem.

> Dave AB7E

With that, I agree.
Bruce, N1RX

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