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KX3 AM-breakthrough

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Klaus Dittrich

KX3 AM-breakthrough

My KX3 when driven by a allband shortwave antenna
shows am-breakthough at all bands above 30M
depending on conditions.

The source are far shortwave broadcast stations
(relative to Germany),
Iran, Pakistan, India and sometimes Deutsche Welle.

The stations hearable then are different each time
and very loud, S4 to S5, and so disturbing that working
in cw is impossible for me.

The antenna I use is an asymmetrical dipole(30m/40m long), tuned
at the feedpoint by an SGV-230 autotuner and works well at all bands
from 160m to 6m.

The KX3 is designed as a portable trx. Outdoors people
will use the long antennas which they have no room for at
home.

It seems the KX3-RX can not withstand the rf-levels
delivered by such long antennas.

ARLL and Sherweng measurents do not capture the situation
thus showing that measurements at best always do picture
only a part of reality.

Is Elecraft working at this problem and is there a solution
at the horizon?

--
73, Klaus DF1TL

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DL6OAP

Re: KX3 AM-breakthrough

Hi Klaus,

I tried to provoke some AM breakthrough with my active antenna in april and used a very strong (peaked up to 0 dBm (!) on my Perseus SDR the next day) broadcast signal on 3965 (I think). The only thing I could provoke even with this signal was some AM on the second harmonic, however no AM breakthrough.

My current antenna used with my KX3 is a center fed dipole (same size as G5RV), fed with 8 metres of ladder line and tuned by a Palstar BT1500 true symmetric tuner. The only non-linearity I have noticed is on 15 metres in the evening, but only when the 20 dB preamp in the KX3 is on. I cannot tell wether this is 3rd order from 41 mtr broadcast or second order from 9 and 11 MHz (the tuner's settings for 15 and 30 are similar, so I believe it is the latter process). Interestingly, the 20dB amp is in front of the attentuator, so "att" does not help.

I made the observation that some people report strong breakthrough while others (like me) are not experiencing AM breakthrough at all - with similar antennas - and thought a little bit about this.

The AM breakthrough might be a result of your AC installation. When I started using my KX3 with an indoor antenna I noticed a hum (or buzz) on some bands. Using my ipad with a audio spectrum analyzer app, I found that It consisted of 100 Hz and harmonics. The hum was reduced when the 10dB preamp was on and disappeared when I turned the 8kHz if shift feature on my KX3 on.

I did some internet research on this and ended up with the following explanation: some power from the KX3's local oscillator is emitted and caught by some nearby AC lines in my shack. This rf signal mixes with the AC frequency in a rectifier of one of the power supplies connected and is reradiated by the AC lines and then detected by the KX3.

Related to this, there is what is called "Ortssenderproblem" in german. Strong AM stations mix with the AC mains frequency and this causes them to have a strong hum (even on a superhet receiver - I used to have this on all receivers I ever tried with Deutsche Welle on 3995 and 6075 kHz and the local medium wave station in Hemmingen near Hanover).

If you combine both things, you arrive at the following possible scenario.

Strong AM signals are 'caught' by your AC lines as well as the local oscillator of your KX3. These two mix and create (among others) a AM (cross-)modulated signal on your local oscillators frequency. This signal is then reradiaded by your AC lines and detected by your KX3. This would look like AM breakthrough. If I am true, one should be able to detect the AM modulated KX3 oscillator signal with a nearby (maybe portable?) receiver. And a second test might be: putting a 10 dB attentuator in front of the KX3 and turning on the 10 dB preamp should result in less "breakthrough" than no attentuator and 10 dB off (because of the improved local oscillator isolation).

So it might be possible that you (or your neighbor) have a device connected to the AC that mixes the AM signals and the local oscillator of the KX3. LED lamps and small switching power supplies seem to be good candidates for this. There is a LED "christmas light chain" example in the german qrp forum that can be explained by this "theory".

greetings

Ralf, DL6OAP

Am 29.07.2013 um 11:49 schrieb Klaus Dittrich <[hidden email]>:

>
> My KX3 when driven by a allband shortwave antenna
> shows am-breakthough at all bands above 30M
> depending on conditions.
>
> The source are far shortwave broadcast stations
> (relative to Germany),
> Iran, Pakistan, India and sometimes Deutsche Welle.
>
>
> The stations hearable then are different each time
> and very loud, S4 to S5, and so disturbing that working
> in cw is impossible for me.
>
> The antenna I use is an asymmetrical dipole(30m/40m long), tuned
> at the feedpoint by an SGV-230 autotuner and works well at all bands from 160m to 6m.
>
> The KX3 is designed as a portable trx. Outdoors people
> will use the long antennas which they have no room for at
> home.
>
> It seems the KX3-RX can not withstand the rf-levels
> delivered by such long antennas.
>
> ARLL and Sherweng measurents do not capture the situation
> thus showing that measurements at best always do picture
> only a part of reality.
>
> Is Elecraft working at this problem and is there a solution
> at the horizon?
>
> --
> 73, Klaus DF1TL
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
>
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WM3M

