Re: K3, Elecraft Transverter K144XV-K

[hf4me]

I too am very dissatisfied with my internal transverter and sent it to
Elecraft to be "fixed".  It returned with the comment that it was "operating
as expected".  I recall my range was about 4 watts, roughly 4 to 8 watts.
My need was for a max of 2 watts and that isn't going to happen.  I can't
believe Elecraft would produce a product that is implied to operate from .1
to 10 watts and then say this is acceptable.  It is only fair to believe
that this product would operate accurately and precisely as the HF portion
of this fine radio and all of their other excellent products.

Sorry for being disgruntled but this is one option I am sorry I bought.

73, Jim KG0KP

    David> I have just measured my K144XV power output with an accurate
power output meter and find that with the K3 set for 1mW the output is
10.5W.  But setting the K3 to 0.1mW (fully counter-clockwise) the output
goes down to only about 7W.  No matter what I do, I am unable to reduce the
power further.
    David> It will be interesting to see if other K144XV users find the
same.

Mine doesn't go below 6W as measured with the W2.


--
Pierfrancesco Caci, ik5pvx
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[wayne burdick]

Jim (KG0KP) wrote:

> I recall my range was about 4 watts, roughly 4 to 8 watts.
> My need was for a max of 2 watts and that isn't going to happen.

Hi Jim,

At the time we designed this module, we were trying for maximum power output, and I'm sorry to say that we didn't attempt to ensure any particular minimum. Field testers for the unit were all asking for even higher power, and there was no discussion that I recall of an application for less.

Even though the sales brochure and the manual for the K144XV only mention "maximum power output" and never make a claim for "minimum", I can see why you would expect less than 4 watts, given the available 10-to-1 drive range.

There appears to be significant variance in results at minimum drive (0.1 mW), so I've asked the engineer who designed the unit to investigate. There are only a few factors that control power output and gain, so it could be that a very simple modification might be possible to increase the output range.

I'll post the results of our investigation.

73,
Wayne
N6KR



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[Edward R Cole]

David and Lexa,

My observations on most RF power amplifiers is that gain is higher at
lower drive levels so proportionally there is more output.  e.g. full
drive =10w, half drive = 7w, quarter drive = 5w.  So one finds that
an amplifier hits a minimum output with lowered drive that is not
linear with change in drive level.  Yet these amplifiers sound fine
in SSB so must have good linearity.

My 50w 2m transverter actually will produce nearly 60w with 1.5mw
drive and 35w with 0.73 mw, but minimum output with 0.1mw is about
15w.  I insert a 3-dB attenuator to get down to 7w output to drive my
150w amp to 55w which is the drive required for 1400w with my
2m-8877.  I prefer this arrangement vs running the transverter near
max at 55w when running digital modes (less heat stress on the
transverter amp which also translates as less thermal frequency
drift).  My 25w 1296 transverter runs 20w at full output and about 8w
with minimum drive.  I've seen this consistently with RF power
amplifiers (my HF amps operate similarly)

73, Ed - KL7UW
http://www.kl7uw.com
     "Kits made by KL7UW"
Dubus Mag business:
     [hidden email]

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[Joe Subich, W4TV-4]

 > My observations on most RF power amplifiers is that gain is higher at
 > lower drive levels so proportionally there is more output.  e.g. full
 > drive =10w, half drive = 7w, quarter drive = 5w.

You are describing classic compression in the amplifier [chain].  Where
you have cascaded amplifiers, measure the Po/Pi slope *for each device*
and adjust the relative gains/drive levels so that each device has a
similar curve - or at least all begin to compress at the same level -
and operate below the onset of compression.

 > Yet these amplifiers sound fine in SSB so must have good linearity.

You can't say that.  Non-linearity will show up first in IMD products
*outside the SSB bandwidth* - your neighbors will hear the distortion
before your QSO partner does or you hear it in your monitor.

Now, there is no issue using these amplifiers in CW/RTTY/JT-mode as all
of those modes are "one tone at a time" and do not generate significant
IMD when feeding even a class C amplifier (transitions will become a
bit sharper/more "clicky").  However in general, one should keep any
*amplifier chain* used for "linear" modes (SSB, PSK31/63/125, etc.)
below the 1 dB compression point.  In other words, if 10W drive gives
750W output you should need any more than 25W for 1500W output.

The 1 dB compression point is generally associated with IMD in the -33
to -35 dB range provided other issues (e.g. crossover distortion, bias
stability, etc.) are well controlled.  Ideally one would keep any gain
compression well below 1 dB (20%) but that is often difficult with
solid stage devices at high power levels - particularly since solid
state devices tend to be rated for saturated mode (class C, pulse)
outputs without regard for compression.

73,

    ... Joe, W4TV


On 2015-01-08 12:03 PM, Edward R Cole wrote:

> David and Lexa,
>
> My observations on most RF power amplifiers is that gain is higher at
> lower drive levels so proportionally there is more output.  e.g. full
> drive =10w, half drive = 7w, quarter drive = 5w.  So one finds that an
> amplifier hits a minimum output with lowered drive that is not linear
> with change in drive level.  Yet these amplifiers sound fine in SSB so
> must have good linearity.
>
> My 50w 2m transverter actually will produce nearly 60w with 1.5mw drive
> and 35w with 0.73 mw, but minimum output with 0.1mw is about 15w.  I
> insert a 3-dB attenuator to get down to 7w output to drive my 150w amp
> to 55w which is the drive required for 1400w with my 2m-8877.  I prefer
> this arrangement vs running the transverter near max at 55w when running
> digital modes (less heat stress on the transverter amp which also
> translates as less thermal frequency drift).  My 25w 1296 transverter
> runs 20w at full output and about 8w with minimum drive.  I've seen this
> consistently with RF power amplifiers (my HF amps operate similarly)
>
> 73, Ed - KL7UW
> http://www.kl7uw.com
>      "Kits made by KL7UW"
> Dubus Mag business:
>      [hidden email]
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

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