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K3 - Performance on 6M?

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VK4XA

K3 - Performance on 6M?

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W7GJ, Lance

Re: K3 - Performance on 6M?

Hello Jeff,

The K3 is an outstanding rig on 6m. The flat bandpass is ideal for weak signal
digital work, and the noise blanker really shines on 6m, where noise seems to be
so prevalent. The PR6 preamp is excellent, and you WILL need it. If you keep
your feedline loss under 1.0 dB, you will not gain anything by instead mounting a
preamp at the antenna. GL and VY 73, Lance

On 4/2/2010 2:03 AM, Jeff Cochrane - VK4BOF wrote:

> Hi everyone,
> Sorry to trouble you all again but I'd like to find out more on the K3's 6M performance as very little seems to be mentioned on the Elecraft website.
> The 6M band is rather important to me and my new station will have at least a 7 element yagi at 60' or so and maybe higher.
> I currently own a late series Yaesu FT847 which has been my mainstay VHF/UHF rig since I was licenced a few years ago and it has a proven to have good performance on 6M and higher.
> What I'd like to know from those of you that regularly use the K3 on 6M is what you think of its performance on that band, compared to other radios.
> Is it sensitive enough compared to the other radios and if not, is the Elecraft pre-amp worth it or should I go for a masthead mounted pre-amp in preference?
>
> Thanks in advance,
>
> Jeff Cochrane - VK4BOF
> Innisfail, QLD
> Australia.
> (But not for much longer!)
> ______________________________________________________________
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>

--
Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8, E51SIX)
P.O. Box 73
Frenchtown, MT 59834 USA
QTH: DN27UB
TEL: (406) 626-5728 URL: http://www.bigskyspaces.com/w7gj
LIVE MESSENGER CHAT: [hidden email]
2m DXCC #11, 6m DXCC #815

Interested in 6m EME? Ask me about subscribing to the Magic Band EME email!
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Re: K3 - Performance on 6M?

In reply to this post by VK4XA

Jeff, I don't claim to be a 6 meter expert. The K3 is the only radio I have ever used on 6 meters, but I have operated some with my SteppIR beam and I am happy. Elecraft makes a 6 meter preamp and the folks that have it seem to be happy with its performance. I am using the regular preamp that comes with the stock K3 and I am happy.
Willis 'Cookie' Cooke
K5EWJ

________________________________
From: Jeff Cochrane - VK4BOF <[hidden email]>
To: [hidden email]
Sent: Thu, April 1, 2010 9:03:34 PM
Subject: [Elecraft] K3 - Performance on 6M?

Hi everyone,
Sorry to trouble you all again but I'd like to find out more on the K3's 6M performance as very little seems to be mentioned on the Elecraft website.
The 6M band is rather important to me and my new station will have at least a 7 element yagi at 60' or so and maybe higher.
I currently own a late series Yaesu FT847 which has been my mainstay VHF/UHF rig since I was licenced a few years ago and it has a proven to have good performance on 6M and higher.
What I'd like to know from those of you that regularly use the K3 on 6M is what you think of its performance on that band, compared to other radios.
Is it sensitive enough compared to the other radios and if not, is the Elecraft pre-amp worth it or should I go for a masthead mounted pre-amp in preference?

Thanks in advance,

Jeff Cochrane - VK4BOF
Innisfail, QLD
Australia.
(But not for much longer!)
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Jeff Cochrane - VK4XA

Re: K3 - Performance on 6M?

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K6LMP

Re: K3 - Performance on 6M?

In reply to this post by VK4XA

Jeff, I bought my K3 in large part for VHF/UHF contesting. The receiver is excellent for 6 meter weak signal work, but you will want to get the PR6 preamp. I concur with others that it is highly desirable, and also that it will give you as much performance, with less hassle, than a masthead mounted pre-amp. To install the PR6, you should also get the transverter interface/receive antenna module, which greatly simplifies installation and makes for easier operation.

N5GE posted a very nice little analysis to the Elecraft reflector some time back, showing his experience in puling in a weak 6 meter beacon located in Buenos Aires. He reports that the PR6 improves weak signal reception better than using the internal preamp in the K3, and that for very, very weak signals using both preamps together is helpful. See his report at

http://www.mail-archive.com/elecraft@.../msg86350.html

The PR6 preamp is desirable/necessary because receiver sensitivity on 6 meters is inherently less than on HF bands in the K3, due to the basic architecture of the rig. It's not a design flaw, but rather the result of a tradeoff of design considerations.

