[Elecraft] Re: More Quests: Driving (big) linear amps with the K2?

[George, W5YR]

Brian, you raise some interesting possibilities re QRO for real . . .   <:}

I would have two concerns about the setup you describe. First to raise 5
watts to 1300 watts requires a total power increase of just over 24 dB. FCC
regulations say that an amplifier in the amateur service must be driven
with no less than 50 watts and may not have over 15 dB overall gain.

Now, if the K2 drove its companion 100-watt amp which then drove the big
final, I suppose one could say that the final is being driven to 1300 watts
output with 100 watts input and only 11 dB gain is involved. So, probably
no problem there.

But there is another gotcha in Part 97 concerning amplifiers and that is
the total power produced by an amplifier at frequencies other than the
fundamental. There is a fixed power limit of 50 milliwatts on spurious
frequency components.

Now, comes the question: is the output of the K2 sufficiently clean such
that it can drive the 100 watt amp for a total gain of 5 watts to 1300
watts or 24 dB and keep the spurious components to a maximum of 50 mw or
less?

I can't recall seeing a spurious report on the K2 lately so I just don't
know the answer to that one. But, it might come up in the scenario you
describe.

The Harris amplifier as briefly described would appear to violate Part 97
if driven to a KW output with 100 mw input. That is 40 db of gain . . .

73/72/oo, George W5YR - the Yellow Rose of Texas         
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe   
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735
Icom IC-756PRO #02121  Kachina 505 DSP  #91900556  Icom IC-765 #02437

Brian Murphy wrote:
> 
> Hello Peter,
> 
> First the K2 issue.
> 
> Mine is #204.  I just missed the field trial 100!  Prior to the K2 I have
> used the TS520, TS820, and an old ship-to-shore HF.  I used a R390A for
> years, but now have a RACAL 6790.  I also have a 40m SST (now this is a neat
> radio!!!  Only 17 mA for receive and very narrow filters).
> 
> The K2 was a great jump in technology from the Kenwoods.  I strongly
> recommend it.  It is probably the best radio for the money anywhere. It is
> my primary rig.  Building it is not trivial, though.  There must be a
> thousand parts.  The good part is that with the support you can get from
> Elecraft, you have a very high probability of finishing with an excellent
> radio.  This is THE key point--the risk of not getting a fine radio at the
> end of the process is very low, indeed.
> 
> Over the last few years, I have added the tuner, internal battery (a
> dynamite combination for operating class "BY" (BackYard mobile) under the
> stars with a wire thrown over the oak tree branch above my deck).  I also
> added the 160m and SSB.  All work fine and no problems with my SSB audio,
> either with PSK31 or with voice on either sideband on any band.  More
> recently, I ordered the NB since electric fences are a problem at my new
> QTH.  To sum it up, there is little to no risk of disappointment with the
> K2.  Just do not get into a hurry--if you feel rushed, then stop immediately
> and take a break.
> 
> Now for the QRO issue.
> 
> Like you, I could not see paying 3K+ for high power every now and then,
> although the 11 year cycle will make an amp more useful for the next few
> years.  Since I am new to the QRO (1KW + arena), I may not be the best
> source for information on those issues.  With that caveat, here is my
> experience so far.
> 
> I have used a horizontal loop at 100W fed by real open wire line and was
> very pleased with its operation.  I have to agree with the recent QST
> article about horizontal loops--they are underrated!  Wire antennas are
> cheap if you have some trees at strategic locations near your shack.  And,
> it sure beats burying radials.  Before I put 1KW on a horizontal loop, I
> will have to do the rf radiation review now required by the FCC.  There is
> an easy calculation for dipoles, though.
> 
> I have used a GAP vertical without radials (the Voyager had 3 counterpoises)
> with fairly good results.  In that QTH I had no suitable trees, though.
> 
> Most of the 500 watt + amps need 220vac, but some can also run on 110v at
> reduced power.  Again, I feel that if I am going to the trouble and expense,
> then why not go for at least 1200-1500watts.
> 
> Now, as you may have gathered, I am perfectly comfortable with experimenting
> with antennas, transmission lines, amps, and radios that are non-mainstream.
> So, the Harris solution was attractive to me.  I am a little jittery about
> putting my fingers around a high power, high voltage power supply, though.
> Thus, I would rather buy an amp rather than build one.  Also, amplifying
> from 5 watts to 1300 watts takes some real tricks to isolate the input from
> the output so feedback will not occur.
> 
> Try the internet search for Harris and RF110.  Just remember that the power
> supply is separate from the amp.  Fair Radio sells them for about $1400
> without the power supply.  The power supply should run $200-$300 or maybe
> less.  The amp has a two stage, 4 tetrode tube configuration and is
> conservatively designed.  So the power supply must supply both plate and
> screen supply voltages for all 4 tubes plus control power, etc--it is not a
> trivial power supply to make yourself.  One common power supply for the
> Harris is a 3 phase 400 cycle unit that was apparently used on military
> aircraft ( a lot of 400 cycle there).
> 
> The keying circuit from Elecraft website is nice, but I manually switch mine
> on SSB so far.  It is a little more trouble, but did I mention that I am
> remodeling my house!  I also have a remote bandswitch for the amp.  The
> Harris amp is pretuned in about 20 bands from 2-30 MC so you do not have to
> dip the plate as in the Kenwood radios and most tube amps.  The Harris amp
> is milspec and well constructed and designed.  It has many safety features
> so it will probably last longer than most Ham amps.
> 
> By the way, I used my K2 maritime mobile last year.  I sailed a 45 foot
> sloop from Rhode Island to North Carolina and used the K2 for daily e-mail
> position reports to the XYL.  It was fairly easy to contact people in the
> mid-USA on 20m during the day via PSK31.  The K2/PSK31 combination is
> nothing short of phenomenal!  I was amazed at what 5 watts and PSK31 could
> do.
> 
> As you can see, I have had a good experience with my K2--no regrets
> whatsoever.  QRP is always a fun challenge, but as I said earlier,
> propagation has been good the last year or two.  Regarding the amp, it
> certainly complicates your life and operation with many more considerations,
> procedures, "super-sized" components, extra heat in the room, but the power
> company will love you for using it.  100 watts is a good compromise that
> will work most times; 5-10 watts is not always so lucky.  It is much easier
> to have the 100 watts available when needed and go read a good book when
> that is not enough.  At around $350 for the 100 watt amp from Elecraft, this
> is hard to beat.  But then again, did I say I loved challenges?
> 
> Good luck on your choice.  Let me know what you decide.  The main thing is
> to have fun doing it safely and not to spend so much money that you cannot
> recover it by selling the equipment later when your needs change.
> 
> Brian  N4YTL