K3 Observations Digital Modes and SSB

[KD8NNU]

I spent a lot of time with the K3 this weekend working SSB and data
modes mostly PKS.

The K3 the more I use it the more I like it and am amazed by its
performance with a standard 2.7 5 pole filter and 2.1 8 pole filter.

First for ssb I was joining a new that had .5 khz signal above the net
signal.  I was able to dial down to a .95 khz filter and shift it such
that I could still join in on the roundtable net.  It was absolutly
amazing.

Then I spent a ton of time on the digital modes.  I wanted to try and
make a lot of contacts and use the extra punch you get with these narrow
signals.   First I have learned that PKS guys dont care if they get
right on top of your transmitt and receive.  I was able to narrow down
to .15 khz on the dsp filter and could eleminate completey the
interference from nearby signals that would get hammered by the qrn.   I
do not believe that everyone has a K3 but that they depend on the
computer extra filtering.  However, I could eleminate the close signals
with the K3 which greatly enhanced the copy.

Finally I learned really dial in my output from the pc for the digital
modes so that the ALC would be at a solid 3 bars and just tickel the 4th
bar.  In this condition I could go to 100w out and still have a clean
signal.  I was able to punch some dx at high power that i could not get
at 50w or less.

Spending a lot of time over 50w and the PA temp never went above 43C.

The more I use it the better it gets.  I can only wonder how much better
it would be with a 500hz and 250hz filter.

Also if the new amp is as clean for 500w as the standard 100w built in
amp it will be a winner.

Now how to save more money for my two hobbies.  One is ham radio and the
other is my Jeep (Just Empty Every Pocket).

I wonder what I could do if I had more than a dipole at 30 ft.

Don
KD8NNU


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[Don Wilhelm-4]

  Don,

You are doing it right - except --

Crank up either the K3 line-in gain or the computer audio line-out a bit
more - the proper setting is to have 4 "ALC" bars on solid and the 5th
one flickering.  I put "ALC" in quotes, because the K3 ALC meter is like
a VU meter for the first 4 bars.  The onset of ALC is indicated by the
5th bar.

73,
Don W3FPR

On 1/30/2011 9:45 PM, [hidden email] wrote:
> Finally I learned really dial in my output from the pc for the digital
> modes so that the ALC would be at a solid 3 bars and just tickel the 4th
> bar.  In this condition I could go to 100w out and still have a clean
> signal.  I was able to punch some dx at high power that i could not get
> at 50w or less.
>
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[KD8NNU]

Don,

How do you know so much detail,  did you help design these things?  :-)

You always have help for everyone to make our experience even better so
thank you very much!!!

Don
KD8NNU


On Sun, Jan 30, 2011 at 9:56 PM, Don Wilhelm wrote:

> Don,
>
> You are doing it right - except --
>
> Crank up either the K3 line-in gain or the computer audio line-out a
> bit more - the proper setting is to have 4 "ALC" bars on solid and the
> 5th one flickering.  I put "ALC" in quotes, because the K3 ALC meter
> is like a VU meter for the first 4 bars.  The onset of ALC is
> indicated by the 5th bar.
>
> 73,
> Don W3FPR
>
> On 1/30/2011 9:45 PM, [hidden email] wrote:
>> Finally I learned really dial in my output from the pc for the
>> digital
>> modes so that the ALC would be at a solid 3 bars and just tickel the
>> 4th
>> bar.  In this condition I could go to 100w out and still have a clean
>> signal.  I was able to punch some dx at high power that i could not
>> get
>> at 50w or less.
>>

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[Don Wilhelm-4]

   Don,

Thanks for your fine compliments.

I do have a good memory for those kind of things, and will do a perusal
of the .pdf version of the  manual when required.

I do what I can to help others.  When I started my ham radio adventures
as a teen, I had a whole radio club in a small town (about 20 members -
town population was about 5000) who helped me along and tried to set me
on a proper path to not only ham radio, but to a satisfying career in
electrical engineering.  Most of them are gone now, and I cannot thank
them directly, but they shared their knowledge with me, and I pass along
what I can in hopes of helping others the way they helped me.
BTW: The East Palestine (Ohio) radio club has been continuously active
for over 50 years.  If you hear W8GMM on the air, that is the one.  I
believe that remains one of the greater ham licenses per capita than for
any other area.