>From my experience, the K3 will serve you very well on 6 meters, and very, very well with the addition of the PR6 preamp.

Lew K6LMP

On Apr 1, 2010, at 7:03 PM, Jeff Cochrane - VK4BOF wrote:

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Dave, G4AON

Re: K3 - Performance on 6M?

In reply to this post by VK4XA

Jeff, you will probably need a pre-amp with the K3. My experience of 6m
over the past 3 or 4 years with a 4 ele quad is that many signals are
very weak and the K3 lacks the sensitivity to deal with them unless you
either add a pre-amp or have a high level of local noise masking those
signals.

My K3, serial 80, gives 10 dB SINAD at -126 dBm in a 400 Hz bandwidth
using the internal pre-amp. Adding an external Advanced Receiver
Research P50VDG pre-amp via the KXV3 RX ANT IN/OUT sockets improved the
sensitivity by 10 dBm which is a huge improvement for weak signal work.
The Elecraft pre-amp is a similar specification and should give similar
results. For those who compare figures using MDS the "with and without"
figures in a 400 Hz bandwidth are -136 dBm and -146 dBm. Image rejection
is marginal at 62 dB.

Power output on 6m is fine and the worse case harmonic is -60 dB.

73 Dave, G4AON
---------------------------------

Hi everyone,
Sorry to trouble you all again but I'd like to find out more on the K3's
6M performance as very little seems to be mentioned on the Elecraft website.
<SNIP>

Jeff Cochrane - VK4BOF
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Bill VanAlstyne W5WVO

Re: K3 - Performance on 6M?

This is an excellent thread, and one that I would like to see continued. I
use the K3 exclusively on 6 meters right now. I work both SSB and CW during
sporadic-E conditions and WSJT digital modes on meteor scatter at other
times when the band is "dead." Eagerly anticipating some F2 on the band in
three or four years.

I have used the K3 both with and without the PR6 preamplifier.

Dave's comment brings up a crucial point:

> "...many signals are very weak and the K3 lacks the sensitivity to deal
> with them unless you either add a pre-amp or have a high level of local
> noise masking those signals."

Right. This is the salient point I want to explore further.

It has been said by many hams over the years that if you connect an antenna
to a receiver and you can hear the noise level increase, then you don't need
a preamp, as it will simply amplify the noise and the signal equally. In
general, I've found that to be true. HOWEVER...

Let's say that the noise figure of the receiver's internal preamp is 1.5 dB,
and the noise figure of the external preamp is 0.5 dB. Each preamp will give
you about 10 dB of gain. It seems clear that using the external preamp
instead of the internal one would give you another dB of signal+noise to
noise. Is my reasoning accurate on that score? If so, then it would be
useful to know the noise figure of the K3's internal preamp at 50 MHz. I
don't know what it is.

Second, in my experience, the gain of the PR6 and the gain of the internal
preamp are NOT the same, with the PR6 having more gain -- more gain than I
need, actually, given my ambient noise level caused by living in a large
metro area.

Third, since I live in the shadow of a large number of high-powered VHF
broadcasting stations, there is a LOT of powerful out-of-band RF floating
around. Thankfully, its effect on 6 meters was vastly decreased when our
local Channel 2, 4, and 5 TV stations went to UHF digital. Before that
happened, the PR6 would be badly overloaded and create some nasty IMD
products on 6 meters unless I put my rather hefty DMI 8-pole bandpass filter
in-line with the preamp (on receive only). This cured the overload/IMD
problem, but at a cost of about 1 dB of insertion loss. Now that the
low-band TV broadcasters have been evicted, I need to try the PR6 again
without the DMI filter and see if the PR6 is still overloaded by out-of-band
RF. I haven't yet tried that yet. But if I really don't need it, why bother?

I just recently put the K3 back in the station setup after having it on the
bench for several months with a transmit section problem. Replacing the
KPAIO3 board seems to have cured that. Thanks, Elecraft. But now I'm back to
the "preamp-or-no-preamp" decision point. Currently, it is set up without
the PR6, and since my antenna noise level is at least 3 dB above the
receiver MDS even in my most quiet beam direction (NNW), I'm thinking I
don't really need to use it.

But am I wrong in my thinking? I'd like to hear some knowledgeable comments.

Bill W5WVO

--------------------------------------------------
From: "Dave, G4AON" <[hidden email]>
Sent: Friday, April 02, 2010 4:25 AM
To: <[hidden email]>
Subject: Re: [Elecraft] K3 - Performance on 6M?

