[600MRG] Amp
Edward R Cole
kl7uw at acsalaska.net
Mon Aug 3 12:09:33 CDT 2015
Ken (and John):
Good that you have such good memory (or archives) and certainly CW
was the prime mode in the first twenty years of Ham radio so much
attention was being given at the outset of narrow band RF (vs spark).
AM was emerging then, as well. I suppose the general architecture of
the time was using unmodulated drivers and applying modulation
directly to the final amplifier (as my DX-35 did). I used
plate-modulated AM on 2m in the mid-60's and not sure what method of
keying was used for CW (it was a Johnson 6N2 which used xtal
osc-driver-5894 amp).
But even if you drive an amp into non-linearity with a sine wave
input, you will see harmonics. For those of you that build your own
CW transmitters not using a commercial ham radio as driver perhaps
you can tweak good operation on CW, but most hams do not build
(anymore or ever), so not a good thing to recommend a mode that
requires special solutions that are not in modern print.
Therefore, the best option is (for me) to just offer a linear amp;
least chance of transmitting interference, which very important on
600/630m (as we all know).
I run an 8877 on 2m and can adjust my bias to run any class. I've
not detected any significant advantage to doing that. I can generate
2kW with enough drive in any mode. I run 100ma resting current and
about 700ma with 55w drive for about 1400w output (its an old pull so
not real efficient); this is class-AB for all modes. I can turn down
the active bias so no current is drawn without drive. The cutoff
resistor generates about -25v bias. I am running about -18 to -16 (I
think); recommended design uses a 12v zener which more into
class-A. I have a bias control transistor with pot for adjustment.
73, Ed
At 07:58 AM 8/3/2015, Kenneth G. Gordon wrote:
>What I find particularly interesting about THIS discussion is that
>these issues
>were discussed, and solutions found and implemented beginning in the
>1920s...
>
>Ken W7EKB
>
>
>On 3 Aug 2015 at 10:54, John Langridge wrote:
>
> > >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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> > >> >> 600MRG at w7ekb.com
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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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> > >> >
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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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>
>
>
>Kenneth G. Gordon W7EKB
>
>"Courage is being scared to death but saddling up anyway."--- John Wayne
>
>
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73, Ed - KL7UW
http://www.kl7uw.com
"Kits made by KL7UW"
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