Re: KX3 AM-breakthrough

In reply to this post by Klaus Dittrich

This happens to my KX3 too, but only sometimes, and I can not duplicate it.
I have not been able to track down what causes it.
I use wire antennas fed with coax, OCF dipoles and double size G5RV, it has
done it on all 3 antennas.
When the AM breakthrough happens it is very loud and can be heard across the
entire 20 mtr band.
But then it will go weeks and not do it?
First few times it happened I spent couple hours tracking down the AM
station, it was a independent AM broadcast station, I believe in Kentucky,
very strong somewhere around 9 Mhz?
If anyone figures it out please let me know.
Emory WM3M

-----Original Message-----
From: Klaus Dittrich
Sent: Monday, July 29, 2013 5:49 AM
To: [hidden email]
Subject: [Elecraft] KX3 AM-breakthrough

My KX3 when driven by a allband shortwave antenna
shows am-breakthough at all bands above 30M
depending on conditions.

The source are far shortwave broadcast stations
(relative to Germany),
Iran, Pakistan, India and sometimes Deutsche Welle.

The stations hearable then are different each time
and very loud, S4 to S5, and so disturbing that working
in cw is impossible for me.

The antenna I use is an asymmetrical dipole(30m/40m long), tuned
at the feedpoint by an SGV-230 autotuner and works well at all bands
from 160m to 6m.

The KX3 is designed as a portable trx. Outdoors people
will use the long antennas which they have no room for at
home.

It seems the KX3-RX can not withstand the rf-levels
delivered by such long antennas.

ARLL and Sherweng measurents do not capture the situation
thus showing that measurements at best always do picture
only a part of reality.

Is Elecraft working at this problem and is there a solution
at the horizon?

--
73, Klaus DF1TL

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Uwe Hermanns

Re: KX3 AM-breakthrough

In reply to this post by Klaus Dittrich

Hi Klaus,

my KX3 has sometimes also strong AM-Breakthrough. It is very annoying :-(

73 de Uwe, DL4AC
Am 29.07.2013 11:50 schrieb "Klaus Dittrich" <[hidden email]>:

>
> My KX3 when driven by a allband shortwave antenna
> shows am-breakthough at all bands above 30M
> depending on conditions.
>
> The source are far shortwave broadcast stations
> (relative to Germany),
> Iran, Pakistan, India and sometimes Deutsche Welle.
>
>
> The stations hearable then are different each time
> and very loud, S4 to S5, and so disturbing that working
> in cw is impossible for me.
>
> The antenna I use is an asymmetrical dipole(30m/40m long), tuned
> at the feedpoint by an SGV-230 autotuner and works well at all bands from
> 160m to 6m.
>
> The KX3 is designed as a portable trx. Outdoors people
> will use the long antennas which they have no room for at
> home.
>
> It seems the KX3-RX can not withstand the rf-levels
> delivered by such long antennas.
>
> ARLL and Sherweng measurents do not capture the situation
> thus showing that measurements at best always do picture
> only a part of reality.
>
> Is Elecraft working at this problem and is there a solution
> at the horizon?
>
> --
> 73, Klaus DF1TL
>
> ______________________________**______________________________**__
> Elecraft mailing list
> Home: http://mailman.qth.net/**mailman/listinfo/elecraft<http://mailman.qth.net/mailman/listinfo/elecraft>
> Help: http://mailman.qth.net/mmfaq.**htm<http://mailman.qth.net/mmfaq.htm>
> Post: mailto:[hidden email].**net <[hidden email]>
>
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> Please help support this email list: http://www.qsl.net/donate.html
>

Matt Zilmer

Re: KX3 AM-breakthrough

Setting RX SHFT = 8.0 solves this problem.

73,
matt W6NIA

On Mon, 29 Jul 2013 14:35:16 +0200, you wrote:

>Hi Klaus,
>
>my KX3 has sometimes also strong AM-Breakthrough. It is very annoying :-(
>
>73 de Uwe, DL4AC
>Am 29.07.2013 11:50 schrieb "Klaus Dittrich" <[hidden email]>:
>
>>
>> My KX3 when driven by a allband shortwave antenna
>> shows am-breakthough at all bands above 30M
>> depending on conditions.
>>
>> The source are far shortwave broadcast stations
>> (relative to Germany),
>> Iran, Pakistan, India and sometimes Deutsche Welle.
>>
>>
>> The stations hearable then are different each time
>> and very loud, S4 to S5, and so disturbing that working
>> in cw is impossible for me.
>>
>> The antenna I use is an asymmetrical dipole(30m/40m long), tuned
>> at the feedpoint by an SGV-230 autotuner and works well at all bands from
>> 160m to 6m.
>>
>> The KX3 is designed as a portable trx. Outdoors people
>> will use the long antennas which they have no room for at
>> home.
>>
>> It seems the KX3-RX can not withstand the rf-levels
>> delivered by such long antennas.
>>
>> ARLL and Sherweng measurents do not capture the situation
>> thus showing that measurements at best always do picture
>> only a part of reality.
>>
>> Is Elecraft working at this problem and is there a solution
>> at the horizon?
>>
>> --
>> 73, Klaus DF1TL
>>
>> ______________________________**______________________________**__
>> Elecraft mailing list
>> Home: http://mailman.qth.net/**mailman/listinfo/elecraft<http://mailman.qth.net/mailman/listinfo/elecraft>
>> Help: http://mailman.qth.net/mmfaq.**htm<http://mailman.qth.net/mmfaq.htm>
>> Post: mailto:[hidden email].**net <[hidden email]>
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>______________________________________________________________
>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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Don Wilhelm-4