> Jeff, you will probably need a pre-amp with the K3. My experience of 6m
> over the past 3 or 4 years with a 4 ele quad is that many signals are
> very weak and the K3 lacks the sensitivity to deal with them unless you
> either add a pre-amp or have a high level of local noise masking those
> signals.
>
> My K3, serial 80, gives 10 dB SINAD at -126 dBm in a 400 Hz bandwidth
> using the internal pre-amp. Adding an external Advanced Receiver
> Research P50VDG pre-amp via the KXV3 RX ANT IN/OUT sockets improved the
> sensitivity by 10 dBm which is a huge improvement for weak signal work.
> The Elecraft pre-amp is a similar specification and should give similar
> results. For those who compare figures using MDS the "with and without"
> figures in a 400 Hz bandwidth are -136 dBm and -146 dBm. Image rejection
> is marginal at 62 dB.
>
> Power output on 6m is fine and the worse case harmonic is -60 dB.
>
> 73 Dave, G4AON
> ---------------------------------
>
> Hi everyone,
> Sorry to trouble you all again but I'd like to find out more on the K3's
> 6M performance as very little seems to be mentioned on the Elecraft
> website.
> <SNIP>
>
> Jeff Cochrane - VK4BOF
> ______________________________________________________________
> 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
>
>

Mike Harris

Re: K3 - Performance on 6M?

In reply to this post by K6LMP

G'day,

No big deal but to avoid any confusion the archived mail quoted is
rather a hybrid, the analysis is my observations on reception of the
BA beacon.

Not been listening on 6M much just lately because the coax for the
beam has been diverted to a temporary 80M dipole, soon to come down.
I prefer the hiss to the ear crunching QRN.

Regards,

Mike VP8NO

>
> N5GE posted a very nice little analysis to the Elecraft reflector
> some time back, showing his experience in puling in a weak 6 meter
> beacon located in Buenos Aires. He reports that the PR6 improves
> weak signal reception better than using the internal preamp in the
> K3, and that for very, very weak signals using both preamps
> together is helpful. See his report at
>
> http://www.mail-archive.com/elecraft@.../msg86350.html
>
> The PR6 preamp is desirable/necessary because receiver sensitivity
> on 6 meters is inherently less than on HF bands in the K3, due to
> the basic architecture of the rig. It's not a design flaw, but
> rather the result of a tradeoff of design considerations.
>
>>From my experience, the K3 will serve you very well on 6 meters,
>>and very, very well with the addition of the PR6 preamp.
>
> Lew K6LMP

W8JI

Re: K3 - Performance on 6M?

In reply to this post by Bill VanAlstyne W5WVO

It has been said by many hams over the years that if you
connect an antenna
to a receiver and you can hear the noise level increase,
then you don't need
a preamp, as it will simply amplify the noise and the signal
equally. In
general, I've found that to be true. HOWEVER...

Let's say that the noise figure of the receiver's internal
preamp is 1.5 dB,
and the noise figure of the external preamp is 0.5 dB. Each
preamp will give
you about 10 dB of gain. It seems clear that using the
external preamp
instead of the internal one would give you another dB of
signal+noise to
noise. Is my reasoning accurate on that score? If so, then
it would be
useful to know the noise figure of the K3's internal preamp
at 50 MHz. I
don't know what it is.>>>>

I don't know the figures of the K3, but here is how it would
work out for some arbitrary numbers:

.5 dB NF preamp 10 dB gain to 1.5 dB amp 10 dB gain to 8 dB
NF 8 db gain mixer. = 0.85 dB NF

1.5 dB NF 10 dB gain RF amp to 8 dB NF 8dB gain mixer = 2.89
dB composite NF

There can be a larger NF increase than the difference in NF
between the preamps.

I doubt any of us would actually need a 0.5 db NF with a
terrestrial aimed antenna of normal beamwidth and gain on
six meters. I certainly don't and I'm in a quiet rural
location on a dirt road. A few dB NF is enough here.

What noise figure do other people **really** find they
need?? Anyone know exact figures?

73 Tom

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n7ws

Re: K3 - Performance on 6M?

In reply to this post by VK4XA

I'm going to violate the "Top posting is the rule" rule for this one.

