Chuck, thank you ! Exactly what I was after....great explanation....on a side
note, the array seems to be working great, quieter on receive than my previous
home brew Christman type array, with great front to back....
Sent from my iPad
> On Dec 2, 2018, at 9:30 PM, Chuck Lewis <clewis@knology.net> wrote:
>
> Jamie, the impedance reading you are seeing now is (48.3 + j14.4); but your
> instructions want (46 + j12). So you’re “pretty close”. The “j“ term and “X”
> refer to the same thing (reactance).
>
> Impedance has two components: resistance (R) and reactance (X). Impedance is
> often shown as (R + jX), which is shorthand for (Resistance and Reactance).
> The reactance term (jX) will be positive if the reactance is inductive and it
> will be negative if the reactance is capacitive. The reactance shown by your
> analyzer (X=+14.4) is slightly positive, because it’s inductive. You really
> want it to be X=+12 (a little less inductive). Your instructions might help
> you understand whether (48.3 + j14.4) is close enough, or that you still need
> to tweak it a little. There should be others on this reflector who have
> experience with these kinds of arrays and can tell you whether, in this case,
> “pretty close” is close enough.
>
> Don’t sweat the “j” business. For now, just think of “j” as a clue that the
> following number is the reactance (X). When you dig into the math, the “j”
> will make more sense. Please dig into the math!
>
> Here’s the relationship among the three parameters: Z(impedance) = √(R2 +
> X2) . Let’s use your numbers for #2:
>
> Z= 40.8 R= 40.6 X=3.2
>
> R(squared) = 1648.36, and X(squared) = 10.24 . Add those together to get
> 1658.6 . When we take the square root of that, we get 40.725. Your analyzer
> said the impedance (Z) is 40.8. Yay! The math worked! Try it for some other
> sets of values…
>
> If you think that looks a lot like solving for the hypothenuse of a right
> triangle, you would be right.
>
> Chuck, N4NM
>
>> On 12/2/2018 3:47:49 PM, Jamie WW3S <ww3s@zoominternet.net> wrote:
>>
>> I'm preparing for the 2 ELE DXE array.....and now, with just about 3 ft of
>> coax, at the target freq of 7.125 mc, #1 vert measures Z=41.1, R=40.8 and
>> X=.93 and #2 measures Z=40.8, R=40.6 and X = 3.2. I then attached the 75
>> ohm 1/4 wave stubs, and the Tee adapter, and measure right at the Tee and
>> got Z=51.2, R=48.3 and X=14.4...the instructions say it should read close
>> to 46 ohms +j 12 ohms.....so am I close? I'm stuck on what the j+12 ohms
>> means in relation to the other readings....
>>
>> -----Original Message-----
>> From: Tim Duffy
>> Sent: Sunday, December 02, 2018 4:11 PM
>> To: 'Wes N7WS' ; jim@audiosystemsgroup.com
>> Cc: towertalk@contesting.com
>> Subject: Re: [TowerTalk] 39 +j0 ohms?
>>
>> Jamie:
>>
>> Is this a full size vertical (1/4 wavelength) with a proper radial field?
>>
>> If the VSWR is 1.3:1 at 7125 KHz - what is the problem you are trying to
>> solve? What frequency is X=0?
>>
>> 73,
>> Tim K3LR
>>
>> -----Original Message-----
>> From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Wes
>> N7WS
>> Sent: Sunday, December 02, 2018 4:05 PM
>> To: jim@audiosystemsgroup.com
>> Cc: towertalk@contesting.com
>> Subject: Re: [TowerTalk] 39 +j0 ohms?
>>
>> No, you just need to calibrate at the far end of the coax.
>>
>> Sent from my iPhone
>>
>> > On Dec 2, 2018, at 1:27 PM, Jim Brown wrote:
>> >
>> > Where are you measuring? You'll only get the actual impedance measuring
>> right at the feedpoint with a very short piece of coax connecting the
>> analyzer.
>> >
>> > Now, it IS possible to transform a measurement made at the end of a long
>> piece of coax to the feedpoint Z, but to do that you need to save the data
>> to a file and export to software like AC6LA's ZPlots or AE6TY's SimSmith.
>> AND you need to know the length of the feedline, know the exact type of
>> coax, and plug both into the software.
>> >
>> > 73, Jim K9YC
>> >
>> >> On 12/2/2018 12:07 PM, Jamie WW3S wrote:
>> >> trying to understand a 40m vertical, my Rigexpert analyzer has Z, X, R
>> and C.......when I measure the vertical at 7.125 (target freq) the SWR is
>> 1.3:1, but the Z is 50 ohms, I'm told the impedance needs to be 39+j) ohms?
>> How can I read that with my rigexpert.....I can get around 39 ohms at
>> 7.400.....is my vertical too long, or too short?
>> >> _______________________________________________
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