73,
Don W3FPR


On 1/30/2011 10:02 PM, [hidden email] wrote:

> Don,
>
> How do you know so much detail,  did you help design these things?  :-)
>
> You always have help for everyone to make our experience even better so
> thank you very much!!!
>
> Don
> KD8NNU
>

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[ik1bxn]

by the way .... I wonder, without having a certain indication to trust right now, what should be the suggested maximum RF power in PSK and RTTY , without taking the risk of stressing finals. Could you give me an indication ? Normally I stay at 40-45 w....I feel (or better I hope) that's ok
Many thanks in advance
73 de Giorgio

[doberman]

PSK is a low power mode- 40-45 watts is overkill to say the least -
20-25 is even strong. QRPers run 5 watts or less quite successfully with
PSK.

Dan - KI4YZE

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of ik1bxn
Sent: Tuesday, February 01, 2011 4:07 PM
To: [hidden email]
Subject: Re: [Elecraft] K3 Observations Digital Modes and SSB


by the way .... I wonder, without having a certain indication to trust
right
now, what should be the suggested maximum RF power in PSK and RTTY ,
without
taking the risk of stressing finals. Could you give me an indication ?
Normally I stay at 40-45 w....I feel (or better I hope) that's ok
Many thanks in advance
73 de Giorgio
--
View this message in context:
http://elecraft.365791.n2.nabble.com/K3-Observations-Digital-Modes-and-S
SB-tp5976035p5982666.html
Sent from the [K3] mailing list archive at Nabble.com.
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[Don Cunningham-2]

45 watts might not be so bad from Italy on PSK, and certainly wouldn't be on
RTTY.
73,
Don, WB5HAK

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[Don Wilhelm-4]

  Giorgio,

The safe power for the K3 is 100 watts.  A operator using more than 20
to 50 watts for PSK31 is IMHO a "band hog" - PSK31 operation at QRP
levels is quite common and should not be abused by those running high
power (even though many do it).

OTOH, RTTY is different because many operators are running the full
legal limit, but I have worked several RTTY stations in a contest using
only 100 watts.

73,
Don W3FPR

On 2/1/2011 4:07 PM, ik1bxn wrote:
> by the way .... I wonder, without having a certain indication to trust right
> now, what should be the suggested maximum RF power in PSK and RTTY , without
> taking the risk of stressing finals. Could you give me an indication ?
> Normally I stay at 40-45 w....I feel (or better I hope) that's ok
> Many thanks in advance
> 73 de Giorgio
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[ik1bxn]

Thanks you all for clarification (fast and shape response as usual....that's wonderful)! 73 de Giorgio

[Julian, G4ILO]

Many people object to the use of high power with PSK modes because many people operate within a small section of the band and a strong signal can make life difficult for other users. But the difference between 40W and 100W is only about 4dB, less than an S point, less than the difference between a good antenna and a so-so one and less than the typical variation in signal strength caused by QSB. If you are close (geographically) to someone else using PSK31 they are going to be strong whatever the power they are running.

The most important thing when using PSK modes is not how much power you are using, but that the signal is *clean*, with the minimum of IMD products. And that is why with a barefoot K3 or any other 100W radio you should not exceed about 40W output. The K3 will certainly handle running 100W output without overheating. But you will not be a good neighbour to other users because the IMD will deteriorate substantiually as the power increases. If you had a KPA100 then I dare say you could run 100W output and be a better neighbour than someone running 40W with a barefoot rig.

The reason it is necessary to run higher power when using RTTY is that it is an antiquated mode designed before the advent of DSP and it requires a stronger signal to produce good copy than PSK31. The reason it is OK to run 100W of RTTY using a barefoot K3 is because RTTY is a constant amplitude FSK mode and does not cause any IMD.

Don Wilhelm-4 wrote

  Giorgio,

The safe power for the K3 is 100 watts.  A operator using more than 20
to 50 watts for PSK31 is IMHO a "band hog" - PSK31 operation at QRP
levels is quite common and should not be abused by those running high
power (even though many do it).

OTOH, RTTY is different because many operators are running the full
legal limit, but I have worked several RTTY stations in a contest using
only 100 watts.

[Julian, G4ILO]

I meant "... if you had a KPA*500* you could drive it to 100W output and ..."

