K3 Key Clicks

[w1gd]

This past weekend, I took my K3 (SN 1428) to the W2GD 160M Contest station in West Creek, NJ where we used it as the run station.  We used another K3 for the mult station.  Both were connected through an Acom lockout box to the same  amplifier and antennas.  Following the contest, I received an email from Tony, K2SG, telling us that he heard key clicks across all of 160M when the run station was transmitting but not when the mult station was transmitting.  Tony lives about 2 miles from our contest station and has two K3s and P3.  He heard the "clicks" on both K3s and could see them on the P3.

This is the first contest that we used my K3 at the run station -- in past contests, we used it for the mult station.  I noticed that  this year the mult station was not able to hear as well when the run station was transmitting.  I now suspect this was due to the clicks from my K3.

I've been able to replicate the problem at my station  with a combination of using the K3 transmitting into my inverted-L  while receiving on an IC-736 using a EWE about 100 feet from teh inverted-L. I can hear the clicks across 160M when sending with either the internal keyer (paddles connected to Paddle jack on the back of the K3) or an external keyer (connected to Key jack on the back of the K3).  The clicks are very evident on 160M running between 0 and 100 watts.  They are slightly evident on 80M and I could not detect them on 40M or above.

I found that I can eliminate the clicks by using PTT when sending CW.  I first noticed this when using the PC to send CW. (I use the RS-232 interface to send CW and that relies on PTT).  If I use my foot switch to trigger PTT, there are no clicks.  However, if I release the foot switch, the clicks return and don't go away if I depress the foot switch again.

I've been able to find some references to K3 clicks and spurious signals on 160M caused by the T/R switching PIN diodes.  I've also seen a brief reference to a fix to this problem but there were no specifics.

I need help fixing this key click problem before I can take the K3 to a multi-op station.

Gerry, W1GD
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[Jim Brown-10]

On 1/29/2013 4:45 PM, [hidden email] wrote:
> I need help fixing this key click problem before I can take the K3 to a multi-op station.

Hmmm. I've never heard of a K3 causing clicks, but I guess it might if
something broke.  Don't rule out amplifier bias as the cause of the
problem at W2GD. W8JI, who has designed a lot of power amps, made the
following post to the Topband list this morning. Based on what he's
heard on the air from certain Acom amps, he suspects that they have this
problem.  On the NCCC list today, N6RK noted that he had to fix a
similar issue with an Intech amp.

73, Jim K9YC

=   =   =   =   =   =   =   =   =   =   =   =

If your amplifier uses automatic bias, it can cause clicks. There are
two things that will prevent or minimize this.

1.) Any auto bias system should not fully cut the tubes off. The tubes
should stay very slightly into conduction, very near class B but
slightly on the AB side of B. (B is exactly zero idle current, AB is any
amount of idle current)

2.) The bias system should be fast on with a hang time on off. It should
activate much faster than the envelope rise time, and deactivate slower
than the fall time.

3.) The bias system should activate with almost zero power. Even -30 dB
background noise on SSB mode should turn on the bias. If it sounds
choppy on SSB, it is certainly messing up the CW signals.

A good test is to go to SSB mode with constant room background noise and
gradually turn up mic gain while watching the plate current meter. With
a 100 watt drive requirement auto bias should fully activate at 10
milliwatts drive (0.7 volts RMS input drive voltage). This is the type
of power level we are used to from signal generators, not transmitters.

The AL80B, for example, activates the operating bias with ONE milliwatt
of RF power. This prevents the amplifier from changing the rise time of
CW envelopes. Some amplifiers activate much higher levels, and this will
cause keying artifacts that are as K9YC describes.

Anyone using auto bias and getting complaints should read this:

http://www.w8ji.com/electronic_bias.htm

Having a K3 does not make all signals clean, and not having one does not
make all signals dirty. It is the entire system that matters, and there
is certainly more than one clean radio in the world.

73 Tom
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[w1gd]

Tnx Jim.  One of my first thoughts was with the amplifier.  But we had no issues with K9RS's K3.  Also, I was able to hear these clicks running barefoot even with the power in the K3 turned down to 0 watts.  Of course, my transmit and receive antennas are pretty close together.  

Right now, I feel this has something to do with T/R switching but only when using VOX and not PTT.

73,
Gerry, W1GD