--- On Fri, 4/2/10, Bill VanAlstyne W5WVO <[hidden email]> wrote:

> Let's say that the noise figure of the receiver's internal
> preamp is 1.5 dB,
> and the noise figure of the external preamp is 0.5 dB. Each
> preamp will give
> you about 10 dB of gain. It seems clear that using the
> external preamp
> instead of the internal one would give you another dB of
> signal+noise to
> noise. Is my reasoning accurate on that score? If so, then
> it would be
> useful to know the noise figure of the K3's internal preamp
> at 50 MHz. I
> don't know what it is.

There is no correlation between the NF of an amplifier and its gain. So your "each preamp will give you about 10 dB gain" is true only by accident. I'm not going to try to express the math in the forum*, but the noise figure of a cascaded pair is well-known and shows that the overall noise figure is dependent upon the individual noise figures of the two amplifiers and the gain of the first.

After you study this you will know that it *isn't* clear that using the external preamp will give you another 1 dB S/S+N, it could be anything.

*Google "cascaded noise figure" and you will get more info than you want to know.

>
> Second, in my experience, the gain of the PR6 and the gain
> of the internal
> preamp are NOT the same, with the PR6 having more gain --
> more gain than I
> need, actually, given my ambient noise level caused by
> living in a large
> metro area.

It is no surprise that the two preamps differ in gain. It would be more surprising if they did. Again, considering the cascaded NF equation will show the necessity for higher gain in the first amplifier when the NF of the second is high. It's a pity that your local situation is what it is, but that doesn't negate the need for a higher gain external preamp ahead of the poor NF of the K3's internal preamp in lower noise environments.

BTW, a noise factor >1 (NF>0 dB) *always* degrades the received SNR. It may not be significant, but it is a fact.

I don't know what the K3's NF actually is, but it is stone deaf on six meters and isn't much better on ten. I can hear signals that are Q5 on my TS870 that are Q2 on the K3.

>
> Third, since I live in the shadow of a large number of
> high-powered VHF
> broadcasting stations, there is a LOT of powerful
> out-of-band RF floating
> around. Thankfully, its effect on 6 meters was vastly
> decreased when our
> local Channel 2, 4, and 5 TV stations went to UHF digital.

I'm going to bite my tongue and leave U.S. politics out of this but if a TV station pops up on channel 2 again don't be surprised.

http://www.broadband.gov/download-plan/

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James Duffey

Re: K3 - Performance on 6M?

In reply to this post by VK4XA

No need to speculate on the 6M K3 NF, we can calculate it. Computing the K3 noise figure from the minimum discernable signal (MDS) gives

preamp off 18 dB (K3/100 test) to 20 dB (K3/10 test)

preamp on 12 dB (Same in both tests)

compare these to other 6M rigs out there:

IC-551D
preamp on 6dB

internal rf amplifier not switchable

DEM 50-28CK transverter with TS-850S IF

preamp on 2.1 dB

FT736R
preamp on 5.7 dB

TS2000

preamp off 20 dB

preamp on 5 dB

IC756 Pro III

preamp off 15 dB

preamp on 5 dB

FT2000
preamp off 26 dB

preamp on 8 dB

So the K3 is pretty deaf on 6M and yes, that is a result of the design emphasis on HF strong signal handling capability. The Elecraft external preamp with 0.7 dB noise figure and 18 dB gain helps a lot:

K3 with PR6 external preamp

preamp on 0.9 dB

And the preamp is pretty robust to strong signals.

For terrestrial signals in a quiet rural area, a noise figure of 4dB or less is probably adequate. For EME, you want less. For urban and suburban areas, the noise is often high and many people, unfortunately won't notice the inadequacy of the K3's front end on 6M. - Duffey
--
James Duffey KK6MC
DM65tc
Cedar Crest NM

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Eric Swartz - WA6HHQ

Re: K3 - Performance on 6M?

Administrator

The K3's typical MDS on 6M, with the internal pre-amp ON, out of the
factory is closer to -133 to -135 dBM. (I just confirmed this with our
production test techs.)

If you are seeing something in the mid -120s on any band with internal
pre-amp ON, there is something wrong.

73, Eric WA6HHQ

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Bill K9YEQ

Re: K3 - Performance on 6M?

In reply to this post by James Duffey

how do you calculate... I want to work more 6m signals and need to know the
testing method. If signals are that better then I need to add the external
unit.

Bill
K9YEQ

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of James Duffey
Sent: Friday, April 02, 2010 4:54 PM
To: [hidden email]
Cc: James Duffey
Subject: Re: [Elecraft] K3 - Performance on 6M?