[ik1bxn]

I share what Julian wrote 100% . My question was only oriented to take care of my rig . k3 makes the difference, not only in rx ! I have a vertical multiband antenna that works fine but it's a vertical, however k3 let me to receive and decode even weak signals. In tx k3 has a clean and perfect modulation and keeping ALC settings as suggested I receive always perfect comments to my waterfall track. In the past, using another rig, comments were different.
With the goal to keep an eye to modulation quality/clean, in a previous post I suggested to add to p3 (sleeping at tx time HI) the possibility to show during tx time info about wave form or whatever else useful. This, in my opinion, would help to optimize the rig settings and have the maximum without producing rubbish into the air .... not only when in PSK, isn't it ?
73 to everybody !
Giorgio

[Ross Primrose N4RP]

On 2/2/2011 4:37 AM, Julian, G4ILO wrote:
> The reason it is necessary to run higher power when using RTTY is that it is
> an antiquated mode designed before the advent of DSP and it requires a
> stronger signal to produce good copy than PSK31. The reason it is OK to run
> 100W of RTTY using a barefoot K3 is because RTTY is a constant amplitude FSK
> mode and does not cause any IMD.

You don't need a lot of power to run RTTY. In the fall of 2009 in one of
the RTTY contests I worked all continents with an IC-703+ at 5W into
(big) wire antennas...

73, Ross N4RP

--
FCC Section 97.313(a) “At all times, an amateur station must use the minimum transmitter power necessary to carry out the desired communications.”

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[Kok Chen]

On Feb 2, 2011, at 2/2    1:37 AM, Julian, G4ILO wrote:

> The most important thing when using PSK modes is not how much power  
> you are
> using, but that the signal is *clean*, with the minimum of IMD  
> products. And
> that is why with a barefoot K3 or any other 100W radio you should  
> not exceed
> about 40W output.

I agree completely with Julian about this.  PSK31 is a weak signal  
mode when conditions are good.  How much power you need to use depends  
on the SNR of your signal at the receiving end.

Think about it. A 3 dB difference in your signal can only affect the  
blocking dynamic range of the receiver by 3 dB.  But if your transmit  
IMD is 6 dB worse (I have seen some "QRP" signals with -25 dBc IMD),  
you are ruining the band for many more people than just your nearby  
neighbors who have receivers with poor dynamic range.

With the K3, there is no practical difference in transmit IMD between  
using 20 watts and 50 watts.  See the two tables halfway down this page:

http://homepage.mac.com/chen/Technical/K3/Digital/digital.html

In practice, it is non-productive to run power once your SNR at the  
receiver is over 0 dB in a 300 Hz noise bandwidth.  When there is  
multipath, PSK31 will not get through no matter how much power you  
use.  Even though RTTY is 3 dB less sensitive than PSK31 when  
conditions are good, it can still get through even flutter if you have  
a good SNR at the receiving end (i.e., transmit with more power).  
PSK31 will not get through flutter no matter how much power you apply.

73
Chen, W7AY




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[KD8NNU]

Thank you for the post, however I am confused.

However, maybe you can help me out with some target numbers.

What is a good IMD report number and good SN number from a receiveing
station and what are the numbers that state you are messing up the
bands.  Lots of contacts kick back and IMD and SN number, as I do with
my macros.

 From my perspective, I can see a trace from someone else and with my
filters easily work around it with the K3 no problem, but I can not tell
if I am creating a problem with IMD products.

I am trying to understand the best way to set up my radio, and when I
look at the tables in the link, it tells me that keeping ACL at a
maximum of 4 with maybe an ocassional ticke to 5 was the key to a clean
signal with a K3 and output power did not matter.

Also I have found that there are instances where I can hear DX with the
filters tight and for me to respond I have to turn the power up to 80 to
make contact.

Additionally, I try and find an open spot between frequiences in use and
observe to see if I am close to anyone before any TX of any kind.  I am
amaized but the amount of guys who run with the AFC turned on in their
software and they are constantly drifting around and drift close to you
and then would be offended that you are interferring with them.

Anyway, as stated above, my only feedback on my signal is when someone
provides the IMD and SN report, so target numbers would be appreciated
as we all have to share the space and contacts.

Thanks in advance for your help.

