[600MRG] Amp

Mon Aug 3 10:54:48 CDT 2015

>CW is a square wave modulation that is full of harmonic
energy which will cause horrible clicks out many KHz if not properly
conditioned.

I think the key here is "properly conditioned" and specifically related to
the RF source.  If the rise and fall times of the *source* CW signal is
purely square, then yeah, you are going to have a clicky, harmonic-filled
signal.  If, however, the source signal rounds that waveform off at the
transitions like it should be, you are not going to generate additional
trash (assuming the PS has capacity and is not AMing, for example).  This
was the topic of discussion for years on the topband reflector WRT various
radio manufacturers and their click problems.  If you are using an HF rig
as an exciter, the quality of that signal source is largely
going to determine the quality of what comes out of the amp.

One of the amps that I built uses a fixed signal source where the amp's
drain is keyed directly and, in fact, through RC networks, the rise and
fall times are modified accordingly.  The CW waveform is clean, there are
no
clicks and there is no broadening of the signal because the shape of that
input square wave from the driver is rounded appropriately.
Neither of the techniques that I use for making a CW signal is clicky or
wide because the source signal is "clean" coming into the amp.

I think you are correct about linear if we assume that the driver signal is
poor.  But it does not have to be and many guys who have been running
topband for a long time have either switched to clean radios or modified
their existing radios, as I have done.

73,
John XIQ

On Mon, Aug 3, 2015 at 10:28 AM, Edward R Cole <kl7uw at acsalaska.net> wrote:

> John,
>
> Unfortunately too many hams believe this.  An unswitched carrier is fine
> with non-linear modes.
>
> This was topic was just thoroughly discussed recently on the Elecraft
> Reflector.  CW is a square wave modulation that is full of harmonic energy
> which will cause horrible clicks out many KHz if not properly conditioned.
> A carrier with harmonic energy will have the harmonics amplified greatly by
> a non-linear amp;  that is why they are used for triplers and multipliers.
> If you want harmonics just overdrive an amp into non-linear operation.
>
> You will not find any class-C amps offered for hams since CW is now
> generated by an exciter and not by direct keying of the amplifier as was
> done years ago (of course these amps also are used for SSB, but no mfr
> offers a bias adj to place the amp into class-C for CW).  Also, CW
> modulation is not zero bandwidth; only a carrier with zero phase modulation
> is zero bw.  Even back in pre-SSB years when one used grid-block keying the
> CW voltage still had to be shaped to avoid clicks; something that modern
> transceiver mfr's seem of have forgotten (except a few wise one's).
>
> If you run CW thru a non-linear amp the result will be broadening of the
> bandwidth and co-channel interference.  FM and some FSK modes are OK.
>
> Therefore, my amplifiers will be linear; its not that hard to do!  Output
> filtering is a must to reduce harmonic output even with linear amps.
>
> 73, Ed - KL7UW
>
> At 03:33 AM 8/3/2015, John Langridge wrote:
>
>> >Linear is needed for CW
>>
>> Linear is NOT required for CW.. only when amplitude and/phase varies is
>> linear required.  It would be needed for PSK, which has been rarely used
>> in
>> the last few years.
>>
>> 73!
>>
>> John XIQ
>>
>> On Sun, Aug 2, 2015 at 11:25 PM, Edward R Cole <kl7uw at acsalaska.net>
>> wrote:
>>
>> > Jim, and all:
>> >
>> > The K3 can be upgraded to operate down as low as 100-KHz by upgrading
>> the
>> > Synth board for $219.95.  Reception is improved by a minor change in the
>> > General Coverage band filter and one component on the main board.
>> >
>> > So it is capable at this time by incorporating those changes.  Elecraft
>> > has just rolled out a new model called the K3S which comes standard with
>> > these.
>> >
>> > 100w seems a good target for 5w ERP (depends on your antenna
>> efficiency).
>> >
>> > I think one should just figure on using a linear amp.  Linear is needed
>> > for CW and psk modes and gain is not difficult to achieve at 500-KHz.  I
>> > would guess 60-65% efficiency in the high power stage so you need
>> > dissipation of say 50% of RF output as a minimum to have a safe margin.
>> > 100w dissipation would ensure almost bullet proof running of any mode.
>> >
>> > Not sure you saw my recent post on the Elecraft reflector regarding 630m
>> > amplifiers?  I will be looking at making up a 100w linear amp that runs
>> > with 1mw drive sometime this winter when outdoor stuff is not as nice to
>> > do.  I am giving thought to offering it as a kit or partial-kit for
>> sale.
>> > I was once considering transverters but others have beat me to that and
>> > with the K3 and TS590S both able to run 630m an amplifier is the needed
>> > item (probably a preamp too).
>> >
>> > Don't ask for particulars at this point - just an idea that needs some
>> > research and building a proof of concept.  No idea of cost.  Most likely
>> > will use FETs and run with 13.6v for simplicity, though 28v and 50v
>> > transistor specs are better.  Driving with 1mw makes such an amp usable
>> > with simple mixer schemes, as well.
>> >
>> > I discussed this with Wayne-N6KR of Elecraft and the market is too small
>> > for them to consider making an amp.
>> >
>> > 73, Ed - KL7UW
>> > http://www.kl7uw.com/kits.htm
>> >
>> > At 05:10 PM 8/2/2015, Jim Miller wrote:
>> >
>> >> Now that the K3 is getting closer to being a 630 capable machine and
>> the
>> >> FCC is lumbering toward a band decision I'm thinking more about an amp.
>> >> I'm
>> >> assuming the market is too small for an Elecraft offering.
>> >>
>> >> The K3 puts out 1mW on the transverter output. I'm assuming that I'll
>> need
>> >> 50-100w to get to 5w ERP.
>> >>
>> >> Assuming 100w for a minute and assuming 10-15db for the final amp stage
>> >> then you only need 5-10w before then. That should mean that even with
>> poor
>> >> efficiency not a lot of power will be dissipated until the finals. That
>> >> means that I could keep the chain to that point linear and make the
>> output
>> >> stage decision based on what modes are most prevalent.
>> >>
>> >> I assume CW for historical reasons and JTXX for practical reasons,
>> WSPR as
>> >> well. Not sure about PSK or other modes which would require a more
>> linear
>> >> final.
>> >>
>> >> So I could build a 1mW to 10W linear then wait and see about the
>> finals.
>> >>
>> >> Thoughts?
>> >>
>> >> 73
>> >>
>> >> jim ab3cv
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>> >>
>> >
>> > 73, Ed - KL7UW
>> > http://www.kl7uw.com
>> >     "Kits made by KL7UW"
>> > Dubus Mag business:
>> >     dubususa at gmail.com
>> >
>> >
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>
> 73, Ed - KL7UW
> http://www.kl7uw.com
>     "Kits made by KL7UW"
> Dubus Mag business:
>     dubususa at gmail.com
>
>