Re: KX3 AM-breakthrough

In reply to this post by Klaus Dittrich

That is a problem with any zero frequency IF (direct conversion) receiver.
Try turning on RX SHIFT. It is a locked menu item. See page 38 and
also the comment on this subject on page 43.

73,
Don W3FPR

On 7/29/2013 5:49 AM, Klaus Dittrich wrote:
>
> My KX3 when driven by a allband shortwave antenna
> shows am-breakthough at all bands above 30M
> depending on conditions.
>

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Uwe Hermanns

Re: KX3 AM-breakthrough

Hi Don,

but with shift on I loose dual watch.

73 de Uwe, DL4AC
Am 29.07.2013 14:49 schrieb "Don Wilhelm" <[hidden email]>:

> That is a problem with any zero frequency IF (direct conversion) receiver.
> Try turning on RX SHIFT. It is a locked menu item. See page 38 and also
> the comment on this subject on page 43.
>
> 73,
> Don W3FPR
>
> On 7/29/2013 5:49 AM, Klaus Dittrich wrote:
>
>>
>> My KX3 when driven by a allband shortwave antenna
>> shows am-breakthough at all bands above 30M
>> depending on conditions.
>>
>>
> ______________________________**______________________________**__
> Elecraft mailing list
> Home: http://mailman.qth.net/**mailman/listinfo/elecraft<http://mailman.qth.net/mailman/listinfo/elecraft>
> Help: http://mailman.qth.net/mmfaq.**htm<http://mailman.qth.net/mmfaq.htm>
> Post: mailto:[hidden email].**net <[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: KX3 AM-breakthrough

Yes, that is true. You have to choose between the better of those "two
evils".

73,,
Don W3FPR
On 7/29/2013 8:54 AM, Uwe Hermanns wrote:

> Hi Don,
>
> but with shift on I loose dual watch.
>
> 73 de Uwe, DL4AC
> Am 29.07.2013 14:49 schrieb "Don Wilhelm" <[hidden email]>:
>
>> That is a problem with any zero frequency IF (direct conversion) receiver.
>> Try turning on RX SHIFT. It is a locked menu item. See page 38 and also
>> the comment on this subject on page 43.
>>
>> 73,
>> Don W3FPR
>>

pa0pje

Re: KX3 AM-breakthrough

And isn't the activation of the VFO isolation amplifier (RX ISO>On) a
solution?

At least that prevents the VFO signal to exit via the antenna and enter
the mains wiring.

I have yet to experience this breakthrough.

73,
Peter

Don Wilhelm schreef:

> Yes, that is true. You have to choose between the better of those "two
> evils".
>
> 73,,
> Don W3FPR
> On 7/29/2013 8:54 AM, Uwe Hermanns wrote:
>> Hi Don,
>>
>> but with shift on I loose dual watch.
>>
>> 73 de Uwe, DL4AC
>> Am 29.07.2013 14:49 schrieb "Don Wilhelm" <[hidden email]>:
>>
>>> That is a problem with any zero frequency IF (direct conversion)
>>> receiver.
>>> Try turning on RX SHIFT. It is a locked menu item. See page 38 and
>>> also
>>> the comment on this subject on page 43.
>>>
>>> 73,
>>> Don W3FPR
>>>
>
> ______________________________________________________________
> 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
>

Les Gasser W9XC

Re: KX3 AM-breakthrough (RX ISO)

In reply to this post by DL6OAP

If Ralf's hypothesis is correct, another approach (besides RX-shift)
might be to turn on the RX ISO menu item. Doing that helps
reduce the radiation of the local oscillator.