Don
KD8NNU


On Wed, Feb 2, 2011 at 12:13 PM, Kok Chen wrote:

> On Feb 2, 2011, at 2/2    1:37 AM, Julian, G4ILO wrote:
>
>> The most important thing when using PSK modes is not how much power
>> you are
>> using, but that the signal is *clean*, with the minimum of IMD
>> products. And
>> that is why with a barefoot K3 or any other 100W radio you should
>> not exceed
>> about 40W output.
>
> I agree completely with Julian about this.  PSK31 is a weak signal
> mode when conditions are good.  How much power you need to use depends
> on the SNR of your signal at the receiving end.
>
> Think about it. A 3 dB difference in your signal can only affect the
> blocking dynamic range of the receiver by 3 dB.  But if your transmit
> IMD is 6 dB worse (I have seen some "QRP" signals with -25 dBc IMD),
> you are ruining the band for many more people than just your nearby
> neighbors who have receivers with poor dynamic range.
>
> With the K3, there is no practical difference in transmit IMD between
> using 20 watts and 50 watts.  See the two tables halfway down this
> page:
>
> http://homepage.mac.com/chen/Technical/K3/Digital/digital.html
>
> In practice, it is non-productive to run power once your SNR at the
> receiver is over 0 dB in a 300 Hz noise bandwidth.  When there is
> multipath, PSK31 will not get through no matter how much power you
> use.  Even though RTTY is 3 dB less sensitive than PSK31 when
> conditions are good, it can still get through even flutter if you have
> a good SNR at the receiving end (i.e., transmit with more power).
> PSK31 will not get through flutter no matter how much power you apply.
>
> 73
> Chen, W7AY
>
>
>
>
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[ac0h]

Short of using something like the KK7UQ IMD meter the best way to know
how clean you signal is is to have the guy at the other end send you a
screen shot of your signal on his waterfall.

If you use something like the IMD meter, the lower the number the
better. Your shooting for -25 or lower.
If you get a screen shot you want NO tracks outside of the two main
carriers.
Treat reported IMD numbers from others like S meter readings. The
quality of that number has a lot to do with the software they're using
and how strong your signal is.



On Wed, 2 Feb 2011 12:47:44 -0500 (EST)
[hidden email] wrote:

> Thank you for the post, however I am confused.
>
> However, maybe you can help me out with some target numbers.
>
> What is a good IMD report number and good SN number from a receiveing
> station and what are the numbers that state you are messing up the
> bands.  Lots of contacts kick back and IMD and SN number, as I do
> with my macros.
>
>  From my perspective, I can see a trace from someone else and with my
> filters easily work around it with the K3 no problem, but I can not
> tell if I am creating a problem with IMD products.
>
> I am trying to understand the best way to set up my radio, and when I
> look at the tables in the link, it tells me that keeping ACL at a
> maximum of 4 with maybe an ocassional ticke to 5 was the key to a
> clean signal with a K3 and output power did not matter.
>
> Also I have found that there are instances where I can hear DX with
> the filters tight and for me to respond I have to turn the power up
> to 80 to make contact.
>
> Additionally, I try and find an open spot between frequiences in use
> and observe to see if I am close to anyone before any TX of any
> kind.  I am amaized but the amount of guys who run with the AFC
> turned on in their software and they are constantly drifting around
> and drift close to you and then would be offended that you are
> interferring with them.
>
> Anyway, as stated above, my only feedback on my signal is when
> someone provides the IMD and SN report, so target numbers would be
> appreciated as we all have to share the space and contacts.
>
> Thanks in advance for your help.
>
> Don
> KD8NNU

--
R. Kevin Stover
AC0H
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[Kok Chen]

On Feb 2, 2011, at 2/2    9:47 AM, [hidden email] wrote:

> What is a good IMD report number and good SN number from a  
> receiveing station and what are the numbers that state you are  
> messing up the bands.

The transmit IMD that you see bandied about are 3rd order IMD numbers.

If you take a look at a PSK31 signal that is idling (i.e., sending the  
Idle Varicode), you should see two carriers that are space 31.25 Hz  
apart.

Third order IMD will therefore create an extra pair of sidebands.  One  
that is 31.25 Hz away from the lower carrier and one that is 31.25 Hz  
away from the upper carrier.

Like CW and RTTY keyclicks, these are not useful and only uses more  
spectrum that you need to pass information.

The reason the idling PSK31 signal looks like two carriers idle signal  
is that it in not just phase modulated.  There is also a cosinusoidal  
amplitude component.  I had attempted to describe it a little when I  
wrote the PSK31 section in Chapter 16 of the 2010 ARRL Handbook.

(For old timers, think "double sideband suppressed carrier" signals.  
There too, you have the same thing -- two carriers on the RF spectrum  
when you transmit a single audio tone DSB signal.)

