Hi again... some updates on my issue.
First of all, thanks for the replies concerning my first problem, which
actually wasn't a problem, but some misunderstanding about how the subs
Now I have a second issue to deal with.
I have trimmed the stubs separately, using the X reading on my MFJ259.
I followed the example from W2VJN book, for 40m band:
1/4 wave coupling cable (between TX and "stub pack")
1/4 wave shorted (nulls 20 & 10m)
1/16 wave coupling cable
1/4 wave shorted (nulls 20 & 10m)
1/12 wave open (nulls 15m)
1/6 wave short (nulls 15m)
After I assembled that, I used the MFJ259 as a signal generator, and
radio B listening, I see that I have quite a big difference, with stubs
inline and out. S9+60 vs S9 on 20m, S9+60 vs S9+20 on 15m. )
When I plug radio A, on its minimum power level, to the stubs, and my
40m antenna, and listen with radio B on the tribander, there is no
significant difference when I put the stub online or offline.
For the sake of simplicity, I removed amplifier and the sixpak. Just
radioA-stub-antenna and radioB-antenna.
Seems now that I have some RF leakage between my radio's output and the
stubs input, right?
David Robbins K1TTT wrote:
> With the mfj meter you should plug the stub straight into the meter and just
> read the max or min impedance points for the pass and stop bands. Cut the
> stub to tune the If you add a piece of cable and try to measure the dips
> at the reject points, that is where the stub looks like a short circuit, you
> are measuring the very low impedance transformed by the length of cable,
> which will be different than the real impedance. You should be able to read
> the pass band ok, but there you are going to see a very wide peak because of
> the high impedance presented by the stub in parallel with the dummy load.
> David Robbins K1TTT
> e-mail: mailto:firstname.lastname@example.org
> web: http://www.k1ttt.net
> AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
>> -----Original Message-----
>> From: email@example.com [mailto:towertalk-
>> firstname.lastname@example.org] On Behalf Of Felipe Ceglia - PY1NB
>> Sent: Tuesday, August 19, 2008 01:30
>> To: email@example.com
>> Subject: [TowerTalk] stubs for the SO2R setup
>> I am trying to make a set of stubs to be used on my SO2R station setup.
>> Those stubs should be plugged to a six pak box.
>> When I measure the 1/4 wave shorted 40m stub, plugged directly on the
>> MFJ-259, with a dummy load paralelled by a tee connector, I can see the
>> nulls on 14 and 28mhz.
>> When I plug that stub and that very dummy load on the six pak 40m port,
>> things change. Nulls go to 12.9mhz and 24.9mhz.
>> The obvious explanation is that the length of cable between the amp
>> output and the six pak input is being added to the stub, right?
>> If so, also seem obvious that I should have the same length of cable
>> between both of the amps and the six pak, right?
>> If so, I should take this length into account, and things will change if
>> I turn the amplifier online, offline, right?
>> If so, how can I deal with it in situations where I have multiple stubs?
>> For example: on 40m, I plan to have 2 1/4 wave shorted stubs nulling 14
>> and 28mhz, and the 1/6 + 1/12 wave for nulling 21mhz
>> If so, I have quite a terrible problem in hands.
>> 73 and thanks in advance for your advice,
>> Felipe - PY1NB
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