No need to speculate on the 6M K3 NF, we can calculate it. Computing the K3
noise figure from the minimum discernable signal (MDS) gives

preamp off 18 dB (K3/100 test) to 20 dB (K3/10 test)

preamp on 12 dB (Same in both tests)

compare these to other 6M rigs out there:

IC-551D
preamp on 6dB

internal rf amplifier not switchable

DEM 50-28CK transverter with TS-850S IF

preamp on 2.1 dB

FT736R
preamp on 5.7 dB

TS2000

preamp off 20 dB

preamp on 5 dB

IC756 Pro III

preamp off 15 dB

preamp on 5 dB

FT2000
preamp off 26 dB

preamp on 8 dB

So the K3 is pretty deaf on 6M and yes, that is a result of the design
emphasis on HF strong signal handling capability. The Elecraft external
preamp with 0.7 dB noise figure and 18 dB gain helps a lot:

K3 with PR6 external preamp

preamp on 0.9 dB

And the preamp is pretty robust to strong signals.

For terrestrial signals in a quiet rural area, a noise figure of 4dB or less
is probably adequate. For EME, you want less. For urban and suburban areas,
the noise is often high and many people, unfortunately won't notice the
inadequacy of the K3's front end on 6M. - Duffey
--
James Duffey KK6MC
DM65tc
Cedar Crest NM

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Joe Subich, W4TV-4

Re: K3 - Performance on 6M?

In reply to this post by James Duffey

> The Elecraft external preamp with 0.7 dB noise figure and 18
> dB gain helps a lot:
>
> K3 with PR6 external preamp
>
> preamp on 0.9 dB
>
> And the preamp is pretty robust to strong signals.
>

Is this calculated with both preamplifiers on (cascaded) or
with the PR-6 only?

73,

... Joe, W4TV

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of James Duffey
> Sent: Friday, April 02, 2010 5:54 PM
> To: [hidden email]
> Cc: James Duffey
> Subject: Re: [Elecraft] K3 - Performance on 6M?
>
>
> No need to speculate on the 6M K3 NF, we can calculate it.
> Computing the K3 noise figure from the minimum discernable
> signal (MDS) gives
>
> preamp off 18 dB (K3/100 test) to 20 dB (K3/10 test)
>
> preamp on 12 dB (Same in both tests)
>
> compare these to other 6M rigs out there:
>
> IC-551D
> preamp on 6dB
>
> internal rf amplifier not switchable
>
> DEM 50-28CK transverter with TS-850S IF
>
> preamp on 2.1 dB
>
>
> FT736R
> preamp on 5.7 dB
>
> TS2000
>
> preamp off 20 dB
>
> preamp on 5 dB
>
> IC756 Pro III
>
> preamp off 15 dB
>
> preamp on 5 dB
>
> FT2000
> preamp off 26 dB
>
> preamp on 8 dB
>
> So the K3 is pretty deaf on 6M and yes, that is a result of
> the design emphasis on HF strong signal handling capability.
> The Elecraft external preamp with 0.7 dB noise figure and 18
> dB gain helps a lot:
>
> K3 with PR6 external preamp
>
> preamp on 0.9 dB
>
> And the preamp is pretty robust to strong signals.
>
> For terrestrial signals in a quiet rural area, a noise figure
> of 4dB or less is probably adequate. For EME, you want less.
> For urban and suburban areas, the noise is often high and
> many people, unfortunately won't notice the inadequacy of the
> K3's front end on 6M. - Duffey
> --
> James Duffey KK6MC
> DM65tc
> Cedar Crest NM
>
>
>
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
>
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James Duffey

Re: K3 - Performance on 6M?

In reply to this post by Eric Swartz - WA6HHQ

Eric - I used the numbers from the January 2009 QST tests, where the ARRL measured -136 dBm MDS with the internal preamp on, and either -130 dBm in a 400 Hz bandwidth or -128 dBm in a 500 Hz bandwidth with the preamp off.

using

MDS = -174 dBm + Noise Figure + 10*log(Bandwidth)

Noise Figure = 174 + MDS -10*log(Bandwidth)

QST measured an MDS of -136 dBm in a 400 Hz bandwidth with the preamp on, which gives a noise figure of

NF = 174 -136 -10*log(400)

= 11.98 dB

Which I rounded up to 12 dB in my note.