The existence of 3rd order IMD will just take up more spectrum space,  
and if they are loud enough, will bother everybody trying to copy the  
signal that is next to yours.

If you hard clip a PSK31 signal (as in using severe amounts of ALC),  
the cosinusoidal waveshape becomes a square wave.  Severe clipping  
will cause around -11 to -13 dB IMD.

But wait!  If you do PSK31 for long enough, you probably have seen  
signals with even worse IMD.

Careful look at those signals will show that they were not just  
clipping but there are overshoots in the square wave envelopes!  I  
have seen IMD as bad as -9 dBc.

I would prefer that the station transmits with 10 times more power but  
staying inside a PSK31 passband, than spreading their energy over the  
entire PSK sub-band!

If the SNR of a station is much worse than 25 dB, and his IMD is -25  
dBc, you will not visually see any extra "rails" on his signal.  
However, with sufficient integration, you can measure the IMD of a  
stable signal even below its SNR.  In practice however, I don't trust  
those measurements.  So, if someone tells you that they can barely  
copy you, I won't trust their IMD report.  Very often, they are just  
reporting the noise amplitude where the IMD component would have  
been.  Sometimes, it is their receiving chain that is producing the IMD!

Personally, I consider -25 dBc IMD to be barely acceptable.  It is  
something like transmitting an extra 1/2 watt signal on the sides of a  
100 watt signal.

Most stations that are properly adjusted will run between -25 dBc and  
-35 dBc IMD.  You can find some stations with obviously experienced  
PSK31 operators who do much better than that.  They are often both  
loud and clean.

My own K3 will not do any better than -35 dB transmit IMD.

In fact, this K3 produces around -30 dBc IMD if you use PSK-D at 5  
watts; so you are much better off using DATA-A from a good software  
program.  -30 dBc IMD is starting to fall into the "mediocre" range.

With my FT-1000MP at 5 watts, I have gotten -40 dBc IMD reports.  But  
you need to be loud at the receiving end for them to properly measure  
IMD that is that low -- the few times I got numbers that high were  
from a local station and with KH6 -- we have a pipeline from Portland  
to KH6 :-).   A signal has to be really loud to reliably measure -40  
dBc IMD.

> I am trying to understand the best way to set up my radio, and when  
> I look at the tables in the link, it tells me that keeping ACL at a  
> maximum of 4 with maybe an ocassional ticke to 5 was the key to a  
> clean signal with a K3 and output power did not matter.

The IMD numbers may be the same, but remember that you are referencing  
the IMD number to the carrier power.

Transmitting a -20 dBc IMD signal will produce a 1 watt image when you  
run 100 watts, while it produces a 0.1 watt image when you run 10 watts.

The reason IMD is important is that a 100 watt station with -40 dBc  
IMD will produce an extra intermodulation image that is only as strong  
as a 10 watt station with -30 dBc IMD.

The other way of looking at it is that a station running 100 watts  
with -40 dBc IMD uses up no more spectrum (no matter how far in  
terrestrial distance you are from him) than if he reduced his power to  
10 watts but his IMD has degraded to -30 dBc.

73
Chen, W7AY





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[KD8NNU]

Hi Kevin,

Thanks that now makes sense to me.  However, than almost every signal
that I am looking at is outside of the two main carriers.  Like little
spikes, I don't know how else to define it.

Is this not also a function of the filtering set up in the software that
you would be using, which supports your statement its kind of like a S
meter so take it with a grain of salt.


I will have to set up a sked with some fellow K3 users to play with them
sending some screen shots back and forth of the waterfall.

The IMD Meter you mention looks like a good investment.



Don
KD8NNU


On Wed, Feb 2, 2011 at 1:19 PM, R. Kevin Stover wrote:

