How to get SWR

[Holger Schurig-2]

Hi ho,

I want to programmatically get the SWR, or at least an approximation of the
SWR via the serial cable.

I found an old application kx3swr.py (http://robert.butera.org/?p=380), but
somehow this one returned always 0.0 as SWR back, which I didn't really
believe. Basically the program does this:

select ATU menu: MN023;
turn ATU to bypass: MP001;
turn menu off: SWT09;
set frequency: FA ... ;
wait a bit
turn TUNE button: SWH16;
wait a bit
get VFO data: DS;
try to decipher it
release TUNE button: SWT16;

However, my KX3 with firmware 2.38 always returns DS@@@@@>>@; as response.
Even when I do the steps manually. Did this change with some recent
firmware update, or did I miss something important?  Only when outside of
TUNE I get some value, e.g. DS14³60°00.


Also, dear Elecraft, in the K3&KX3 Programmers manual you wrote in the BG
command description "CWT, SWR, and CMP readings not yet available". How
long is "not yet" going to take?  :-)

Or, dear Elecraft, maybe you implement the RM command like the Kenwood
TS850 or TS870 ...  (I have found them used in the hamlib source).


73, Holger
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[Holger Schurig-2]

Hi Walter,

I'm not going to learn NodeJS, npm, gulp and JavaScript to get the SWR out
of my KX3 :-)   I'd rather learn in a generic way how to get the SWR.

I however checked out the source, and
in wizkers/oem/radio/www/js/app/instruments/elecraft/driver_frontend.js it
does in this.tune = something similar: MN023;MP001;MN255;SWH16;. I didn't
found where it sends the DS; command, but the parsing of the DS commands
output is is at the end
of wizkers/oem/radio/www/js/app/instruments/elecraft_siggen/display_numeric.js.
However, if the radio returns DS@@@@@>>@; as response, than there is still
nothing to decode.

So the question stands: why does my KX3 return "DS@@@@@>>@;", what am I
doing wrong?
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[Holger Schurig-2]

Hi Walter,

btw, thanks for all your input!


I tried the swr_sweep.py program from this discussion and here I still get
only the DS output that doesn't tell me anything:

WRITE: MN023;
WRITE: MN023;MP001;
WRITE: SWH16;
WRITE: FA00014000000;
WRITE: FA;
READ: FA00014000000;
WRITE: FA00014000000;
WRITE: FA;
READ: FA00014000000;
WRITE: DS;
READ: DS@@@@@>>@;
WRITE: SWH16;
WRITE: MN023;MP002;

Even when I manually set the TX Power to 0.5W and press(hold) the TUNE
button and issue the DS command by hand, I don't get anything usable back.
Despite I'm seeing an SWR value of 3 in the display.

73, Holger
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[w4sc-2]

The commands are being sent too close together.  Place a minimum 100ms delay between the SWH16 and following DS command.  Do not send any other commands until after second SWH16.

Four macros were setup to allow “manual” delay between commands.  I don’t see a direct way to allow a command-command delay in the command tester.  Reducing the baud rate may help.

Macro 1  FA;DS;
Macro 2  DS;
Macro 3  SWH16;
Macro 4  DS;DS;DS;


The following results were realized:

FA;DS;
FA00007123610;DS@7±23¶1@€€;SWH16;
DS;
DS@@@@1³>I€€;DS;
DS@@@@1³>I€€;DS;
DS@@@@1³>I€€;SWH16;
FA;DS;
FA00007123610;DS@7±23¶1@€€;
DS@7±23¶1@€€;SWH16;
DS;DS;DS;
DS@@@@1³>I€€;DS@@@@1³>I€€;DS@@@@1³>I€€;DS;
DS@@@@1³>I€€;SWH16;

The SWR returned is 1.3-1 as displayed on VFO-A.  The @ in the returned data means there is NO data in that byte position. The returned DS data will require “massaging” to get a proper text string as there is display Icon data mixed in.

A KX2 was used for this test, but KX3 should be the same.

de Ben W4SC
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[Holger Schurig-2]

Okay, figured it out.

I don't have a real dummy load, but a BNC terminator with 50 Ohm. This one
is rated for only 0.5W, which I used as PWR setting.

The SWR bargraph (while TUNE is active) start to appear when I use a TX
power of 0.4W ... 0.5W.  However, the SWR display (e.g. "6.6-1") in the
VFOA display only appears above 0.7 .. 0.9W PWR setting.
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[w4sc-2]

Holger,

Glad you solved the problem.

For “TUNE” hold, I have my KX2 is set to a fixed level (3 Watts) by the TUN PWR menu entry.  So the power level issue was masked in my setup.  I don’t know what minimum power level is required for an accurate SWR reading, and ATU tuning.  The designers may want to comment.  For KX3 ref pg 14 in owners reference.

The KX3 may be “fast enough” to not need a delay in your code.  The KX2 appears to not be.

73 de Ben W4SC





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[Matt Zilmer-3]

All diode-based SWR bridges have significant error at lower power levels.  I suggest the use of 3W or higher for TUN PWR.

73!

-Matt
Always store beer in a dark place. - R. Heinlein
[iPhone]

> On Sep 24, 2016, at 04:02, Holger Schurig <[hidden email]> wrote:
>
> Okay, figured it out.
>
> I don't have a real dummy load, but a BNC terminator with 50 Ohm. This one
> is rated for only 0.5W, which I used as PWR setting.
>
> The SWR bargraph (while TUNE is active) start to appear when I use a TX
> power of 0.4W ... 0.5W.  However, the SWR display (e.g. "6.6-1") in the
> VFOA display only appears above 0.7 .. 0.9W PWR setting.
> ______________________________________________________________
> 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
> Message delivered to [hidden email]

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