K3: PRE/ATT Bug or feature?

[Bill McDowell]

My K3 (SN 1069, fw 4.03) has always exhibited the ability to have PRE and ATT on simultaneously.  If one engages ATT by a long hold, then hits PRE with a tap (same button), the display shows both functions engaged.  The converse is true too, i.e. PRE engaged with a tap, followed by ATT with a long hold.

Signal levels by ear and S-meter seem to indicate both features are on simultaneously.  The appropriate length hold will turn one feature off, as indicated by the display.  Levels change accordingly.

Is this a bug, or an undocumented feature?  The feature(s) being a PRE function with less gain or a ATT with less attenuation.

73
Bill, K4CIA
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[Don Wilhelm-4]

Bill,

Normal operation.  The attenuator is -10 dB and the preamp is +12 dB.  
So if you only need +2 dB of preamp, turning both on will give it to you.

73,
Don W3FPR

Bill McDowell wrote:
> My K3 (SN 1069, fw 4.03) has always exhibited the ability to have PRE and ATT on simultaneously.  If one engages ATT by a long hold, then hits PRE with a tap (same button), the display shows both functions engaged.  The converse is true too, i.e. PRE engaged with a tap, followed by ATT with a long hold.
>
>  

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[W8JI]

It might make gain 2dB, but what does that do overall to dynamic range? Has
anyone measured performance with both attenuator and preamp on??


----- Original Message -----
From: "Don Wilhelm" <[hidden email]>
To: "Bill McDowell" <[hidden email]>
Cc: "elecraft reflector" <[hidden email]>
Sent: Tuesday, August 10, 2010 8:47 AM
Subject: Re: [Elecraft] K3: PRE/ATT Bug or feature?

> Bill,
>
> Normal operation.  The attenuator is -10 dB and the preamp is +12 dB.
> So if you only need +2 dB of preamp, turning both on will give it to you.
>
> 73,
> Don W3FPR
>
> Bill McDowell wrote:
>> My K3 (SN 1069, fw 4.03) has always exhibited the ability to have PRE and
>> ATT on simultaneously.  If one engages ATT by a long hold, then hits PRE
>> with a tap (same button), the display shows both functions engaged.  The
>> converse is true too, i.e. PRE engaged with a tap, followed by ATT with a
>> long hold.
>>
>>
>
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[The Smiths]

This is NOT a bug, this is working EXACTLY as it should.  Some time you want to have a little extra gain, but not as much as the Pre does alone.  In this case you will run the Pre ON, and the ATT on at the same time.  No bug there.  Just another way Elecraft has made the K3 a versatile rig for finding weak signals in a loud noise floor.

 

> Date: Tue, 10 Aug 2010 08:31:15 -0400
> From: [hidden email]
> To: [hidden email]
> Subject: [Elecraft] K3: PRE/ATT Bug or feature?
>
> My K3 (SN 1069, fw 4.03) has always exhibited the ability to have PRE and ATT on simultaneously. If one engages ATT by a long hold, then hits PRE with a tap (same button), the display shows both functions engaged. The converse is true too, i.e. PRE engaged with a tap, followed by ATT with a long hold.
>
> Signal levels by ear and S-meter seem to indicate both features are on simultaneously. The appropriate length hold will turn one feature off, as indicated by the display. Levels change accordingly.
>
> Is this a bug, or an undocumented feature? The feature(s) being a PRE function with less gain or a ATT with less attenuation.
>
> 73
> Bill, K4CIA
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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[Mike Markowski-2]

This is available on the K2 as well, but only by sending commands via
the KIO2.  I made a little program to do that so I can set pre/att on
each band depending on noise before adjusting RF Gain.  It goes in the
Feature category.  :-)

73,
Mike ab3ap

On 08/10/10 12:53, The Smiths wrote:
> This is NOT a bug, this is working EXACTLY as it should [...]
>
>> From: [hidden email]
>> Subject: [Elecraft] K3: PRE/ATT Bug or feature?
>>
>> My K3 (SN 1069, fw 4.03) has always exhibited the ability to have
>> PRE and ATT on simultaneously [...]
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[Guy, K2AV]

This is one of those things that has always been possible in radios
that had both.  In the MP, with the 0-6-12-18 ATT and both IPO and
menu selected preamp function, it has always been possible to do
preamp with the ATT set.  Make any sense?  Maybe, but don't think so.
Even  less so on a K3

A lot of the design decisions in the K3 appear to have been made with
an eye to keeping the APPEARANCE of analog function, e.g. so called RF
gain.  The menu driven RF gain on the Orion was always a startup
learning issue.  I'm sure Wayne was watching.