> Short of using something like the KK7UQ IMD meter the best way to know
> how clean you signal is is to have the guy at the other end send you a
> screen shot of your signal on his waterfall.
>
> If you use something like the IMD meter, the lower the number the
> better. Your shooting for -25 or lower.
> If you get a screen shot you want NO tracks outside of the two main
> carriers.
> Treat reported IMD numbers from others like S meter readings. The
> quality of that number has a lot to do with the software they're using
> and how strong your signal is.
>
>
>
> On Wed, 2 Feb 2011 12:47:44 -0500 (EST)
> [hidden email] wrote:
>
>> Thank you for the post, however I am confused.
>>
>> However, maybe you can help me out with some target numbers.
>>
>> What is a good IMD report number and good SN number from a receiveing
>> station and what are the numbers that state you are messing up the
>> bands.  Lots of contacts kick back and IMD and SN number, as I do
>> with my macros.
>>
>>  From my perspective, I can see a trace from someone else and with my
>> filters easily work around it with the K3 no problem, but I can not
>> tell if I am creating a problem with IMD products.
>>
>> I am trying to understand the best way to set up my radio, and when I
>> look at the tables in the link, it tells me that keeping ACL at a
>> maximum of 4 with maybe an ocassional ticke to 5 was the key to a
>> clean signal with a K3 and output power did not matter.
>>
>> Also I have found that there are instances where I can hear DX with
>> the filters tight and for me to respond I have to turn the power up
>> to 80 to make contact.
>>
>> Additionally, I try and find an open spot between frequiences in use
>> and observe to see if I am close to anyone before any TX of any
>> kind.  I am amaized but the amount of guys who run with the AFC
>> turned on in their software and they are constantly drifting around
>> and drift close to you and then would be offended that you are
>> interferring with them.
>>
>> Anyway, as stated above, my only feedback on my signal is when
>> someone provides the IMD and SN report, so target numbers would be
>> appreciated as we all have to share the space and contacts.
>>
>> Thanks in advance for your help.
>>
>> Don
>> KD8NNU
>
>
>
>
> --
> R. Kevin Stover
> AC0H

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[Kok Chen]

On Feb 2, 2011, at 2/2    11:14 AM, [hidden email] wrote:

> Thanks that now makes sense to me.  However, than almost every signal
> that I am looking at is outside of the two main carriers.  Like little
> spikes, I don't know how else to define it.

You only see two clean rails (plus IMD rails) when the PSK31 signal is  
idling.

When someone types, their PSK31 signal will produce other sidebands --  
so you see that fuzzy signal on a waterfall.

With enough trickery, you can measure 3rd order IMD even when a  
station is actively transmitting.  But the best time to measure is  
when a station is idling.

> The IMD Meter you mention looks like a good investment.

An even better investment is the Elecraft Directional Coupler.  You  
can then tap the output from the K3 and feed that into a second  
receiver that has a computer connected to the second receiver's sound  
card.

Measuring IMD is not so good if you just use a short sense antenna.  
Best to tap off of a directional coupler.

73
Chen, W7AY



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[Jim Brown-10]

On 2/2/2011 11:08 AM, Kok Chen wrote:
> My own K3 will not do any better than -35 dB transmit IMD

An important source of IMD (and harmonic distortion) is the sound card
used to generate the digital signal.  The sound cards in IBM T-series
Thinkpads are better than average, but their distortion increases by
10dB as you get close to clip level, even without clipping. Reducing the
output level by only 6dB reduces distortion by 10dB.

Thus, my advice for setting up sound card levels is to first crank the
output level up to the point where you just begin to hear distortion (or
see it on a scope), then back it off by at least 6dB (half the voltage).

Audio transformers can also be a source of IMD (and harmonic
distortion), and that distortion increases dramatically if they are
driven from a high impedance source, even at relatively low signal
levels. The ideal way to drive an audio transformer is from a source
having a very low output impedance. Adding resistors in series with the
source is a very bad idea, and CAUSES the transformer to produce
distortion. This was a problem with the line output in early production
K3s. .

It's OK to add a 10dB pad (resistive voltage divider) between a sound
card and the rig (K3 or other) IF the pad has a low output impedance.  
That's easy to do -- simply use a low value for the output resistor.
Most sound cards are designed to drive headphones to about 1 volt peak,
with load impedances between 8 and 600 ohms, so a good 10 dB voltage
divider would be something like 220 ohms in series and 68 ohms as the
load, or 180 in series and 56 ohms as the load, or 150 ohms in series
and 47 ohms as the load. This range of values won't overload the sound
card, and will minimize any distortion produced by the input transformer
in the K3.

BTW -- the same sort of precautions should be taken with ANY input
transformer, not only those used in the K3.

Finally, one must also be careful not to overdrive the K3 with too much
audio gain. Follow instructions in the manual carefully for this.

Note that these precautions apply to ALL audio feeds to a ham rig,
including all digital modes and voice playback for contesting.

73, Jim Brown K9YC
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