[AMPS] TS-2000

[Tom Rauch]

Hi Paul,

> > Such a response can be likened to a 10Hz to 10,000Hz response
> > on a SSB transmitter.
> 
> The waveform that I referred to in the 1998 ARRL Handbook is certainly not
> the best for intelligibility, primarily due to the long decay which leads
> to the bell-like characteristic.  Again , the sine rise - sine decay would
> be most appropriate.  And, the Ten-Tec Omni V and early Omni Sixes come
> pretty close, but not quite.

I don't understand what you mean by "bell like". Do you mean the 
shape or the sound? If you mean shape, that shape is not optimum 
for bandwidth. What you hear is entirely different anyway, unless 
the receiver you are using has a very wide filter.

We can draw a perfect analogy by considering a SSB signal. While 
what you hear is the sum of the shapes and group delays in all the 
filters, the narrowest filter will set the shape of what comes out the 
speaker. It does no good to transmit 30-5000Hz audio in a SSB rig 
if the receiver limits at 300-3000 Hz. All the excessive bandwidth 
does is bother people up and down the band. 

Same in a CW system. It does absolutely no good to transmit 
sidebands outside the passband of the selectivity past that point 
elsewhere in the system. Nor can you make a clicky signal with a 
sharp turn down or turn up in the waveform sound "hard" once it is 
run through a narrow filter in a receiver. All the clicks do is 
aggravate others.

So if you are using a 500Hz filter with very sharp rolloff, it does no 
good to allow response beyond 250Hz in the keying filter of the 
radio, since that waveform modulates the rig with a DSB signal.

Rather than look at a scope and guess if the waveform is correct or 
try to verbally describe a correct waveshape, the most direct 
approach is to spend 35 cents for an multisection op-amp and build 
a four pole or eight pole lowpass filter for the transmitter.

If you set the transmitter filter for 250 Hz cutoff, no one using a 
500Hz or narrower CW filter would ever know the difference when 
tuned to your signal. Yet you could be in the noise just 400Hz 
above your transmit frequency instead of clicking the heck out of 
the band.   

> Yeah Tom, but the keyed waveform I referred to does sound awfully good
> particularly from a clean oscillator, albeit at the expense of some
> additional bandwidth.  Sure, It's an aesthetics v. efficiency tradeoff but
> I can live it and in my opinion it's not excessive if the rise/fall is ~ 2
> mS.  Anyway, I let you know where I'm parked before the next contest.

Nothing can sound better than it sounds after running through all 
the filters anyway, so unless you and everyone else are using SSB 
filters you might as well clamp the transmitter keying waveform at 
250Hz.

You be amazed at what comes out the speaker compared to what 
goes in the antenna. There is hardly any difference between a 
perfect square wave and a raised sine waveform when tuned to the 
signal. The problems are all several hundred Hz away. 
 
> Perhaps the majority cannot discern the difference but I sure can.  When
> fading becomes problematic or there's a high level of QRN, I can copy a
> hard-keyed signal much better.

Only if you use a wide filter. I sometimes use a 2KHz filter during 
lightning storms in my FT1000 because the group delay in the 
narrow filters is horrible (causing ringing, by making the parts of the 
sidebands of the signal out-of-phase with each other), but that only 
works when the band is empty around me. Someone would be out 
of their mind using more than a 500Hz filter during a contest, or on 
a crowded band!

What I most often do is switch to my highly modified R4C's since I 
can use 250Hz filtering even with heavy noise. 

Perhaps if I listened through a 2kHz filter more often I'd grow to like 
hard waveform signals, but to transmit them the people listening to 
me would have to use wide filters also...otherwise I'm just wasting 
space.

> Right.  The shape of the edge *together* with the ramp time contribute to
> the bandwidth.  For example, within a 2 mS ramp time, if the initial 1 mS
> of the leading edge is near vertical, but the remaining 1 mS is a sine
> slope, then there's an awful lot of occupied bandwidth.  

It is worse than that Paul. A subtle difference you almost can not 
even see on an oscilloscope can be a 20 dB increase in clicks. 
The duration (time) of the sharp rise or fall does not have to be long 
and it does not have to be tall to cause a problem, it simply needs 
to be a tiny sharp change in the display. That can happen at any 
point in the waveform.

Looking at a scope will get us in trouble every time. We give a rat's 
behind what the rise and fall is, as long as it doesn't click a 
needless amount. In any case, there is no reason to make the 
transmitter wider than the average receiver unless you want to 
QRM people.

That's true on CW, and true on SSB.
73, Tom W8JI
W8JI@contesting.com 

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