It certainly is possible in firmware to not allow the PRE to be set
when the ATT is on.  But why put up with the support calls about can't
turn on PRE when it doesn't behave like predecessor radios, when most
will intuitively understand that ATT+PRE equals neither.

Most of the time I don't need to be protected from myself.  The other
times no one can help me anyway. : >)

73, Guy.

On Tue, Aug 10, 2010 at 9:32 AM, Tom W8JI <[hidden email]> wrote:

> It might make gain 2dB, but what does that do overall to dynamic range? Has
> anyone measured performance with both attenuator and preamp on??
>
>
> ----- Original Message -----
> From: "Don Wilhelm" <[hidden email]>
> To: "Bill McDowell" <[hidden email]>
> Cc: "elecraft reflector" <[hidden email]>
> Sent: Tuesday, August 10, 2010 8:47 AM
> Subject: Re: [Elecraft] K3: PRE/ATT Bug or feature?
>
>
>> Bill,
>>
>> Normal operation.  The attenuator is -10 dB and the preamp is +12 dB.
>> So if you only need +2 dB of preamp, turning both on will give it to you.
>>
>> 73,
>> Don W3FPR
>>
>> Bill McDowell wrote:
>>> My K3 (SN 1069, fw 4.03) has always exhibited the ability to have PRE and
>>> ATT on simultaneously.  If one engages ATT by a long hold, then hits PRE
>>> with a tap (same button), the display shows both functions engaged.  The
>>> converse is true too, i.e. PRE engaged with a tap, followed by ATT with a
>>> long hold.
>>>
>>>
>>
>> ______________________________________________________________
>> 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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>> Please help support this email list: http://www.qsl.net/donate.html
>
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[W8JI]

> This is NOT a bug, this is working EXACTLY as it should.  Some time you
> want to have a little extra gain, but not as much as the Pre does alone.
> In this case you will run the Pre ON, and the ATT on at the same time.  No
> bug there.  Just another way Elecraft has made the K3 a versatile rig for
> finding weak signals in a loud noise floor.


The question is not gain, because 2 dB of additional gain is not
significant.

The question is how running both the preamp and attenuator affects dynamic
range. It probably decreases dynamic range.

I guess no one has measured it.

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[drewko]

Actually, you will probably LOSE a couple of db by switching on both
preamp and attenuator compared to having both switched off. (Measure
your MDS and compare results if you don't believe...)

Regarding weak signals, one factor that is overlooked is the ATU. By
switching it to bypass you can gain 5 or 6 db in MDS. Of course, you
would want to switch it back on when you transmit.

I wonder if the ATU could be programmed to automatically be bypassed
on receive? You would perhaps not want the ATU to be switched in and
out at break-in speeds, but after a suitable semi-breakin delay. I
think that would be a handy option for weak signal work for those of
us who must use the ATU.

73,
Drew
AF2Z



On Tue, 10 Aug 2010 13:28:01 -0400, Tom W8JI wrote:

>> This is NOT a bug, this is working EXACTLY as it should.  Some time you
>> want to have a little extra gain, but not as much as the Pre does alone.
>> In this case you will run the Pre ON, and the ATT on at the same time.  No
>> bug there.  Just another way Elecraft has made the K3 a versatile rig for
>> finding weak signals in a loud noise floor.
>
>
>The question is not gain, because 2 dB of additional gain is not
>significant.
>
>The question is how running both the preamp and attenuator affects dynamic
>range. It probably decreases dynamic range.
>
>I guess no one has measured it.
>

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[ab2tc]

Why do you think you gain in MDS (presumably you mean a *lower* MDS) by bypassing the ATU? If the ATU is needed for transmit, it will also be benficial in receive. I don't have the K3 ATU, but both manual and automatic tuners in my antenna system and can certainly certify that when switching in the tuner when needed, the receive signal goes up (mismatch loses receive signal too).

