[Elecraft] KPA-1500 ATU not working well

[Wes Stewart]

I don't quite understand your methodology but there is one, apparently little 
known caveat with the use of the "Elecraft" coupler topology.    AFAIK, this was 
first used by John Grebenkemper, KI6WX, in his Tandem Match, described in QST, 
January 1987.

Paul Kiciak, N2PK, mentions in his paper, "An HF In-Line Return Loss And Power 
Meter", that this coupler suffers from poor input match at lower frequencies.  
So the SWR meter has high SWR!

If the CP1 wasn't so expensive, I'd buy one just to measure it.

Wes  N7WS


On 6/22/2018 1:20 PM, John Oppenheimer wrote:
> Putting the Elecraft CP1 through the paces with a 2 port VNA can be
> enlightening. The CP1 seems to be representative of Elecraft directional
> couplers across the line. There's a picture of the W2 high power HF
> coupler in the manual, it's just larger cores.
>
> Sweeping a 20 dB CP1 across the band with a VNWA with a 60 Ohm load,
> 1.2:1, results with a relative constant -40 dB reflected gain and a -20
> forward gain. A closer match to 50 Ohm fall's apart with a wide -40 db
> to -70 dB dip at 7 MHz reflected across the band at 50 Ohm.
>
> I can agree, 1.2 : 1 is about the limit.
>
> John KN5L
>
> On 06/22/2018 01:11 PM, Wes Stewart wrote:
>> That's a return loss of ~20 dB.  Now I have
>> no idea of what the directivity of the coupler is in the KAT500 or KPA1500 but
>> considering it has to work from 1.8 to 54 MHz and to keep the numbers easy, 20
>> dB wouldn't be unreasonable.
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