[Elecraft] I am flummoxed about my antenna

David Gilbert xdavid at cis-broadband.com
Sat Dec 1 23:51:34 EST 2018 

I'm not "determining resonance" at all.  I agree that lowest SWR doesn't 
correlate to resonance, but according to what he's given us so far the 
point of lowest SWR has shifted down with a MUCH broader curve.  That 
indicates some kind of additional loading, in inductive and resistive.  
And in spite of what K3ICH says, such a change could have occurred just 
as likely in the vertical portion as in the radial portion.

And I don't see how you get the idea his characteristic impedance is far 
from 50 ohms.  Did you read his SWR curve?  One way or another his net 
feedpoint impedance is pretty close to 50 ohms.   We're not talking 
general theory here ... we're talking the numbers he has given us and 
won't have a better idea of anything until he gives us more 
information.  I merely suggested some things he should check.

Dave   AB7E


On 12/1/2018 2:38 PM, Charlie T wrote:
> How are you determining resonance?
>
> If you are measuring strictly voltage standing wave ratio with for example,  a Bird 43 meter, then a reactive system whose characteristic impedance is far from 50 Ω, may in fact show the lowest SWR meter reading at a point well off the actual antenna resonance.
>
> 73, Charlie k3ICH
>
>
>
>
> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> On Behalf Of David Gilbert
> Sent: Saturday, December 01, 2018 3:39 PM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] I am flummoxed about my antenna
>
>
> Agree on both points.  The resonant point appears to be well below 1.8 MHz and there is clearly a lot of loss in there somewhere.  He says he changed out the coax so water in the coax seems less likely.
>
> The fact that the resonance has dropped is odd, since it implies more length instead of less like you'd get with a bad connection.  I wonder if the end of the wire that is in the tree has lost it's insulation and there is actually contact to wet wood there.  That would add both additional loading and loss.
>
> 73,
> Dave   AB7E
>
>
>
> On 12/1/2018 10:04 AM, Vic Rosenthal wrote:
>> 1. The resonant point seems to be at 1.80 or below.
>> 2. The broad response indicates high loss somewhere. If you hadn’t said that you changed it, I would suspect water in the coax.
>>
>> Victor 4X6GP
>>
>>> On 1 Dec 2018, at 18:54, Leroy Buller <lee.buller at gmail.com> wrote:
>>>
>>> There
>>> I tried to get on 160 with my Inverted L last night.  60 feet up and the
>>> rest over to a tree, 130 feet total.  About 20 random length radials in the
>>> yard.  The best I can do with a city lot.  This antenna worked last year
>>> very well, but now I get this
>>>
>>> 12/1/2018 10:46:08 AM     NOTES:
>>>
>>> Frequency     SWR
>>> ---------     ---
>>> 001800000     1.3
>>> 001810000     1.4
>>> 001820000     1.4
>>> 001830000     1.4
>>> 001840000     1.4
>>> 001850000     1.5
>>> 001860000     1.6
>>> 001870000     1.6
>>> 001880000     1.5
>>> 001890000     1.5
>>> 001900000     1.6
>>> 001910000     1.6
>>> 001920000     1.6
>>> 001930000     1.6
>>> 001940000     1.6
>>> 001950000     1.6
>>> 001960000     1.6
>>> 001970000     1.7
>>> 001980000     1.8
>>> 001990000     2.0
>>> 002000000     2.1
>>>
>>> There seems to be NO resonance at all with this antenna.  Before, I could
>>> operate the bottom of the band but nothing above 1850 without a tuner.  I
>>> have changed out the coax feeding the antenna which hepl bring signals up,
>>> but it seems to be a dummy load.
>>>
>>> Anyone have an idea what is going on?  Shucks, I am out of ideas.  Unless
>>> my ground plane has gone wonky
>>>
>>> My tuner can't find a match for it either.  I have an automatice tuner now,
>>> but it cannot find a match.  Something is wrong here and I am stumped.
>>>
>>> Any help from the antenna gurus out there?
>>>
>>> Lee - K0WA
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