AB2TC - Knut

<quote author="drewko">
Actually, you will probably LOSE a couple of db by switching on both
preamp and attenuator compared to having both switched off. (Measure
your MDS and compare results if you don't believe...)

Regarding weak signals, one factor that is overlooked is the ATU. By
switching it to bypass you can gain 5 or 6 db in MDS. Of course, you
would want to switch it back on when you transmit.

I wonder if the ATU could be programmed to automatically be bypassed
on receive? You would perhaps not want the ATU to be switched in and
out at break-in speeds, but after a suitable semi-breakin delay. I
think that would be a handy option for weak signal work for those of
us who must use the ATU.

73,
Drew
AF2Z


<snip
</quote>

[W8JI]

> Actually, you will probably LOSE a couple of db by switching on both
> preamp and attenuator compared to having both switched off. (Measure
> your MDS and compare results if you don't believe...)

MDS, like dynamic range, can go either direction with changes in gain. It is
possible to have a gain increase and lose MDS.

This is why it is important to know how things really change in abnormal
configurations, not how we "feel" they change.

> Regarding weak signals, one factor that is overlooked is the ATU. By
> switching it to bypass you can gain 5 or 6 db in MDS. Of course, you
> would want to switch it back on when you transmit.

That large amount surprises me, although a smaller amount certainly would
not. Systems with loss are often not bilateral. For example on receiving
feedline losses associated with feedline SWR are determined by the radio's
input impedance, not by antenna SWR. On receiving the receiver impedance
determines feedline SWR.

On transmitting, the antenna is the load and sets feedline SWR....affecting
feedline losses.

6 dB is a pretty big change. Maybe your receiver input impedance is not so
close to 50 j0, or your 6 dB is not 6 dB though some sort of errors in
calibration????

73 Tom

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[alsopb]

As Tom said.

The cause of the signal "gain" when using a tuner is really a matter of
having a badly matched situation without the tuner.

In the old days (with manual tuners!), it was easy to demonstrate how a
mismatched load seen by the RX degrades signal.

Just start with random tuner settings.  Then tune to maximum RX noise.
This ends up being darn close to a perfect match to the RX.  It's pretty
  close for TX too for most RX's.

In fact, there was a tuning method using a milliwatt level noise
generator that some advocated be used for setting the tuner.  Their goal
was to eliminate any significant RF being transmitted during the tuning
process.  Don't forget with manual tuner, it wasn't a fraction of a
second process.  Depending on the skill of the user it could take some
time-- unless he had some presetting info available.


73 de Brian/K3KO



Tom W8JI wrote:

>> Actually, you will probably LOSE a couple of db by switching on both
>> preamp and attenuator compared to having both switched off. (Measure
>> your MDS and compare results if you don't believe...)
>
> MDS, like dynamic range, can go either direction with changes in gain. It is
> possible to have a gain increase and lose MDS.
>
> This is why it is important to know how things really change in abnormal
> configurations, not how we "feel" they change.
>
>> Regarding weak signals, one factor that is overlooked is the ATU. By
>> switching it to bypass you can gain 5 or 6 db in MDS. Of course, you
>> would want to switch it back on when you transmit.
>
> That large amount surprises me, although a smaller amount certainly would
> not. Systems with loss are often not bilateral. For example on receiving
> feedline losses associated with feedline SWR are determined by the radio's
> input impedance, not by antenna SWR. On receiving the receiver impedance
> determines feedline SWR.
>
> On transmitting, the antenna is the load and sets feedline SWR....affecting
> feedline losses.
>
> 6 dB is a pretty big change. Maybe your receiver input impedance is not so
> close to 50 j0, or your 6 dB is not 6 dB though some sort of errors in
> calibration????
>
> 73 Tom
>
> ______________________________________________________________
> Elecraft mailing list
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[drewko]

You are right about the ATU. It was my mistake comparing the ATU-ON
which had been tuned at other than 50 ohm load compared to the
ATU-OFF.

As for PRE+ATT, I just measured MDS with the  PRE and ATT settings
either both on or both off. Having both PRE and ATT switched on gives
2 db poorer MDS than having both off. That is unnoticeable of course,
just a point of interest since the specs would seem to indicate it
should be a couple of db better.

