Blair,
If you do a Google search on "Smith Chart", you will find many
resources about this useful tool to graphically display impedance and
how a match can be achieved. Chapter 28 of my copy of the ARRL
Antenna Book (19th Edition) is devoted to this topic.
73,
Bob N7XY
On Nov 15, 2008, at 1:45 PM, Blair S Balden wrote:
> Well, I suppose my understanding was not quite right. I had
> assumed that, if you could get the load impedance to a value of 50
> ohms (when using 50-ohm coax), you would get a 1:1 SWR. I thought
> this is how antenna tuners and matching networks worked, by
> inserting the appropriate amount and type of reactance to arrive at
> 50 ohms, or as close to it as possible.
>
> I had reasoned that if my resonant dipole had an impedance of less
> than 50 ohms, with the resulting SWR, I could reduce the SWR by
> changing the length, thereby "unbalancing" the reactive component
> and raising the total impedance to 50 ohms.
>
> Apparently, I need to study this further.
>
> Thanks to all who commented.
>
> 73,
> Blair NP2F
>
>
> ----- Original Message -----
> From: Jim Brown <jim@audiosystemsgroup.com>
> Date: Friday, November 14, 2008 6:46 pm
> Subject: Re: [TowerTalk] wire antenna question
>
>> On Fri, 14 Nov 2008 23:37:41 +0000, Steve Hunt wrote:
>>
>>> Minimum VSWR: Freq = 21.03 MHz, Z = 101.1 - j16.64, VSWR = 2.09
>>> Resonance: Freq = 21.13 MHz, zZ= 112.2+j0, VSWR = 2.25
>>
>>> The "anomaly" occurs because the VSWR is being referenced to
>> something
>>> significantly different than the resonant impedance of the antenna;
>>
>> Here's yet another situation where 75 ohm coax would be a better
>> choice than 50
>> ohm coax.
>>
>> 73,
>>
>> Jim K9YC
>>
>>
>>
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