- Les, W9XC

> Hi Klaus,
>
> I tried to provoke some AM breakthrough with my active antenna in
> april and used a very strong (peaked up to 0 dBm (!) on my Perseus SDR
> the next day) broadcast signal on 3965 (I think). The only thing I
> could provoke even with this signal was some AM on the second
> harmonic, however no AM breakthrough.
>
> My current antenna used with my KX3 is a center fed dipole (same size
> as G5RV), fed with 8 metres of ladder line and tuned by a Palstar
> BT1500 true symmetric tuner. The only non-linearity I have noticed is
> on 15 metres in the evening, but only when the 20 dB preamp in the KX3
> is on. I cannot tell wether this is 3rd order from 41 mtr broadcast or
> second order from 9 and 11 MHz (the tuner's settings for 15 and 30 are
> similar, so I believe it is the latter process). Interestingly, the
> 20dB amp is in front of the attentuator, so "att" does not help.
>
> I made the observation that some people report strong breakthrough
> while others (like me) are not experiencing AM breakthrough at all -
> with similar antennas - and thought a little bit about this.
>
> The AM breakthrough might be a result of your AC installation. When I
> started using my KX3 with an indoor antenna I noticed a hum (or buzz)
> on some bands. Using my ipad with a audio spectrum analyzer app, I
> found that It consisted of 100 Hz and harmonics. The hum was reduced
> when the 10dB preamp was on and disappeared when I turned the 8kHz if
> shift feature on my KX3 on.
>
> I did some internet research on this and ended up with the following
> explanation: some power from the KX3's local oscillator is emitted and
> caught by some nearby AC lines in my shack. This rf signal mixes with
> the AC frequency in a rectifier of one of the power supplies connected
> and is reradiated by the AC lines and then detected by the KX3.
>
> Related to this, there is what is called "Ortssenderproblem" in
> german. Strong AM stations mix with the AC mains frequency and this
> causes them to have a strong hum (even on a superhet receiver - I used
> to have this on all receivers I ever tried with Deutsche Welle on 3995
> and 6075 kHz and the local medium wave station in Hemmingen near
> Hanover).
>
> If you combine both things, you arrive at the following possible scenario.
>
> Strong AM signals are 'caught' by your AC lines as well as the local
> oscillator of your KX3. These two mix and create (among others) a AM
> (cross-)modulated signal on your local oscillators frequency. This
> signal is then reradiaded by your AC lines and detected by your
> KX3. This would look like AM breakthrough. If I am true, one should be
> able to detect the AM modulated KX3 oscillator signal with a nearby
> (maybe portable?) receiver. And a second test might be: putting a 10
> dB attentuator in front of the KX3 and turning on the 10 dB preamp
> should result in less "breakthrough" than no attentuator and 10 dB off
> (because of the improved local oscillator isolation).
>
> So it might be possible that you (or your neighbor) have a device
> connected to the AC that mixes the AM signals and the local oscillator
> of the KX3. LED lamps and small switching power supplies seem to be
> good candidates for this. There is a LED "christmas light chain"
> example in the german qrp forum that can be explained by this
> "theory".
>
> greetings
>
> Ralf, DL6OAP
>

Klaus Dittrich

Re: KX3 AM-breakthrough

In reply to this post by Don Wilhelm-4

Thank you all for taking the time to answer to this issue.

I will respond to some of the arguments and tips ..

Klaus, I already have current baluns at both ends of the coax cable.

The KX3 is driven by an analog old PS30 power supply, not a switching
power supply.

I already mentioned the AM stations are far ones.
The last "Ortssender" around, Stuttgart Mühlacker, has been put out of
service.

Emory, same here, only when the broadcast bands open, good conditions,
the effect takes place. Your double size G5RV delivers similar strong
rf-levels as my antenna then. It is not one AM-station, depending
on ionospheric conditions it may be and often is every time another one.

Uwe, "very annoying", that's the point.

Ralf, I think, because the AM-breakthrough signals are hearable
at every frequency they are not mixing products from a nearby
electronic device or a diode build by corrosion. This would cause
a lot of but discrete signals.

Matt and Don, if this is a problem with _any_ zero
frequency IF (direct conversion) receiver then the KX3's
concept would be a design error. ( I hope it is not.)

If I switch to RX SHIFT I will have a receiver with the
most advertised KX3 feature, narrow spaced dynamic range,
dropping to values of rigs of the last century, like IC-735
or Lowe HF-235 or Drake SW8.
(see http://www.sherweng.com/table.html)

Additional I would have thrown the money for the roofing filters
out of the window, as we say here in Germany.

I hope there is a possiblity of rejection by software, but I
have no expertise in SDR at all.

No one of Elecraft has answered up to now, so I stay curious.

--
73 Klaus DF1TL

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Ken Alexander-2

Re: KX3 AM-breakthrough

Hello Klaus,

I wonder if it's possible that some of the foreign stations you reported hearing are being relayed by a European broadcast station much closer to you, and that's why they are strong enough to contribute to your break through problems. Just a thought.

73,

Ken Alexander
VE3HLS

________________________________
From: Klaus Dittrich <[hidden email]>
To: [hidden email]
Sent: Monday, July 29, 2013 4:01:22 PM
Subject: Re: [Elecraft] KX3 AM-breakthrough

Thank you all for taking the time to answer to this issue.

I will respond to some of the arguments and tips ..

Klaus, I already have current baluns at both ends of the coax cable.

The KX3 is driven by an analog old PS30 power supply, not a switching
power supply.

I already mentioned the AM stations are far ones.
The last "Ortssender" around, Stuttgart Mühlacker, has been put out of service.

Emory, same here, only when the broadcast bands open, good conditions,
the effect takes place. Your double size G5RV delivers similar strong rf-levels as my antenna then. It is not one AM-station, depending
on ionospheric conditions it may be and often is every time another one.

Uwe, "very annoying", that's the point.

