K3 power out - key down

[Wes (N7WS)]

Or, when they're patting your face with a shovel saying, "I wish I'd spent more
time working QRP."

On 7/20/2014 12:36 PM, Edward R Cole wrote:
> Subject: Re: [Elecraft] K3 power out - key down
> Message-ID: <011e01cfa426$5fba6f80$1f2f4e80$@wjschmidt.com>
> Content-Type: text/plain;       charset="us-ascii"
>
> Have you ever listened to the interviews of the Indy car drivers after a
> race?  Do they say: "I wish I had a less powerful engine to make it a more
> challenging race."?

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[Wes (N7WS)]

Sounds good to me. http://sadxa.org/n7ws.html#amp




On 7/20/2014 2:09 PM, Bill Turner wrote:

> ORIGINAL MESSAGE:          (may be snipped)
>
> On 7/20/2014 12:36 PM, Edward R Cole wrote:
>> The software provides about 10-dB better SNR (making the 10w JT65 signal
>> equivalent to 100w CW).
>
> REPLY:
>
> I find an 8877 provides about 22 dB SNR over ten watts. :-)
>
> 73, Bill W6WRT
>
> ___________________________

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[Jim Brown-10]

On 7/20/2014 10:32 PM, Wes (N7WS) wrote:
> Not if exchanging call signs takes 10 minutes instead of ten seconds.

There are excellent reasons for QRP.

As chance would have it, I spent an hour or two today at the NCDXC club
picnic chatting with AF6RT, who spent Friday and Saturday lighting up a
very rare grid on 6M (CM79, I think) that involves lots of hiking over
rough terrain carrying your gear, then making additional round trips to
get more gear. The hike is on the order of 2-3 hours one way. He's not a
CW op, and he said he ran down his batteries calling CQ.

The objective is to pass out this very rare grid (99.99% is water) to
those pursuing the Fred Fish Award to work all grids in the US.

One of my suggestions was to encourage him to use JT9 (24dB of noise
rejection referenced to a 2.8 kHz bandwidth) and a strategy where he
announces (on the Ping Jockey JT65 chat) a JT9 window where the
deserving will call him, and he will respond only to those who he hears.
W7GJ/KH8 is successfully using this strategy on a moon-bounce expedition
to American Samoa. I also suggested that he try to use the KX3 barefooot
when the indicated S/N is better than about -10 dB, and use only enough
amp to make the Q. The objective, of course, is to minimize current
drain, and thus maximize operating time.

The WSJT-X software has a multii-decoder, and gives a readout of the S/N
for each signal it copies. I also encouraged him to replace his K3 with
a KX3 and KXPA100, because of the KX3's greatly reduced current drain on
RX (250 mA as opposed to about 1A for a K3).

I'm looking at Li-Ion battery packs that we might pitch in and buy for
him, and that raises a few questions for Wayne. I can find nice Li-Ion
packs with 3 cells (11.1V nominal) or 4 cells (14.8V nominal).

1) Can the KXPA100 and KX3 tolerate the higher voltages of a fully
charged 14.8V battery pack? (In the range of 16V).

2) Do the KX3 or KX3 pull proportionally less current for the same power
output from a 4-cell pack as compared to a 3-cell pack?

3) I'm seeing some 20Ah packs rated for a max of 10A and 14A load
current, with active protection to limit the current to those levels.
How would the KXPA100 react to that, if he wanted to run 40-50W?

4) Where can we access a graph of KXPA100 load current vs. 6M power out,
not considering tolerances from one piece to another?

5) Am I correct that a KX3 does not benefit from an outboard preamp in
this application?  That is, a very quiet QTH, he's current starved, the
guys who want to work him have power and big antennas (but probably more
RX noise), and he's got to fight for every dB.

Weight for a K3 as compared to a KX3 + KXPA100 is about equal,
especially when interconnect cables are taken into account. The
advantage is current drain, and is a big deal if 90% of your time is RX.

He's already carrying a very nice M-Squared antenna and mast to hold it,
and LMR-400 to feed it.

Those reading the mail should appreciate this as a very practical
engineering problem. :)

We don't need fast response on this -- thanks to work commitments, his
next window of opportunity is Memorial Day 2015. :)

73, Jim K9YC
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[Jim Brown-10]

On 7/20/2014 10:42 PM, Wes (N7WS) wrote:
> Sounds good to me. http://sadxa.org/n7ws.html#amp

Beautiful work, Wes

73, Jim K9YC
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[Lyle Johnson]

Two answers below.

73,

Lyle KK7P

> 1) Can the KXPA100 and KX3 tolerate the higher voltages of a fully
> charged 14.8V battery pack? (In the range of 16V).

No.  The products are not guaranteed to FAIL if you apply 16 V, but they
are not designed to operate from 16 V, either.

> 2) Do the KX3 or KX3 pull proportionally less current for the same
> power output from a 4-cell pack as compared to a 3-cell pack?

The KX3 low voltage supplies are primarily switching supplies, so
current drain at a higher input voltage will be less than the current
drain at low supply voltage.  The PA (KX3 or KXPA100) operates directly
off the supply power and current is proportional to power level and
drive, but not supply voltage.


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[Paul Gordon N6LL]

Very FB, Wes, and it has the requisite two meters: plate current and
grid current.
73, Paul N6LL
On 7/21/2014 9:38 AM, Jim Brown wrote:

> On 7/20/2014 10:42 PM, Wes (N7WS) wrote:
>> Sounds good to me. http://sadxa.org/n7ws.html#amp
>
> Beautiful work, Wes
>
> 73, Jim K9YC
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[Jim Brown-10]

On 7/21/2014 9:51 AM, Lyle Johnson wrote:
> The PA (KX3 or KXPA100) operates directly off the supply power and
> current is proportional to power level and drive, but not supply voltage.

Thanks, Lyle. The additional question I was asking here is if the
KXPA100 pull proportionally less current from a 14.8V supply to achieve
the same output power than from an 11.1V supply?  (The difference is one
less cell in the Li-Ion pack.) The calculation I'm getting at here is
for a given pack weight, do 11.1V or 14.8V packs give me the most power
out per pound?

73, Jim K9YC
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[Stephen M. Shearer]

I think some where my original question go lost.  Can the K3 operate key
down at 100W's.
I did get an answer, yes - 120w for 24hr's...  So the answer is yes.

I complicated things by adding JT65 and that I operate at 0.5 to 2 watts
with my KX3, but up to 20w with an IC-706.  Yes, if I am -25db at 0.5
watts, I can/should up the power so the "guy" at the other end can hear
me better.  Yes, it IS weak signal not low power...

The NAQP contest this past weekend was fun (I used the O2).
It has been a few years since I got the chance to operate a digital mode
contest.
The great receiver in the O2 did fine and is why I would only think of
replacing the O2 with a K3.

everyone have a great day!
steve WB3LGC
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[Stephen M. Shearer]

Well, yes...  {less powerful engine} After the late 60's the rules were
changed to require all cars to operate under the same limits. NO more
turbine cars... (for a $6 ball bearing...)
steve WB3LGC
> On 21-Jul-14 1:34 AM, Wes (N7WS) wrote:
>> Or, when they're patting your face with a shovel saying, "I wish I'd
>> spent more time working QRP."
>>
>> On 7/20/2014 12:36 PM, Edward R Cole wrote:
>>>   Do they say: "I wish I had a less powerful engine to make it a
>>> more challenging race."?
>>
>

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