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KX3 SWR meter accuracy on 50 MHz?

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Drew Arnett

KX3 SWR meter accuracy on 50 MHz?

After getting my KX3 back from repair (before my next planned contest
operation, thanks!), I ran some measurements to both see how great the
repairs were and to get a new baseline for future measurements. TX
efficiency problem was gone.

However, I'm left to wonder about the accuracy of the internal SWR
meter for 50 MHz. Using a microwave dummy load of adequate power
rating and just a coaxial adapter, I measured the following:

14 MHz @ 1 W setting
VSWR 1.0 to 1 (per KX3)

28 MHz @ 1 W setting
VSWR 1.0 to 1

50 MHz @ 1 W setting
VSWR 1.5 to 1

50 MHz @ 4 W setting
VSWR 1.6 to 1

Not horrible. Not great.

It's fine if it's not as accurate on 50 MHz. I just want to know if
this is normal. Has anyone else looked at that and can share what
they see?

Thanks and best regards,

Drew
n7da
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Nr4c

Re: KX3 SWR meter accuracy on 50 MHz?

Well, it depends on the “Dummy” load. Have you swept the load with a good spectrum analyzer or VNA? It may not be 50 ohms at 50 MHz

Sent from my iPhone
...nr4c. bill

> On Sep 12, 2020, at 11:51 AM, Drew Arnett <[hidden email]> wrote:
>
> After getting my KX3 back from repair (before my next planned contest
> operation, thanks!), I ran some measurements to both see how great the
> repairs were and to get a new baseline for future measurements. TX
> efficiency problem was gone.
>
> However, I'm left to wonder about the accuracy of the internal SWR
> meter for 50 MHz. Using a microwave dummy load of adequate power
> rating and just a coaxial adapter, I measured the following:
>
> 14 MHz @ 1 W setting
> VSWR 1.0 to 1 (per KX3)
>
> 28 MHz @ 1 W setting
> VSWR 1.0 to 1
>
> 50 MHz @ 1 W setting
> VSWR 1.5 to 1
>
> 50 MHz @ 4 W setting
> VSWR 1.6 to 1
>
> Not horrible. Not great.
>
> It's fine if it's not as accurate on 50 MHz. I just want to know if
> this is normal. Has anyone else looked at that and can share what
> they see?
>
> Thanks and best regards,
>
> Drew
> n7da
> ______________________________________________________________
> 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]

______________________________________________________________
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]

Drew Arnett

Re: KX3 SWR meter accuracy on 50 MHz?

I did before shipping in for repair with a directional coupler. Looked great.

On Sat, Sep 12, 2020 at 7:13 PM Nr4c <[hidden email]> wrote:

>
> Well, it depends on the “Dummy” load. Have you swept the load with a good spectrum analyzer or VNA? It may not be 50 ohms at 50 MHz
>
>
>
> Sent from my iPhone
> ...nr4c. bill
>
>
> > On Sep 12, 2020, at 11:51 AM, Drew Arnett <[hidden email]> wrote:
> >
> > After getting my KX3 back from repair (before my next planned contest
> > operation, thanks!), I ran some measurements to both see how great the
> > repairs were and to get a new baseline for future measurements. TX
> > efficiency problem was gone.
> >
> > However, I'm left to wonder about the accuracy of the internal SWR
> > meter for 50 MHz. Using a microwave dummy load of adequate power
> > rating and just a coaxial adapter, I measured the following:
> >
> > 14 MHz @ 1 W setting
> > VSWR 1.0 to 1 (per KX3)
> >
> > 28 MHz @ 1 W setting
> > VSWR 1.0 to 1
> >
> > 50 MHz @ 1 W setting
> > VSWR 1.5 to 1
> >
> > 50 MHz @ 4 W setting
> > VSWR 1.6 to 1
> >
> > Not horrible. Not great.
> >
> > It's fine if it's not as accurate on 50 MHz. I just want to know if
> > this is normal. Has anyone else looked at that and can share what
> > they see?
> >
> > Thanks and best regards,
> >
> > Drew
> > n7da
> > ______________________________________________________________
> > 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]

Drew Arnett

Re: KX3 SWR meter accuracy on 50 MHz?

