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<arnett.d...@gmail.com> wrote:
I did before shipping in for repair with a directional coupler. Looked great.
On Sat, Sep 12, 2020 at 7:13 PM Nr4c<n...@widomaker.com> 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<arnett.d...@gmail.com> 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
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