Is there an error in my methodology? The -133 dBm to -135 dBm you quote as typical would only make the noise figure worse than the 12 dB NF I calculated from the ARRL data. Did I miss something? I don't think I ever referred to MDS in the mid -120s. - Duffey

--
James Duffey KK6MC
DM65tc
Cedar Crest NM
< [hidden email] >

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James Duffey

Re: K3 - Performance on 6M?

In reply to this post by Joe Subich, W4TV-4

Joe - I went back and did the calculation again for both conditions. I had made a small mistake in calculating the combination previously.

K3 external preamp on, internal off, Noise Figure for combination = 3.3 dB

Which should be good for most work.

K3 external preamp on, internal on, Noise Figure for combination = 1.5 dB

Which is probably overkill for most people.

Here are the details of the calculation. I hope there are no more mistakes:

The noise factor for stages in parallel is

Ftotal = F1 +(F2-1)/G, where these are all ratios, not expressed in dB

where F is the noise factor, F1 the PR6, F2 the K3, and Ftotal the noise factor for the total system. The noise factor is a measure of how much noise a stage adds to a signal

F= SNRin/SNTout

Where SNRin is the signal to noise ratio (power) of the signal into the stage and SNRout is the signal to noise ratio (power) out of the stage. So F is a measure of how much noise a stage adds.

NF=10log(F)

so F =10**(NF/10)

for the K3 with the preamp off, NF =18 dB, F2 = 63.1

for the PR6 NF=0.7 dB, F1= 1.17, G= 63 (18 dB)

so Ftotal = 1.17 + (62.1)/63 = 1.17 + 0.98 = 2.15

which is 3.3 dB Noise figure

with the internal preamp on, NF = 12 db; F2= 15.8

F = 1.17 + 15.8/63 = 1.42

NF= 1.52 dB

The 0.7 dB noise figure is the preamp spec, it also says that typical values run 0.5 dB which would improve things even more.

Sorry for the miscalculation in the combined noise figure the first time. - Duffey

On Apr 2, 2010, at 4:58 PM, Joe Subich, W4TV wrote:

>
>
>> The Elecraft external preamp with 0.7 dB noise figure and 18
>> dB gain helps a lot:
>>
>> K3 with PR6 external preamp
>>
>> preamp on 0.9 dB
>>
>> And the preamp is pretty robust to strong signals.
>>
>
> Is this calculated with both preamplifiers on (cascaded) or
> with the PR-6 only?

--
James Duffey KK6MC
DM65tc
Cedar Crest NM
< [hidden email] >

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Edward R Cole

Re: K3 - Performance on 6M?

In reply to this post by VK4XA

Very good inquiry into how much improvement the PR6 preamp will provide.

I suspect that the average ham is not very familiar with calculations
of noise figure, MDS, etc.
One common error is to think that preamp gain has the sole effect on
minimum detectable signal (weakest signal one can hear). In fact
there is a direct connection between MDS (listed as -136 dBm by
Elecraft for the K3) and noise figure (NF). Gain and noise figure
both combine to produce receiver sensitivity.

But not only receiver sensitivity (MDS) determines what you can
hear. Sky noise, man-made interference, and antenna efficiency
factor into whether you can receive a particular signal level. Hams
involved in satellite, weak-signal operation (typ. VHF+), and eme
(MoonBounce) deal with getting the MDS as low as possible.

Most commercial HF radios are spec'd at an MDS of -122 dBm for SSB/CW
with a 2.7-KHz bandwidth (this is equivalent to a NF of 18 dB)

So the K3 is 14-dB more sensitive that the bulk of ham radios made
(NF=5 dB). With the PR6 it increases to 24-dB better (NF=0.76 dB).

100-MHz is the point where noise figure begins to make significant
impact in MDS. This is because sky noise is much higher as you go
down in frequency. In Urban areas local man-made noise raises the
noise floor even higher. So in those areas the 6m preamp may not
help do anything more than increase the noise in the receiver. If
you can afford the 6m preamp it is probably worth trying out,
though. Unless you are doing eme there will not be any advantage to
installing the preamp at the antenna. But you do want to use good
low-loss feedline to the antenna to reduce the affect on the total
receiver NF. Every dB of coax loss is directly added to receiver NF
(e.g. use 3-dB coax loss with a 0.5 dB NF preamp and the result is
3.5 dB NF). As a rule of thumb for 6m, I would try to achieve an
overall receiver NF=1.5 dB.