Ralf, I think, because the AM-breakthrough signals are hearable
at every frequency they are not mixing products from a nearby
electronic device or a diode build by corrosion. This would cause
a lot of but discrete signals.

Matt and Don, if this is a problem with _any_ zero
frequency IF (direct conversion) receiver then the KX3's
concept would be a design error. ( I hope it is not.)

If I switch to RX SHIFT I will have a receiver with the
most advertised KX3 feature, narrow spaced dynamic range,
dropping to values of rigs of the last century, like IC-735
or Lowe HF-235 or Drake SW8.
(see http://www.sherweng.com/table.html)

Additional I would have thrown the money for the roofing filters
out of the window, as we say here in Germany.

I hope there is a possiblity of rejection by software, but I
have no expertise in SDR at all.

No one of Elecraft has answered up to now, so I stay curious.

-- 73 Klaus DF1TL

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DL6OAP

Re: KX3 AM-breakthrough

In reply to this post by Klaus Dittrich

Sorry but I do not agree:

If the "mixing process" involves the local oscillator (cross-modulating the local oscillator's "carrier" in the AC mains), the KX3 detects the AM wherever it is set and would not show discrete signals. If the modulated local oscillator's signal is re-radiated by the AC wiring, a AM signal is exactly on your rx frequency, whatever the rx frequency would be.

Discrete signals would only occur if the mixing process does not involve the local oscillator but only different AM stations.

The two Deutsche Welle signals I mentioned would not be local stations ("Ortssender") for me, but especially the 3995 one used to be very strong in the evenings. I order to have the "Ortssenderproblem", one only needs a strong signal, however it doesn't have to be a local one.

What I call "true AM breakthrough" (rectification of a strong signal somewhere in the mixer), is a potential problem of any d.c. receiver. This rectification occurs in any receiver, but if you are not using "zero-if" you don't notice it (the if filtering will not pass the audio frequencies to the following stages). This is the reason why the 8kHz shift "solves" the problem.

When I had my "hum problem", I started having the KX3 connected to a FP757HD analog power supply and changed to running it from the internal batteries (which didn't solve the problem).

I really was concerned about the AM breakthrough problem, and the discussion on the internet was the reason why I ordered my KX3 without the roofing filter. Testing for AM breakthrough with the strong (swiss?) broadcast signal on 3965 was one of the first things I tried when I obtained my KX3. The interesting result was that a true 0 dBm (measured on the calibrated Perseus s-meter the following evening) signal did not produce AM breakthrough but only 2nd order IMD.

I think a more systematic approach (calibrated signal generator with AM modulation) is needed to figure out if the KX3 itself produces the breakthrough or if it is produced somewhere in the "environment". Maybe someone with this kind of lab equipment could perform a quick test and find out at what signals the KX3 starts to directly rectify AM signals.

Maybe someone experiencing AM breakthrough can check if he detects AM on the signal emitted by the local oscillator of the KX3.

If the AM breakthrough is a real (direct rectification) one, the 90 degree phaseshift between the two quadrature "channels" would probably not occur (in contrast to "true" signals). This could probably be used for suppressing it by software (?)

Vy 73

Ralf, DL6OAP

Am 29.07.2013 um 22:01 schrieb Klaus Dittrich <[hidden email]>:

> Thank you all for taking the time to answer to this issue.
>
> I will respond to some of the arguments and tips ..
>
> Klaus, I already have current baluns at both ends of the coax cable.
>
>
> The KX3 is driven by an analog old PS30 power supply, not a switching
> power supply.
>
> I already mentioned the AM stations are far ones.
> The last "Ortssender" around, Stuttgart Mühlacker, has been put out of service.
>
> Emory, same here, only when the broadcast bands open, good conditions,
> the effect takes place. Your double size G5RV delivers similar strong rf-levels as my antenna then. It is not one AM-station, depending
> on ionospheric conditions it may be and often is every time another one.
>
> Uwe, "very annoying", that's the point.
>
> Ralf, I think, because the AM-breakthrough signals are hearable
> at every frequency they are not mixing products from a nearby
> electronic device or a diode build by corrosion. This would cause
> a lot of but discrete signals.
>
> Matt and Don, if this is a problem with _any_ zero
> frequency IF (direct conversion) receiver then the KX3's
> concept would be a design error. ( I hope it is not.)
>
> If I switch to RX SHIFT I will have a receiver with the
> most advertised KX3 feature, narrow spaced dynamic range,
> dropping to values of rigs of the last century, like IC-735
> or Lowe HF-235 or Drake SW8.
> (see http://www.sherweng.com/table.html)
>
> Additional I would have thrown the money for the roofing filters
> out of the window, as we say here in Germany.
>
> I hope there is a possiblity of rejection by software, but I
> have no expertise in SDR at all.
>
> No one of Elecraft has answered up to now, so I stay curious.
>
>
> --
> 73 Klaus DF1TL
>
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Igor Sokolov-2

Re: KX3 AM-breakthrough

In reply to this post by Klaus Dittrich

Hi Klaus,

>Matt and Don, if this is a problem with _any_ zero
>frequency IF (direct conversion) receiver then the KX3's
>concept would be a design error. ( I hope it is not.)

