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[K2] lack of sensitivity...?

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Gil G.

[K2] lack of sensitivity...?

Hello,

I knew this title would grab some attention ;-)

Well, since my K1 worked so well, I decided to build a K2.
It took me 30 hours over three days. Everything works, but…

First, the receiver is pretty deaf on 20m. Not much static at all, faint signals.
I plugged in my K1 on the same wire, and what I could barely hear on 20m on the K2 came in full blast on the K1.
The preamp helps a little, but not much.
On 40m, the score is closer, but still advantage to the K1 over the K2 with preamp on.
I can use FL1 and FL2, but with 3, the signal is very attenuated, with 4 (200Hz), usually gone.
The other bands, I haven't listened enough yet to make a diagnosis… I can hear more static than on 20m.
I have set the filters as indicated in the manual.

The K1 has the ATU, would that make such a difference?
I use a 35.5ft wire with 13ft counterpoise, directly out the BNC via a binding post.

By the way, I do get full output power on the K2 on all bands.
I precisely peaked all bands on receive, then on transmit with my QRP wattmeter.

Any advise?

Thanks!

Gil.
--
New site: http://radiopreppers.com
PGP Key: http://keskydee.com/gil.asc

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Andrew Moore-3

Re: [K2] lack of sensitivity...?

Gil - ATU on the K1 shouldn't make a difference.

Only thing that comes to mind other than proper alignment is it sounds like
a problem I had during construction of my K2. Post follows:

+++++++++++++++++
Date: Mon, 02 Jun 2003 13:22:31 -0400
To: elecraft at mailman.qth.net
From: Andrew Moore <andrew.m.moore at verizon.net>
Subject: [Elecraft] 40m low sig: problem solved

Thanks for all the responses to my troubleshooting questions.

Further tracing brought me to C6 (4.7 pF) at the back edge of the board,
which the manual states should be installed across the two outer pins of
the three-pin jumper block. I interpreted "two outer" to mean the two
adjacent pins near the "outer" side of the board edge -- i.e. in the
direction of the side panel instead of the center of the edge.

40 meters is incredibly noisy at my location right now, so I still hear no
signals, but the noise level has com'll assume I'm in good shape now --
will listen to some real signals tonight. I've never been so happy to hear
noise on the band!

Thanks N0SS for the terrific lesson in quick and dirty signal tracing.

--Andrew, NV1B
CFO 963

On Thu, Aug 30, 2012 at 2:03 AM, Gil G. <[hidden email]> wrote:

> Hello,
>
> I knew this title would grab some attention ;-)
>
> Well, since my K1 worked so well, I decided to build a K2.
> It took me 30 hours over three days. Everything works, but…
>
> First, the receiver is pretty deaf on 20m. Not much static at all, faint
> signals.
> I plugged in my K1 on the same wire, and what I could barely hear on 20m
> on the K2 came in full blast on the K1.
> The preamp helps a little, but not much.
> On 40m, the score is closer, but still advantage to the K1 over the K2
> with preamp on.
> I can use FL1 and FL2, but with 3, the signal is very attenuated, with 4
> (200Hz), usually gone.
> The other bands, I haven't listened enough yet to make a diagnosis… I can
> hear more static than on 20m.
> I have set the filters as indicated in the manual.
>
> The K1 has the ATU, would that make such a difference?
> I use a 35.5ft wire with 13ft counterpoise, directly out the BNC via a
> binding post.
>
> By the way, I do get full output power on the K2 on all bands.
> I precisely peaked all bands on receive, then on transmit with my QRP
> wattmeter.
>
> Any advise?
>
> Thanks!
>
> Gil.
> --
> New site: http://radiopreppers.com
> PGP Key: http://keskydee.com/gil.asc
>
> ______________________________________________________________
> 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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Geoffrey Mackenzie-Kennedy-3

Re: [K2] lack of sensitivity...?

In reply to this post by Gil G.

Hello Gil,

The ATU in your K1 could be making the difference. It will or should
transform the impedance presented by the 33.5 ft wire and 13 ft counterpoise
to 50 ohms resistive, which is the source impedance which the K1's receiver
likes to see. The K2's receiver would also like to see a 50 ohm resistive
source, but without an ATU it will see whatever source impedance is
presented by the wire and counterpoise.

On 20m the wire and counterpoise would be seen by the K2's receiver as a
fairly high impedance source, 2000 ohms or more resistive with some
inductance in series. On 40m, and depending on how you have the wire and
counterpoise deployed and the effects of nearby objects, the receiver could
be seeing a source whose resistive part is 20 ohms or less with some
capacitance in series. These are rough values simply to illustrate one
possible reason why your K2 is deaf on 20m, and not quite as deaf on 40m.

