Re: phase noise

Rob Sherwood
 

Field Day is the most likely place we run into both transmitted composite noise and serious RMDR limitations.  Multi-transmitter contesters, too, but they already know that is a big problem. 

Rob, NC0B


On Jan 12, 2019, at 6:11 PM, James C. Hall, MD via Groups.Io <heartdoc@...> wrote:

This has been a great thread and I spent a lot of today studying phase noise. It sounds like it’s really not a good idea to amplify QRP transceivers such as FT-817/818, KX1/2/3, etc.

Been looking at how this effects Field Day operations as well.

73, Jamie
WB4YDL


On Jan 12, 2019, at 5:17 PM, Rob Sherwood <rob@...> wrote:

Hi Fred,

 

You are not hurting the amp or the K3, but you are making the transmitted noise much worse.

 

Here is an example. 

 

I use an IC-7300 on 630 meters with a transverter that only requires 5 watts of drive. If I back off the Icom to 5 watts, my transmitted noise seriously degrades.  Since on 630m I need more loss on receive anyway, I put a 10-dB 75-watt Bird attenuator between the output of the 7300 and the input of the transverter.  Now I can run the 7300 at 50 watts instead of 5 watts.  This improved my transmitted noise by 9 dB.

 

On another subject in respect to the K3, if you are running the K3 at 10 watts, the PA is out of the circuit.  On SSB the odd-order transmit IMD (splatter) at 10 to 12 watts is poor compared if the K3 is run at 35 to 45 watts.  If I wanted a cleaner SSB signal from a transmit IMD standpoint, I would run the rig at around 35 watts and whatever the KPA-500 put out.  I would also have my K3 power supply set for 14. 5 volts, and have a nice short power cable from the power supply to the rig so the voltage drop in the wire was minimal.

 

Rob, NC0B

 

From: Elecraft-K3@groups.io [mailto:Elecraft-K3@groups.io] On Behalf Of Fred-K0FG
Sent: Saturday, January 12, 2019 3:23 PM
To: Elecraft-K3@groups.io
Subject: [Elecraft-K3] phase noise

 

After the discussion about phase noise I have a question.   When I want to operate at an output power of 100 watts, or a little above, I frequently turn on the KPA500 and turn the power out on the K3 down to 6-10 watts.  Was thinking I was being kind to the amp and to the K3.   Am I wrong in doing that?   Am I doing more harm than good?

Fred, K0FG

 


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