[Towertalk] Stub tuning

[Michael Tope]

Yes, but the SWR curves are typically pretty broad, so
sensitivity is not the greatest. Better to put a wattmeter
between the T and the globar and look at forward power
at the harmonic. Forward power will be minimum at the
frequency that the stub is tuned match. This is generally
a very sharp null and will give a better indication of the
tuning of the stub than looking at passband VSWR.

I use a VSWR meter with adjustable sensitivity to perform
this measurment as this allows me to make the measurement
with a minimum of TX power (remember you are loading
up the rig into a dead short when you do this measurment).
An LMR-400 stub will provide 20 to 25 dB of rejection
at the 2nd harmonic, so for 10 watts of TX power you will
need a meter that is sensitive enough to see 10's of milliwatts
in order to properly resolve the null.

73 de Mike, W4EF...................

----- Original Message -----
From: "Tom Osborne" <w7why@harborside.com>
To: "TowerTalk" <towertalk@contesting.com>
Sent: Friday, September 13, 2002 8:46 AM
Subject: [Towertalk] Stub tuning


>
> Hi All
>
> I have a big Globar 50 ohm resistor.  If I hook it to one side of
> a "T" connector and the stub to the other side of the "T"
> connector, will it show minimum SWR at the right length of the
> stub for the band I'm making it for?  Thanks and 73
> Tom W7WHY
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