It is not a design error. Simply every design has it's own limitations.

>If I switch to RX SHIFT I will have a receiver with the
>most advertised KX3 feature, narrow spaced dynamic range,
>dropping to values of rigs of the last century, like IC-735
>or Lowe HF-235 or Drake SW8.
>(see http://www.sherweng.com/table.html)

Please compare apples with apples (not with oranges). KX3 is a portable
travel radio with possibility to be used with internal batteries. Compare it
with the similar stuff like FT817. Besides even without roofing filter and
with 8 kHz IF it has much better DR then IC735 and many others.

>Additional I would have thrown the money for the roofing filters
>out of the window, as we say here in Germany.

That is the way I thought first, when I have discovered the direct AM
detection problem. Then I realized that this problem only exists part time.
All the other time I can use roofing and dual receive. Therefore your money
are not thrown out of the window.
My KX3 is SN 051. Unlike me, you could find the information about direct
detection of KX3 with zero IF setting here on the reflector, prior to
purchase. The problem exist mainly in Europe and many of the US customers
are not affected.
Yes, this design has some limitations but still IMHO this is the best radio
of its class and it costs every dollar we have paid for it.

>I hope there is a possibility of rejection by software, but I
>have no expertise in SDR at all.

Wayne once wrote to me that he may try to enable dual receive even with 8
kHz IF but so far it is not implemented. I doubt that direct AM detection is
possible to be rejected by software.

>No one of Elecraft has answered up to now, so I stay curious.
Did you send message to elecraft technical support? Or do you expect them to
answer your concerns here on the reflector? They sure are not obliged to do
the latter.

BTW, later you may discover couple of other issues with KX3 which are not
that obvious and which I have already discovered. Or you may just search
this reflector and find out.

73, Igor UA9CDC

--
>73 Klaus DF1TL

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wayne burdick

Re: KX3 AM-breakthrough

Administrator

"Igor Sokolov" <[hidden email]> wrote:

> Every design has it's own limitations.

Yes, AM IP2 exists in all quadrature DC receivers to some degree because perfect mixer balance is not possible. We have a goal to improve balance using DSP techniques.

But read on...

Klaus wrote:

>> If I switch to RX SHIFT I will have a receiver with [reduced] narrow spaced dynamic range…

True; according to Sherwood and our own lab tests, when the roofing filters are turned off, the dynamic range at 2 kHz drops from 104 dB or so to about 96 dB, which still puts the KX3 into the top 6 of all radios Sherwood has tested. His third listed value of 65 dB was a worst-case AF opposite-sideband (OSB) image, not IMD. OSB images are related to just one extremely strong nearby signal, and are less problematic than IMD, which results from multiple combinations of signals. (The AF OSB image drops considerably when you apply RX SHFT=8.0, because it is now well out of the audio passband.)

Fortunately the RX SHFT setting is per-band, so you only need apply it on affected bands. You also have the alternative of reducing preamp gain from 20 to 10 dB. PREAMP gain, too, is a per-band setting.

The KX3's direct-conversion architecture simultaneously satisfies the requirements of small size and low current drain, optimizing for portable/battery use. A superhet (like the K3) would have taken too many parts (in particular, at least three crystal filters), and a direct-digital-downconversion architecture would have required much greater supply current, as well as being far higher in cost.

73,
Wayne
N6KR

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Klaus Dittrich

Re: KX3 AM-breakthrough

Again, thank you all for taking the time to contribute to
the issue.

Ken, there was a relay of Radio China in Albania but
I don't know if it is actually active.

Ralf, this morning I "measured" the vfo leakage with my
second receiver a NRD-535 connected to a R&S active antenna
positioned at about two meters distance from the feedpoint
of my dipole.

At 15m the received vfo signal was about S3, dropping down
to just noticeable if I switched on the isolation
amplifier.

I wonder why this isolation amplifier is off by default,
but assume the reason is to save battery power which
does not matter in case of use as home station.

So I would like to know if there are any degradations
in IP3 or more probable in opposite sideband suppression
if this amplifier is permanent in the signal path because
of additional phase shifts.
As far as I remember this case is not included
in the OSB adjustment procedure.

I was astonished to see during OSB adjustment how
sensitve the procedure is to frequeny dependend phase
shifts which I never thought they could be of importance.

Every 10th mm on the circuit board and every ns in software
seems to matter.

Wayne, could you please drop a few words about this?

I assume such small rf-levels are not able to cross-modulating
the local oscillator's "carrier" in the AC mains.
In general I agree with your technical analysis and hope we met
us on the bands some day for a longer talk.

"If the AM breakthrough is a real (direct rectification) one, the 90
degree phaseshift between the two quadrature "channels" would probably
not occur (in contrast to "true" signals). This could probably be used
for suppressing it by software (?)"

I such a direction my hopes went.

Wayne, thank you very much for answer, technical statements,
clarification and your offer.

Now the reason of this AM-breakthrough is determined by the relevant
authority.