Tech support said they saw 1.5 to 1 on 50 MHz with their dummy load.
HF looked great, of course. They didn't mention if they also used a
microwave load. :-)

Best regards,

Drew
n7da

On Sun, Sep 13, 2020 at 2:20 AM Drew Arnett <[hidden email]> wrote:

>
> I did before shipping in for repair with a directional coupler. Looked great.
>
> On Sat, Sep 12, 2020 at 7:13 PM Nr4c <[hidden email]> wrote:
> >
> > Well, it depends on the “Dummy” load. Have you swept the load with a good spectrum analyzer or VNA? It may not be 50 ohms at 50 MHz
> >
> >
> >
> > Sent from my iPhone
> > ...nr4c. bill
> >
> >
> > > On Sep 12, 2020, at 11:51 AM, Drew Arnett <[hidden email]> wrote:
> > >
> > > After getting my KX3 back from repair (before my next planned contest
> > > operation, thanks!), I ran some measurements to both see how great the
> > > repairs were and to get a new baseline for future measurements. TX
> > > efficiency problem was gone.
> > >
> > > However, I'm left to wonder about the accuracy of the internal SWR
> > > meter for 50 MHz. Using a microwave dummy load of adequate power
> > > rating and just a coaxial adapter, I measured the following:
> > >
> > > 14 MHz @ 1 W setting
> > > VSWR 1.0 to 1 (per KX3)
> > >
> > > 28 MHz @ 1 W setting
> > > VSWR 1.0 to 1
> > >
> > > 50 MHz @ 1 W setting
> > > VSWR 1.5 to 1
> > >
> > > 50 MHz @ 4 W setting
> > > VSWR 1.6 to 1
> > >
> > > Not horrible. Not great.
> > >
> > > It's fine if it's not as accurate on 50 MHz. I just want to know if
> > > this is normal. Has anyone else looked at that and can share what
> > > they see?
> > >
> > > Thanks and best regards,
> > >
> > > Drew
> > > n7da
> > > ______________________________________________________________
> > > 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]

Wes Stewart-2

Re: KX3 SWR meter accuracy on 50 MHz?

There are so many variables here that it kind of defies analysis. First of all,
the KX3 uses a BNC connector. Almost always, as you have done, connecting to a
good load, that will handle some power, probably requires adapting to type N. A
reasonable load might be something like a NARDA 366NM which has a VSWR spec of
1.2:1. I personally use a series of Narda 766 attenuators which are 1.1:1.
Adding a typical BNC to type N adapter, Pasternack PE9002, which is rated at
1.3:1. (A lot of manufacturers like Amphenol don't even rate for VSWR)

Converting these two values to reflection coefficient, adding them (worst case)
and converting back to VSWR gives 1.57:1. So the load could be the 1.5:1 that is
measured. But this is only a part of the issue. The KX3 VSWR bridge has
unknown directivity and sensitivity since it uses diodes at very low power.
Furthermore, it's not driven by a good 50 ohm source, the amplifier output is
unknown and there is a BPF in the circuit. At the output side there are at
minimum some relays before getting to the output spigot.

In summary, I wouldn't worry about it. If you really want to know what the load
Z (antenna) is, measure it with an appropriate instrument calibrated with known
standards.

Wes N7WS

First, On 9/17/2020 7:36 PM, Drew Arnett wrote:

> Tech support said they saw 1.5 to 1 on 50 MHz with their dummy load.
> HF looked great, of course. They didn't mention if they also used a
> microwave load. :-)
>
> Best regards,
>
> Drew
> n7da
>
> On Sun, Sep 13, 2020 at 2:20 AM Drew Arnett<[hidden email]> wrote:
>> I did before shipping in for repair with a directional coupler. Looked great.
>>
>> On Sat, Sep 12, 2020 at 7:13 PM Nr4c<[hidden email]> wrote:
>>> Well, it depends on the “Dummy” load. Have you swept the load with a good spectrum analyzer or VNA? It may not be 50 ohms at 50 MHz
>>>
>>>
>>>
>>> Sent from my iPhone
>>> ...nr4c. bill
>>>
>>>
>>>> On Sep 12, 2020, at 11:51 AM, Drew Arnett<[hidden email]> wrote:
>>>>
>>>> After getting my KX3 back from repair (before my next planned contest
>>>> operation, thanks!), I ran some measurements to both see how great the
>>>> repairs were and to get a new baseline for future measurements. TX
>>>> efficiency problem was gone.
>>>>
>>>> However, I'm left to wonder about the accuracy of the internal SWR
>>>> meter for 50 MHz. Using a microwave dummy load of adequate power
>>>> rating and just a coaxial adapter, I measured the following:
>>>>
>>>> 14 MHz @ 1 W setting
>>>> VSWR 1.0 to 1 (per KX3)
>>>>
>>>> 28 MHz @ 1 W setting
>>>> VSWR 1.0 to 1
>>>>
>>>> 50 MHz @ 1 W setting
>>>> VSWR 1.5 to 1
>>>>
>>>> 50 MHz @ 4 W setting
>>>> VSWR 1.6 to 1
>>>>
>>>> Not horrible. Not great.
>>>>
>>>> It's fine if it's not as accurate on 50 MHz. I just want to know if
>>>> this is normal. Has anyone else looked at that and can share what
>>>> they see?
>>>>
>>>> Thanks and best regards,
>>>>
>>>> Drew
>>>> n7da
>>>> ______________________________________________________________