Does anyone use both PRE+ATT ON and find it noticeably better? I can't
hear any difference myself.

73,
Drew
AF2Z



On Wed, 11 Aug 2010 06:21:05 -0700 (PDT), AB2TC - Knut wrote:

>
>Why do you think you gain in MDS (presumably you mean a *lower* MDS) by
>bypassing the ATU? If the ATU is needed for transmit, it will also be
>benficial in receive. I don't have the K3 ATU, but both manual and automatic
>tuners in my antenna system and can certainly certify that when switching in
>the tuner when needed, the receive signal goes up (mismatch loses receive
>signal too).
>
>AB2TC - Knut
>
>
>drewko wrote:
>>
>> Actually, you will probably LOSE a couple of db by switching on both
>> preamp and attenuator compared to having both switched off. (Measure
>> your MDS and compare results if you don't believe...)
>>
>> Regarding weak signals, one factor that is overlooked is the ATU. By
>> switching it to bypass you can gain 5 or 6 db in MDS. Of course, you
>> would want to switch it back on when you transmit.
>>
>> I wonder if the ATU could be programmed to automatically be bypassed
>> on receive? You would perhaps not want the ATU to be switched in and
>> out at break-in speeds, but after a suitable semi-breakin delay. I
>> think that would be a handy option for weak signal work for those of
>> us who must use the ATU.
>>
>> 73,
>> Drew
>> AF2Z
>>
>>
>> <snip
>>

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[Vic K2VCO]

The K3 ATU is not removed from the circuit when it is set to bypass. It is set to
compensate for stray reactance in traces, etc. so that the SWR will be close to 1:1 for a
true 50 ohm load.

So any variations in MDS are not caused by losses inherent in the tuner.

On 8/11/2010 6:34 AM, Tom W8JI wrote:

>
>> Actually, you will probably LOSE a couple of db by switching on both
>> preamp and attenuator compared to having both switched off. (Measure
>> your MDS and compare results if you don't believe...)
>
> MDS, like dynamic range, can go either direction with changes in gain. It is
> possible to have a gain increase and lose MDS.
>
> This is why it is important to know how things really change in abnormal
> configurations, not how we "feel" they change.
>
>> Regarding weak signals, one factor that is overlooked is the ATU. By
>> switching it to bypass you can gain 5 or 6 db in MDS. Of course, you
>> would want to switch it back on when you transmit.
>
> That large amount surprises me, although a smaller amount certainly would
> not. Systems with loss are often not bilateral. For example on receiving
> feedline losses associated with feedline SWR are determined by the radio's
> input impedance, not by antenna SWR. On receiving the receiver impedance
> determines feedline SWR.
>
> On transmitting, the antenna is the load and sets feedline SWR....affecting
> feedline losses.
>
> 6 dB is a pretty big change. Maybe your receiver input impedance is not so
> close to 50 j0, or your 6 dB is not 6 dB though some sort of errors in
> calibration????
>
> 73 Tom
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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[James Good]

For those on the reflector that have endured the various products from
Microsoft over the years and decades, and for those too young to remember,
during the time when it seemed that Microsoft was releasing a product update
and/or patch almost every week bugs and glitches in a given product  were
described in the following manner:  "A Bug is an Undocumented Feature."

Jim  KD5VXH

----- Original Message -----
From: "ab2tc" <[hidden email]>
To: <[hidden email]>
Sent: Wednesday, August 11, 2010 8:21 AM
Subject: Re: [Elecraft] K3: PRE/ATT Bug or feature?


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[The Smiths]

I find it to be much better in some circumstances.  I find that the noise floor is actually reduced, not brought up by the 2dB that would be expected.  This is very similar to when I adjust the RF Gain down to about 3 o'clock.  Yet it works much faster because I can simply push the button on and off when I need it.
 