Good to hear as well that the dynamic range at 2 kHz drops not as far as
I assumed because of the data measured by Sherweng.

To your offer, which is much appreciated, I have several technical
questions but these we will handle in separate e-mails as desired.

Igor, I agree the problem is not a permanent one, as I already
wrote and in no way my intention was to cast a bad light on the KX3.

I already had a lot of fun and fine dx qso's with it.
But if your are in a cw-qso at 15m and suddenly because of this
AM-breakthrough you can't complete it, that's annoying.

"Did you send message to elecraft technical support? Or do you expect
them to answer your concerns here on the reflector? They sure are not
obliged to do the latter."

Shure they are not, but in practice they do. :-)

I contacted qrp-project (main Elecraft distributor in Germany) before.
They told me the problem is already known but the reason unclear.

Now, now it is clear. :-)

"BTW, later you may discover couple of other issues with KX3 which are
not that obvious and which I have already discovered. Or you may just
search this reflector and find out."

I will look at your contributions to find out or contact you direct. OK?
I am always interested in problems. :-)

--
73 es mny tnx
Klaus DF1TL

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Rich Heineck

Re: KX3 AM-breakthrough

Hello Klaus,

On 07/30/2013 02:20 AM, Klaus Dittrich wrote:

> ...
> I wonder why this isolation amplifier is off by default,
> but assume the reason is to save battery power which
> does not matter in case of use as home station.
>
> So I would like to know if there are any degradations
> in IP3 or more probable in opposite sideband suppression
> if this amplifier is permanent in the signal path because
> of additional phase shifts.
> As far as I remember this case is not included
> in the OSB adjustment procedure.

It consumes about 10 to 15 mA, and when used at the 0 dB gain level
(strictly for isolation) it degrades MDS slightly. If used at the 10 dB
gain setting (10 dB preamp), it will improve MDS slightly. This circuit
has a very high IP3 so it's affect on IMD3 dynamic range is mostly due
to the change in MDS and signal gain to downstream circuits. This stage
is before the signal is split into quadrature components, so it doesn't
directly affect opposite sideband rejection.

> I was astonished to see during OSB adjustment how
> sensitve the procedure is to frequeny dependend phase
> shifts which I never thought they could be of importance.
>
> Every 10th mm on the circuit board and every ns in software
> seems to matter.
>
> Wayne, could you please drop a few words about this?

Getting high levels of OSB rejection requires very precise phase and
gain matching between the quadrature signal paths. 40 dB requires gain
matching to be about 0.1 dB and phase matching to be about 1 degree.
With precision components, 40 to 50 dB is about the practical limit of
what can be done in hardware. The rest is done in DSP. Every 20 dB
improvement requires about a 10x decrease in both phase and gain
mismatch, so 80 dB of OSB rejection requires the phase balance to be
about 0.01 degrees and the gain balance to be about 0.001 dB. It's
possible to get a deep null during OSB calibration, but it takes very
little change in the balance to move away from that point.

73,
Rich AC7MA
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Peter Wollan-2

Re: KX3 AM-breakthrough

This thread has moved way beyond my technical level. As I understand, the
problem arises in locations where there are very strong broadcast stations,
well outside the ham bands. Presumably a bandpass filter doesn't help --
is it that the mixing products are occurring in the antenna? Wouldn't the
solution then be in the antenna, in the form of directional nulls or stub
filters?

Peter W0LLN
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DL6OAP

Re: KX3 AM-breakthrough

In reply to this post by Klaus Dittrich

Hi Klaus,

My understanding is that the iso amp is identical to the 10 dB preamp but with a reduced gain (there is a "iso amp hi" control signal which seems to be used to set the overall gain of that stage). So I would expect the IP3 to settle somewhere between the "no preamp" and the "10 dB preamp" value if the iso amp is on. Turning on the iso amp should increase the noise figure but I don't think this is a big issue (and applies only if you use otherwise no preamp). I would not expect OSB suppression to change because the amp affects both quadrature channels the same way.

Concerning the "local oscillator crossmod theory", and your measurements, I would say it doesn't seem to apply in your case. I think you could make a final check for AM on the vfo leakage signal with your JRC rx in a situation where you are experiencing breakthrough, just to be sure, but I believe it is not very probable in your case.

I just finished a measurement of the vfo leakage. I connected the antenna output of the KX3 directly to the input of my Perseus SDR (which provides an accurate level meter).

With no preamp, the level is between -75 dBm (S8) on 160 and 80 meters and increases to about -50 dBm (S9+20dB) on 17 meters. With the 10 dB preamp on it is barely detectable (less than -110dBm)

Given these numbers, assuming something like -20dB of "gain" for the AC wiring "antenna" and some "free space attentuation", the signal that is re-radiated from the AC wiring should be to weak to be detected in most setups and the local oscillator leakage is not likely to explain the AM breakthrough.

