[Elecraft] K1 carrier rise/fall times unequal?

Mon Apr 21 16:46:01 2003

Think possibly that the CW contest scenario defines the needed bandwidth. 

Short version: K2 keying needs to be shaped well enough that an MP, tuned up or down 500 hz with matched INRAD 400's in the 2nd and 3rd IF, does not hear any clicks. K2 has significant clicks with this test.

Long version:

At this date, CW stations calling CQ in a contest will align themselves about every 500 hz up and down the band. This means every calling station will be listening their frequency plus/minus 200 hz or plus/minus 150 hz. Stations farther away calling are mostly likely to be someone calling the station up or down from you. Hearing the station up or down 200 hz calling you just as well as you hear dead on is required. Easily half the calling stations are not dead on frequency.

The CQing stations are frequently running max power and 20 or 30 over S9. At the same time the station up or down 500 hz is 20/30 over, the station calling on frequency may not even kick the s-meter lights or even be substantially in the noise. Even S1 key clicks from the station up or down can cover such a weak station calling on frequency.

The weak station scenario happens a lot (one growing reason is DX stations running K2's with limited antennas, e.g. loaded whip on a balcony!). Them who cannot work the QRP guys with limited antennas are not going to work as many QSO's. The serious contester MUST work the QRP layer.

An example of the best filter arrangement for this separation is an MP with matched 400hz INRAD filters in second and third IF's.

Listening to my K2 (1239) at S9 in the MP using aforementioned filters, with the MP tuned up or down 500 hz from the K2's frequency, the clicks are S1 or S2. If I tune up or down 1000 hz, the clicks are almost gone. If the test setup is set for the K2 to be 30 over, the clicks at plus/minus 500 are very loud.

Doing the same test with the transmitter an MP modified to reduce clicks, the clicks cannot be heard tuned up or down 500 hz. The transitions ARE too sharp. This is also shown in a spectrum analyzer plot on the INRAD web site that shows a NUMBER of rigs, including the K2.

Those of us who want to operate a contest with the K2 high power with a 1.5 KW amplifier behind, to get the benefits of the receiver, will need to soften the CW keying transitions, the same way our MP's need their transitions softened.

Any clue as to what to modify? I had been looking at the schematic but haven't figured it out yet.

73, Guy.

> 
> From: "George,  W5YR" <[email protected]>
> Date: 2003/04/21 Mon PM 02:59:12 EDT
> To: "Vic Rosenthal" <[email protected]>, 
> 	"Don Wilhelm" <[email protected]>
> CC: "David Steere" <[email protected]>,  <[email protected]>
> Subject: Re: [Elecraft] K1 carrier rise/fall times unequal?
> 
> Vic is entirely correct on this one, guys. I know that there are all sorts
> of formulas for bandwidth that seem to involve code speed only, but they
> make a lot of assumptions and do not really give correct answers most of the
> time.
> 
> In addition to the rise and fall time aspects of keyed bandwidth, there is
> another more subtle cause involved. That is the manner of the transition
> from carrier off to the leading edge; from leading edge to full amplitude;
> from full amplitude to trailing edge; and finally from trailing edge to full
> off.
> 
> Those four transitions can be anything from very abrupt to very gentle. It
> has been found that waveforms with abrupt transitions have wider bandwidths
> than the rise and fall times would predict, even at a fixed speed. I know
> from measuring the waveforms on my IC-765, two PROs and the K2 that there is
> a wide variation in how these four transitions are accomplished. Each radio
> does the four transitions differently.
> 
> My K2 has fairly short rise and fall times - about 3 msec for the rise time
> and about 1.5 msec for the fall time. But the off-to-risetime is abrupt
> while the risetime-to-on is very smooth and gentle. Similarly the
> on-to-falltime is very abrupt while the falltime-to-off is less so.
> 
> So, the keying is pretty hard on my K2, but careful receiver monitoring does
> not reveal that excessive bandwidth is involved with clicks.
> 
> My PRO2 has adjustable rise and fall times from 2 to 8 msec. Two msec is
> very hard and clicky while 8 is rather  soft and narrow. I use either 4 or 6
> and like the sound.
> 
> I mentioned this to Wayne and sent him a photo of the K2 envelope of a dot
> and he agreed that it was pretty sharp.
> 
> I think that the final arbiter is performance. If the keying is not
> offensive to your band neighbors and sounds good to you and is easily read
> when the going gets tough, then it is doing its job.
> 
> But first principles tell us that the time-domain characteristics of each
> keyed element determine its spectrum, not the repetition rate of a string of
> elements, as Vic reminds us
> 
> 73/72, George
> Amateur Radio W5YR -  the Yellow Rose of Texas
> Fairview, TX 30 mi NE of Dallas in Collin county EM13QE
> "In the 57th year and it just keeps getting better!"
> <mailto:[email protected]>
> 
> 
> 
> 
> 
> ----- Original Message -----
> From: "Vic Rosenthal" <[email protected]>
> To: "Don Wilhelm" <[email protected]>
> Cc: "David Steere" <[email protected]>; <[email protected]>
> Sent: Monday, April 21, 2003 1:28 PM
> Subject: Re: [Elecraft] K1 carrier rise/fall times unequal?
> 
> 
> > Don Wilhelm wrote:
> >
> > > As far as bandwidth of the signal goes - the waveshape alone does not
> tell
> > > the whole story because the keying speed is also a primary factor - a 10
> wpm
> > > CW signal is more narrow than a 30 wpm CW signal and so on.
> >
> > Actually, this is incorrect.  It is true that the faster you send, the
> > harder the keying needs to be (otherwise the elements start to run into
> > each other), so faster CW requires harder keying, which makes the signal
> > wider.  But speeding up or slowing down does not change the actual
> > bandwidth that the signal takes.  The bandwidth is dependent on the rise
> > and fall times of the elements.
> >
> > To the original poster:
> > Having said that, I suspect that it's a little more complicated.  You
> > can have different shaped leading and trailing edges with the same
> > overall rise/fall time, so just looking at a scope is not sufficient to
> > determine whether your signal is clean.  I suggest using a second
> > receiver with a sharp IF filter.  Adjust it so the signal from your K1
> > is S9 and carefully tune across the signal.  If you hear clicks for more
> > than about 500 Hz above or below the signal itself, then perhaps it is
> > too wide.  Note that you cannot determine if a signal is too hard by
> > listening ON the frequency of the signal, because the receiver's filter
> > will soften what you hear.  What you are listening for is clicks on make
> > and break when you do NOT hear the tone of the signal.
> >
> > By the way, if you do have excessive clicks, you may be interfering with
> > other band users even if you are well within the band, so if there's a
> > problem you have to fix it!
> >
> > 73
> > Vic K2VCO
> >
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