We usually measure noise as an equivalent temperature in units of
Kelvin (K). At 50-MHz the sky temperature is about 2000K (higher in
urban areas). A 0.5 dB NF preamp has a noise temperature of
35.4K. Total noise temperature received is Te = Tr + Tsky +
Tant. Tant for a good eme array is about 30K and probably about 70K
for the average 6m yagi. So Te = 2100K if you use a good preamp like
the PR6. Most ham receivers are not very low NF (the best are maybe
6-dB and its typ for a radio to be 12 dB NF) The FT-847 is 12 dB NF
(Tr=4000K) at 144-MHz. So adding this up Te = 4000+2000+70
=6070K. You can see this is much worse in noise performance.

But this must be converted into noise power into dBm. This way
beyond what I can cover in this e-mail, but I have a spreadsheet
program that allows you to input your performance figures like NF,
coax loss, receiver bandwidth, sky noise and antenna noise to
determine MDS. You can pretty quickly see how much improvement in
sensitivity (MDS) is produced by improving various characteristics of
your station
http://www.kl7uw.com/emelink.xls

73, Ed - KL7UW
------------------------------

Message: 15
Date: Fri, 2 Apr 2010 06:56:08 -0600
From: "Bill VanAlstyne W5WVO" <[hidden email]>
Subject: Re: [Elecraft] K3 - Performance on 6M?
To: <[hidden email]>, <[hidden email]>
Message-ID: <9C5E39E63A1A481EAC0D9643FD409029@BILLHP9250>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original

This is an excellent thread, and one that I would like to see continued. I
use the K3 exclusively on 6 meters right now. I work both SSB and CW during
sporadic-E conditions and WSJT digital modes on meteor scatter at other
times when the band is "dead." Eagerly anticipating some F2 on the band in
three or four years.

I have used the K3 both with and without the PR6 preamplifier.

Dave's comment brings up a crucial point:

> "...many signals are very weak and the K3 lacks the sensitivity to deal
> with them unless you either add a pre-amp or have a high level of local
> noise masking those signals."

Right. This is the salient point I want to explore further.

It has been said by many hams over the years that if you connect an antenna
to a receiver and you can hear the noise level increase, then you don't need
a preamp, as it will simply amplify the noise and the signal equally. In
general, I've found that to be true. HOWEVER...

Let's say that the noise figure of the receiver's internal preamp is 1.5 dB,
and the noise figure of the external preamp is 0.5 dB. Each preamp will give
you about 10 dB of gain. It seems clear that using the external preamp
instead of the internal one would give you another dB of signal+noise to
noise. Is my reasoning accurate on that score? If so, then it would be
useful to know the noise figure of the K3's internal preamp at 50 MHz. I
don't know what it is.

Second, in my experience, the gain of the PR6 and the gain of the internal
preamp are NOT the same, with the PR6 having more gain -- more gain than I
need, actually, given my ambient noise level caused by living in a large
metro area.

Third, since I live in the shadow of a large number of high-powered VHF
broadcasting stations, there is a LOT of powerful out-of-band RF floating
around. Thankfully, its effect on 6 meters was vastly decreased when our
local Channel 2, 4, and 5 TV stations went to UHF digital. Before that
happened, the PR6 would be badly overloaded and create some nasty IMD
products on 6 meters unless I put my rather hefty DMI 8-pole bandpass filter
in-line with the preamp (on receive only). This cured the overload/IMD
problem, but at a cost of about 1 dB of insertion loss. Now that the
low-band TV broadcasters have been evicted, I need to try the PR6 again
without the DMI filter and see if the PR6 is still overloaded by out-of-band
RF. I haven't yet tried that yet. But if I really don't need it, why bother?

I just recently put the K3 back in the station setup after having it on the
bench for several months with a transmit section problem. Replacing the
KPAIO3 board seems to have cured that. Thanks, Elecraft. But now I'm back to
the "preamp-or-no-preamp" decision point. Currently, it is set up without
the PR6, and since my antenna noise level is at least 3 dB above the
receiver MDS even in my most quiet beam direction (NNW), I'm thinking I
don't really need to use it.

But am I wrong in my thinking? I'd like to hear some knowledgeable comments.

Bill W5WVO

73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ 500 KHz - 10-GHz www.kl7uw.com
500-KHz/CW, 144-MHz EME, 1296-MHz EME
DUBUS Magazine USA Rep [hidden email]
======================================

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Jeff Cochrane - VK4XA

Re: K3 - Performance on 6M?