Vy 73

Ralf, DL6OAP

Am 30.07.2013 um 11:20 schrieb Klaus Dittrich <[hidden email]>:

> Again, thank you all for taking the time to contribute to
> the issue.
>
> Ken, there was a relay of Radio China in Albania but
> I don't know if it is actually active.
>
> Ralf, this morning I "measured" the vfo leakage with my
> second receiver a NRD-535 connected to a R&S active antenna
> positioned at about two meters distance from the feedpoint
> of my dipole.
>
> At 15m the received vfo signal was about S3, dropping down
> to just noticeable if I switched on the isolation
> amplifier.
>
> I wonder why this isolation amplifier is off by default,
> but assume the reason is to save battery power which
> does not matter in case of use as home station.
>
> So I would like to know if there are any degradations
> in IP3 or more probable in opposite sideband suppression
> if this amplifier is permanent in the signal path because
> of additional phase shifts.
> As far as I remember this case is not included
> in the OSB adjustment procedure.
>
> I was astonished to see during OSB adjustment how
> sensitve the procedure is to frequeny dependend phase
> shifts which I never thought they could be of importance.
>
> Every 10th mm on the circuit board and every ns in software
> seems to matter.
>
> Wayne, could you please drop a few words about this?
>
> I assume such small rf-levels are not able to cross-modulating
> the local oscillator's "carrier" in the AC mains.
> In general I agree with your technical analysis and hope we met
> us on the bands some day for a longer talk.
>
> "If the AM breakthrough is a real (direct rectification) one, the 90 degree phaseshift between the two quadrature "channels" would probably not occur (in contrast to "true" signals). This could probably be used for suppressing it by software (?)"
>
> I such a direction my hopes went.
>
> Wayne, thank you very much for answer, technical statements, clarification and your offer.
>
> Now the reason of this AM-breakthrough is determined by the relevant authority.
>
> Good to hear as well that the dynamic range at 2 kHz drops not as far as I assumed because of the data measured by Sherweng.
>
> To your offer, which is much appreciated, I have several technical
> questions but these we will handle in separate e-mails as desired.
>
>
> Igor, I agree the problem is not a permanent one, as I already
> wrote and in no way my intention was to cast a bad light on the KX3.
>
> I already had a lot of fun and fine dx qso's with it.
> But if your are in a cw-qso at 15m and suddenly because of this
> AM-breakthrough you can't complete it, that's annoying.
>
> "Did you send message to elecraft technical support? Or do you expect them to answer your concerns here on the reflector? They sure are not obliged to do the latter."
>
> Shure they are not, but in practice they do. :-)
>
> I contacted qrp-project (main Elecraft distributor in Germany) before.
> They told me the problem is already known but the reason unclear.
>
> Now, now it is clear. :-)
>
> "BTW, later you may discover couple of other issues with KX3 which are not that obvious and which I have already discovered. Or you may just search this reflector and find out."
>
> I will look at your contributions to find out or contact you direct. OK?
> I am always interested in problems. :-)
>
> --
> 73 es mny tnx
> Klaus DF1TL
>
>

Bill K9YEQ

Re: KX3 AM-breakthrough

In reply to this post by wayne burdick

Wayne, Thank you for this very informative technical explanation. When I
operated my HW-8 in the early 80's, I loved it because it was so simple to
build, easy to operate and required little power. However, the KX3 is so
superior I really cannot compare what you have engineered the KX3 to be vs.
what the very challenged HW-8 was. Incredible contrast; excellent design
using the modern techniques available, to produce an amazing piece of
equipment.

73,
Bill
K9YEQ

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Wayne Burdick
Sent: Monday, July 29, 2013 11:28 PM
To: Igor Sokolov
Cc: Elecraft Reflector; Klaus Dittrich
Subject: Re: [Elecraft] KX3 AM-breakthrough

"Igor Sokolov" <[hidden email]> wrote:

> Every design has it's own limitations.

Yes, AM IP2 exists in all quadrature DC receivers to some degree because
perfect mixer balance is not possible. We have a goal to improve balance
using DSP techniques.

But read on...

Klaus wrote:

>> If I switch to RX SHIFT I will have a receiver with [reduced] narrow
spaced dynamic range.

True; according to Sherwood and our own lab tests, when the roofing filters
are turned off, the dynamic range at 2 kHz drops from 104 dB or so to about
96 dB, which still puts the KX3 into the top 6 of all radios Sherwood has
tested. His third listed value of 65 dB was a worst-case AF
opposite-sideband (OSB) image, not IMD. OSB images are related to just one
extremely strong nearby signal, and are less problematic than IMD, which
results from multiple combinations of signals. (The AF OSB image drops
considerably when you apply RX SHFT=8.0, because it is now well out of the
audio passband.)

Fortunately the RX SHFT setting is per-band, so you only need apply it on
affected bands. You also have the alternative of reducing preamp gain from
20 to 10 dB. PREAMP gain, too, is a per-band setting.

The KX3's direct-conversion architecture simultaneously satisfies the
requirements of small size and low current drain, optimizing for
portable/battery use. A superhet (like the K3) would have taken too many
parts (in particular, at least three crystal filters), and a
direct-digital-downconversion architecture would have required much greater
supply current, as well as being far higher in cost.

73,
Wayne
N6KR

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