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Power Settings for no AGC in Elecraft Radios

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John Huggins, kx4o

Power Settings for no AGC in Elecraft Radios

All (especially Don),

I have heard it explained on this reflector the Elecraft power control
loop is such that the usual advice to...

"max out the power setting and adjust the audio level input to avoid
AGC action"

...is not appropriate for the K2 and, I suppose, the K3.

I accept this, but don't quite understand the reasoning. Don can you
please explain the key differences between a rig, such as my Icom 746,
and the K2 that mandate this?

Are there other radio brands with power control loops like Elecraft
products?

Thanks.

John, kx4o
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Guy, K2AV

Re: Power Settings for no AGC in Elecraft Radios

Why would you want to "avoid" level control in the transmitter? What issue
do you avoid by doing that? 73, Guy.

On Thu, Jul 5, 2012 at 8:46 PM, John <[hidden email]> wrote:

> All (especially Don),
>
> I have heard it explained on this reflector the Elecraft power control
> loop is such that the usual advice to...
>
> "max out the power setting and adjust the audio level input to avoid
> AGC action"
>
> ...is not appropriate for the K2 and, I suppose, the K3.
>
> I accept this, but don't quite understand the reasoning. Don can you
> please explain the key differences between a rig, such as my Icom 746,
> and the K2 that mandate this?
>
> Are there other radio brands with power control loops like Elecraft
> products?
>
> Thanks.
>
> John, kx4o
> ______________________________________________________________
> 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
>

Re: Power Settings for no AGC in Elecraft Radios

Any time your amplifier cuts back your driver power it introduces a certain amount of distortion which is undesirable, but not as undesirable as over-driving your amplifier. The best practice is to turn your driver power down until the AGC is used only to eliminate spikes in power when something overdrives your transceiver. This is good practice with any transceiver but the K2 and K3 have better controls than some other transceivers. I have never owned a K2 but my K3 can be set at any output power very reliably. I can't say as much for my Kenwood TS-440 which has a control, but it is too sensitive at high power settings.

Willis 'Cookie' Cooke
K5EWJ & Trustee N5BPS, USS Cavalla, USS Stewart

----- Original Message -----
From: Guy Olinger K2AV <[hidden email]>
To: John <[hidden email]>
Cc: [hidden email]
Sent: Friday, July 6, 2012 12:45 AM
Subject: Re: [Elecraft] Power Settings for no AGC in Elecraft Radios

Why would you want to "avoid" level control in the transmitter? What issue
do you avoid by doing that? 73, Guy.

On Thu, Jul 5, 2012 at 8:46 PM, John <[hidden email]> wrote:

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Don Wilhelm-4

Re: Power Settings for no AGC in Elecraft Radios

In reply to this post by John Huggins, kx4o

John,

Other transceivers normally control the drive with a potentiometer that
adjusts the gain of one of the transmit stages.
The K2 and K3 do it differently - they actually measure the power output
and compare that to the power level that you have requested. The
microprocessor then adjusts the drive to make the actual power equal to
the requested power.

If you attempt to follow the advice for data modes normally given for
other transceivers "set the power to maximum and adjust the audio to
produce the power level you want" That will result in "power creep" if
that technique is used with Elecraft gear. The K2 or K3 will sense that
there is not as much output as was requested and will increase the drive
level.

So when operating Data modes with the K2 or K3, adjust the audio to
produce no ALC - with the K2 increase the audio level until you see one
bar in the ALC meter and then back it down until that one bar goes off -
for the K3 adjust until you have 4 ALC bars lighted with the 5th bar
flickering.

Then set the power level desired with the power knob.

73,
Don W3FPR

On 7/5/2012 8:46 PM, John wrote:

Joe Subich, W4TV-4

Re: Power Settings for no AGC in Elecraft Radios

In reply to this post by John Huggins, kx4o

> Are there other radio brands with power control loops like Elecraft
> products?

I know of no amateur transceiver that uses the same approach to power
setting as Elecraft but it is common in commercial transmitters.

> I accept this, but don't quite understand the reasoning. Don can you
> please explain the key differences between a rig, such as my Icom 746,
> and the K2 that mandate this?

Elecraft *measure* the gain of the driver and final amplifier when
calibrating and set the IF output to the level necessary to drive the
amplifiers to the desired power output. Other amateur transceivers
simply measure the level of grid/base/gate current of the final
amplifier and reduce gain in an IF amplifier to prevent the current
from reaching an "overload" point. The problem with the typical "ALC"
circuit is that the excess current level must be exceeded before the
IF gain can be reduced *and* that point is dynamic which means the
ALC action introduces distortion by its very nature.

The Elecraft ALC is not a "feedback" design - instead it acts on the
audio input to slowly increase/decrease the IF output to the proper
level for the desired output. The K3 "ALC" indicator serves two
purposes - below the nominal "five bars" it shows expansion (additional
audio gain) needed to bring up the output level and above that it shows
the gain reduction used to prevent the driver/final from being driven
beyond the desired power level.

By knowing the gain characteristics of the driver/final *on each band*
Elecraft are able to prevent problems like the "power spike" and
"flat-topping" inherent in the feedback design. The modulator output
is set on each band for the exact level needed for the desired output
power. Unless the user changes the input level (too much audio) the
K2/K3 will not flat-top or spike and the gain does not "hunt" and thus
cause additional transmit IMD..

73,

... Joe, W4TV

On 7/5/2012 8:46 PM, John wrote: