[Elecraft] Final Update To Keying Mod Change

Wed Apr 14 22:14:01 2004

Ron;
For this measurement, I used units of dBc/Hz.  You have to multiply by the
bandwidth of your receiver to get the received power.  This is the correct
units of measurement for a signal that covers a wide bandwidth.  So if you
are using a 100 Hz bandwidth, add 20 dB to get the power that your receiver
actually sees.  If it is a 500 Hz bandwidth, add 27 dB.

Does that make it clearer?
-John
 KI6WX

----- Original Message ----- 
From: "Ron D'Eau Claire" <[email protected]>
To: <[email protected]>
Sent: Tuesday, April 13, 2004 5:21 PM
Subject: RE: [Elecraft] Final Update To Keying Mod Change

That really interesting John. Thank you for the good effort.

Let's see if I understand the levels correctly. A "stock" K2 has a peak
energy in the sidebands at 500 Hz from the carrier that is about 62 db below
the carrier. If I'm scribbling correctly here, that means that if the
carrier is at 100 watts output, then the energy at the peak of the "click"
is about 0.000064 watts or 64 microwatts.

If we use the common scale of 6 db per S-unit, if signal from a "stock" K2
at someone's receiver is S9+10 db then the clicks 500 Hz away are just at
S-zero. At 1 kHz from the carrier, the signal would have to be about S9+20
db for the clicks to be as loud as S-zero. Using the conventional definition
of 50 uV for an S-9 signal, an S9+20 db signal is putting a full 1/2 VOLT on
the antenna terminals.

That's certainly audible if the transmitter is very close to a receiver is
capable of handling that sort of RF voltage at the antenna without
overloading. In installations where transmitters and receivers are very
close to each other, the mods can make a significant improvement, obviously.

However, in normal on-the air use, I'm not sure the bands are quiet enough
for me to hear a noise pulses at S0 or even S1. And they drop in level very
quickly as we tune more than 500 Hz from the carrier.

Ron AC7AC

-----Original Message-----
I've posted a final update to the 180K resistor value change for the
Elecraft Keying Modification.  This update adds a new way to measure key
clicks from a transmitter.  The new method can distinguish the peak
intensity of a key click rather than the average intensity measurements that
are made with a spectrum analyzer.  This better reflects the true effect of
a key click on a receiver.

The new method also measures the peak intensity of a key click for both the
rising and falling edges of the waveform.  The measurements on the K2 show
that in some cases one edge of the keying waveform can generate 10 dB
greater intensity than the other edge.

The latest version of this document can be accessed at:

http://home.pacbell.net/johngreb/improving_elecraft_keyingmod.pdf

-John
 KI6WX

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