CONTENTS DELETED

The author has deleted this message.

Jim Brown-10

Re: K3 - Performance on 6M?

In reply to this post by Bill K9YEQ

On Fri, 2 Apr 2010 17:50:23 -0500, Bill K9YEQ wrote:

>I want to work more 6m signals and need to know the testing method. If
>signals are that better then I need to add the external unit.

As often happens, this thread has gotten way out of hand, with Busby
Berkeley swarms of angels dancing on the head of the pin. Let's take it
back to basics.

The RX in the K3 is decent on 6M, but it does need an external preamp.
As a relative OT on 6M (since 1957), I already owned a mast-mountable
ARR GasFET, which I inserted at the RX antenna patch point in my K3. As
our British friends would say, it works a treat! If I hadn't already
owned that preamp, I would have bought the Elecraft unit, which adds
some quite useful switching so that you can also use Beverages at the RX
antenna input. I had to roll my own switching for that. BTW -- although
my primary 6M antenna is on a 120 ft tower, it's a 3-el SteppIR whose
primary function is HF. If I had a dedicated 6M array, that preamp would
be on the tower.

73,

Jim Brown K9YC

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Joe Subich, W4TV-4

Re: K3 - Performance on 6M?

In reply to this post by James Duffey

Jim,

> Joe - I went back and did the calculation again for both
> conditions. I had made a small mistake in calculating the
> combination previously.

Thanks. The PR-6 only should be good for most activity
and the cascaded configuration saved for times when there
are no strong signals on the band. I haven't calculated
it but I suspect unless one is boresight to an EME array
or one of the big contesters, the cascaded configuration
(internal preamp) will probably not overload.

73,

... Joe, W4TV

> -----Original Message-----
> From: James Duffey [mailto:[hidden email]]
> Sent: Friday, April 02, 2010 7:35 PM
> To: Joe Subich, W4TV
> Cc: James Duffey; [hidden email]
> Subject: Re: [Elecraft] K3 - Performance on 6M?
>
>
> Joe - I went back and did the calculation again for both
> conditions. I had made a small mistake in calculating the
> combination previously.
>
> K3 external preamp on, internal off, Noise Figure for
> combination = 3.3 dB
>
> Which should be good for most work.
>
> K3 external preamp on, internal on, Noise Figure for
> combination = 1.5 dB
>
> Which is probably overkill for most people.
>
>
> Here are the details of the calculation. I hope there are no
> more mistakes:
>
> The noise factor for stages in parallel is
>
> Ftotal = F1 +(F2-1)/G, where these are all ratios, not expressed in dB
>
> where F is the noise factor, F1 the PR6, F2 the K3, and
> Ftotal the noise factor for the total system. The noise
> factor is a measure of how much noise a stage adds to a signal
>
> F= SNRin/SNTout
>
> Where SNRin is the signal to noise ratio (power) of the
> signal into the stage and SNRout is the signal to noise ratio
> (power) out of the stage. So F is a measure of how much noise
> a stage adds.
>
> NF=10log(F)
>
> so F =10**(NF/10)
>
> for the K3 with the preamp off, NF =18 dB, F2 = 63.1
>
> for the PR6 NF=0.7 dB, F1= 1.17, G= 63 (18 dB)
>
> so Ftotal = 1.17 + (62.1)/63 = 1.17 + 0.98 = 2.15
>
> which is 3.3 dB Noise figure
>
> with the internal preamp on, NF = 12 db; F2= 15.8
>
> F = 1.17 + 15.8/63 = 1.42
>
> NF= 1.52 dB
>
> The 0.7 dB noise figure is the preamp spec, it also says that
> typical values run 0.5 dB which would improve things even more.
>
> Sorry for the miscalculation in the combined noise figure the
> first time. - Duffey
>
>
>
> On Apr 2, 2010, at 4:58 PM, Joe Subich, W4TV wrote:
>
> >
> >
> >> The Elecraft external preamp with 0.7 dB noise figure and 18
> >> dB gain helps a lot:
> >>
> >> K3 with PR6 external preamp
> >>
> >> preamp on 0.9 dB
> >>
> >> And the preamp is pretty robust to strong signals.
> >>
> >
> > Is this calculated with both preamplifiers on (cascaded) or
> > with the PR-6 only?
>
>
> --
> James Duffey KK6MC
> DM65tc
> Cedar Crest NM
> < [hidden email] >
>
>
>
>
>