> From: [hidden email]
> To: [hidden email]
> Date: Wed, 11 Aug 2010 10:16:40 -0400
> CC: [hidden email]
> Subject: Re: [Elecraft] K3: PRE/ATT Bug or feature?
>
> You are right about the ATU. It was my mistake comparing the ATU-ON
> which had been tuned at other than 50 ohm load compared to the
> ATU-OFF.
>
> As for PRE+ATT, I just measured MDS with the PRE and ATT settings
> either both on or both off. Having both PRE and ATT switched on gives
> 2 db poorer MDS than having both off. That is unnoticeable of course,
> just a point of interest since the specs would seem to indicate it
> should be a couple of db better.
>
> Does anyone use both PRE+ATT ON and find it noticeably better? I can't
> hear any difference myself.
>
> 73,
> Drew
> AF2Z
>
>
>
> On Wed, 11 Aug 2010 06:21:05 -0700 (PDT), AB2TC - Knut wrote:
>
> >
> >Why do you think you gain in MDS (presumably you mean a *lower* MDS) by
> >bypassing the ATU? If the ATU is needed for transmit, it will also be
> >benficial in receive. I don't have the K3 ATU, but both manual and automatic
> >tuners in my antenna system and can certainly certify that when switching in
> >the tuner when needed, the receive signal goes up (mismatch loses receive
> >signal too).
> >
> >AB2TC - Knut
> >
> >
> >drewko wrote:
> >>
> >> Actually, you will probably LOSE a couple of db by switching on both
> >> preamp and attenuator compared to having both switched off. (Measure
> >> your MDS and compare results if you don't believe...)
> >>
> >> Regarding weak signals, one factor that is overlooked is the ATU. By
> >> switching it to bypass you can gain 5 or 6 db in MDS. Of course, you
> >> would want to switch it back on when you transmit.
> >>
> >> I wonder if the ATU could be programmed to automatically be bypassed
> >> on receive? You would perhaps not want the ATU to be switched in and
> >> out at break-in speeds, but after a suitable semi-breakin delay. I
> >> think that would be a handy option for weak signal work for those of
> >> us who must use the ATU.
> >>
> >> 73,
> >> Drew
> >> AF2Z
> >>
> >>
> >> <snip
> >>
>
> ______________________________________________________________
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[ab2tc]

Oof. Having the attenuator and preamp on at the same time is completely nonsensical. The gain of the preamp is ~11 dB and the loss of the attenuator is ~10dB so they almost completely cancel each other out gainwise. But *all* the noise from the preamp will be added, so your noise floor will be significantly raised and there is *no* advantage gained. The total dynamic range will be reduced by at least the increase in the noise floor (that's assuming that the preamp is completely distortion free).

AB2TC - Knut

The Smiths wrote

I find it to be much better in some circumstances.  I find that the noise floor is actually reduced, not brought up by the 2dB that would be expected.  This is very similar to when I adjust the RF Gain down to about 3 o'clock.  Yet it works much faster because I can simply push the button on and off when I need it.
 
<snip>

[Bill K9YEQ]

Agreed!!! The preamp creates the amplification of incoming noise. Adding an
attenuator after the preamp makes little sense.

I do not use the preamp unless the noise floor is low.  I use the ATT  when
the noise is high without the Preamp.  Really helps pull sigs in.  Forget
the S meter readings other than to help you decide on how to use the ATT and
Preamp settings....  This helps the dynamic range.  I would rather listen to
a clean S7 signal than an S9 + without clarity.  Hope that makes sense.

Bill
K9YEQ

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of ab2tc
Sent: Wednesday, August 11, 2010 3:50 PM
To: [hidden email]
Subject: Re: [Elecraft] K3: PRE/ATT Bug or feature?


Oof. Having the attenuator and preamp on at the same time is completely
nonsensical. The gain of the preamp is ~11 dB and the loss of the attenuator
is ~10dB so they almost completely cancel each other out gainwise. But *all*
the noise from the preamp will be added, so your noise floor will be
significantly raised and there is *no* advantage gained. The total dynamic
range will be reduced by at least the increase in the noise floor (that's
assuming that the preamp is completely distortion free).

AB2TC - Knut


The Smiths wrote:

>
>
> I find it to be much better in some circumstances.  I find that the
> noise floor is actually reduced, not brought up by the 2dB that would
> be expected.  This is very similar to when I adjust the RF Gain down
> to about
> 3 o'clock.  Yet it works much faster because I can simply push the
> button on and off when I need it.
>  
> <snip>
>

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