If possible bypass the ATU in the KX1, and then make a comparison between
your K1 and K2. If your K1 becomes deaf as well, then buy an Elecraft ATU
for your K2. If buying an ATU is not an option, it is not difficult to
homebrew a L Network for use as an ATU. If you do decide to homebrew a L
network, I suggest that the coil be solenoid wound rather than wound on a
toroidal core.

73,

Geoff
LX2AO

On August 30, 2012 at 8:03 AM, "Gil G." <[hidden email]> wrote:

> Hello,

> I knew this title would grab some attention ;-)

> Well, since my K1 worked so well, I decided to build a K2.
> It took me 30 hours over three days. Everything works, but…

> First, the receiver is pretty deaf on 20m. Not much static at all, faint
> signals.
> I plugged in my K1 on the same wire, and what I could barely hear on 20m
> on the K2 came in full blast on the K1.
> The preamp helps a little, but not much.
> On 40m, the score is closer, but still advantage to the K1 over the K2
> with preamp on.
> I can use FL1 and FL2, but with 3, the signal is very attenuated, with 4
> (200Hz), usually gone.
> The other bands, I haven't listened enough yet to make a diagnosis… I can
> hear more static than on 20m.
> I have set the filters as indicated in the manual.

> The K1 has the ATU, would that make such a difference?
> I use a 35.5ft wire with 13ft counterpoise, directly out the BNC via a
> binding post.

> By the way, I do get full output power on the K2 on all bands.
> I precisely peaked all bands on receive, then on transmit with my QRP
> wattmeter.

> Any advise?

> Thanks!

> Gil.

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

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Andrew Moore-3

Re: [K2] lack of sensitivity...?

Clarification - when I said the K1 ATU wouldn't make a difference, I mean
"just as an installed option" and wasn't considering it actually inline at
the time

--Andrew

On Thu, Aug 30, 2012 at 9:37 AM, Geoffrey Mackenzie-Kennedy <[hidden email]>wrote:

> Hello Gil,
>
> The ATU in your K1 could be making the difference. It will or should
> transform the impedance presented by the 33.5 ft wire and 13 ft
> counterpoise
> to 50 ohms resistive, which is the source impedance which the K1's receiver
> likes to see. The K2's receiver would also like to see a 50 ohm resistive
> source, but without an ATU it will see whatever source impedance is
> presented by the wire and counterpoise.
>
> On 20m the wire and counterpoise would be seen by the K2's receiver as a
> fairly high impedance source, 2000 ohms or more resistive with some
> inductance in series. On 40m, and depending on how you have the wire and
> counterpoise deployed and the effects of nearby objects, the receiver could
> be seeing a source whose resistive part is 20 ohms or less with some
> capacitance in series. These are rough values simply to illustrate one
> possible reason why your K2 is deaf on 20m, and not quite as deaf on 40m.
>
>
> If possible bypass the ATU in the KX1, and then make a comparison between
> your K1 and K2. If your K1 becomes deaf as well, then buy an Elecraft ATU
> for your K2. If buying an ATU is not an option, it is not difficult to
> homebrew a L Network for use as an ATU. If you do decide to homebrew a L
> network, I suggest that the coil be solenoid wound rather than wound on a
> toroidal core.
>
> 73,
>
> Geoff
> LX2AO
>
>
> On August 30, 2012 at 8:03 AM, "Gil G." <[hidden email]> wrote:
>
>
>
> > Hello,
>
> > I knew this title would grab some attention ;-)
>
> > Well, since my K1 worked so well, I decided to build a K2.
> > It took me 30 hours over three days. Everything works, but…
>
> > First, the receiver is pretty deaf on 20m. Not much static at all, faint
> > signals.
> > I plugged in my K1 on the same wire, and what I could barely hear on 20m
> > on the K2 came in full blast on the K1.
> > The preamp helps a little, but not much.
> > On 40m, the score is closer, but still advantage to the K1 over the K2
> > with preamp on.
> > I can use FL1 and FL2, but with 3, the signal is very attenuated, with 4
> > (200Hz), usually gone.
> > The other bands, I haven't listened enough yet to make a diagnosis… I can
> > hear more static than on 20m.
> > I have set the filters as indicated in the manual.
>
> > The K1 has the ATU, would that make such a difference?
> > I use a 35.5ft wire with 13ft counterpoise, directly out the BNC via a
> > binding post.
>
> > By the way, I do get full output power on the K2 on all bands.
> > I precisely peaked all bands on receive, then on transmit with my QRP
> > wattmeter.
>
> > Any advise?
>
> > Thanks!
>
> > Gil.
>
> ______________________________________________________________
> 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
>

Don Wilhelm-4

Re: [K2] lack of sensitivity...?

In reply to this post by Gil G.

Gil,

It is difficult to make a definite answer without some additional data.
Yes, the atu in the K1 could make some difference, but not an extreme
difference on receive.

The most likely guess is that you missed a solder connection somewhere
in the receive section of the K2. Go over the board with a suspicious
eye. The receive portion of the K2 is between the MCIO IC (in the
middle of the board) and the front panel.

The fact that you have full transmit power on all bands says that the
problem is *not* in the bandpass filter nor the Low Pass filter.

73,
Don W3FPR

On 8/30/2012 2:03 AM, Gil G. wrote:

Geoffrey Mackenzie-Kennedy-3

Re: [K2] lack of sensitivity...?

In reply to this post by Andrew Moore-3

Hello Andrew,

Thanks for the clarification, you had me wondering :-)

73,

Geoff
LX2AO

On August 30, 2012 at 4:03 PM, Andrew Moore wrote:

> Clarification - when I said the K1 ATU wouldn't make a difference, I mean
> "just as an installed option" and wasn't considering it actually inline at
> the time

> --Andrew

______________________________________________________________
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Gil G.

Re: [K2] lack of sensitivity...?

In reply to this post by Don Wilhelm-4

Thank you everyone for your suggestions.

I did have one bad solder joint on TR7, fixed it by soldering one lead on top. Maybe the problem is related to that.
Tuning L34 doesn't seem to do much of anything. There was no 3.3pf capacitor for C22 on the RF board, but I had one 2.7pf left over after finishing, so I assumed I had to use that..
I did try to compare the K2 with the K1 without the ATU, it does make a difference, now it is closer (with preamp on). Maybe I'm being too picky. I was assuming the K2 would run circles around the K1.
Don, what kind of additional data can I gather that would help make a diagnosis?
I do not have an RF signal generator, but I have a K1 and a dummy load.
It is peculiar that the 20m band is the most affected… Could filter setting be the cause?
I do have spectrogram on my iPod, but the interface is different than on the PC version, not usable for filter adjustments.
(I use a Mac…)

Gil.
--
New site: http://radiopreppers.com
PGP Key: http://keskydee.com/gil.asc

On Aug 30, 2012, at 10:16 AM, Don Wilhelm wrote:

> Gil,
>
> It is difficult to make a definite answer without some additional data. Yes, the atu in the K1 could make some difference, but not an extreme difference on receive.
>
> The most likely guess is that you missed a solder connection somewhere in the receive section of the K2. Go over the board with a suspicious eye. The receive portion of the K2 is between the MCIO IC (in the middle of the board) and the front panel.
>
> The fact that you have full transmit power on all bands says that the problem is *not* in the bandpass filter nor the Low Pass filter.
>
> 73,
> Don W3FPR

Don Wilhelm-4

Re: [K2] lack of sensitivity...?

Gil,

Hopefully you are not being confused by the amount of audio reserve.
The audio in the K2 is adequate, but limited, while the K1 has an LM386
audio driver followed by an LM380 amplifier and has lots of reserve audio.

It is difficult to tell what you are describing without some form of
measurable signal injection. I would suggest that you tune around the
ham bands for the weakest signal that you can find and compare those.
If you try to compare raw signal audio, the K1 will win every time, but
you really need to determine "what is the weakest signal that I can
receive on this radio" In that context, the K2 will usually be better
than the K1.

What I do as a sanity check for every radio I repair is to set the
output of my HP8640 signal generator at -130 dBm and see just how far
above the receiver noise level that signal is displayed on the
Spectrogram screen. While that is not a true MDS measurement, it does
give me some assurance that the receiver will be acceptable - the
Spectrogram display shows me how much above the receiver noise floor
that -130 dBm signal rises. If I were to go to pains and add additional
attenuators and calculate the MDS of each receiver, I would find them
quite close - my expectation for the K2 would be in excess of -135 dBm
while the K1 and the KX1 would be close behind at about -132 dBm A 3 dB
difference, -- that is twice the receive sensitivity. You cannot hear
that difference with your ears unless you are comparing signals just
barely above the noise level, but you certainly can measure it.

All that information does you no good in operation unless the
atmospheric band noise is less than the MDS of the receiver. Not
typical on the bands 20 meters and below.

73,
Don W3FPR
On 8/30/2012 6:36 PM, Gil G. wrote:

> Thank you everyone for your suggestions.
>
> I did have one bad solder joint on TR7, fixed it by soldering one lead on top. Maybe the problem is related to that.
> Tuning L34 doesn't seem to do much of anything. There was no 3.3pf capacitor for C22 on the RF board, but I had one 2.7pf left over after finishing, so I assumed I had to use that..
> I did try to compare the K2 with the K1 without the ATU, it does make a difference, now it is closer (with preamp on). Maybe I'm being too picky. I was assuming the K2 would run circles around the K1.
> Don, what kind of additional data can I gather that would help make a diagnosis?
> I do not have an RF signal generator, but I have a K1 and a dummy load.
> It is peculiar that the 20m band is the most affected… Could filter setting be the cause?
> I do have spectrogram on my iPod, but the interface is different than on the PC version, not usable for filter adjustments.
> (I use a Mac…)
>
>